Page 1

New Zealand Guide to Specifications for

Concrete Production and

Concrete Construction


Index SCOPE ....................................................................................................................... 3 INTRODUCTION ........................................................................................................ 3 1.

GENERAL........................................................................................................ 5

2.

CONCRETE SUPPLY...................................................................................... 7

3.

EQUIPMENT ................................................................................................. 13

4.

FORMWORK ................................................................................................. 14

5.

SUB-BASE..................................................................................................... 16

6.

UNDERLAY MEMBRANE.............................................................................. 19

7.

PLACING AND FIXING REINFORCEMENT ................................................. 20

8.

PLACING AND FINISHING ........................................................................... 21

9.

CURING......................................................................................................... 28

10.

JOINTS .......................................................................................................... 32

11.

PROTECTION OF CONCRETE SLABS........................................................ 36

12.

TESTING AND ACCEPTANCE OF CONCRETE .......................................... 37

13.

CONSTRUCTION TOLERANCES................................................................. 42

14.

REMOVAL AND REPLACEMENT OF DEFECTIVE AREAS......................... 44

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New Zealand Guide to Specifications for Concrete Production and Concrete Construction SCOPE This document has been developed to show how specification matters might be dealt with. It utilizes, as the primary Standards for compliance, the NZ Standard NZS 3109:97 Concrete Construction (including amendments No1 and No2) in conjunction with NZS 3104:03 Specification for Concrete Production and NZS 3114 Specification of Concrete Surface Finishes. Any specification needs to define the term “Construction Reviewer” used in clauses3.3.5, 5.5, 5.6.1, 7.4.1, 7.7.6, 7.7.8, 7.8.4, and 7.8.5 of NZS 3109. In this specification the Engineer to the contract has been defined as the “Construction Reviewer”. While generic aspects of workmanship are covered in NZS 3109 the specifics relating to slab construction are not included. For special floor applications an alternative approach is for the designer to provide outline requirements for the performance of the floor but the actual design, detailed specification, and construction is passed to the specialist flooring contractor. Some clauses within the specification have a line in the left margin. This indicates that the information supplied within the clause is reasonably well defined in NZS 3109 and if a slimmer specification is required these clauses could be deleted.

INTRODUCTION The specification for a concrete slab on ground project would typically be divided into the following parts: • • • • •

Site works Drainage Sub-grade preparation Sub-base construction Concrete slab construction.

The purpose of this specification is to provide typical clauses for the parts dealing either with the construction of the concrete slab, or the parts which affect this construction. It is not appropriate to include a copy of this document in a project New Zealand Guide to Specifications for Concrete Production and Concrete Construction

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specification, nor to refer to it as a standard specification, since each clause will have to be reviewed as to its relevance. This guide specification does not include clauses related to general requirements such as order of works, setting out, records, inspections, etc., nor does it cover requirements for clauses of the work not directly related to concrete. Disclaimer The information provided in this document is intended for general guidance only, and requires amendment by Professional Consultants. No legal liability can be accepted by the NZ Concrete Society or NZ Cement and Concrete Association.

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1.

GENERAL

1.1

Reference Documents

1.1.1

New Zealand and Australian Standards

The following Standards are referred to and form a part of this specification to the extent indicated in the appropriate clause: NZS 3104:03

Specification for Concrete Production

NZS 3109:97

Concrete Construction

NZS 3114:87

Specification for Concrete Surface Finishes

NZS 3121:86

Specification for Water and Aggregate for Concrete

NZS 3122:95

Portland and Blended Cements

AS/NZS 4671:01 Steel Reinforcing Materials AS 1478.1:00

Admixtures for Concrete

AS/NZS 3582:02 Supplementary Cementitious Materials for use with Portland and Blended Cement, Part 3: Amorphous Silica

1.1.2

AS 3582

Supplementary Cementitious Materials for use with Portland and Blended Cement Part 1:98 Fly Ash Part 2:01 Slag – Ground Granulated Iron Blast-Furnace

AS 3799:98

Liquid Membrane-Forming Concrete

Curing

Compounds

for

American Society for Testing and Materials (ASTM)

C 171–03 Standard Specification for Sheet Materials for Curing Concrete is referred to, and forms part of, this specification to the extent indicated in the appropriate clause.

1.2

Construction Reviewer

In terms of NZS 3109, the Construction Reviewer shall be (…..) Commentary: The name of the Construction Reviewer should be specified, typically this would be the Engineer to the contract and this specification is based on this assumption. New Zealand Guide to Specifications for Concrete Production and Concrete Construction

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1.3

Quality Assurance

It is the Contractor’s responsibility to ensure that the construction works complies in all respects with the drawings and specification. The Contractor shall advise the Engineer in writing, as to the name of the Contractor’s suitably qualified representative responsible for quality control. Quality control records shall be stored in an orderly manner on site, and be available for inspection at any time. Upon completion of the works the Contractor’s quality control representative shall provide a statement that work has been conducted by suitably qualified persons, and in accordance with the drawings, specification, and any contract instructions.

1.4

Protection of the Slab from the Elements

Commentary: In this clause the designer should outline guidance on the level of protection the slab should be provided from the elements. The best protection is achieved if the building envelope is constructed before the ground slab. Probably the most common causes of dissatisfaction with a slab on grade is random cracking, and the most prevalent reason for these cracks are plastic shrinkage or restrained early thermal contraction. The risk of these occurring is significantly reduced if the slab is constructed after the building envelope. If the slab needs to be constructed first, it is strongly recommended that anti-evaporation sprays and early entry saw are used (see section 8 and 10).

1.5

Design of Floor

Commentary: In some instances the design of the floor is nominated as the responsibility of a Specialist Supplier. A common example is Post Tensioned floors. Only include this section if the design is to be done by others. This section should include comments on: ƒ ƒ ƒ ƒ

The ground conditions The design loads The need to submit drawings for approval Requirements at joints (i.e. armouring of free joints)

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2.

CONCRETE SUPPLY

2.1

Concrete Required

The concrete for the various elements of the slab shall contain the specific types of materials listed in Table 2.1. Table 2.1: Summary of concrete materials Element

Specified compressive strength

Type

Maximum aggregate size

For Special concrete refer clause -

Floor slab in warehouse

35 MPa

Normal

19 mm

Not Applicable

Floor slab containing shrinkage compensating admixtures

35 MPa

Special

19 mm

2.3

Commentary: Fill out table as appropriate.

2.2

Normal Concrete

Normal concrete shall be used in the locations specified in Table 2.1. The concrete shall be produced in accordance with NZS 3104 from a plant possessing a current Certificate of Audit consistent with the Grade of concrete specified. The Contractor, Concrete Placer, and Concrete Supplier shall determine the appropriate slump of the concrete to achieve the desired workability consistent with the method of placement being utilized.

2.3

Special Concrete

For concrete specified as Special in Table 2.1; a.

The concrete shall be supplied by a plant possessing a current Certificate of Audit.

b.

Unless modified elsewhere all Special concrete shall, as a minimum, meet the requirements of Normal concrete as specified in NZS 3104.

c.

The following additional requirements shall apply.

Commentary: The reasons for specifying special concrete could include, but is not limited to, specifying any of the following examples presented below. Note there is also a requirement for the specifier to record the methods of conformance testing required. This has been provided in section 12.3.

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Special Concrete Example - Use of Cements other than GP The cement used in the mix shall be (‌.) conforming to section 2.9.2. Batching records shall record the cement type. Conformance testing shall be in accordance with 12.3 of this specification. Commentary: An example could be the specification of early strength cements, HE cement. This is typically used where early age strengths (up to 3 days) are required. Rather than specify the cement type a more specific special requirement could be the strength required at the specific early age. In this case the specification would record the strength required, when the test would be conducted, and how the samples will be cured. Special Concrete Example Strengths Greater than 50 MPa The concrete grade shall be ( with 12.3 of this specification.

) MPa. Conformance testing shall be in accordance

Commentary: For testing and commentary on this refer to 12.3. Special Concrete Example Air content for Freeze Thaw Resistance The fresh concrete shall have an air content of ( )%. Conformance testing shall be in accordance with 12.3 of this specification. Commentary: Refer section 12.3 for testing. Special Concrete example Use of SCM such as Fly ash, Amorphous Silica and GGBS The concrete shall include ( )% Fly Ash as a proportion of the total cementitious component. The fly ash shall conform with section 2.9.2. Or The concrete shall include ( )% Amorphous Silica as a proportion of the total cementitious component. The Amorphous Silica shall conform with section 2.9.2. Or The concrete shall include ( )% GGBS as a proportion of the total cementitious component. The GGBS shall conform with section 2.9.2. The Concrete Supplier shall produce either computerised batch data or a QA system to provide assurance that the SCM has been added to all batches.

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Special Concrete Example Use of Aggregates Greater than 37.5 mm The concrete shall include a minimum (….)kg of aggregate of minimum nominal size 37.5 mm. This shall be verified by inspection of the batching records. Commentary: Typically minimum aggregate sizes are specified as a way of controlling drying shrinkage or reducing heat of hydration. A better approach might be to specify the minimum total aggregate content and maximum water content. Be wary that the mix design has to match the equipment used to transport the concrete to its final site and the placing and finishing equipment. Special Concrete Example Fibre Reinforced Concrete The concrete shall include (…)kg of steel fibre with a minimum aspect ratio of (…) and tensile strength of (…) MPa. Steel fibres with lower aspect ratios may be acceptable providing the dose is correspondingly lifted. The Concrete Supplier shall produce either computerised batch data or a QA system to provide assurance that the SCM has been added to all batches. Test data shall be provided for approval of the Construction Reviewer providing proof of steel tensile values. Commentary: Steel fibres in New Zealand are from many sources. While there are many from reputable international companies many others are bought in simply because they are cheap and resemble one of the major supplier’s brands. Unless the importer has a regular local testing programme in place this steel fibre should be treated with caution. Special Concrete Example Use of Specified Shrinkage Values The concrete shall have a maximum 56 day drying shrinkage value of (…) microstrain when tested in accordance with AS 1012.13. Prior to the concrete being used on site, the concrete shall be tested from a batch of concrete produced to the mix design and slump to be used in the contract. Testing shall be carried out in accordance with AS 1012.13. Commentary: The contractor must be aware that shrinkage testing takes 63 days from sampling through to final testing and is relatively expensive. In New Zealand, shrinkage testing of mixes is not a standard procedure. The shrinkage test does not show the designer the shrinkage that will be exhibited in practice. The factors in AS 3600 may be used to estimate what the in-place shrinkage might be. In order of priority the drying shrinkage will be driven by:

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1.

The type of aggregate – this can alter shrinkage from a low of around 600 microstrain using Auckland basalt to 1,200 microstrain using some of the lower North Island greywackes.

2.

The volume of aggregate in the mix – this acts as a restraint to the shrinkage of the paste. An increase in total aggregate content can reduce the total shrinkage.

3.

Water content – for a given cement content increasing the water will increase the shrinkage. The amount of increase will depend on the cement content but 15 litres per m3 will increase shrinkage by around 100 microstrain.

4.

Size and grading of aggregate does not itself decrease shrinkage except that it allows the use of leaner mixes with greater aggregate content.

Special Concrete Example - Maximum w/c Ratio The concrete shall have a maximum w/c ratio of ( ). The manufacturer shall state how they monitor water content in the mix. In particular how they assess sand moisture and the control and measurement of wash-down and temp water.

2.4

Chloride Content

The total chloride content in Normal and Special concrete shall not exceed the limits specified in Clause 6 of NZS 3109 and chloride salts or chemical admixtures, formulated with greater than 0.1% by weight of chloride, shall not be added to any steel reinforced concrete. Commentary: NZS 3109 specifies total chloride content of concrete based on measurements of acid soluble chloride content arising from aggregate, mixing water, and admixtures expressed as mass of chloride ion per unit volume of concrete as follows; Prestressed concrete Reinforced concrete in dry or protected environment RC in moist environment or exposed to chlorides

0.5 kg/m3 1.6 kg/m3 0.8 kg/m3

The restriction of 0.1% by weight of chloride comes from 3.14.1.1 of NZS 3101. Strictly it only applies to exposure classifications B1, B2 or C. The last sentence may be deleted if required in exposure classification A1 or A2. Refer to NZS 3101 for exposure classifications.

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2.5

Sulphate Content

The sulphate content in Normal and Special concrete shall not exceed the limits specified in Clause 6 of NZS 3109. Commentary: NZS 3109 specifies a maximum sulphate content, expressed as the percentage by mass of acid soluble SO3 to mass of cement, of less than 5%.

2.6

Workability of Concrete Mix

The selection, proportioning and mixing of the concrete materials shall be such as to produce a mix which works readily into corners and angles of the forms, and around reinforcement, but without permitting the material to segregate or excess free water to collect on the surface.

2.7

Consistency of Delivered Slump

The slump of the concrete at time of delivery shall be consistent and within the tolerances specified in Table 9.1 of NZS 3109.

2.8

Cement and Cementitious Materials

2.8.1

Cement for Normal Concrete

Cement for Normal concrete shall comply with the requirements of NZS 3122: Type GP – General Purpose Portland Cement. 2.8.2

Cement and Supplementary Cementitious Materials for Special Concrete

Where required by Clause 2.3, cements and supplementary cementitous materials shall comply with the following: a. b. c. d. e. f.

Type GPGeneral Purpose Cement Type GBGeneral Purpose Blended Cement Type HEHigh early strength Cement Amorphous silica Fly Ash GGBS, Ground Granulated iron Blast-furnace Slag

NZS 3122 NZS 3122 NZS 3122 AS/NZS 3582 Part 3 AS 3582 Part 1 AS 3582 Part 2

Commentary: NZS 3122 also covers Type LH (Low Heat Cement.), Type SR (Sulphate Resisting Cement), Type SL (Shrinkage Limited Cement). However, these are not commonly used in New Zealand and therefore not included in the list. Typically low heat concretes would be achieved with the use of supplementary cementitious materials, and shrinkage limitation would be achieved using water reducing admixtures. New Zealand Guide to Specifications for Concrete Production and Concrete Construction

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2.9

Aggregates

Aggregates shall comply with NZS 3121. Commentary: NZS 3121 provides requirements for grading, cleanness limits for deleterious materials, and sampling. Alkali aggregate reaction is incorporated into this specification by a limit on the total alkali content of the concrete as specified in 2.4. A Cement & Concrete Association of New Zealand publication ‘Alkali Aggregate Reaction – Guidelines on Minimising the Risk of Damage to Concrete TR 3’ will help specifiers to understand the practical issues raised by this phenomenon.

2.10 Water Water shall be free from matter which in kind and quantity will prevent the achievement of the durability requirements of the Building Code. Water quality shall be consistent for all concrete supplied in a pour, and shall not adversely influence the workability and placing characteristics of the concrete. Water shall meet the requirements of NZS 3121. Commentary: Most plants in New Zealand use recycled water which is desirable from an environmental perspective, and permitted within NZS 3104.

2.11 Chemical Admixtures Chemical admixtures, where utilised in Normal concrete, or specified directly or indirectly for Special concrete in 2.3, shall comply with the requirements of AS 1478.

2.12 Attendance at Pre-pour Meeting The Concrete Supplier and Concrete Placer shall attend a meeting organised by the Contractor prior to the pouring of the first concrete slab. Commentary: A pre-pour meeting is recommended to ensure that everyone understands the performance requirements and risk management strategies. The probable characteristics of the concrete mix and how the placing and finishing characteristic may vary from common concrete mixes should be discussed.

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3.

EQUIPMENT

3.1

General

Dependable and sufficient equipment that is appropriate and adequate to meet the approved plan and schedule for the work specified shall be furnished by the Contractor. It shall be assembled at the site of the work in sufficient time before the start of placing to permit thorough inspection, calibration, adjustment of parts, and the making of any repairs that may be required. Commentary: The range of equipment suitable for use in constructing slab on grade is wide and varied. This section has been written in this form so as not to restrict the use of equipment which the contractor owns, nor with which the contractor is familiar; or to restrict innovation. The conditions of tendering should include the requirement that details of the intended equipment to be used are to be provided.

3.2

Maintenance

The approved equipment shall be maintained in good working condition. It shall be checked regularly for wear, setting and calibration. If not up to the required standard, the equipment shall be repaired or replaced prior to its continued use on the project.

3.3

Pumping Equipment

Equipment for pumping concrete shall be capable of safely and efficiently pumping concretes with slumps as low as 80 mm with mixes based on a maximum aggregate size specified in Table 2.1. Commentary: Pumping concrete is a common construction method. To avoid the situation where the concrete mix is designed for the capability of the pump, rather than using an appropriate capacity pump to place the correct type of concrete, minimum requirements have been specified. This has been done in terms of the concrete slump and maximum aggregate size the pump can efficiently handle. In most instances the maximum aggregate size will be 20 mm. The slump value specified in this clause should, in no instances, be interpreted as a desirable slump. The delivered slump of pumped concrete will typically have slumps considerably greater than 80 mm. The specification of an 80 mm slump is to provide a degree of confidence that the pump will be able to operate with low slumps if slump loss was to occur.

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4.

FORMWORK

4.1

Comply with NZS 3109

The design, surface finish, tolerances and stripping times shall comply with NZS 3109, unless modified in this section.

4.2

Forms to be Rigid

Forms shall be of steel or seasoned, dressed timber planks. The forms shall be rigid to ensure they do not deform when concrete is placed and vibrated.

4.3

Tolerances for Slab Edge Formwork

Forms shall be free of warps, bends or kinks, and the tolerances of the top surface of the form shall ensure compliance with the finished floor tolerances specified in section 13.

4.4

Formwork Where Dowels or Ties Bars are Used

Where dowels or tie bars are required in construction joints, the forms shall allow for their insertion and for rigidly supporting them in the correct alignment.

4.5

Quality Control of Forms

Formwork shall be set and checked prior to placing the concrete and the setting of the forms shall be approved by the Contractor before any concrete is placed. Records of the quality control shall be kept and be available for inspection if requested. Commentary: The Contractor’s Supervisor should check the forms for alignment, continuity and rigidity. Any problems should be rectified before approval is given to place concrete.

4.6

Care when Removing Forms

Forms shall be removed without damaging the concrete, dowel bars or tie bars. Bars or other tools shall not be used as a lever against the concrete in removing the forms. Commentary: The appropriate time for the stripping of forms will vary according to the environment and the type of concrete used. NZS 3109 provides good guidance on appropriate stripping times. These may require modification in special situations, e.g. very thick slabs, when heat of hydration considerations necessitates the use of insulated forms. The use of blended cements may also influence form stripping times.

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4.7

Repair of Damage

Any damage to the concrete occurring during form removal shall be repaired promptly by an approved method, at the Contractor’s expense.

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5.

SUB-BASE

5.1

Excavation

The site shall be excavated to the levels shown on the drawings. All top soil shall be removed from under concrete work and shall be kept separate from the excavated subsoil.

5.2

Disposal of Materials

All excavated material shall become the property of the Contractor except where otherwise provided. Remove from site as the work proceeds.

5.3

Sub-grade Preparation

The sub-grade shall be solid and compacted to receive the sub-base and concrete. The sub-grade shall be inspected and approved by the Construction Reviewer before any backfilling with sub-base. Commentary: To ensure that the slab can perform satisfactorily throughout its intended service life, the full support offered by the sub-grade should be fully assessed and evaluated before the sub-base is placed upon it. Problems can arise if the condition of the sub-grade varies from hard to soft as this site condition can lead to variable support and subsequent differential settlement when in service. Variable materials need to be removed and replaced with uniform backfill product to avoid the risk of differential settlement.

5.4

Sub-base

The sub-base shall comprise of continuously graded granular materials with not more than 5% passing a 2.2 mm sieve and with 100% passing the 63 mm sieve. The material should be suitably graded to permit compaction. The material shall have sufficient crushing resistance to ensure that the grading limits are maintained after compaction. The sub-base shall be free of foreign matter, waste concrete and other debris at all times. Commentary: The specified maximum aggregate size assumes that the sub-base thickness is at least 150 mm deep.

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5.5

Compaction of Sub-base

The sub-base shall be compacted to ensure that it is free from movement under compaction equipment, and does not weave under the weight of a laden concrete truck. Wheel track depths of less than 5 mm shall be recorded after loading with a laden concrete truck. Commentary: The sub-base layer is provided for several reasons including: ƒ ƒ ƒ ƒ

Providing a clean working platform. Providing a surface which will not puncture any vapor barrier. Providing support for construction traffic. Transferring loads from the floor slab to the sub-grade.

Of these purposes, the last is probably the least onerous requirement. The design thickness of the slab is only marginally influenced by the load spreading ability of the sub-base, and therefore its presence is often ignored in design. Satisfactory performance under construction traffic is typically a satisfactory indicator of adequate performance. Wheel track depths of less than 5 mm after proof loading with a concrete truck is normally an indicator of adequate compaction. Other methods of ensuring adequate compaction would be to specify that sub-base materials shall be compacted to say 95% of New Zealand Standard compaction.

5.6

Finished Sub-base Surface

The surface of the sub-base should be closed, flat, level, and shall be free of material likely to puncture the underlay membrane. Sand maybe used for closing the surface, however any residual layer of sand on the surface shall be less than 5 mm thick. Commentary: Modern laser controlled construction equipment can place materials such as granular materials to very tight tolerances and it should be possible to restrict the maximum thickness of the sand blinding layer to no more than 5 mm. Thickness in excess of this will lead to unacceptable tracking under construction traffic loads.

5.7

Tolerances of Sub-base

The finished surface of the sub-base shall be surveyed on a 3 m grid to determine the sub-base level. The finished surface shall be within +0, -10 mm of the datum for the bottom of the slab. Records of the survey shall be kept by the Contractor and shall be available for inspection if requested. Commentary: In some instances a 3 m grid maybe considered overly onerous and should be modified appropriately. Tight tolerances are desirable to ensure that the friction coefficient under the slab is kept as low as possible. To avoid disputes over the volume of concrete used, the New Zealand Guide to Specifications for Concrete Production and Concrete Construction

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payment schedule should make it clear who will cover the cost if the sub-base is constructed to the extremes of the acceptable tolerances.

5.8

Maintenance of Sub-base

The sub-base shall be maintained in a smooth, compacted condition in conformity with the required profile and level, until the concrete is in place.

5.9

Sub-base Preparation when Vapor Barriers not Used

In situations where the concrete is placed directly on top of the sub-base, the subbase shall be dampened (but not saturated) and kept damp prior to placing concrete. Commentary: This section is not applicable when concrete is placed directly over an impermeable material (e.g. polythene vapour barrier) or a material of relatively low permeability (e.g. bituminous sealed surface or leanmix concrete).

5.10 Inspection of Sub-base The Construction Reviewer shall be advised at least one working day in advance of covering the sub-base. The Contractor is to make available to the Construction Reviewer all records showing site tests on the sub-grade and sub-base together with survey data to confirm levels are in accordance with the design.

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6.

UNDERLAY MEMBRANE

6.1

Underlay Membrane

The underlay membrane shall be flexible, polymeric film, nominally 0.25mm thick and manufactured from suitable high-quality ingredients satisfying the requirements of the New Zealand Building Code. Commentary: Note, if no underlay membrane is necessary, these clauses will not be required. Typically an underlay membrane is specified to control moisture transmission and to reduce sub-base friction.

6.2

Storage

The underlay shall be delivered to the site in suitable protective packaging. The packaging, handling and storing of the underlay shall ensure that it is not punctured, torn, or otherwise damaged at any time. The underlay material shall have sufficient resistance to sunlight and associated radiation, so that its specified properties are unaffected by its exposure.

6.3

Laying

The underlay shall be laid over the levelled and compacted sub-base. Sheets of a maximum practical width shall be used to suit the layout and be arranged such that overlaps face away from the direction of concrete placement. The sheets shall be lapped as recommended by the manufacturer, but not less than 150 mm.

6.4

Repairing of Membrane

The membrane shall be inspected after laying and before the concrete is placed. Any punctures or tears shall be patched and sealed.

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7.

PLACING AND FIXING REINFORCEMENT

7.1

Reinforcement Materials

Reinforcement shall comply with AS/NZS 4671.

7.2

Compliance with NZS 3109

The detailing of hooks and bends, surface condition of reinforcement, spacing and fixing of reinforcement, splices, cover and placing tolerances, shall comply with NZS 3109 unless modified in the drawings or this specification.

7.3

Dowels

Dowels shall be of the type shown on the drawings. Where steel bars are used they shall be one-piece, straight, plain, round/square steel bars complying with the requirements of AS/NZS 4671, and of the sizes shown in the drawings. They shall be saw-cut to length prior to delivery to the site, and the ends shall be square and free from burrs. Commentary: It is desirable that dowels should allow both for longitudinal and transverse movement. There are proprietary systems which can provide for two directional movement.

7.4

Tie Bars

Tie bars shall be deformed bars complying with AS/NZS 4761, and of the size shown in the drawings.

7.5

Reinforcement Shall be Placed on Chairs

Reinforcement shall be provided in the locations shown in the drawings and shall be placed and securely held in its correct position by the use of approved supports. Commentary: The practice of laying reinforcing fabric on the sub-base and hooking the reinforcing into position after concrete is placed is not acceptable. Also unacceptable is working the fabric in from the surface of the concrete, as both of these methods provide no assurance that the reinforcement will end up in a true plane, at the required level.

7.6

Supports

The supports shall be adequate to withstand construction traffic and shall be sufficient in number and spacing to maintain the reinforcement in its correct position during the concrete placing operation. Cementitious spacers shall at least match the quality of the concrete being cast and shall have a minimum compressive strength of 40 MPa. New Zealand Guide to Specifications for Concrete Production and Concrete Construction

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8.

PLACING AND FINISHING

8.1

Planning and Pre-pour Meeting

The Concrete Placer shall attend the pre-pour meeting organised by the Contractor as specified in 2.13.

8.2

Placing Team

All concrete shall be placed and finished by appropriately skilled and trained personnel.

8.3

Inspection Prior to Pouring

The Contractor shall give at least one working day’s notice of intention to place concrete in any area, to enable the area to be inspected by the Construction Reviewer prior to commencement of placing. Unless approval is given by the Construction Reviewer, no concrete shall be placed in that section of the works. Any concrete placed without authorisation may require removal from the works at the Contractor's expense.

8.4

Compliance with NZS 3109

All placing and finishing shall comply with NZS 3109 unless modified in this specification.

8.5

Placing and Finishing Tolerances

The tolerances for finishing and placing shall be as specified in Section 13.

8.6

Slump

The slump of the concrete at time of delivery shall be consistent, and within the tolerances specified in Table 9.1 of NZS 3109.

8.7

Addition of Water

Water maybe added to the concrete as delivered only by the Concrete Supplier within the restriction provided in 2.9.3.1 of NZS 3104.

8.8

Limitation on Placement of Concrete

When the possibility of heat, wind, rain, or low humidity could prevent the requirements of this specification being met, the Contractor shall take appropriate precautions to ensure compliance with this specification. New Zealand Guide to Specifications for Concrete Production and Concrete Construction

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Commentary: Most contractors see rain as the only impediment to pouring concrete. However, most cases of cracking arise from hot and/or windy conditions causing premature drying of the top surface or plastic cracking. See Section 8.9

8.9

Elimination of Plastic Shrinkage Cracking

Where there is a risk of plastic shrinkage cracking, the Concrete Placer shall apply an anti-evaporation agent over the concrete surface after screeding and any floating operation, to prevent excessive evaporation of water from the concrete surface.

8.10 Placing 8.10.1

Working Face

The concrete shall be placed so that its working face is generally vertical, and normal to the direction of placing. It shall be placed uniformly over the width of the slab and in such a manner as to minimize segregation. 8.10.2

Walking on the Concrete

Workers shall not be permitted to walk on the concrete during placing with boots coated with soil or other deleterious substances. 8.10.3

Hand Spreading

Hand spreading of concrete shall be done with shovels, or rakes with blades. Vibrators or rakes with tynes shall not be used. Commentary: Vibrators or tyned rakes must not be used to spread concrete as they may cause segregation of the concrete mix. 8.10.4

Construction Joints

Concrete placing shall be carried out continuously between forms and/or construction joints and in such a manner that a plastic concrete face is maintained. Where their location is shown in the drawings, construction joints shall neither be relocated nor eliminated without approval. Where no construction joints are shown in the drawings, their location shall be approved before work starts. Commentary: The proper location of construction joints, which are also free joints, is critical to the functioning of the slab. The Contractor should consult the designer before giving any approval to the relocation of construction joints or the inclusion of new ones.

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8.11 Compacting 8.11.1

Compaction

All concrete, including that adjacent to forms or existing concrete, shall be compacted by mechanical vibration through the use of internal vibrators and/or vibrating surface screeds as detailed herein. Commentary: The method of compaction to be employed is dependent on the pavement thickness. A guide to the most appropriate method can be summarised as follows:

8.11.2

•

For pavements over 200 mm thick, surface vibration may not be sufficient to compact the concrete over its full depth, and internal vibration is required.

•

Internal vibration should be used adjacent to all construction joints and edges.

Slabs Less Than 200mm Thick

Pavements up to 200 mm thick may be compacted using an immersion vibrator complying with NZS 3109, vibrating beam, vibrating truss screed, vibrating screed, or laser screeds. The method selected shall ensure that the specified surface tolerances are achieved. Internal vibrators shall be used to supplement the compaction adjacent to the side forms and at construction joints. Commentary: Hand held vibrating screeds are only suitable for domestic slabs and should not be considered vibration for commercial slabs. 8.11.3

Slabs Greater than 200mm thick

Pavements greater than 200 mm thick shall be compacted using immersion vibrators complying with NZS 3109. 8.11.4

Requirements for Vibrating Beams

Vibrating beams shall incorporate double beams made of extruded aluminium or steel, or metal-shod timber sections with edges at least 75 mm wide. They shall be at least 300mm longer than the width of the strip being compacted, and equipped with handles to allow the assembly to be drawn over the concrete surface from outside the forms.

8.12 Floating Commentary: This specification has been developed on the assumption that the floor will, as a minimum, be power floated. This would be the norm for most floors but in some instances, such as when a exposed New Zealand Guide to Specifications for Concrete Production and Concrete Construction

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aggregate finish is specified, floating would not be necessary and section 8.12 could be deleted. 8.12.1

Power Floating

Floating shall be undertaken using powered mechanical equipment. 8.12.2

Commencement of Floating

Floating shall not commence until all surplus water is removed or evaporated from the surface of the concrete, and the surface is sufficiently hard to resist displacement under the action of the float. Commentary: It is important that power floating is not commenced until the concrete has stiffened sufficiently. The time interval before the initial power floating can commence depends on the concrete mix and the weather. 8.12.3

Regular Pattern

Floating shall be undertaken in a regular pattern over the entire surface of the concrete.

8.13 Finishing 8.13.1

General

Finishing operations comprising leveling, floating, trowelling and texturing, shall commence following compaction of the concrete, and shall be completed as soon as possible with due diligence. 8.13.2

Addition of Water

The addition of water to the surface of the concrete to assist in finishing operations shall not be permitted. However, in hot weather or dry, windy conditions the application of water to the surface in the form of a fog, or fine mist spray, or the spraying of the surface with an approved aliphatic alcohol shall be permitted. Commentary: Spraying with aliphatic alcohol immediately after initial finishing will limit evaporation of water and reduce plastic shrinkage cracking in hot weather conditions. 8.13.3

Schedule of Required Finishes

The finished surface shall be as specified in Table 8.1.

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Table 8.1: Schedule of required finishes Element

Surface finish

Specification clause

Floor slab in warehouse

U3, Trowelled

8.12

U5, Shallow texture

8.13

Hardstand area outside of warehouse.

Proprietary surface products

Commentary: The specification covers the following potential surface finishes. If other finishes are required, appropriate specification clauses will need to be developed; ƒ

Nil, i.e. float finish only, suitable if the floor will be covered.

ƒ

Trowelled, the most common for internal warehouse floors.

ƒ

Shallow texture (broomed) the most common for exterior slabs requiring texture for skid resistance.

8.14 Trowelling 8.14.1

General

Where a trowelled finish is specified in Table 8.1, the requirements of 8.14 shall apply. 8.14.2

Equipment

Trowelling shall be undertaken using approved powered mechanical equipment. Commentary: A power trowel is similar to a power-float but fitted with small individual steel trowel blades. The small blades can be slightly tilted during trowelling operations. This clause shall not prevent the use of hand trowelling to finish the surface along edges, and small areas unable to be covered by mechanical equipment. 8.14.3

Commencement of Trowelling

Trowelling shall commence after the surface has been power floated. Trowelling shall not commence until the surface is sufficiently hard to resist displacement under the action of the trowel. Commentary: The power trowelling is commenced when the excess moisture brought to the surface by initial power-floating has largely evaporated and the concrete has lost its stickiness. The waiting time before power trowelling also depends on both the concrete mix and the New Zealand Guide to Specifications for Concrete Production and Concrete Construction

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weather. A practical test to check the readiness for each trowelling operation is to place the palm of the hand on the concrete surface. If mortar sticks to the palm when the hand is taken away from the surface, the concrete is not ready for trowelling. If trowelling is started too early, the trowel blades will leave ridges. 8.14.4

Tilting of Trowelling Blades

The blades of the trowel shall be tilted such that maximum pressure is applied without leaving ridges on the surface of the concrete. Commentary: The first power trowelling of the slab is undertaken in a systematic pattern with the trowel blades set at a slight angle (the angle depends on the concrete stiffness but as large a tilt as possible to suit the surface should be used). If the tilt on the blades is too great, the concrete surface will be marked.

8.15 Shallow Texture 8.15.1

General

Where a shallow texture finish is specified in Table 8.1, the requirements of 8.15 shall apply. 8.15.2

Commencement of Finishing

Texturing shall not commence whilst the condition of the concrete is such that the surface could be torn and coarse aggregate particles displaced, or whilst there is free water on the surface. 8.15.3

Broom Texturing

The whole surface of the slab shall be broomed in a direction perpendicular to the direction of placing or as shown in the drawings. Brooms shall be at least 500mm wide with bristles of natural material, nylon or flexible wire. The broom shall be drawn across the full width of the slab in a series of overlapping strokes. The marks in the slab surface shall be uniform in appearance and approximately 2-6mm in depth without disfiguring marks. Commentary: For most slabs, no additional force other than the self weight of the broom need be applied to the surface. To improve traction in ramped or inclined areas, a coarser texture can be achieved by applying extra force to the broom.

8.16 Early Entry Sawing Where early entry saw cuts are specified on the drawings, all equipment required for cutting shall be on site prior to the commencement of the final finishing operation. New Zealand Guide to Specifications for Concrete Production and Concrete Construction

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8.17 Protection of the Environment All wash water associated with concrete shall be managed as stipulated in the New Zealand Ready Mixed Concrete Association’s publication “Safe Environmental Guidelines - On Site Management of Concrete Washwater”.

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9.

CURING

9.1

General

The concrete shall be cured by protection against loss of moisture for a period of not less than seven days from the completion of the finishing operations. Curing shall comprise initial curing followed by final curing. Commentary: Properties of concrete such as strength and wear resistance improve with age as long as conditions are favorable for continued hydration of the cement. The improvement is rapid at an early age, but continues more slowly thereafter. Evaporation of water from newlyplaced concrete can cause the hydration process to stop. It follows that concrete should be protected so that moisture is not lost during the early hardening period.

9.2

Equipment shall be on Site

Before concrete placing commences, all equipment needed for adequate curing of the concrete shall be on hand and ready for use.

9.3

Sides to be Cured

The sides of panels exposed by the removal of forms shall be cured by one of the methods detailed herein. This shall commence within one hour of removal of forms.

9.4

Initial Curing

Immediately after the finishing operations have been completed and until the membrane, sheet, or water curing has been applied, the surface of the concrete shall be kept continuously damp by means of a water fog or mist applied with approved equipment. Commentary: The use of a sprayed film of aliphatic alcohol is not a part of the curing process, it is simply a temporary moisture-retention facility for use during placing and finishing operations.

9.5

Final Curing

9.5.1

Contractor to Determine Method

The final curing shall be either water curing complying with 9.6, membrane curing complying with 9.7, or impermeable sheet curing complying with 9.8. The Contractor shall determine the most appropriate method consistent with this specification, and obtain approval where specified.

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9.5.2

Quality Control

The Contractor shall monitor the curing process and compliance with this specification. Records of the quality control shall be kept and be available for inspection if requested.

9.6

Water curing

9.6.1

General

As soon as possible after the finishing operations have been completed and the concrete has set sufficiently to prevent marring the surface, the forms and entire surface of the newly-laid concrete shall be prevented from drying by the continuous application of a mist spray, or by ponding. Where approved by the construction reviewer, the slab maybe covered with Hessian mats which are kept continuously wet for the specified curing time. Commentary: The use of Hessian may result in slight shade variations in the colour of the concrete. In most industrial situations this would be of no consequence, however if the appearance of the floor is a prime consideration, extra care should be taken to ensure curing is as even as possible. 9.6.2

Hessian Mats

When permitted, Hessian mats shall have sufficient width, after shrinkage, to cover the entire width and faces of the concrete slab. Provision shall be made to securely anchor the mats to ensure that they remain in place in windy conditions. The mats shall overlap each other at least 150 mm. The mats shall be saturated before placing and shall be kept continuously wet and in intimate contact with the slab edges and surface for the duration of the required curing period.

9.7

Sprayed Membrane Curing

9.7.1

Approval to use Membrane Curing

The Contractor shall obtain approval to use any curing compound from the Construction Reviewer. The request for approval shall include a statement on compliance with 9.7.2, the compatibility it has with any subsequent specified treatment, and the potential for discolouration. Membrane curing shall not be used where the surface will be painted, coverings are adhered to the surface, or where the covering supplier requires specified moisture readings in the concrete prior to the application of the product. Commentary: If floor slab coatings are specified, the compatibility of the coating with the curing compound needs to be determined. For some floor coverings, the manufacturer will require confirmation that the surface is appropriately dry before the covering is applied. Typically this is New Zealand Guide to Specifications for Concrete Production and Concrete Construction

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determined using a hygrometer. When curing membranes are used it can take a very long time before the slab sufficiently dries to accept the covering. 9.7.2

Membrane curing materials

Liquid membrane-forming curing compounds shall comply with the requirements of AS 3799 or ASTM C 30937. Commentary: Of the many different forms of liquid membrane-forming curing compounds available, the wax-based emulsions and chlorinated rubber types are preferred and recommended. Recent research has shown that special safety precautions are necessary for the use of chlorinated rubber compounds. A fugitive dye is suitable to visually check that the slab has been sprayed. Most of the silicate type agents are used for surface hardening and are not curing membranes. Before using as a curing membrane ask for proof they meet the requirements of AS 3799 or ASTM C 30937. However, they generally are then compatible with many of the various surface finishes used. Wax-based curing compounds are generally efficient in terms of moisture retention, but can provide a slippery surface. For this reason, it is recommended that they not be used when the slab is to be subject to early foot or vehicular traffic. 9.7.3

Application

On completion of initial curing the entire exposed surface of the concrete, including edges, shall be uniformly coated with the approved membrane curing compound applied in accordance with the manufacturer’s recommendations. 9.7.4

Spread evenly

The curing compound should be sprayed uniformly at the rate recommended by the manufacturer to achieve compliance with AS 3799. Commentary: Where chemically compatible with individual curing compounds, the use of coloured fugitive dyes are effective in providing for a visual check of uniform coverage.

9.8

Impermeable Sheet Curing

Commentary It is common to get some shade variation in the colour of the concrete when using sheet curing. When not acceptable, this method of curing should be deleted from the specification.

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9.8.1

Impermeable Sheet Materials

Impermeable sheet materials shall comply with the requirements of ASTM C171. 9.8.2

Application

On completion of initial curing and for the remainder of the curing period, the moistened concrete surfaces shall be covered with approved impermeable curing sheets. The curing sheets shall be in pieces large enough to cover the entire width and edges of the slab. Adjacent sheets shall overlap not less than 500mm and the lapped edges securely tied or weighted down along their full length to prevent displacement or billowing by wind. Sheets shall be folded down over the side of the pavement edges, continuously weighted, and secured. Tears and holes appearing in sheets during the curing period shall be repaired immediately. Commentary: The most commonly used impermeable covering is waterproof plastic sheeting, such as clear polyethylene or its equivalent. The sheeting should be placed as soon as the condition of the concrete is such that the surface will not be marked or damaged.

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1 0 . JOINTS Commentary: This specification refers to four types of joints, defined below: ƒ

Free joint- a joint designed to open up as shrinkage occurs without any restraint across the joint.

ƒ

Tied joint- either the reinforcement is continuous through the joint, or when used as a construction joint, bars (tie bars) are used to tie each side of the joint together.

ƒ

Isolation joint- these isolate the slab from other elements, typically other structures.

ƒ

Construction joints.

10.1 General All joints shall conform to the details, and shall be constructed in the locations shown in the drawings.

10.2 Free Joints 10.2.1

As specified on drawings

Free joints shall be as specified on the drawings. Where proprietary systems are used they shall be installed in accordance with the manufacturer’s recommendations. Commentary: For industrial application where heavy loads or pallet stackers are used it is recommended that free joints have steel armoured edges and are dowelled. Many very good proprietary systems are available. Where the joints are not trafficked, or where they will only be crossed by pneumatic tires, then need to amour the edges can be omitted. 10.2.2

Dowels to be Accurately and Securely Positioned

Where specified, dowels shall be placed across joints where indicated in the drawings. The dowel system shall be precisely aligned and securely held parallel to the surface of the finished slab during placing and finishing operations. The method used to hold dowels in position shall be sufficiently rigid to ensure that individual dowels do not deviate by more than 3 mm in 300 mm from their specified alignment. 10.2.3

Dowel Tolerances

Unless specified otherwise by the dowel manufacture, the vertical and horizontal tolerances shall not be exceeded the lesser of 5% of the slab thickness; or ±10 mm.

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10.2.4

Spacing of Dowels

The spacing of dowels in longitudinal construction joints shall be as indicated on the drawings. Dowels shall be omitted when the centre of the dowel would be occurring within 200 mm (horizontally) of a transverse free joint.

10.3 Isolation Joints 10.3.1

General

Isolation joints shall be formed by means of an approved preformed bond breaker. 10.3.2

Location

Isolation joints shall be formed about structures and features that project through, into or against the slab, using joint filler of the type, thickness and width as indicated, and installed in such a manner as to form a complete, uniform separation between the slab and the element to be isolated.

10.4 Tied Joints Commentary: Tied joints can be constructed in numerous ways including: ƒ

construction joints incorporating tie bars,

ƒ

saw cuts, which can be early entry or cut with diamond blades,

ƒ

proprietary crack inducers, with reinforcement through joint,

ƒ

tooled joint in reinforced slab.

The following clauses give recommendations for generic systems. It assumes that the types of joints will be shown on the drawings, and if saw cutting is specified the drawings will indicate if early entry or diamond blade saw cutting is to be used. 10.4.1

Tied Joints as Shown on Drawings

The location and type of tied joints shall be as shown on the drawings. Tied joints shall be constructed in accordance with Clause 10.4. 10.4.2

Tied Joints Constructed by Diamond Blade Saw Cutting

Sawn tied joints shall be constructed by sawing a groove not less than 3 mm and not more than 5 mm in width for a depth of quarter the slab depth unless shown otherwise on the drawing.

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The time of sawing shall be varied, depending on weather conditions, and shall be such as to prevent uncontrolled cracking of the pavement. Sawing of the joints shall commence as early as possible, typically within 24 hours, and be commensurate with the concrete having hardened sufficiently to permit cutting without excessive chipping, spalling or tearing. A chalk line or other suitable guide shall be used to mark the alignment of the joint. The saw cut shall be straight from edge to edge of the panels and shall not vary more than 10 mm from the true joint alignment. Commentary: These joints are designated as tied joints so in no circumstances should the reinforcement through the joint be cut. 10.4.3

Tied Joints Constructed by Early Entry Saw Cutting

Early entry sawn joints shall be created as early as possible after initial set of the concrete without raveling of the joint. The depth of the cut shall be the greater of 25mm or one eighth of the slab thickness. Commentary: Early entry saws ensure that saw cuts are in place immediately after finishing. These provide a degree of protection against random cracking due to restrained early thermal contraction. There is a limited window of opportunity for these types of saw cutting hence the requirement in 8.16 that the saws are on site before the start of the final finishing operation.

10.5 Construction Joints Construction joints shall conform to NZS 3109, type B, unless notified otherwise. Their location shall be as shown on the drawings, or if not shown, agreed in advance with the Construction Reviewer.

10.6 Joint Sealing Commentary This section assumes that the joints which require sealing are indicated on the drawings. It is important to note that the sealing of free and tied joints is very different. The reinforcement crossing a tied joint is expected to remain elastic and therefore movement across the joint is small. For tied joints the joint can simply be filled with the sealant. When free or isolation joints require sealing, specific design of the dimensions of the sealant is required. For these joints it is important that a bond breaker is used to ensure that the sealant does not stick to the bottom of the joint (it should stick only to the sides) and to avoid excessive demands on the sealant the sealing process should be delayed as much as possible to avoid large movement demands on the sealant due to shrinkage of the concrete.

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10.6.1

Seal Joints as Shown on Drawings

The location and type of joints requiring sealing shall be as shown on the drawings. 10.6.2

Widening of Tied Sawn Joints Requiring Sealing

After expiration of the curing period and immediately prior to joint sealing operations, an 8-10 mm groove for the joint sealer shall be sawn to a depth of 20 mm in the top of sawn joints. Where multiple cuts are necessary to saw the groove to the specified dimensions, the groove shall be washed out between successive saw cuts so that a check can be made of the alignment over the joint edge. The sides of the sawn groove shall be parallel. 10.6.3

Sealant Installation in Tied Joints

Immediately before the installation of the sealer, the joints shall be thoroughly cleaned so that the entire joint space is free from concrete, dirt, dust and other materials. The joint shall be filled with (…..) sealant applied in accordance with the manufacturer’s recommendations. 10.6.4

Sealant Installation in Free Joints

The dimensions and details of the sealing of free joints shall be as shown on the drawings. A bond breaking tape shall be provided at the bottom of the joint to ensure that the sealant only adheres to the sides of the joint. The sealant shall be installed (…) days after the completion of curing of the slab. Commentary: Specific design of the joint sealant is required so this specification assumes that the details will be provided on the drawings.

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1 1 . PROTECTION OF CONCRETE SLABS 11.1 General Concrete slabs shall be protected against all damage prior to final acceptance of the work.

11.2 Construction Traffic Irrespective of age, trafficking of pavements by tracked or solid-wheeled construction equipment shall be permitted only if protective matting, steel plates, or timbers are placed under their wheels or tracks.

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1 2 . TESTING AND ACCEPTANCE OF CONCRETE 12.1 General The finished floor tolerances shall be in accordance with Section 13, and the concrete shall be tested for compliance with the specification in accordance with this section.

12.2 Compression Testing of Normal and Special Concrete 12.2.1

Testing in Accordance with NZS 3104

For both Normal and Special concrete, the Concrete Supplier shall conduct all tests required by NZS 3104 for Normal concrete. The results of tests shall be recorded and be available on request. The Concrete Supplier shall also be able to demonstrate compliance with Section 2 of this specification. Commentary: Clauses 2.3 and 2.9.2 in Section 2 relate only to Special concretes. Testing to NZS 3104 ensures that: ƒ

Aggregates are test for grading and cleanliness per 100-300 m3.

ƒ

Sands are tested every 50-150 m3.

ƒ

Total alkali content is less than 2.5kg/m3.

ƒ

Compression tests of one test (2-3 cylinders) per 75m3 up to 15,000 m3 per annum and over this volume, one test per 250 m3.

ƒ

Slump testing, as a minimum with each compression test.

ƒ

Air content tests, one a day to once a week.

ƒ

Monthly results monitored by the plant engineer.

ƒ

Annual audit of plant by independent engineer (for plants with audit certificate).

Random testing to NZS3104 will not however guarantee that the concrete supplied to your project is sampled and compression tested. Where this is considered desirable this needs to be specified as indicated in 12.2.2. 12.2.2

Schedule of Supplementary Testing

In addition to the testing provided in 12.2.1, representative samples of fresh concrete shall be taken on site in accordance with NZS 3112:Part 1 for compression strength testing and slump testing in the locations and frequency defined in Table 12.1. New Zealand Guide to Specifications for Concrete Production and Concrete Construction

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Table 12.1: Frequency of onsite compression testing Element

Sample and test frequency

Floor

One test per ?? m3

All personnel conducting tests shall be adequately trained having satisfied the requirements of New Zealand Qualification Authority unit standard 12019 - Carry out Routine Tests on Concrete. Testing shall be in accordance with NZS 3112. A compression test shall comprise of three cylinders of the same batch of concrete. A compression test result, as specified in 9.4 of NZS 3109, shall be the average of the three cylinders. Commentary: Only use the above clause if you require tests above that specified in NZS 3104 or specifically want tests on your concrete.. Tests carried out by untrained personnel may not be recognised by the concrete supplier. If the customer opts to carry out a testing programme under their own auspices, the work must be done in strict accordance with the relevant documents or else the results could be challenged or rejected by the supplier. As an alternative, the client could delegate these responsibilities to an INZ (TELARC) accredited laboratory. The customer may, at his or her discretion, request that samples be taken from their concrete for testing to determine its strength. This work may or may not be charged for by the supplier as it is, strictly speaking, in addition to the normal testing programmes as defined in NZS 3104. 12.2.3

Rejection Criteria

The assessment of test results shall be in accordance with 9.4 and 9.5 of NZS 3109.

12.3 Testing of Special Concrete Commentary: The test requirements for special concrete need to be linked to the criteria requested in Section 2.3 of this specification. It is recommended that the testing required build upon what would normally be specified for Normal concrete. 12.3.1

Additional test for Special concrete

In addition to the testing specified in 12.2.1 or 12.2.2, the following tests shall be conducted. New Zealand Guide to Specifications for Concrete Production and Concrete Construction

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Commentary: Any other requirements regarding the sampling and testing of concrete over and above that contained in NZS 3104 for Normal concrete, should be specified. The clause needs to be linked to 2.3 and should contain details of sampling and testing frequency. The following are some examples linked to those given in 2.3. Use of Cements Other Than GP Commentary: 12.2.2 would necessitate some compression test results and 2.3 requires batching records document the type of cement used. This maybe sufficient in many cases. If a performance criteria was set rather than the type of cement, the following would need to be placed in this section: ƒ

How and when the concrete will be tested.

ƒ

How the samples will be cured.

ƒ

What will be the conformance criteria.

Strengths Greater Than 50MPa Commentary: As the concrete supplier may not have a performance record for concretes over 50 MPa, it is desirable to specify the testing required. A possible solution could be to specify the following: Representative samples of fresh concrete shall be taken in accordance with NZS 3112 every (….) cubic metres with a set of four cylinders. one to be broken at seven days and three at 28 days. All personnel conducting tests shall be adequately trained having satisfied the requirements of New Zealand Qualification Authority unit standard 12019 - Carry out Routine Tests on Concrete. Testing shall be in accordance with NZS 3112. The target strength for a set of 30 consecutive tests shall be (…) MPa. The cautionary limit for six tests shall be (…) MPa. If the mean strength of any consecutive set of six tests is less than the cautionary limit, the mix design, batching and cylinder testing shall be reviewed. A compression test shall comprise of three cylinders tested at 28 days, from the same batch of concrete. A compression test result, as specified in 9.4 of NZS 3109, shall be the average of the three cylinders. The rejection limit for concrete shall be in accordance with 9.4 and 9.5 of NZS 3109. Commentary: For strengths greater than 50 MPa the specifier may need to liaise with the manufacturer’s plant engineer as to the Sd value used to set target strength and COV requirements for monitoring purposes. New Zealand Guide to Specifications for Concrete Production and Concrete Construction

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Monitoring concrete by way of mean strengths and test variation gives an engineer greater control of concrete quality than relying only on rejection limits. Air Content for Freeze Thaw Resistance Testing shall be carried out initially every 20 m3 until three consecutive tests show an air content within 1.5% of target. Then air tests shall be carried out every 75 m3. Tests shall be in accordance with NZS 3112. Use of SCM such as Fly Ash, Amorphous Silica and GGBS Commentary: No tests are specified above the tests specified for Normal concrete. If additional testing is required it should be specified here. Use of Aggregates Greater Than 37.5mm Commentary: No tests are specified above the tests specified for Normal concrete. If additional testing is required it should be specified here. Fibre Reinforced Concrete Commentary: No tests are specified above the tests specified for Normal concrete. If additional testing is required it should be specified here. Use of Specified Shrinkage Values Commentary: It is assumed that shrinkage tests will be conducted on a trial mix, and once an acceptable mix has been determined, conformance testing will be limited to monitoring batching records. If shrinkage testing is to form part of the conformance requirements it would need to be specified here. It should be noted, however, that shrinkage tests take a considerable amount of time and therefore have little use as a conformance test. 12.3.2

Rejection Criteria for Special Concrete

Commentary: The criteria for rejection of the concrete will depend on the reasons for specifying Special concrete. The criteria against which concrete will be rejected should be specified in this clause.

12.4 Rejection Criteria In addition to the criteria set in 12.2.3 and 12.3.2, where appropriate, hardened concrete shall be liable to rejection if any of the following defects occur:

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It is porous, segregated or honeycombed.

The reinforcing steel has been displaced from its correct location.

Inserts and other items embedded in the concrete have been displaced from their specified position.

The concrete work can be shown to be otherwise defective.

12.5 Concrete That is Liable to Rejection May Be Permitted Concrete that is liable to rejection may be permitted to be retained on the basis of satisfactory results being obtained from one or more of the following: •

An appraisal of the statistical information related to the concrete strength.

A structural investigation.

Additional tests (such as outlined in NZS 3109).

Approved remedial work.

12.6 Rejected Concrete Where concrete work has been finally rejected it shall be removed to the extent determined, and replaced in accordance with Clause 14.

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1 3 . CONSTRUCTION TOLERANCES Commentary: The surface tolerances and profile of the floor need to reflect the planned use of the floor. Typically floor regularity is controlled in two ways- flatness (i.e. bumpiness), and levelness. There are several ways in which these variables can be measure and evaluated. It is important, regardless of the method used, that appropriate limits are set. Generally the tighter the tolerances the more expensive the construction method. Following NZS 3109 and a U3 finish (trowelled) in NZS 3114 would provide surface tolerances of level +/- 10 mm and gradual deviations of 5mm measured over a 3 m length. Note this requirement is often modified to be +/- 3 mm measured using a 3 m straight edge. The TR 34 produced by the UK Concrete Society specifies different tolerances for different floor classifications. FM 1 has the tightest tolerances and FM 3 the least restrictive. Levelness is measured by levels taken on a 3m grid, and flatness by elevational distance over a 600mm length. This is typically measured by specialist equipment. In the US, ACI 302 provides an evaluation method using a F number system. Two numbers are determined using a machine, the floor flatness FF and floor levelness FL. In this specification it has been assumed that New Zealand Standards will be used, with some modification. If either the TR 34 or the ACI 302 method is used, then appropriate clauses will need to be developed.

13.1 General Following completion, the finished surfaces of the various sections of the pavement shall be tested for conformance to the grades, lines and levels shown in the drawings, and for surface smoothness by the methods detailed hereunder.

13.2 Surface Levels The finished surface of the slab measured on a 3m grid coinciding with the grid used for the sub-base shall conform to the levels, grades and cross sections shown in the drawings to the extent that: a.

All points shall be within +/- (‌)mm of the level specified in the drawings.

b.

The difference in level between adjacent grid points shall be less than (‌)mm.

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c.

95% of the results from (b) shall be less that (…)mm.

Commentary: Note the above clause assumes that the floor is supposed to be flat. It will need to be modified if the floor is to be constructed to a specified fall. NZS 3109 specifies that the limit on (a) is +/-10 mm but provides no tolerance or acceptance criteria associated with these clauses. TR 34 specifies that 100% of the levels of (a) should be within +/- 15 mm. Items (b) and (c) are not a requirement of NZS 3109 but have been taken from TR 34. TR 34 specifies limits of 4.5 mm, 8 mm, and 10 mm for item (b) for FM 1, FM 2, and FM 3 floors respectively. For item (c) these limits are 7.0 mm 12.0 mm, and 15 mm. Consideration should be given as to whether to use this clause rather than rely on the clauses relating to surface flatness and slab thickness.

13.3 Surface Flatness The finished surfaces of the various sections of the pavement shall not deviate from the testing edge of an approved 3m straightedge by more than (…)mm. Refer to NZS 3114. Commentary: The requirements of NZS 3114 give acceptance criteria for an individual point. There are however, no criteria for what proportion of measurements exceeding the limit might be considered acceptable. Some American specifications provide for financial effects for exceeding or not meeting the flatness specification. The American F number system has been specified on many slabs as it provides a statistical measure of a slab’s flatness and levelness. However, this does not measure close to joints or slab edges which will be of interest to an end user. This would require separate acceptance criteria.

13.4 Remedial Works Where the tolerances of this specification are not achieved, the Contractor shall submit for approval, the proposed remedial work.

New Zealand Guide to Specifications for Concrete Production and Concrete Construction

43/44

July 2009


1 4 . REMOVAL AREAS

AND

REPLACEMENT

OF

DEFECTIVE

14.1 Defective Pavement Areas Slab areas outside the tolerances specified in Section 13, and areas rejected in accordance with Clause 12.4 shall be considered as defective pavement areas.

14.2 Removal and Replacement The Contractor shall submit the proposed remedial works for approval. Where the suggested remedial works is not approved, defective slab areas shall be removed and replaced as specified herein with pavements of the thickness and quality required by this specification.

14.3 Jointing to Existing Pavement Jointing of the replacement concrete to the existing concrete shall be by an approved method.

New Zealand Guide to Specifications for Concrete Production and Concrete Construction

44/44

July 2009


2nd Edition

Designing Comfortable Homes Guidelines on the use of GLASS, MASS AND insulation for energy efficiency


Designing Comfortable Homes 2nd Edition Guidelines on the use of glass, mass and insulation for energy efficiency

ISBN 978-0-908956-20-3 ISBN 978-0-908956-21-0 (pdf) TM37 Cement & Concrete Association of New Zealand Level 6, 142 Featherston St, Wellington. PO Box 448, Wellington. Tel: (04) 499 8820, Fax: (04) 499 7760. E-mail: admin@ccanz.org.nz www.ccanz.org.nz ŠCement & Concrete Association of New Zealand 2010 ŠEnergy Efficiency and Conservation Authority 2010


Preface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

4. EXPECTED PERFORMANCE . . . . . . . . . . . . . . . . 41

1. INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Performance Calculations . . . . . . . . . . . . . . . . . . 41

Basic Principles of Passive Solar Design . . . . . . . . 5

The electronic buildings . . . . . . . . . . . . . . . . . . 42 Locations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 Expected performance in other climates . . . . 42

Glass, Mass and Insulation Explained . . . . . . . . . . 6 Glass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Mass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Insulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Energy Modelling . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Other Considerations . . . . . . . . . . . . . . . . . . . . . . 10 Cost effectiveness . . . . . . . . . . . . . . . . . . . . . . . Health . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Occupant behaviour . . . . . . . . . . . . . . . . . . . . . Energy efficient appliances . . . . . . . . . . . . . . . Embodied energy . . . . . . . . . . . . . . . . . . . . . . . Sustainability . . . . . . . . . . . . . . . . . . . . . . . . . . .

10 11 11 11 13 13

2. glass, Thermal Mass and Insulation . . . . 16 Glass – Heat Collection . . . . . . . . . . . . . . . . . . . . 16 Orientation . . . . . . . . . . . . . . . . . . . . . . . . . . . . Heat loss from glass . . . . . . . . . . . . . . . . . . . . . Area of glass . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sunspaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

16 17 18 18

Thermal Mass – Heat Storage . . . . . . . . . . . . . . . 20 How thermal mass works . . . . . . . . . . . . . . . . 20 How much thermal mass? . . . . . . . . . . . . . . . . 22 Thermal mass and energy efficiency . . . . . . . . 22

Insulation – Heat Containment . . . . . . . . . . . . . . 23 How much insulation . . . . . . . . . . . . . . . . . . . . 23 Install insulation correctly . . . . . . . . . . . . . . . . 23 Insulating timber floors . . . . . . . . . . . . . . . . . . 23 Insulating concrete floors . . . . . . . . . . . . . . . . 24 Insulating timber-framed walls . . . . . . . . . . . . 24 Insulating thermal mass walls . . . . . . . . . . . . . 25 Roof insulation . . . . . . . . . . . . . . . . . . . . . . . . . 26

3. additional important DESIGN PRINCIPLES . 28 Avoid Overheating . . . . . . . . . . . . . . . . . . . . . . . . 28 Shading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 Ventilation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 Direct ventilation . . . . . . . . . . . . . . . . . . . . . . . 32

Heat Distribution . . . . . . . . . . . . . . . . . . . . . . . . . 33

Variations in Construction . . . . . . . . . . . . . . . . . . 44 Glass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 Mass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46 Insulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

Performance Results . . . . . . . . . . . . . . . . . . . . . . 48 Comfort . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48 Energy use . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48 Your specific design . . . . . . . . . . . . . . . . . . . . . 50

Auckland . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51 Construction details . . . . . . . . . . . . . . . . . . . . . Temperature fluctuations . . . . . . . . . . . . . . . . Cooling need . . . . . . . . . . . . . . . . . . . . . . . . . . . Overnight temperature drop . . . . . . . . . . . . . . Purchased energy for heating . . . . . . . . . . . . . Required heater size . . . . . . . . . . . . . . . . . . . . .

51 52 53 54 54 55

Wellington . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56 Construction details . . . . . . . . . . . . . . . . . . . . . Temperature fluctuations . . . . . . . . . . . . . . . . Cooling need . . . . . . . . . . . . . . . . . . . . . . . . . . . Overnight temperature drop . . . . . . . . . . . . . . Purchased energy for heating . . . . . . . . . . . . . Required heater size . . . . . . . . . . . . . . . . . . . . .

57 57 58 59 60 61

Christchurch . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62 Construction details . . . . . . . . . . . . . . . . . . . . . Temperature fluctuations . . . . . . . . . . . . . . . . Cooling need . . . . . . . . . . . . . . . . . . . . . . . . . . . Overnight temperature drop . . . . . . . . . . . . . . Purchased energy for heating . . . . . . . . . . . . . Required heater size . . . . . . . . . . . . . . . . . . . . .

62 63 64 65 65 66

5. NEW ZEALAND BUILDING CODE REQUIREMENTS . . . . . . . . . . . . . . . . . . . . . 68 Determining insulation values . . . . . . . . . . . . 68 Methods of compliance . . . . . . . . . . . . . . . . . . 68

6. APPENDICES . . . . . . . . . . . . . . . . . . . . . . . . . . . 70 Appendix 1 – Two-storey house results . . . . . . 71

Airtightness . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

Appendix 2 – Climate zones . . . . . . . . . . . . . . 75

Using Plan Layout to Improve Comfort . . . . . . . . . 34

Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86

Size and shape . . . . . . . . . . . . . . . . . . . . . . . . . . Orientation . . . . . . . . . . . . . . . . . . . . . . . . . . . . Site selection . . . . . . . . . . . . . . . . . . . . . . . . . . . Sunpath diagrams . . . . . . . . . . . . . . . . . . . . . . . Topography . . . . . . . . . . . . . . . . . . . . . . . . . . . . Ground surface cover around the house . . . . Water moderates temperatures . . . . . . . . . . . . Wind contributes to heat losses . . . . . . . . . . .

35 36 37 37 38 38 38 39

contents


T

he first edition of this book was published in 2001 and quickly became recognised as an invaluable plain English guide for anyone interested in designing comfortable energy efficient homes. As well as providing general guidance on solar design considerations that are important to enhance energy efficiency and comfort, the book also provided data on expected performance of homes based on three different combinations of glass, mass and insulation. These were defined as ‘code minimum’, ‘better’ and ‘best’. As a direct result of the 2001 edition of Designing Comfortable Homes, Standards New Zealand published a specification document (SNZ PAS 4244) in 2003. This specification used the ‘code minimum’, ‘better’ and ‘best’ insulation options from Designing Comfortable Homes as its basis. When the Department of Building and Housing put in place new minimum insulation requirements in 2007 they were almost identical to the ‘better’ level first defined in this book in 2001 and subsequently published in SNZ PAS 4244. With Code minimum now at the level defined as ‘better’ in the 2001 edition, and the development of improved products and systems making very high energy efficiency more achievable, it was time to create this second edition. If it is as successful as the first, perhaps we will see the code minimum requirements being increased further in the future based on the ‘better’ level defined in this edition, and perhaps a third edition of Designing Comfortable Homes following that change. Authors Michael Donn, School of Architecture, Victoria University of Wellington Grant Thomas, Independent Consultant Research Associates Morten Gjerde, School of Architecture, Victoria University of Wellington Ralf Kessel, Cement & Concrete Association Alana Hamill, School of Architecture, Victoria University of Wellington Nick Smith, School of Architecture, Victoria University of Wellington Peer Reviewers Roger Buck, Roger Buck and Associates, Architects Dene Cook, NZ Concrete Society Allen Davison, EECA

Christian Hoerning, EECA Peter Parkes, Strategic Architecture Brenda Vale, School of Architecture, Victoria University of Wellington Peer reviewers have provided invaluable input into the content and presentation of this book. They are not, however, responsible for the opinions and recommendations offered, or for any errors or omissions. Design and Layout City Print Communications Limited Illustrations Many thanks to the following people for permission to use their images: Tim Barton, Roger Buck, Martin Hanley, . Rory Hocking, Philip Kennedy, Darren Matthews, Tim Nees, Hugh Tennent, . Anna Kemble Welch, Deborah Dewhirst Photography (Beacon Pathway NowHome), Kevin Hawkins Photography (Cranko Architects), Craig Robertson Photography (Beacon Pathway NowHome), Ralf Kessel (Architects: Novak Middleton), . Deborah Cranko (Cranko Architects), . Simon Devitt Photography (Architects: Parsonson). . Cover Photo: Michael Nicholson Photography Building Plans Building plans used for the computer studies were kindly provided by Mark Rantin and Ray McElroy of MRA Architects and by Universal Homes Ltd. Special Thanks Special thanks to Michael Deru, Ron Judkoff and Paul Torcellini of the National Renewable Energy Laboratory, Golden Colorado, USA for their support in the use of SUNREL. Except where the Copyright Act allows, no part of this publication may be reproduced, stored in any retrieval system in any form, or transmitted by any means, without the prior permission in writing of the Cement & Concrete Association of New Zealand and the Energy Efficiency and Conservation Authority. The information provided in this book has been prepared with all due care; however the Cement & Concrete Association of New Zealand and the Energy Efficiency and Conservation Authority accept no liability arising from its use. ISBN 978-0-908956-20-3 ISBN 978-0-908956-21-0 (pdf)

preface


introduction

1


Chapter 1: Introduction

T

his book’s primary aim is to provide you with an understanding of the basic principles of passive solar design – the key to comfort and reduced energy use in New Zealand homes. The premise of this book is that homes can be naturally warm in winter and cool in summer – provided appropriate combinations of glass, thermal mass and insulation are used. Designing Comfortable Homes is written with the ‘average’ home owner in mind, rather than the committed passive solar enthusiast. Passive solar design principles are not only essential for good home design but they are also generally easy to understand. We encourage you to embrace these simple concepts when you build so that you get a much more comfortable and energy efficient home. This book is also intended to address a widely held misconception that compliance with the energy efficiency requirements of the New Zealand Building Code is best practice – this is far from the truth. The Code sets minimum performance requirements only – in other words they are the levels that it is illegal to go below. To get better performance, you need to move beyond Code requirements. This book defines two higher levels of insulation – Better Practice and Best Practice – and through computer modelling shows the comfort and energy efficiency benefits these and other improvements can provide. This first chapter provides a brief introduction to passive solar design and its benefits, followed by: • Chapter Two – Key design considerations for glass, thermal mass and insulation • Chapter Three – Information on other important design considerations such as site selection • Chapter Four – The value of passive solar design demonstrated through computer modelling.

Basic Principles of Passive Solar Design The principles of passive solar design for a comfortable energy efficient house can be summarised very simply: • INSULATE: Use insulation to slow the flow of heat in and out of the house – heat from the sun is used more effectively in houses that are well-insulated. Insulation helps to maintain more constant internal temperatures and reduces the need for heating in winter and cooling in summer. • GLAZE: Use glazing to bring heat from the sun into the house – though glass must be selected, placed and sized

5


1 introduction carefully as it is a poor insulator (windows should be double glazed as a minimum to reduce heat loss). • ADD THERMAL MASS: Use heavyweight materials (thermal mass) to soak up heat from the sun and release it slowly into the house when temperatures drop. A house with appropriate mass will maintain more comfortable temperatures – it will overheat less often and not get as cold overnight. • STOP AIR LEAKAGE: Use weather-stripping, high-quality sealants and less complicated house designs to reduce air leakage. Once a house is well-insulated and appropriately glazed, the biggest potential heat loss is through draughts around windows, doors and other construction joints. • SHADE: Use external shading to manage the heat gain from the sun. Well-designed window systems must not only collect heat from the sun when desirable, but also exclude it at times when it might cause overheating. • VENTILATE: Use openable windows and other ventilation to reduce overheating and maintain good indoor air quality. Appropriate placement of windows for good cross flow of air through rooms will make them more effective for cooling on hot days. Good ventilation also helps to reduce condensation and remove cooking and other odours. Other important factors that you should consider when designing a house, such as site selection, house placement and orientation, are covered in Chapter Three. It is important to consider these, in combination with the factors above, when designing a comfortable energy efficient house.

Glass, Mass and Insulation Explained Although this book provides information on a wide range of factors that you should consider when designing a comfortable energy efficient house, Chapter Two focuses on the three factors that are most important to gaining benefit from the free energy from the sun: • Glass – to collect the sun’s heat • Thermal mass – to store the heat Glass to collect the sun’s heat Mass to store the heat Insulation to keep the heat in

6

• Insulation – to keep the heat in.

Glass Glass is typically not only the single greatest source of heat gain, but also the greatest contributor to heat loss in a house. A single sheet of glass can conduct over 10 times more heat than the same area of insulated wall.


Fortunately, with the now widespread use of ‘Insulating Glazing Units’ (IGUs), most commonly standard double glazing, heat loss through glass can be substantially reduced. However, performance of an IGU is determined by both the glass and the frame of the window – heat loss through standard double glazing can be significantly reduced by using better frames. More information about the relative benefits of various glazing and frame options is provided in Chapter Two. It is useful to understand that the insulation of the house and its windows is much more important than the heating effect of the sun shining through the windows. The major driver of heating requirement for a house is cold outside temperatures – the varying sunshine levels around the country make very little difference to the heating required. For example, Nelson receives much more sunshine per year than Wellington but its houses must be insulated to a higher level than those in Wellington to maintain the same annual heating energy use because of the colder winter temperatures. The following graph illustrates these differences using the calculated building performance results from Chapter Four1. Energy inputs – solar heating and purchased energy – are shown as positive and heat losses to the outside are shown as negative. These show the house in Wellington – in Building Code Climate Zone Two2 – requires about the same purchased heating energy (the red part of each bar) as the same design house in Nelson, which is insulated to the higher levels of Climate Zone Three.

Thousands of kWh per annum Thousands

Heat losses and gains for the same house in Wellington or Nelson 35

25

15 Solar Solar gain Ground Groundfloor

5

Walls & roof Ambient Windows Windows

-5

Air leakage Infiltration Ventilation Ventilation

-15

Heating Heating

-25

-35 Wellington

Nelson

high mass

1 2

Wellington

Nelson

low mass

The two-storey house referred to on page 41 was used for these calculations. For more information about climate zones, see Appendix 2 on page 75.

7


1 introduction Thermal mass All building materials require a certain amount of heat energy to warm up. In this respect, all building materials have a ‘thermal mass’. Materials like concrete masonry and brick, however, require much more heat to warm up than materials like timber or plastic. They therefore store greater amounts of energy which makes them more effective for heating and cooling a house. In this book, the term ‘thermal mass’ is used to describe materials that have a significant capacity to store heat. Typically, these building materials are also ‘heavy’. Houses that contain high thermal mass are often referred to as being of ‘heavyweight’ construction, in contrast to houses of ‘lightweight’ construction, such as ones built with steelframed or timber-framed walls.

“A house incorporating appropriate levels of thermal mass should be more comfortable in all seasons and less expensive to keep warm in winter as long as it is insulated well.”

A house incorporating appropriate levels of thermal mass should be more comfortable in all seasons and less expensive to keep warm in winter as long as it is insulated well. The most common high thermal mass material used in house construction is concrete (commonly in floor slabs and masonry walls). Concrete is readily available and can be used for the structure of the house as well as providing thermal mass. Other forms of thermal mass used in house construction are rammed earth, natural stone and brick. For ease of reading, ‘concrete’ is often used as an example of a high thermal mass material in this book, though these other forms of thermal mass can provide similar comfort and energy efficiency benefits. High thermal mass materials such as concrete have not been very widely used for house wall construction in the past and as a result you may be concerned about factors such as earthquake resistance. Concrete, like all other materials used for house construction, must meet all the durability and structural safety requirements of the Building Code. You can therefore be assured that houses built from high thermal mass materials such as concrete are at least as safe and durable as timber-framed houses. High thermal mass materials are also fire resistant and reduce airborne noise transmission.

Insulation In winter a solar heated house collects the sun’s heat through glass, then stores it in thermal mass and finally makes sure the house retains heat by wrapping it in insulation. Good insulation is the most important component influencing the benefits that result. All materials have an insulation value; however, materials such as glass have a very low insulation value, which is why

8


condensation forms on the inside of single glazed windows on cold days. It is important to understand that high thermal mass materials like concrete and brick, in the thicknesses commonly used in buildings, also have poor insulation values. Their function as heat storage is in part due to this ability to conduct heat. Wood of the thickness of a rafter or a stud in a wall has a much higher insulation value than high mass materials, but still much lower than that of materials specifically designed to be used as insulation. In keeping with common practice, when this book refers to ‘insulation’ it means materials with a high insulation value such as fibreglass, polyester, wool or polystyrene.

Energy Modelling The first part of this book covers the basic design principles relating to glass, thermal mass and insulation and other issues related to the design of comfortable homes. Chapter Four illustrates the value of these principles through computer modelling. This computer modelling demonstrates expected performance and allows you to predict how your house will perform before it is built. The computer studies are of standard house designs in three different cities and for differing amounts of glass, thermal mass and insulation. These computer studies measure comfort, energy use and heater size requirements. The cities chosen are Auckland, Wellington and Christchurch. Although these cities are not representative of all climates within New Zealand, the results, and the relationship between them, give a reasonable idea of how a particular design will perform in another location3.

3

For more information about climate zones, see Appendix 2 on page 75 and the calculations on page 43 of the performance of the same building in 18 different climates across New Zealand

9


1 introduction The computer studies look at the performance of two specific house designs. Performance will, of course, be different for each individual house design. However, the example houses should provide good guidance on the general effects of various design options. The houses studied in this book are a singlestorey design of around 200 square metres (excluding the garage) and a two-storey house with similar floor areas. If it is important for you to have accurate thermal performance data for your design, you will need to conduct your own computer studies (or get a computer modelling specialist to do it for you). There are a number of suitable programs4 available. The studies in this book were conducted by the Centre for Building Performance Research, School of Architecture, Victoria University of Wellington, using the SUNREL computer performance simulation program developed by the National Renewable Energy Laboratory in the USA (see www.victoria.ac.nz/cbpr).

Other Considerations Cost effectiveness Building is a series of trade-offs. Most people start with a fixed budget and make a series of decisions on where to invest their money within that budget. Although some features, such as high-performing windows, can add significant additional cost, by investing in these features the thermal performance of the house can be dramatically improved. Fortunately most passive solar design principles can be incorporated at little or no additional cost. For example, the additional cost of higher-performing insulating materials is generally relatively small. Major comfort and energy efficiency gains can also be achieved simply through careful consideration of how glazing and mass are placed and used in combination. Sometimes compromises will be made on thermal performance for reasons other than cost, and there will be the inevitable trade-offs between conflicting design requirements. Data provided in Chapter Four of this book should help you to evaluate the effect of trade-offs on energy use and comfort.

4

10

SUNREL (www.nrel.gov), AccurateNZ (www.energywise.govt.nz), IES Virtual Environment (www.iesve.com/A-NZ) and EnergyPlus (http://apps1.eere.energy.gov/buildings/energyplus/).


Health Good passive solar design results in even, comfortable temperatures within a house and this creates a more healthy living environment. This is particularly important for older people and the very young who are more susceptible to cold temperatures. Low temperatures have also been associated with asthma and other allergic reactions. Because the surface temperatures of well-insulated high thermal mass walls are more stable, they are less likely to fall below the level at which condensation occurs. Condensation leads to the growth of mould and fungi which can exacerbate respiratory conditions.

Occupant behaviour One very significant influence on comfort and energy efficiency is occupant behaviour. The number of people who live in the house, when and how they occupy it and how they use appliances (such as heaters and air conditioners) can have a significant impact on energy use and comfort. A house that is occupied for most of the day, most days of the year and with heaters switched on by thermostats will perform quite differently from a ‘weekender’ that is occupied regularly for two days a week and relies on occupants to operate heaters. The ideal mix of glass, thermal mass and insulation is very much dependent on occupant lifestyle, so you should consider this at the outset. For example, a high thermal mass house is less likely to overheat in summer, but in winter will heat up more slowly than a low thermal mass house with similar insulation.

Energy efficient appliances provide further energy gains This book focuses on design for comfortable temperatures and reduced space heating and cooling requirements. However, energy efficient heating is also important to lock in the potential savings from good design. Thorough research into the various space heating options is important, particularly as new technologies emerge. When choosing a heater, refer to the ‘heater size’ notes in Chapter Four. These are for the whole 200 square metre house. Don't install a large heater in the living room unless you have a way of effectively distributing its heat to the other rooms. Go to energywise.govt.nz for impartial advice. In warmer parts of the country a well-designed house may need little or no purchased heating or cooling. To ensure you don’t over invest in heating, it may be wise to delay purchasing heaters until you have lived in the house for a while and assessed your actual heating needs.

11


1 introduction The pie chart5 below shows that for an average existing New Zealand house space heating energy use is about one-third of total energy use. The glass, mass and insulation strategies outlined in this book have the potential to reduce the space heating considerably and therefore increase the proportion of total energy use associated with other aspects such as water heating, lighting and appliances. Typical energy consumption for an average existing NZ house OTHER APPLIANCES

13% LIGHTING

“Space heating is about a third of total energy use in an average existing house. New houses should use much less, making water heating a greater proportion of total energy use”

29%

8%

REFRIGERATION

HOT WATER

10% 6%

RANGE

34%

SPACE HEATING

In most New Zealand houses a major contributor to energy use is water heating. Technologies such as solar water heaters, heat pump water heaters and energy efficient shower heads can significantly reduce the energy costs for hot water (by 50-75% in the case of solar water heating, for example). Appliances are also significant energy users. Energy performance labels are now available on many appliances to assist you to make informed decisions. In addition, electronic controls on some appliances can result in added energy savings. Heated towel rails, for example, have a relatively low energy consumption per hour but use considerable energy if they are left running 24/7. Through the use of timers, that turn off items like towel rails when they are not needed, you can significantly reduce this energy use. Lighting is another area where energy savings can be made. Technology improvements, such as the introduction of compact fluorescents (CFLs) over recent years mean that efficient light bulbs that perform very well are now available at low cost. CFLs are around five times more efficient at producing light than traditional electric light bulbs and last considerably longer. LED (light emitting diode) lighting is another energy efficient lighting technology that is now available. Well-designed windows provide good daylight which also reduces the need to use electric lights.

5

12

BRANZ HEEP Study – Energy use in New Zealand households.


Because ceiling insulation must be kept clear of many types of recessed down-lights to avoid fire risk, this can result in large gaps in the ceiling insulation. A convection effect can also create further heat losses through the ceiling. Recessed down-lights of this type are therefore not recommended.

Embodied energy A more holistic view of energy efficiency takes into account the energy required to produce, transport and construct on site the materials used to build a house – the ‘embodied energy’. Increasingly, this type of analysis also accounts for the embodied carbon dioxide. The cost of this embodied energy is built into the cost of the building materials. The more energy intensive the material, the more expensive it is likely to be. Although larger amounts of glass, thermal mass or insulation increase the embodied energy of a house, if well-designed, the total energy used by that house over its life will be less (relative to an ordinary design). For example, using the higher levels of insulation proposed in this book results in operational energy savings that far outweigh any increased embodied energy. Thermal mass installed with good external insulation can significantly reduce operational energy use. If we assume the thermal mass is concrete, its use in construction adds embodied energy, but the energy savings over time result in an approximately neutral energy impact. A good source of accurate data on embodied energy and CO2 in New Zealand is the Victoria University Centre for Building Performance Research website (www.victoria.ac.nz/architecture/cbpr).

Sustainability If you want to design a more sustainable house there are many other issues to consider besides energy efficiency. Sustainable development is dependent on following sound individual design decisions for every aspect of the house. The sustainable house must balance a wide range of issues in line with your personal needs and aspirations. These include but are not limited to: • using materials from sustainable resources • using materials whose mining and manufacture produces a minimum of pollutants • using materials that minimise the life cycle impact of the house on the atmosphere • using low-maintenance materials

13


1 introduction • avoiding building materials that emit chemical pollutants into the house after they are installed • recycling and re-using materials in construction – and facilitating recycling in the building during its operation. If you are interested in pursuing these issues in more depth there are numerous publications available. A couple of useful starting points are A Deeper Shade of Green – Ed. Johann Bernhardt, Balasoglou Books, Auckland 2008 and The Ministry for the Environment website (www.mfe.govt.nz).

14


glass, thermal mass and insulation

2


2 glass, thermal mass and insulation Chapter 2: Glass, Thermal Mass and Insulation Good passive solar design simply makes effective use of the sun (and, to a lesser extent, other natural resources such as wind and landscape) to ensure comfortable and energy efficient houses. All houses make use of passive solar design to some extent, but many don’t make very good use of the sun. By providing detailed information on passive solar principles and the impact of design decisions, this book should help you to get the most from your house design. This section follows the path of solar heat gain through the house. It starts with glass that allows the sun’s heat to enter the house, moves onto thermal mass which helps to store this heat and concludes with insulation which traps the heat in the house.

Glass – Heat Collection Windows provide the simplest way for heat from the sun to be collected – they are also the most poorly insulated part of the building and therefore allow large heat losses. To maximise solar collection benefits and minimise energy losses, window size, type and orientation need to be carefully planned.

Orientation Window orientation guide

Unobstructed north-facing glazing6 is best as: 1) it captures solar energy in winter (when the sun is low in the sky)

North-facing – more and moderately large East-facing – less and smaller

West-facing – less and smaller South-facing – as few as possible and as small as possible

2) it is easiest to shade from direct sun during summer (when the sun is high in the sky) by providing northfacing eaves. Where practical, the longer axis of a house should be orientated east-west to optimise the north-facing exposure. Rooms may also be stacked or staggered to achieve a greater north-facing aspect. North-facing clerestory windows and skylights can be used to get direct sun into deep plan shapes. Particular care should be taken over the positioning of skylights as they are typically placed in a sloping roof so they tend to collect heat more in summer than in winter and they can be difficult to shade. Heat loss through a skylight, particularly on cold nights, is also much greater than through a window of the same size. East- and west-facing windows allow penetration of morning and evening sun, which can cause problems with glare (morning or evening) and overheating (more often in the evening). These factors should be considered when positioning east and west glazing. Adjustable shading systems such as interior vertical blinds or louvres can help prevent 6

16

See page 45 for information about the effect of different orientations.


“Significant energy and comfort benefits can be achieved by using more energy efficient windows.”

glare problems, but do little to reduce overheating. Exterior shading devices such as awnings are much more effective for preventing overheating. East- or west-facing glazing can be limited in size to reduce these problems. South-facing glazing receives very little direct sun and therefore allows heat loss without any significant compensating solar gain. South-facing windows are generally required for light and air but don’t necessarily need to be large to achieve this. If you want to be able to enjoy a view to the south one effective option is to use smaller windows that frame or shape the view rather than large picture windows.

Heat loss from glass Significant energy and comfort benefits can be achieved by using more energy efficient windows. Double glazing is now widely used throughout New Zealand. In addition to improved energy performance, double glazing also minimises window condensation and reduces noise transmission. The higher the performance specification of double glazing, the higher the inside surface temperature of a double glazed window, and therefore the warmer people will feel when close to this glass. The best performing windows allow less than half the heat loss of standard double glazing, and less than a quarter the heat loss of standard single glazing. Thermally broken metal frames perform 20% better than standard metal frames. Wooden and other low heat conduction frames such as PVC units can perform 40% better than standard metal frames, ‘low-E’ coating on the inner pane of double glazing can provide up to a 30% benefit and argon gas between the double glazing provides an additional benefit. The following graph demonstrates that simple double glazing is only half as effective as the best double glazing option. Comparison of insulation value of window types

R-Values (insulation value – bigger is better)

0.7 0.6 0.5 0.4 0.3 0.2 0.1 0

Double glazed aluminium frame

Double glazed Double glazed Double glazed Double glazed Double glazed Triple glazed thermally PVC frame timber-framed low-E, timber- low-E, argon with low-E broken framed fill, timber- timber-framed aluminium framed frame

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2 glass, thermal mass and insulation For the medium glazed house used in the calculations for this book, the heat losses through the standard double glazed windows alone amount to 25-30% of the total heat losses. This glass represents only 10% of the total external surface area of the building. The roof accounts for only 10% of the heat losses but is 30% of the total external surface area. The benefit from doubling the insulation value of windows will therefore be far greater than doubling the insulation value of the roof. To help in the selection of windows and glass doors that best meet your needs, the Window Association has developed a simple five-star rating system known as WERS (window efficiency rating system). WERS uses an accredited computer program to test specific glass and frame combinations. Window suppliers who participate in this scheme provide a certificate which verifies the WERS rating of the windows and doors supplied. A table of WERS ratings is available at . www.wanz.org.nz Good quality curtains that sit flush against all the window frame surfaces and thus seal well against draughts can significantly improve the performance of double glazing. Pelmets are one way of ensuring an effective seal at the top of the curtains. Of course curtains are only effective if they are drawn and sealed against the window frame when it is cold. Many curtains don’t seal well against the window frame and therefore don’t greatly improve energy efficiency.

Area of glass While north-, east- and west-facing glass is effective in capturing solar energy, this glass is also a major contributor to heat loss from the house. Maximising these window sizes will therefore not necessarily maximise comfort levels or energy efficiency – if it did, we would all live in glass houses! The ideal size for these windows is not easy to determine – factors to take into account include thermal mass, insulation and climate. The information in Chapter Four shows how various combinations of glass, thermal mass and insulation affect the comfort and energy efficiency in a ‘typical’ house. This information should help you to evaluate the likely impacts of various glazing options.

Sunspaces Sunspaces are simply highly glazed rooms, and are otherwise known as sunrooms or conservatories. They are a means of providing additional living area as well as providing a special mechanism for capturing solar energy. Properly operated sunspaces that are more than half the length of the north face of a well-insulated house can reduce space heating energy consumption by as much as 20-30% in the South Island and 40-70% in the north of the North Island. They are, however,

18


a relatively expensive heating system and also require very proactive operation by the occupants to achieve large energy savings. For effective operation, a sunspace should be able to be shut off completely from the main living areas of the house. This is because sunspaces are most effective as solar collectors when they are designed to overheat. The excess heat is then distributed to other rooms. Sunspaces that are designed as effective solar collectors can therefore sometimes get too hot to be used as a normal living space. Because of the high glazing area of sunspaces they also lose heat quickly when the sun is not shining. This means they can be uncomfortably cold on cold cloudy days and cold nights. Roof glazing of sunspaces can often make overheating worse in summer, and increase heat losses in winter. An optimum sunspace therefore has a well-insulated roof and large areas of northfacing glazing.

Winter

Summer

In New Zealand’s breezy climate the inside-outside transition zone provided by a sunspace can be a useful extra living area. It should be designed with good thermal storage or the temperature swings will be huge and much of the solar heat gain will be lost back to the outside. A concrete floor or a concrete or brick wall between the sunspace and the living areas of the house will provide that thermal storage if it sits in the sun for most of the day. A dark colour will greatly increase the ability to absorb heat – coloured concrete or a covering such as tiles can achieve this. Openings such as doors and windows are important for heat distribution. These openings must be to the outside for venting when the sunspace is too hot in summer and to the inside when the sunspace is hot in winter. As sunspaces have such a direct path for heat losses and gains through the glass, they should never be heated. It is quite easy to more than double the whole house heating energy use just by using a sunspace heater ‘to take the chill off’.

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2 glass, thermal mass and insulation Thermal Mass – Heat Storage How thermal mass works High thermal mass materials help to maintain stable, comfortable indoor temperatures and reduce the need for heating and cooling. The obvious advantage of well-utilised thermal mass is that heat energy from the sun is free. Thermal mass works in two ways. Firstly, when the sun shines through windows onto a high thermal mass surface, the solar radiation is absorbed directly – the thermal mass is more effective when it receives direct sunlight and is a dark colour which absorbs more heat. Secondly, thermal mass absorbs heat from the air inside a house when that air is hotter than the thermal mass. The heat stored by the thermal mass is released back into the room when the room temperature drops below that of the thermal mass. High thermal mass materials such as concrete floors and walls need more energy to heat up, so they heat up more slowly than lightweight materials. This reduces overheating as the thermal mass soaks up some of the excess heat. The following graphs illustrate this clearly. In these studies7 the insulation values were the same for both timber and concrete test buildings and the windows were the same size and orientation. The difference in inside temperature can therefore be attributed entirely to the thermal mass. Mean daily minimum and maximum air temperatures in the Lincoln University test buildings

Air temperatures in the Lincoln University test buildings on 11 February 2002

28

30

26

28 Air temperature (ºC)

Air temperature (ºC)

32

24 22 CONCRETE

20

TIMBER

18 16

timber test building

Outdoor

26 24

concrete test building

22 20 18

14

16

J A S O N D J F M A M 2001 2002 MONTH

J

8

9

10

11 12

13 14

15 16

17

18 19 20

21

hours

Even at the same room air temperature, a well-insulated high thermal mass house will often feel warmer than a well-insulated lighter-weight house. This is because our perception of warmth depends not only on the air temperature, but also on the radiant heat from our surroundings. If those surroundings stay warmer as the air temperatures fall, we feel warmer too. If they are cooler, our perception is that the air temperature is colder.

7

20

Data from Bellamy, L.A. & Mackenzie, D.W. (2003). Energy efficiency of buildings with heavy walls, BRANZ Study Report 116. City: Building Research Association of New Zealand.


To be effective in collecting and storing the sun’s heat and maintaining stable indoor temperatures the thermal mass must not be isolated from the inside of the house by carpet or other insulating materials. However, no matter where it is placed inside a building, thermal mass must be insulated from contact with the outside air and the ground. Thermal mass can be provided in a house in a number of ways and potentially by a number of different materials. In practice, however, concrete masonry, concrete floor slabs or pre-cast concrete are the most common means of incorporating thermal mass into a house. Concrete floor slabs are now almost universally used on flat or moderately sloping sites. These floor slabs can be very effective in capturing the sun’s heat as they generally receive a lot of direct sun. Using high thermal mass floor coverings such as ceramic or concrete tiles, or polished or coloured concrete, will ensure the thermal mass of the floor slab is ‘available’ for heat storage.

“Relying on the thermal mass of a floor slab alone may be unwise as it is likely to be carpeted at some stage in its life, thereby reducing its heat storage effect dramatically.”

Many homeowners prefer to have carpets or similar floor coverings which unfortunately isolate the thermal mass. If this is the case, having a one metre wide border of tiles or other high mass materials can be an effective way of still providing some thermal mass, even if the rest of the room is carpeted. Heat storage can also be provided by using thermal mass such as concrete exterior walls, interior walls, intermediate floors, staircases and even ceilings/roofs. Relying on the thermal mass of a floor slab alone may be unwise as it is likely to be carpeted at some stage in its life, thereby reducing its heat storage effect dramatically. Insulation limits heat loss from the room

Insulation limits heat loss to the ground

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2 glass, thermal mass and insulation How much thermal mass? The effectiveness of thermal mass is influenced by the amount and positioning of insulation and glass, the site and the climate in which the building is located. The interactions between these elements are complex, making it difficult to generalise about how much thermal mass to put into a house – more is not always better. The examples in Chapter Four are intended to provide guidance. The basic principle is that a large area of thermal mass should be in contact with the air in the north-facing rooms that get significant sun. This could be most of the floor, all of the walls, or a combination of the two. If you want to more accurately determine the optimal amount of thermal mass for a given climate and design, seek professional advice on one of the growing number of computer programs used for digital building performance simulation (e.g. AccuRateNZ, IES Virtual Environment, Energy Plus, SUNREL).

“Optimal thickness of thermal mass for heat storage from day to night is 100 – 200 mm”

As thermal mass materials like concrete conduct heat very well, they absorb the sun’s heat quickly to their core, storing heat much more effectively than lower mass materials like timber. This happens when the sun shines onto the thermal mass but at other times the heat flow reverses. This pattern means there is a concrete thickness beyond which there is generally no added benefit in terms of solar energy storage. This optimal thickness for storage of heat from day to night is 100-200mm. However, with a house insulated to the Best Practice level in Chapter Four, a greater thickness of thermal mass could be used to store heat for longer periods.

Thermal mass and energy efficiency As thermal mass has the ability to capture free energy from the sun, you might expect that high thermal mass homes will be more energy efficient than lightweight homes. They can be, but only if they are well-insulated and have well-designed glazing. Without insulation, a high mass house would be very hard to heat as thermal mass is a very good heat conductor. A 200mm concrete wall with no insulation loses around six times the heat of a timber-framed wall insulated to Building Code minimums, so there is simply no point in trying to collect solar heat in thermal mass that is not well-insulated. There is also no point in hoping that the sun shining on the outside of a wall will somehow heat the living spaces. Most of the solar heat collected will be lost back out to the outside air as the wind blows across its hot surface. Good design requires that the solar heat is brought inside and heats the externally insulated thermal mass.

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Insulation – Heat Containment Insulation is the most important factor in passive solar design. Appropriate levels of insulation are critical for energy efficiency and comfort in both summer and winter. By slowing the transfer of heat in and out of a house, insulation works in combination with thermal mass and glazing to reduce both heating and cooling needs.

Try to install as much insulation as you can Because insulation is the most important factor influencing energy efficiency and comfort you should always try to use higher levels of insulation than Building Code minimum requirements. In many instances, better-performing insulation materials are only a little more expensive and, although the product cost is a little more the installation cost remains the same. It will always be more difficult and expensive to increase the insulation at some later date, so it pays to insulate really well first time around.

“Insulation is the most important factor in passive solar design.”

Install insulation correctly The correct installation of insulation is critical to getting the best performance from it. For example, squeezing insulation into a space smaller or thinner than it was designed for will reduce its effectiveness markedly. Gaps as small as 2mm can also significantly reduce effectiveness. The New Zealand Standard NZS 4246 Energy Efficiency – Installing Insulation in Residential Buildings provides excellent advice on the best way to install all common insulation materials. It is available free from www.energywise.govt.nz

Insulating timber floors There are two different types of suspended timber floor: 1) floors where there is an enclosed or semi-enclosed ‘basement’ space below the floor where the wind flow is limited 2) floors in pole houses and similar buildings where the floor is exposed to the elements. Insulated floors over a basement space perform better than floors exposed to the elements because floor heat loss goes to the basement space and then through the basement walls. These floors should be insulated to at least two thirds of the R-Value of the walls of the house Pole house floors require more insulation as they are directly exposed to the elements. A good rule of thumb is to insulate these floors to the same level as the walls as they lose heat at a similar rate. The insulation should be protected using materials such as plywood or fibre cement board.

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2 glass, thermal mass and insulation Insulating concrete floors

“You should always try to use higher than Building Code minimum levels of insulation.”

When the floor is intended to be heated, either by an underfloor heating system or by direct sun, under-slab and perimeter insulation should always be used. Fifty millimetre expanded polystyrene is most commonly used. Extruded polystyrene will give greater insulation value; however, it is significantly more expensive. When the floor slab is used to capture direct solar heat, in-slab electric heating systems may be undesirable. For example, before sunrise on a cold winter’s morning you will be likely to turn on the underfloor heating, purchasing electricity in order to store heat in the concrete slab. As the sun comes up, it adds further heat to the floor and the room can overheat. As a result, you are likely to open the windows to cool the house and waste expensive purchased energy. Underfloor heating systems that use circulating fluid in pipes buried in concrete floors can distribute heat from the sun throughout the house, providing a considerable increase in the effectiveness of solar gain. To make the best gains, these systems should be able to be run in circulation mode only, with no purchased energy heating the fluid. There are a number of proprietary concrete flooring systems available with different insulation details. With all these systems you should make sure the insulation under the slab and around the perimeter is continuous to prevent thermal bridging8. Thermal bridging can significantly reduce the overall insulation performance of these systems.

Insulating timber-framed walls Insulating timber-framed walls is relatively simple. There is a range of readily available insulation materials which simply fit in the cavity between the internal lining and the external cladding. It is important to use insulation materials specifically designed for walls to avoid ‘slump’ (where the insulation sinks down the wall over time which reduces thermal efficiency and can encourage mould growth). Another option is to use external insulation systems. The most well known are polystyrene-based systems that fix to the exterior of the timber frame to provide insulation and form the base for an exterior finishing system (most often plaster). With correct detailing of the battens that hold the external wall cladding in place, a range of insulation material can be used as external insulation. Combining external insulation with cavity insulation reduces the thermal bridging effect of the heat losses through the timber frame and significantly improves performance. 8

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Thermal bridging refers to the increased heat loss through the uninsulated area.


To get a high level of thermal efficiency, 150 mm or 200mm framing could be used to allow sufficient space for increased cavity insulation. The thermal bridging effect of timber can be reduced with careful detailing. One approach could be to use the increased strength of the timber to increase the spacing between wall studs. Veneer construction using materials like brick or concrete blocks is popular because of its durability and low maintenance. However, when used as a veneer on timberframe construction the thermal mass is isolated from the interior of the house. From a thermal performance perspective, high thermal mass veneer external walls are the same as a low thermal mass construction with the same insulation level.

Insulating thermal mass walls External insulation External thermal mass walls can be a very effective way of providing heat storage, provided they are well-insulated. However, if insulation is placed on the inside of the wall it isolates the thermal mass from the interior of the house, making its heat storage properties ineffective. Insulation can be either fixed to the exterior surface of the concrete wall, or built into the wall near the exterior surface. Insulation levels can be varied by adjusting the thickness of insulation material. Common external insulation systems are: • fixing polystyrene sheeting to the exterior of concrete masonry or pre-cast concrete walls – all standard finishing systems can be used, including masonry veneers, weatherboards and plaster finishing systems • casting polystyrene sheeting into a pre-cast wall (near the exterior surface) • masonry blocks that have a polystyrene biscuit pre-fitted near the exterior surface. Particular care should be taken to ensure there aren’t any breaks in the continuity of the insulation material as this will significantly reduce the performance. Internal insulation In some situations, it may be sensible to isolate thermal mass; for example, if you want to ensure fast heat-up of rooms on the south side of a house that do not receive direct sun. This

25


2 glass, thermal mass and insulation can be done by carpeting concrete floors and internally insulating high mass walls. It is important to ensure that design and construction of these walls allow construction moisture to be dissipated and prevent trapping of condensation from warm indoor air. Some internal insulation options include: • masonry and pre-cast walls strapped with timber and lined with plasterboard – with insulation between the strapping to improve energy efficiency • masonry or pre-cast walls with polystyrene board directly fixed (usually glued) – finishing can be with plasterboard or applied plaster systems • insulated concrete formwork (ICF) blocks – polystyrene blocks that are filled with ready mixed concrete.

Roof insulation Traditional timber-framed roofs are the most common form of construction for New Zealand houses and insulation methods are well known. A wide range of insulation materials are commercially available and the desired insulation level can be achieved by using insulation material of appropriate insulation rating. As a general rule of thumb, try to install as much insulation as possible. For higher levels of insulation, it is advisable to lay the insulation over the top of the ceiling joists so timber, which has higher heat conduction properties than insulation, does not become a ‘thermal bridge’ leaking heat through the roof between the insulation. Pre-cast and in-situ concrete roofs, though not widely used in New Zealand houses, can provide a useful means of storing heat. They must be insulated externally if the thermal mass of the roof is to be available for thermal storage. Normally, polystyrene sheet is used in a manner similar to the external insulation of concrete walls. Cladding and drainage of concrete roofs require special attention. The thermal storage of an internally exposed roof is much less effective than a wall or floor as its exposed surface receives no direct sun.

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additional important design principles

3


3 additional important design principles Chapter 3: Additional Important Design Principles Avoiding Overheating In New Zealand, houses designed to capture high levels of solar energy have the potential to overheat, particularly in summer. There are a number of ways to protect against unwanted solar gain or to get rid of the excess heat when overheating occurs. Thermal mass and insulation can reduce overheating but these do not always provide sufficient protection alone. The most effective ways to deal with overheating are to: • provide shading to block the sun when it is not wanted • cross-ventilate the house to get rid of excess heat. Common ways of trying to deal with overheating that should be avoided include: • air conditioners (including heat pumps) – these are expensive to install, require purchased energy to work and are only effective in the area of the house where they operate • drawing the curtains or blinds – this tends to trap the heat from the sun in the room (the sun’s heat is inside the room by the time it reaches the curtains), prolonging overheating • tinted windows (or coated with reflective film) – this reduces overheating markedly as heat gain through the glass can drop to a quarter of the clear glass amount. However, in winter this glass will lose the same amount of heat but will still only warm the house via solar gain at a quarter the rate of clear glass.

Shading One simple way to protect against overheating from the sun is to provide appropriately sized fixed overhangs above north-facing windows and external shading on east- and west-facing Insulation limits overheating of the house by hot air in the roof space

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windows. A simple overhang projecting above a window works well on the north of a house because it cuts off the sun when it is high in the sky in summer while allowing it to shine in through the windows when its heat is needed in winter. However, this type of shading is ineffective against the low-angled morning sun from the east and the late afternoon sun from the west. For these situations a vertical screen, such as an external louvred shutter or a blind is ideal. These can be movable to allow access to the view when the sun is not a nuisance. Sun shades can also be in the form of awnings or other similar devices. It is wise for sun-shading devices to be light in colour as heat will tend to build up under and behind them if they are dark coloured. Fixed overhangs need to be sized to allow winter sun to penetrate but also to exclude summer sun. Computer programs9 can model 3D house designs for the sun for a particular location and time. With these programs it is easy to design external shading systems that work well for each compass direction that the house faces. If you don’t have access to these programs, the following calculation works on the principle of excluding all sun on north-facing windows at midday in mid-summer – but only just. This is normally adequate to control overheating, so long as a building does not also have large west-facing windows. Using the table below and the adjacent diagram you can estimate the appropriate overhang size (a) for north-facing windows. Multiply the height of the sunshade above the window sill (h) by the factor in the table for your particular climate below (f1). For example, in Christchurch, if the height (h) of the sunshade above the window sill is 2m then the depth of the sunshade (a) should be 2m x 0.35 = 0.70m (a = h x f1). f1

Auckland Wellington Christchurch Dunedin

0.24 0.32 0.35 0.39

If the top of the window is too close to the sunshade, even low-angle winter sun does not penetrate the top part of the window. The distance from the top of the north-facing windows to the overhang (x), that will ensure the whole window receives winter sun, can be estimated using the following table. For the Christchurch example above, it is . x = 0.15 x 2m = 0.30m (x = h x f2). The ratios in this second table assume the overhang depth (a) has been determined by the first calculation. f2 9

Auckland Wellington Christchurch Dunedin

0.14 0.15 0.15 0.16

E.g. SketchUp, AutoCAD, Revit, Archicad and Microstation.

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3 additional important design principles Sunpath diagrams10 can be used to size overhangs for latitudes not in the tables above – or if you want to provide more or less shading than allowed for in the tables. For the buildings11 studied in Chapter Four, the importance of sunshades was evaluated in warmer and colder parts of the country. In all cases, the buildings without sunshades required slightly less heating, but suffered from significantly more overheating. Reductions in heating energy use were around 5-10%, but there was a doubling or tripling of the number of hours of overheating per year. Having provided adequate shading to protect against unwanted heat gain, it is also important to ensure that overheating and glare do not occur due to sun bouncing off reflective ground surfaces outside the windows. Shading sun from the west is more difficult due to the low position of the sun in the sky. Shading the north-facing windows in the warmer autumn weather, but not in the cooler spring weather, is also difficult as the sun is in the same position in the sky. This shading can be provided by fixed vertical louvres, movable shades or adjustable louvres. Adjustable methods are effective provided they are operated at the appropriate times. Another option is the use of deciduous trees, which are fully leaved during the warmest periods, but do not have leaves during the cooler periods when solar gain is advantageous. However, it is important to realise that even without leaves, shading from tree branches reduces solar gain by at least 20%. Sun from the east does not often present an overheating problem as it occurs early in the morning when the house is at its coolest. In fact the warm-up effect is generally desirable, provided glare does not cause a problem. In climates north of Taupo and in the central South Island where overheating might be a major problem, ensure that surfaces that have high exposure to the summer sun, like roofs, are light in colour. Overheating of the roof space causes heat gains to the interior of the house through the ceiling, which can only partially be prevented by ceiling insulation.

Ventilation Throughout New Zealand, provided care is taken to protect against excessive solar gain in summer, ventilation through windows, doors and sometimes unglazed vents, should generally be all that is required to get rid of any build-up of unwanted heat. In New Zealand’s climate, a house that frequently overheats due to the sun has simply been poorly designed. Hedges and windbreaks that are planted for winter shelter should still allow, and even encourage, cooling summer breezes to penetrate the house. This involves both careful planting and also careful placement of windows and doors. 10 See page 37 for more information. Sunpath diagrams available at www. victoria.ac.nz/cbpr/resources 11 The two-storey house was used for this evaluation.

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The key to effective venting of unwanted heat is openings that are positioned to encourage cross-ventilation. Windows on opposite walls are much more effective than windows on the same wall. To encourage maximum air movement and better venting, efficiency inlets and outlets should be: 1) at different heights 2) not directly in line of each other across a room. The goal is to ensure that cooling breezes pass through the whole of the occupied zone in a room and thus have the greatest chance of cooling people.

3

Fans can create air movement across your skin that can be cooling even on a hot day. Recent research12 has demonstrated that quiet, well-designed, low-energy ceiling fans should provide sufficient cooling for well-designed houses in even the hottest parts of New Zealand. The key to providing good ventilation through opening windows is to design practical openings for all circumstances. Openings should: • be large enough to allow good flow of air • be able to be shut completely and seal well against cold winter weather • be able to be locked in a partially open position to allow continuous cooling during the day but still provide security • still allow cool night air to enter the building, even after people have gone to bed for the night • ensure people, especially children, cannot fall out of them. Casement windows pushed out into wind flow improve the efficiency of a simple opening. Small external projecting walls will also interact with the building to improve ventilation by increasing the area of wall around the window causing wind pressure to build up and force air through the window.

12 Francois Garde: presentation to NZGBC Green Building Summit, October 2009. http://www.propertynz.co.nz/files/Events/Francois%20Garde.pdf (last accessed April 2010).

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3 additional important design principles The natural effect of warm air rising can be exploited by providing a natural chimney through the building. The openings through which this air flows must be large as the driving force is relatively weak. Rooftop openings can enhance this natural heat flow. They can also enhance wind-

assisted ventilation. For wind-assisted ventilation, the effectiveness of these openings depends on the pressure field created by wind. For low pitch roofs, both windward and leeward faces of the roof are subject to suction. For these low pitch roofs, single-sided ventilation systems like clerestories, and inserts into the roof itself (such as skylights) are effective. For high pitch roofs, only leeward faces are subject to suction and rooftop multi-sided opening devices can help create suction when the wind blows. In all cases, the inlets should be at a low level so that the airflow cools the occupied spaces. It is also important that ventilation devices are fully adjustable to control airflow on cold days. Windows should not be of a size and configuration that results in cold drafts when getting rid of cooking and other smells in winter. Combinations of large and small openings provide choice and a greater level of control. Matching opening type to roof pitch

Direct ventilation Bathrooms and kitchens produce both heat and water vapour. While the amount of heat produced is not generally a problem, the water vapour can be. This water vapour, if allowed to condense, is not only unsightly but may also lead to health problems and building maintenance issues. It is therefore important to provide a means of preventing

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condensation and extracting water vapour. Generally mechanical extractor fans are needed to achieve the relatively high ventilation rates that are required. These should extract the waste air to the outside – never into the ceiling. Heaters may also be required, particularly in bathrooms, to maintain the room surface temperatures above condensation point. Although these fans and heaters do require purchased energy, the relatively small cost is justified, for both health and comfort.

Heat Distribution Comfort and energy efficiency can be improved by distributing heat from warm areas to rooms that receive little direct sun. This can be achieved by taking advantage of the natural effect of warm air rising, but may also be assisted by the use of mechanical ventilation systems. These can range from a simple inexpensive fan to reasonably complex and expensive systems. Providing a fan with a thermostat control is an excellent low-cost option. You may of course choose to override this control but the thermostat ensures the design intention is obvious – and that the design will work even when you are not present or taking notice. Large volumes of air need to be moved from warmer to cooler areas of a house before any significant heating results, so for both natural circulation and fan-assisted circulation to be effective, it is important to ensure that openings are large enough to allow adequate airflow. Doorways that open all the way to the ceiling will greatly assist this natural airflow. Allowance should also be made for shutting off openings as it may not always be desirable for heat gains to be distributed throughout the house. Also, colder rooms may need to be shut off from other rooms. For example, you will probably want to contain heat in living areas in the early part of the day (warm up period) and only distribute heat to the rest of the house in the latter part of the day when there is excess in the living areas and a need to warm up the other areas of the house (the bedrooms, for example). For a two-storey house, this requires large openings between downstairs and upstairs and good control. Without good control of these heat flows, overheating of upstairs rooms can also be a major problem as can cold air flowing downstairs. Thermal mass internal walls can be very effective in assisting in the distribution of heat to rooms that don’t receive direct sun. For example, a concrete wall that separates a living area on the north from a bedroom to the south will quite effectively conduct heat through to the bedroom because of its low resistance to heat flow.

33


3 additional important design principles Airtightness There is a link between building complexity and energy performance. More complicated designs with more construction joints tend to have more uncontrolled air leakage – technically known as infiltration - which can have a major impact on heating energy requirements. These leaks can be in the construction materials (for example, weatherboard exterior cladding and timber floorboards are inherently leaky) or they can result from the complexity of the plan itself (for example, corner joints, joints for cladding changes). The main ways to deal with these are: • use sheet materials, or materials mortared together like brick or concrete walls which have fewer inherent leakage properties • simplify the design to have less potential air leakage sites (e.g. fewer corners) • take extra care during construction to seal all corner joints against air leakage • Ensure penetrations in cladding or lining for plumbing or electrical fittings are well sealed • Where design and construction still allow possible air leakage airtightness barriers could possibly be used. However, it is critical that they are vapour permeable and that the design and construction ensures construction moisture will be dissipated and condensation from warm indoor air will not be trapped. For a well-constructed, well-insulated house, air leakage accounts for around 20-25% of the space heating energy use, so any reduction in heat loss from air leakage will have a significant benefit. Wind causes heat loss both through air leakage and by increasing the conduction heat loss, particularly through windows. There are therefore two primary ways of dealing with these heat losses: • Ensure the house is well sealed, both its construction joints and by weather stripping windows and doors • Use external wind breaks to reduce the impact of the wind on the house (these have the added advantage of making outdoor areas usable more often). These should be used in combination. Weather-stripping can't deal with increased heat loss by conduction through the glass itself because the wind strips away the heat from the outer surface. Wind breaks can reduce this heat loss, but on their own only partially solve air leak problems that weatherstripping addresses."

Using Plan and Site Layout to Improve Comfort There are many considerations that will influence the plan layout for a house – the site topography, the orientation to

34


the sun, the views and your likes and dislikes, to mention just a few. There are some simple layout guidelines which will improve the energy efficiency and comfort of your home. It may not always be possible to follow these guidelines completely because of constraints and preferences relating to other design considerations. However, an understanding of these simple guidelines will help you make informed decisions about the trade-offs that are an integral part of any design process.

Size and shape

“Because the two-storey house is more compact it loses approximately 20% less heat than the single-storey house.”

A simplistic analysis of the heat losses through the surfaces of a building demonstrates that the ‘best’ building thermally is one that has the smallest external surface area. This ideal building is a sphere and is clearly impractical. The next best compact shape is a cube. A single-storey house is not cubeshaped but a two-storey house is much closer in overall shape to this ideal cube. Comparing the single-storey and twostorey houses studied in this book, the more compact twostorey house requires around 20% less heating energy than the single-storey house when both are insulated to Building Code minimum for Climate Zone Three13 (when adjusted so the floor areas are identical). The diagrams below show heat energy flows through the various components of a house that has been insulated to the levels required by the Building Code in Climate Zone Three. The single-storey and the two-storey house are very similar in total floor area. However, the diagrams demonstrate that heat losses through the windows are a far more significant proportion of the total heat loss for a two-storey house. This is because the floor and roof exposed to the outside are half the area of floor and roof of the single-storey house. 11% roof

fresh air 14% windows 36% walls 20% floor

19%

“Airflow heat loss from houses that have not been carefully designed and detailed can be two to four times that required to maintain a healthy home.”

6%

roof fresh air 18%

windows 45% walls 20%

floor

11%

13 See Appendix 2 on page 75 for information on climate zones.

35


3 additional important design principles The heat loss figures for fresh airflow are based on the minimums required to maintain a healthy home. In real houses the heat loss through air leaks is sometimes two to four times greater. Air leakage can be by far the single greatest source of heat loss and therefore it is critical to design and detail to control unintended airflows. However, it is important to ensure that design and construction allow construction moisture to be dissipated and prevent trapping of condensation from warm indoor air. Designing a house that is rectangular, so the north-facing facade is larger than the east or west facades, increases solar gain when it is most needed. It is also the easiest to control with simple shades when solar gain needs to be reduced. And the small east and west sides mean there is less potential for overheating and glare from low angle sun. Making the building rectangular makes the plan less deep so that cross ventilation for cooling is easier to achieve. Also, making the plan less deep from north to south makes it far easier to distribute the heat from the north-facing rooms to the other less sunny parts of the house. The heating and cooling requirements of a house are directly related to its size. You should think very carefully about how much space you really need if you are serious about comfort and energy efficiency. If you build a house that is twice the size you need, it will cost you roughly twice as much to heat and cool as a house the size you actually need.

Orientation North-facing glass provides the best access to solar gain. It is therefore preferable to orientate the house with the long axis in the east-west direction. This orientation to north can be plus or minus 20 degrees without having a major impact on solar gain. If the house has northwest and northeast orientation of solar collecting windows, as is the case with the houses studied in Chapter Four14, rotating by plus or minus 45 degrees makes little difference to solar gain. Living areas should be located on the north face to maximise solar gain in these rooms. Living areas should be protected from the cold south face by placing the garage and service rooms to act as a buffer on this face. People often prefer not to heat bedrooms as much as living areas, and generally bedrooms don’t need to be particularly warm during the day. Direct sun in bedrooms is therefore not necessarily important. These rooms can be heated by designing for warm air movement from living areas during the day.

14 See page 45 for results of orientation studies.

36


Site selection It is obvious that a house in Auckland will be exposed to very different climatic conditions from a house in Christchurch and therefore performance will differ from climate to climate. It is less obvious, however, that within each town there can be very large differences in microclimate that impact on the comfort and energy efficiency of a house. Site selection is critical to house performance as a site that receives limited sun during the winter will obviously get very little heating benefit from the sun when it is needed most. Be very cautious of a site that is being marketed as having great afternoon sun – often this means good sun in summer but very limited sun in winter. The following sections are intended to assist with site selection, and to provide a means to optimise your design if you already have a site and want to make best use of what you have. The only accurate way to establish microclimate data is to establish a weather station on the site. This is rarely a practical option, so therefore you must rely on your own observation and experience and that of local residents. Having gathered as much information as you can about the site microclimate, you are in a position to make informed design decisions that will make the most of the site.

Sunpath diagrams

The sun’s azimuth

Visiting a site at various times of the day is a good way of checking how much sun the site gets, but it is rarely possible to do this for the whole year. Sunpath diagrams map the position of the sun relative to the site, both by time of day and time of year. A plan of the objects that will shade the site (currently and in the future) can be drawn onto the sunpath diagram. This diagram can then be used to assess the shading effect on the site and help you make decisions about the

37


3 additional important design principles position of the house on the site, and in particular the position of the north-facing windows (the primary solar collectors). If compromise is necessary, as a minimum, you should aim for unrestricted sun on solar collecting windows between 9am and 3pm in winter. Sunpath diagrams can be downloaded from www.victoria.ac. nz/cbpr/resources. If your region does not have a specific named sunpath diagram you can use that of a nearby region as the differences will be insignificant. Alternatively, several computer programs15 permit you to print diagrams specific to the precise latitude of a building site.

Topography Sites on hillsides tend to experience uphill airflows during the day, as warmer air moves towards the top of the hill. At night this trend reverses, with cool air flowing down the hill and contributing to frosts in the valleys. Hedges and walls can dam this flow, contributing to local frost pockets, unless there are openings to allow the air to flow through. Sloping sites also receive very different amounts of solar radiation. North-facing slopes receive significantly more solar gain than flat sites. This means that ground and air temperatures are higher and therefore heat loss from a building is lower on a north-facing slope. For example, a north-facing Christchurch site will experience temperatures similar to a flat site in Wellington.

Ground surface cover around the house The temperature extremes experienced in and around a house can be made better or worse by the surrounding ground cover. Paving, for example, particularly if it is dark coloured, can get very hot in summer. On the other hand, grass absorbs heat through evaporation and photosynthesis, resulting in temperatures over grass that are considerably lower than bare earth or paving. Air flowing over grass into the home will therefore have a cooling effect in summer. Other vegetation such as trees and shrubs have a similar effect to grass and can also contribute to summer cooling breezes, but of course care needs to be taken that this vegetation does not block winter sun.

Water moderates temperatures The sea, and to a lesser extent lakes, have a temperature moderating effect. This is because the sea temperature varies as little as 10 degrees during the course of the year, and as little as one degree from day to night. In Wellington, for example, a site near the sea will experience maximum temperatures that are 1-2 degrees lower than elsewhere in 15 Autodesk速 Ecotect速 2010 (http://www.autodesk.com/ecotect-analysis) or Climate Consultant 4 (http://www.energy-design-tools.aud.ucla.edu/).

38


Heat loss due to wind exposure

Wellington, and minimum temperatures that are 3-6 degrees higher. The other major effect is that during the day cool sea breezes tend to flow inland and at night the reverse occurs. It is also worth remembering that reflection of the setting sun off the water can as much as double heat gain through westfacing windows.

Wind contributes to heat losses Wind can have a major impact on heat loss from a house. . A house located on top of a ridge can have heat losses 50% greater than if it were on the flat. In considering the need for wind barriers, it may be useful to obtain meteorological data on wind speed, direction and frequency for the region (available from the National Institute of Water and Atmospheric Research www.niwa.cri.nz). It will also be important to assess the local site conditions, which may vary considerably from the general regional data. Channelling in valleys, for example, can add 20% to wind speed. Windbreaks are most effective if they are as close to the house and as high as possible. Porous windbreaks will cause less turbulence downstream. At 20-30% porosity, they will reduce wind speed by 50% for a distance up to 10 times the windbreak height. Solid barriers will provide greater shelter, but over a shorter distance. They will reduce wind speed by 75% for a distance up to five times the windbreak height. Windbreaks should always be at right angles to the wind they are intended to provide shelter from. Unfortunately it is seldom possible to provide optimum protection from winter winds without compromising winter sun, or the cooling breezes that are important in summer. As with most aspects of thermal design, and indeed design in general, compromise is necessary. One way of dealing with conflicting requirements is to provide movable screens. These can be very effective but do require active participation of the house occupants.

39


expected performance

4


Chapter 4: Expected Performance Performance calculations The information in this chapter is based on computer studies of the performance of a single-storey house of around 200 square metres (excluding the garage). It has not been purpose designed for this publication – it is a real house, which was built in Auckland at the time of writing of the first edition of this book. It is not even an optimum solar design, but has been selected because its size and layout are reasonably representative of a new family home in New Zealand today. Its orientation to the sun is likewise not optimum for solar design, but reflects constraints of the actual site on which it was built. The single-storey house

A limited number of studies were also conducted for a twostorey house of similar size. They show that the general trends demonstrated for the two-storey building are consistent with the single-storey building. Ultimately, the goal is to provide the basis for you to evaluate how your own design might perform using the lessons learnt from the various combinations of glass, mass and insulation in these houses. The results of the studies of the two-storey design are summarised in Appendix 1 on pages 71-74.

41


4 expected performance The two-storey house

The electronic buildings ins

ula tio

CODE INSULATION

mass

n

ss

gla

The computer studies have used the SUNREL program, developed by the USA’s National Renewable Energy Laboratory. It is internationally recognised for its ability to accurately model building thermal performance. We have ‘built’ 27 electronic houses in each of three cities in New Zealand to study how three different levels of glass, mass and insulation (3x3x3) affect energy use and comfort.

Locations

ins

ula tio

BETTER INSULATION

mass

n

ss

gla

ins

ula tio

BEST INSULATION

mass

n

ss

gla

The e-buildings were ‘built’ in Auckland, Wellington and Christchurch. These locations were selected because of the large number of new homes built in these cities and because they represent a wide range of New Zealand climates. They are also representative of the three climate zones defined in the New Zealand Building Code. The weather data used in these studies was developed by NIWA for EECA and is freely downloadable from http://tinyurl.com/NZweather1

Expected performance in other climates The performance conclusions were also tested for e-buildings2� insulated to the best level defined in this chapter in all 15 other climates for which NIWA developed weather files. Both low and high mass designs were modelled with a high level of glazing. The following graphs show the results of these calculations. The graphs show positive energy (above the horizontal axis) entering the house as solar energy (in yellow) plus the purchased heating energy (in red) required to maintain comfortable temperatures. They are listed in increasing order of heating energy use. They show heat losses from the house below the horizontal axis. The first two houses are insulated to Climate Zone 1 best level (see page 52); the next 6 are insulated to Climate Zone 2 best level (see page 57); and the rest are insulated to Climate Zone 3 best level (see page 63). 1

2

42

http://apps1.eere.energy.gov/buildings/energyplus/cfm/weather_data3.cfm/ region=5_southwest_pacific_wmo_region_5/country=NZL/cname=New%20 Zealand] The two-storey house was used for these studies.


kWh per annum

Low mass, 55% glazing, best insulation 40,000 30,000 20,000 10,000 Solar gain Ground floor Walls & roof Windows Air leakage Ventilation Heating

0 -10,000 -20,000 -30,000 -40,000

Lauder

Queenstown

Dunedin

Invercargill

Christchurch

Taupo

Hokitika

Masterton

Nelson

Rotorua

Wellington

Manawatu

Napier

Hamilton

Taranaki

Tauranga

Kaitaia

Auckland

-50,000

40,000 30,000 20,000 10,000 Solar gain Ground floor Walls & roof Windows Air leakage Ventilation Heating

0 -10,000 -20,000 -30,000 -40,000

Lauder

Queenstown

Invercargill

Dunedin

Christchurch

Hokitika

Taupo

Masterton

Rotorua

Nelson

Wellington

Manawatu

Hamilton

Napier

Taranaki

Tauranga

Kaitaia

-50,000 Auckland

kWh per annum

High mass, 55% glazing, best insulation

The results show that variation in sunshine hours for the 18 different climates has a relatively small influence on the heating energy requirement – the key factor influencing heating energy needed is the coldness of the climate. When insulated to the same level, houses in colder climates require more heating energy even if they have high sunshine hours. Look carefully at the difference in ‘Ventilation’ energy heat loss between the low mass and the high mass buildings (just below the horizontal axis in the graphs). For the low mass building, the amount of heat that must be vented when the sun makes the building too hot is significantly bigger at the north of the North Island where high sunshine hours combine with high air temperatures. For the high mass building, with the same size windows and same levels of insulation there is much less wastage of solar energy.

43


4 expected performance The standard year for these studies was selected as an ‘average year’ from 30 years of temperature data. If you focus just on annual energy use and not on comfort, then the heating energy use can easily change by as much as 30% from year to year. This becomes obvious when looking carefully at the energy balance represented in the graphs – the purchased energy for heating (in red) is always tiny by comparison with the large heat loss totals below the horizontal axis which are balanced by the equally large solar heat gains. Even relatively small changes in the heat losses or the solar gains are proportionally large compared to the heating energy use. It is therefore not possible to adapt the information on the next few pages into precise predictions of performance for your own situation, whether a different design or different climate. However, there should be sufficient information on the performance of these e-buildings to help you to understand the general principles of solar design and thus anticipate the effect the coldness of climate, the anticipated heating schedule and the levels of glass, mass and insulation. If you want to study these issues in more depth, we recommend you consult a building scientist capable of completing these calculations for a specific design. There are a number of computer programs available, including SUNREL (www.nrel.gov), AccurateNZ . (www.energywise.govt.nz), IES Virtual Environment . (www.iesve.com/A-NZ) and EnergyPlus . (http://apps1.eere.energy.gov/buildings/energyplus/).

Variations in construction For each of the main variables (glass, mass and insulation) three different levels have been selected. The effect on energy use and comfort of the 27 combinations (3x3x3) of these variables has been evaluated.

Glass Glazing levels have been defined as low, medium and high, based on our understanding of typical practice in New Zealand. These levels are defined as a percentage of glazing relative to the total area of each face of the building. The following table summarises the levels selected. These levels are consistent for all three locations. Because the real building is not oriented square to north (because of site constraints) the building faces are NE, NW, SE and SW. Only windows in the NE and NW faces are varied, as these are the primary solar collecting windows.

44


Low glazing

Medium glazing

High glazing

“The effect on heating energy use of orientation of the ‘NE and NW’ glass within a span of plus or minus 45 degrees is small.”

NW face

NE face

SE face

SW face

Total building

Window area

16.2m2

13.7m2

16.3m2

3.2m2

49.4m2

Area ratio

25%

25%

34%

9%

23%

Window area

24.2m2

23.2m2

16.3m2

3.2m2

66.8m2

Area ratio

40%

40%

34%

9%

31%

Window area

34.0m2

31.8m2

16.3m2

3.2m2

85.3m2

Area ratio

55%

55%

34%

9%

38%

It is worth repeating that the e-building modelled for this exercise is not an optimised solar design. It has glass which faces northeast and northwest. It is therefore likely to overheat a little more than a house that faced due north because simple overhangs or eaves to shade against the summer sun are harder to make work well with these orientations. However, the upside of this is that the calculated performance is more likely to be typical of a normal house, rather than one where the whole focus was on solar optimum design. This shows up in the examination of the effect of orientation on the design. Some studies3 looked at the impact of rotating the whole house to see what the effect would be on the heating energy use. The major point of note is how insensitive these houses are to quite large variations in the direction the living room glazing faces. However, when the

kWh per annum

Effect of orientation on average annual increase in heating energy use 3,500 3,000

Auckland 25% Glazing NE & NW facing

2,500

Auckland 55% Glazing NE & NW facing

2,000

Wellington 25% Glazing NE & NW facing

1,500

Wellington 55% Glazing NE & NW facing

1,000

Christchurch 25% Glazing NE & NW facing

500 0

Christchurch 55% Glazing NE & NW facing 45 degrees

20 degrees

180 degrees

Rotation of building from original orientation

3

Energy use is presented as the average of the low, medium and high mass buildings. The two-storey house was used for these studies.

45


4 expected performance “Rotating the e-building 180 degrees dramatically increased energy use.”

house is completely spun on its axis so the living room windows face south (180 degree rotation) there is a very significant increase in the energy use. This is most marked when the house is more dependent on the heat from the sun – when the north window area is at its largest.

Mass The levels of mass have been defined as low, medium and high. The amount of mass has been varied based on logical use of mass for various building components, rather than trying to use scaled steps based on weight of high mass components. The levels of mass have been kept consistent for all three locations and are summarised in the following table.

“The benefits of medium mass are dependent on the floor slab being exposed. Insulating it with carpet will make it perform much the same way as low mass, unless some other mass is available such as high mass walls.”

Ground floor

External walls

Internal walls

Suspended intermediate floor

Ceiling/ roof

Low mass

Concrete with carpet throughout

Timber framed

Timber framed

Timber framed

Timber framed lightweight

Medium mass

Concrete slab finished with tiles

Timber framed

Timber framed

Timber framed

Timberframed lightweight

High mass

Concrete slab finished with tiles

Concrete with Exterior insulation

Concrete

Concrete

Timber framed

Pre-cast concrete walls have been used for all cases where concrete walls are studied. This has been done for consistency only. Concrete masonry, in-situ concrete or other high mass materials can all be used to add mass to a home. Remember, however, that if you wish to get maximum benefit from the thermal mass, the insulation must be on or near the exterior of external walls. For all external pre-cast walls the insulation was expanded polystyrene fixed externally, with a plaster finishing and waterproofing system. Likewise, thermal mass from internal walls, suspended floors and ground floor slabs will work best if insulating material does not isolate the mass. In the low mass examples, the concrete from the floor slab is isolated by carpet and therefore does not contribute significant thermal mass. In the medium and high mass examples, the concrete floor slab has no carpet. The assumption that the carpet in the low thermal mass building insulates the thermal mass in the concrete floor and thus makes it behave as a lightweight building was tested in a series of calculations4. 4

46

The two-storey house was used for these studies.


The following graph shows the effect in the two-storey lightweight house of carpet insulating the concrete floor. It shows energy use for the Code and Best insulated e-building with either 25% or 55% of the northeast and northwest facades glazed. The heating energy use is a little less in the e-building with the concrete floor, despite the mass being isolated by carpet. It would seem that, despite the insulation of the carpet, when the house overheats (when it has 55% north glass) there may be some more heat stored in the concrete floor slab than is able to be stored and used in the timber floor house.

Thousands kWh per annum Thousands kWh

Annual heating energy use by floor type – concrete with carpet and timber with carpet 16 14 12 10 8 6 4 2 0 25% glass

55% glass

25% glass

55% glass

25% glass

55% glass

code insul

best insul

code insul

best insul

code insul

best insul

low mass

low mass

low mass

Auckland Zone 1

Wellington Zone 2

Christchurch Zone 3

Concrete Floor Concrete floor with carpet

Timber Floor Timber floor with carpet

For the medium mass option there is considerable room for variation on where the mass is positioned. There is no precise definition of what constitutes a medium level of thermal mass. Some suggestions of a medium mass level are: • exposed concrete ground floor, concrete external walls, lightweight internal walls • exposed concrete floor, concrete internal walls, lightweight external walls • carpeted floor, concrete external and internal walls.

Insulation The three levels of insulation studied have been defined as: Code Compliance; Better Practice; and Best Practice. Because there are different Building Code minimum insulation requirements for Christchurch compared to Wellington and Auckland, it is not possible to keep the insulation levels consistent for the three locations. There are also quite different minimum insulation requirements for high mass and low mass external walls. This means that the three insulation levels for high mass (solid) external walls are different from the

47


4 expected performance corresponding insulation levels in low mass (non-solid) walls. The insulation levels studied are summarised for Auckland on page 52, for Wellington on page 57 and Christchurch on page 63. The R-values5 used for all components are whole component R-Values. They therefore account for the different conduction of heat through the different elements that make up that building component.

Performance Results Comfort The results of these studies are presented as comfort ratings, energy use and required heater size. The comfort rating has two components: The first is based on the number of hours the living areas fall below 16oC; the second is based on the total number of hours that the living area temperature exceeds 26oC. The calculation models the windows being opened to allow ventilation when the temperature reaches 26oC. The ventilation rate achieved is dependent on the opening sizes of the windows and the amount of wind. Obviously if no one is home to open the windows the overheating problem will be much worse.

Energy use The heating energy required for a home will be dependent on how the occupants heat the home and there is really no typical behaviour pattern. To give an idea of the likely range of energy use we have conducted some studies6 to examine three very different heating schedules for the two-storey house: • heating as required 24 hours a day (bedrooms to 16oC, living areas to 20oC) • heating as required 7.00am-11.00pm only (bedrooms to 16oC, living areas to 20oC) – no heating 11.00pm – 7.00am • heating as required 7.00am-9.00am and 5.00pm-11.00pm (bedrooms to 16oC, living areas to 20oC) – no heating 9.00am – 5.00pm or 11.00pm – 7.00am. The following graph shows the difference in average annual heating energy use for the three heating schedules for both code and best insulation levels. Energy cost can be estimated using roughly $200 per 1,000kWh (at the time of writing).

5 6

48

See page 68 – Determining Insulation Values. Energy use is presented as the average of the low, medium and high mass buildings with medium level of glazing. The two-storey house was used for these studies.


kWh per annum

Comparison of average energy use of different heating schedules 25,000

20,000

Code insulation – 7am-9am & 5pm-11pm Code insulation – 7am-11pm Code insulation – 24 hour heating Best insulation – 7am-9am & 5pm-11pm Best insulation – 7am-11pm Best insulation – 24 hour heating

15,000

10,000

5,000

0

Wellington

Auckland

Christchurch

A much more dramatic change in energy use can be seen when the thermostat is set to a higher level. If the living room areas are heated to 22oC or 24oC instead of 20oC, then the use of energy for heating can dramatically increase. This shows what is likely to happen to your energy bills if you rely on remembering to turn off the heating or if you wait until it begins to feel a bit too hot before turning down the heaters. For the warmer climate zones the effect of raising the thermostat can at least double the energy use. Even in Christchurch the increase can be nearly 50%. The following graph shows the difference in average annual heating energy use for the three heating set points for both code and best insulation levels.

kWh per annum

Comparison of average energy use with different temperature setpoints 30,000

25,000

20,000 20oC

15,000

22oC 24oC

10,000

5,000

0 Auckland best insulation

Auckland code insulation

Wellington best insulation

Wellington code insulation

Christchurch best insulation

Christchurch code insulation

49


4 expected performance Although specific homeowners’ heating patterns will often be quite different, the relationship between the options presented does allow estimation of the likely benefits of the design options. The absolute energy consumption of a design is less important than the comparison between different glass, mass and insulation options – with the same heating schedule. Remember that although energy efficiency is important to many people, comfort is of equal if not greater importance. After all, the reason we use energy for heating (and cooling) is to ensure we are comfortable in our homes. Improved comfort is a significant benefit even if there is no saving in energy costs.

Your specific design The following sections covering expected performance in Auckland, Wellington and Christchurch should be all you need in most design situations. If it is important for you to have precise predictions for your specific design, and your specific location, consult a building scientist capable of conducting simulations. There are a number of computer programs available, including SUNREL (www.nrel.gov), AccurateNZ (www.energywise.govt.nz), IES Virtual Environment (www.iesve.com/A-NZ) and EnergyPlus . (http://apps1.eere.energy.gov/buildings/energyplus/).

50


AUCKLAND Auckland has a relatively warm climate with average ground temperatures of 20.3oC in summer and 12.8oC in winter. Overheating of homes is a much greater problem than in the cooler parts of New Zealand. Although Auckland homes generally require some heating to maintain comfortable temperatures in winter, the amount of heating required is relatively small. Any cost savings are therefore likely to be small in absolute terms, and may not be a major motivator. Reducing overheating is likely to be a much more important benefit to most people.

“Overheating of houses is a much greater problem in Auckland than it is in the cooler parts of New Zealand.”

KEY: Blue middle line = Average day temperature during allocated months Wider red area = Range of day temperatures during allocated months Green solid line = Average direct sunlight per day and month (W/m2) Green dotted line = Average diffuse sunlight per day and month (W/m2) Dark green bars = Comfortable temperature range for months

Summary created using Autodesk® Ecotect® 2010 of the Auckland weather data used in the house performance calculations

There are many ways in which the results presented in the following pages can guide your design. Remember – these studies can’t be used to accurately predict energy use and comfort for different designs or different locations. You can however estimate performance by adjusting for coldness of climate, anticipated heating schedule and levels of glass, mass and insulation.

Construction details The following table provides details of the constructions used to achieve the specified levels of insulation for the three insulation levels and the three mass levels. These construction systems have been chosen as they are all currently used in the New Zealand market. Other construction systems that achieve the same insulation R-Values will perform in the same way.

51


4 expected performance – Auckland Insulation level Low mass

Medium mass

High mass

Concrete ground floor slab

External walls

Roof

Window glazing

Code compliance

Carpeted floor, R1.7 polystyrene edge insulation (R1.9)

Timber frame with R2.2 bulk insulation (R2.1)

Timber frame with R3.2 bulk insulation (R2.9)

Double clear glazing metal frames (R0.26)

Better practice

Carpeted floor, R1.4 polystyrene under slab plus edge insulation (R3.1)

Timber frame with R2.6 bulk insulation (R2.4)

Timber frame withR3.6 bulk insulation (R3.4)

Double low-E Argon filled glazing timber frames (R0.5)

Best practice

Carpeted floor, R1.4 polystyrene under slab plus edge insulation (R3.1)

Timber frame R2.6 + R2.2 bulk insulation (R4.2)

Timber frame with R5.0 + R5.0 bulk insulation (R9.5)

Triple glazing – one pane low-E, timber frame (R0.62)

Code compliance

R1.7 polystyrene edge insulation (R1.7)

Timber frame with R2.2 bulk insulation (R2.1)

Timber frame with R3.6 bulk insulation (R3.4)

Double clear glazing metal frames (R0.26)

Better practice

R1.4 polystyrene under slab plus edge insulation (R2.9)

Timber frame with R2.6 bulk insulation (R2.4)

Timber frame with R4.0 bulk insulation (R3.7)

Double low-E Argon filled glazing timber frames (R0.5)

Best practice

R1.4 polystyrene under slab plus edge insulation (R2.9)

Timber frame R2.6 + R2.2 bulk insulation (R4.2)

Timber frame with R5.0 + R5.0 bulk insulation (R9.5)

Triple glazing – one pane low-E, timber frame (R0.62)

Code compliance

R1.7 polystyrene edge insulation (R1.7)

Concrete with R0.5 external polystyrene insulation (R0.8)

Timber frame with R3.6 bulk insulation (R3.4)

Double clear glazing metal frames (R0.26)

Better practice

R1.4 polystyrene under slab plus edge insulation (R2.9)

Concrete with R2.4 external polystyrene insulation (R2.7)

Timber frame with R5.0 bulk insulation (R4.5)

Double low-E Argon filled glazing timber frames (R0.5)

Best practice

R1.4 polystyrene under slab plus edge insulation (R2.9)

Concrete with R4.2 external polystyrene insulation (R4.5)

Timber frame with R5.0 + R5.0 bulk insulation (R9.5)

Triple glazing – one pane low-E, timber frame (R0.62)

Note: the R-Value of the insulation material is provided along with the R-Value of the complete system (in brackets).

Temperature fluctuations The ‘sparklines’ in the following charts are based on heating the living areas (as required) between 7.00am-11.00pm to 20oC, but no heating between 11.00pm-7.00am. These sparklines show the magnitude of the drop in temperature, below 16oC, between 11.00pm and 7.00am (below the axis) and the magnitude of overheating, above 26oC (above the axis) for all 365 days of the year. They therefore provide a good indication of the expected comfort of each house.

The house in the bottom left corner has a relatively small window area and is insulated to the current minimum required by the Building Code – it mainly needs heating.

52


Increasing the areas of north-facing glass in the bottom row of this code insulated group of houses increases the need for heating and introduces a need for cooling. Moving up a row to the medium thermal mass buildings shows a very large reduction in the swings in temperature. The effect of adding more insulation to a house can be seen by looking at the groups of sparklines for better and best insulation. Improving insulation removes most of the large drops in temperature at night but increases the amount of overheating during the day. Increasing mass levels in these more highly insulated houses has the same effect observed in the code insulated homes – it greatly reduces the swings in temperature.

Cooling need

“Increasing north-facing glass causes more overheating but increasing mass in the house greatly reduces this problem”

Overheating has been calculated as degree hours – the total for all hours over 26oC multiplied by the difference between 26oC and the actual temperature. This is a better indicator of the need for cooling than merely the hours over 26oC. For example, two houses might each total 10 hours over 26oC, but one is just one degree over on average, a total of 10 degree hours; the other being on average 4 degrees over would total 4 degrees times the 10 hours or 40 degree hours. Overheating hours will tend to be afternoon and evening hours in summer. The following tables show the number of overheating degree hours (above 26oC) in each of the houses – even when the windows are opened for natural ventilation cooling. The calculation models the windows being opened to allow ventilation when the temperature reaches 26oC. The ventilation rate achieved is dependent on the opening sizes of the windows and the amount of wind. Obviously if no one is home to open the windows the overheating problem will be much worse. Amount of overheating – degree hours above 26oC

Here the complex interaction of glass, thermal mass and insulation becomes clear. Increasing glass area facing north (left to right in each group) brings big increases in overheating degree hours. A doubling of the number of degree hours is approximately correlated with a doubling of the need for cooling energy. However, increasing the amount of available thermal mass within each insulation group – moving up from one row to the next – results in very large decreases in overheating.

53


4 expected performance – Auckland “In medium and high mass houses temperatures virtually never fall below 16oC overnight.”

Overnight temperature drop A significant amount of energy can be saved by turning off the heating before going to bed for the night, but a major influence on the feeling of comfort in a house is how much the temperature in the house falls overnight. Underheating hours will tend to be pre-dawn hours in winter – they are based on how often the temperature drops below 16oC when the heaters are turned off at 11.00pm and turned on the next day at 7.00am. The following tables show how many degree hours below 16oC occur in each of these e-buildings. Amount of underheating – degree hours below 16oC

The benefit of mass and insulation is obvious in these tables. The moderate amount of mass in the medium mass option is all that is needed to ensure essentially no underheating occurs in the living rooms. Increasing the insulation – moving from left to right across the groups – also reduces underheating.

Purchased energy for heating Energy use is presented for just one heating schedule. You may, of course, operate a quite different heating schedule. The absolute energy use is less important than the comparison between different glass, mass and insulation options – with the same heating schedule. Many New Zealand homes are less well heated than the schedule presented and therefore energy use will be lower. As described earlier on page 49, heating for longer each day will increase your energy use, but not nearly as much as heating to a higher temperature (greater than the 20oC modelled). Energy cost can be estimated using roughly $200 per 1,000kWh (at the time of writing).

“Heating energy consumption decreases dramatically with increases in insulation.”

54

The following tables show purchased energy (x 1,000kWh) required to maintain a minimum temperature of 16oC in bedrooms and 20oC in living rooms between 7.00am and 11.00pm, 365 days a year (no heating 11.00pm-7.00am). Use of air-conditioning units to control overheating has not been modelled so overheating may still occur as control is by opening windows only. Use of air-conditioning units, such as heat pumps, to control overheating can increase energy consumption very significantly.


Heating energy consumption (x 1,000kWh)

The tables above demonstrate that improving insulation is by far the most effective way of reducing energy use. The set of e-buildings with Code level insulation on the left have much higher annual energy use than those to the right with higher levels of insulation. By looking at the energy use, overheating and underheating tables you can see that if you increase the amount of northfacing glazing, in conjunction with increased thermal mass, you generally get heating energy and comfort benefits. When you are comparing specific glass, mass and insulation combinations, don't just look at one factor in isolation. It pays to look at the sparklines, overheating, underheating, energy use and heater capacity tables together to get a good overall picture of the likely performance you can expect.

Required heater size For each computer study, heating capacity required to meet peak demand on the coldest day is also presented for the 7.00am-11.00pm heating schedule. Typical domestic electric heaters have a capacity of 500W to 2.4kW, heat pumps 4-9kW, flued gas heaters 3-7kW and wood burners 8-15kW. Several of the e-buildings require less than 6kW heater capacity for the whole house. Required heater capacity (kW)

55


4 expected performance – Wellington WELLINGTON Wellington has a climate that is generally cooler than Auckland in the summer and warmer than Christchurch in the winter. Average ground temperatures are 18.6ºC in summer and 10.1ºC in winter. Wellington enjoys a relatively high number of sunshine hours. As would be expected from the climate, energy consumption required to maintain comfort in winter is significantly higher than Auckland but significantly lower than Christchurch. Overheating, though less of a problem than in Auckland, can still occur and be significant if not well accounted for in the house design.

“Heating energy needed in Wellington is much higher than Auckland, but lower than Christchurch – overheating is not generally a big problem, particularly in medium and high mass houses.”

56

KEY: Blue middle line = Average day temperature during allocated months Wider red area = Range of day temperatures during allocated months Green solid line = Average direct sunlight per day and month (W/m2) Green dotted line = Average diffuse sunlight per day and month (W/m2) Dark green bars = Comfortable temperature range for months

Summary created using Autodesk® Ecotect® 2010 of the Wellington weather data used in the house performance calculations

There are many ways in which the results presented in the following pages can guide your design. Remember – these studies can’t be used to accurately predict energy use and comfort for different designs or different locations. You can, however, estimate performance by adjusting for coldness of climate, anticipated heating schedule and levels of glass, mass and insulation.


Construction details The following table provides details of the constructions used to achieve the specified levels of insulation for the three insulation levels and the three mass levels. These construction systems have been chosen as they are all currently used in the New Zealand market. Other construction systems that achieve the same insulation R-Values will perform in the same way. Insulation level Low mass

Medium mass

High mass

Concrete ground floor slab

External walls

Roof

Window glazing

Code compliance

Carpeted floor, R1.7 polystyrene edge insulation (R1.9)

Timber frame with R2.2 bulk insulation (R1.9)

Timber frame with R3.2 bulk insulation (R2.9)

Double clear glazing metal frames (R0.26)

Better practice

Carpeted floor, R1.4 polystyrene under slab plus edge insulation (R3.1)

Timber frame with R2.6 bulk insulation (R2.4)

Timber frame with R3.6 bulk insulation (R3.4)

Double low-E Argon filled glazing timber frames (R0.5)

Best practice

Carpeted floor, R1.4 polystyrene under slab plus edge insulation (R3.1)

Timber frame R2.6 + R2.2 bulk insulation (R4.2)

Timber frame with R5.0 + R5.0 bulk insulation (R9.5)

Triple glazing – one pane low-E, timber frame (R0.62)

Code compliance

R1.7 polystyrene edge insulation (R1.7)

Timber frame with R2.2 bulk insulation (R1.9)

Timber frame with R3.6 bulk insulation (R3.4)

Double clear glazing metal frames (R0.26)

Better practice

R1.4 polystyrene under slab plus edge insulation (R2.9)

Timber frame with R2.6 bulk insulation (R2.4)

Timber frame with R4.0 bulk insulation (R3.7)

Double low-E Argon filled glazing timber frames (R0.5)

Best practice

R1.4 polystyrene under slab plus edge insulation (R2.9)

Timber frame R2.6 + R2.2 bulk insulation (R4.2)

Timber frame with R5.0 + R5.0 bulk insulation (R9.5)

Triple glazing – one pane low-E, timber frame (R0.62)

Code compliance

R1.7 polystyrene edge insulation (R1.7)

Concrete with R1.0 external polystyrene insulation (R1.3)

Timber frame with R3.6 bulk insulation (R3.4)

Double clear glazing metal frames (R0.26)

Better practice

R1.4 polystyrene under slab plus edge insulation (R2.9)

Concrete with R2.4 external polystyrene insulation (R2.7)

Timber frame with R4.0 bulk insulation (R3.7)

Double low-E Argon filled glazing timber frames (R0.5)

Best practice

R1.4 polystyrene under slab plus edge insulation (R2.9)

Concrete with R4.2 external polystyrene insulation (R4.5)

Timber frame with R5.0 + R5.0 bulk insulation (R9.5)

Triple glazing – one pane low-E, timber frame (R0.62)

Note: the R-Value of the insulation material is provided along with the R-Value of the complete system (in brackets).

Temperature fluctuations The ‘sparklines’ in the following charts are based on heating the living areas (as required) between 7.00am-11.00pm to 20oC, but no heating between 11.00pm-7.00am. These sparklines show the magnitude of the drop in temperature, below 16oC, between 11.00pm and 7.00am (below the axis) and the magnitude of overheating, above 26oC (above the axis) for all 365 days of the year. They therefore provide a good indication of the expected comfort of each house.

57


4 expected performance – Wellington

The house in the bottom left corner has a relatively small window area and is insulated to the current minimum required by the Building Code – it mainly needs heating. Increasing the areas of north-facing glass in the bottom row of this code insulated group of houses increases the need for heating and introduces a need for cooling. Moving up a row to the medium thermal mass row shows a very large reduction in the swings in temperature. The effect of adding more insulation to a house can be seen by looking at the groups of sparklines for better and best insulation. Improving insulation removes most of the large drops in temperature at night but increases the amount of overheating during the day. Increasing mass levels in these more highly insulated houses has the same effect observed in the code insulated homes – it reduces the swings in temperature.

Cooling need

“Increasing north-facing glass causes more overheating but increasing mass in the house greatly reduces this problem.”

58

Overheating has been calculated as degree hours – the total for all hours over 26oC multiplied by the difference between 26oC and the actual temperature. This is a better indicator of the need for cooling than merely the hours over 26oC. For example, two houses might each total 10 hours over 26oC, but one is just one degree over on average, a total of 10 degree hours; the other being on average 4 degrees over would total 4 degrees times the 10 hours or 40 degree hours. Overheating hours will tend to be afternoon and evening hours in summer. The following tables show the number of overheating degree hours (above 26oC) in each of the houses – even when the windows are opened for natural ventilation cooling. The calculation models the windows being opened to allow ventilation when the temperature reaches 26oC. The ventilation rate achieved is dependent on the opening sizes of the windows and the amount of wind. Obviously if no one is home to open the windows the overheating problem will be much worse.


Because Wellington is relatively windy and has relatively mild temperatures, overheating is less of a problem than in Auckland. Amount of overheating – degree hours above 26oC

“In medium and high mass houses temperatures virtually never fall below 16oC overnight – provided they are insulated above code minimum.”

Here the complex interaction of glass, thermal mass and insulation becomes clear. Increasing glass area facing north (left to right in each group) brings big increases in overheating degree hours. A doubling of the number of degree hours is approximately correlated with a doubling of the need for cooling energy (not accounted for in the energy consumption figures presented). However, increasing the amount of available thermal mass within each insulation group – moving up from one row to the next in each group – results in very large decreases in overheating.

Overnight temperature drop A significant amount of energy can be saved by turning off the heating before going to bed for the night, but a major influence on the feeling of comfort in a house is how much the temperature in the house falls overnight. Underheating hours will tend to be pre-dawn hours in winter – they are based on how often the temperature drops below 16oC when the heaters are turned off at 11.00pm and turned on the next day at 7.00am. The following tables show how many degree hours below 16oC occur in each of these e-buildings. Amount of underheating – degree hours below 16oC

The benefit of mass and insulation is obvious in these tables. For all insulation groups, the underheating figures in the bottom row (low mass) are significantly worse than in the next row up (medium mass). Increasing the insulation – moving from left to right across the groups – also reduces underheating for the low and medium mass houses. Virtually no underheating occurs in any of the high mass houses.

59


4 expected performance – Wellington Purchased energy for heating

“Heating energy consumption decreases dramatically with increases in insulation.”

Energy use is presented for just one heating schedule. You may, of course, operate a quite different heating schedule. The absolute energy use is less important than the comparison between different glass, mass and insulation options – with the same heating schedule. Many New Zealand homes are less well heated than the schedule presented and therefore energy use will be lower. As described earlier on page 49, heating for longer each day will increase your energy use, but not nearly as much as heating to a higher temperature (greater than the 20oC modelled). Energy cost can be estimated using roughly $200 per 1000kWh (at the time of writing). The following tables show purchased energy (x 1,000 kWh) required to maintain a minimum temperature of 16oC in bedrooms and 20oC in living rooms between 7.00am and 11.00pm, 365 days a year (no heating 11.00pm-7.00am). Use of air-conditioning units to control overheating has not been modelled so overheating may still occur as control is by opening windows only. Use of air-conditioning units, such as heat pumps, to control overheating can increase energy consumption very significantly. Heating energy consumption (x 1,000kWh)

The tables above demonstrate that improving insulation is by far the most effective way of reducing energy use. The set of e-buildings with code level insulation on the left have much higher annual energy use than those to the right with higher levels of insulation. By looking at the energy use, overheating and underheating tables you can see that if you increase the amount of northfacing glazing, in conjunction with increased thermal mass, you generally get comfort benefits – and at better and best insulation levels, reduced energy consumption. When you are comparing specific glass, mass and insulation combinations, don't just look at one factor in isolation. It pays to look at the sparklines, overheating, underheating, energy use and heater capacity tables together to get a good overall picture of the likely performance you can expect.

60


Required heater size For each computer study, heating capacity required to meet peak demand on the coldest day is also presented for the 7.00am-11.00pm heating schedule. Typical domestic electric heaters have a capacity of 500W to 2.4kW, heat pumps 4-9kW, flued gas heaters 3-7kW and wood burners 8-15kW. Several of the e-buildings require less than 7kW heater capacity for the whole house. Required heater capacity (kW)

61


4 expected performance – Christchurch CHRISTCHURCH Christchurch has a winter climate that is significantly colder than Wellington, with average ground temperatures of 18.6ºC in summer and 7.1ºC in winter. Energy consumption required to maintain comfort in Christchurch is therefore relatively high. If you live in Christchurch you will probably be very interested in energy efficiency as the potential cost savings are high. Summer temperatures can also get quite high and overheating can be a significant problem.

KEY: Blue middle line = Average day temperature during allocated months Wider red area = Range of day temperatures during allocated months Green solid line = Average direct sunlight per day and month (W/m2) Green dotted line = Average diffuse sunlight per day and month (W/m2) Dark green bars = Comfortable temperature range for months

Summary created using Autodesk® Ecotect® 2010 of the Christchurch weather data used in the house performance calculations

“Heating energy needed in Christchurch is relatively high because of cold winter temperatures – however, high summer temperatures mean overheating can also be a problem.”

62

There are many ways in which the results presented in the following pages can guide your design. Remember – these studies can’t be used to accurately predict energy use and comfort for different designs or different locations. You can, however, estimate performance by adjusting for coldness of climate, anticipated heating schedule and levels of glass, mass and insulation.

Construction details The following table provides details of the constructions used to achieve the specified levels of insulation for the three insulation levels and the three mass levels. These construction systems have been chosen as they are all currently used in the New Zealand market. Other construction system that achieve the same insulation R-Values will perform in the same way.


Insulation level Low mass

Medium mass

High mass

Concrete ground floor slab

External walls

Roof

Window glazing

Code compliance

Carpeted floor, R1.7 polystyrene edge insulation (R1.9)

Timber frame with R2.2 bulk insulation (R1.9)

Timber frame with R3.2 bulk insulation (R2.9)

Double clear glazing metal frames (R0.26)

Better practice

Carpeted floor, R1.4 polystyrene under slab plus edge insulation (R3.1)

Timber frame with R2.6 bulk insulation (R2.4)

Timber frame R3.6 bulk insulation (R3.4)

Double low-E Argon filled glazing timber frames (R0.5)

Best practice

Carpeted floor, R1.4 polystyrene under slab plus edge insulation (R3.1)

Timber frame R2.6 + R2.2 bulk insulation (R4.2)

Timber frame with R5.0 + R5.0 bulk insulation (R9.5)

Triple glazing – one pane low-E, timber frame (R0.62)

Code compliance

R1.7 polystyrene edge insulation (R1.7)

Timber frame with R2.2 bulk insulation (R1.9)

Timber frame with R3.6 bulk insulation (R3.4)

Double clear glazing metal frames (R0.26)

Better practice

R1.4 polystyrene under slab plus edge insulation (R2.9)

Timber frame with R2.6 bulk insulation (R2.4)

Timber frame with R4.0 bulk insulation (R3.7)

Double low-E Argon filled glazing timber frames (R0.5)

Best practice

R1.4 polystyrene under slab plus edge insulation (R2.9)

Timber frame R2.6 + R2.2 bulk insulation (R4.2)

Timber frame with R5.0 + R5.0 bulk insulation (R9.5)

Triple glazing – one pane low-E, timber frame (R0.62)

Code compliance

R1.7 polystyrene edge insulation (R1.7)

Concrete with R1.0 external polystyrene insulation (R1.3)

Timber frame with R3.6 bulk insulation (R3.4)

Double clear glazing metal frames (R0.26)

Better practice

R1.4 polystyrene under slab plus edge insulation (R2.9)

Concrete with R2.4 external polystyrene insulation (R2.7)

Timber frame with R4.0 bulk insulation (R3.7)

Double low-E Argon filled glazing timber frames (R0.5)

Best practice

R1.4 polystyrene under slab plus edge insulation (R2.9)

Concrete with R4.2 external polystyrene insulation (R4.5)

Timber frame with R5.0 + R5.0 bulk insulation (R9.5)

Triple glazing – one pane low-E, timber frame (R0.62)

Note: the R-Value of the insulation material is provided along with the R-Value of the complete system (in brackets).

Temperature Fluctuations The ‘sparklines’ in the following charts are based on heating the living areas (as required) between 7.00am-11.00pm to 20oC, but no heating between 11.00pm-7.00am. These sparklines show the magnitude of the drop in temperature, below 16oC, between 11.00pm and 7.00am (below the axis) and the magnitude of overheating, above 26oC (above the axis) for all 365 days of the year. They therefore provide a good indication of the expected comfort in each house.

The house in the bottom left corner has a relatively small window area and is insulated to the current minimum required by the Building Code – it mainly needs heating. Increasing the areas of north-facing glass in the bottom row

63


4 expected performance – Christchurch of this code insulated group of houses increases the need for heating and cooling. Moving up a row to the medium thermal mass row shows a very large reduction in the swings in temperature. The effect of adding more insulation to a house can be seen by looking at the groups of sparklines for better and best insulation. Improving insulation removes most of the large drops in temperature at night but increases the amount of overheating during the day. Increasing mass levels in these more highly insulated houses has the same effect observed in the code insulated homes – it reduces the swings in temperature.

“Increasing north-facing glass causes more overheating but increasing mass in the house greatly reduces this problem.”

Cooling need Overheating has been calculated as degree hours – the total for all hours over 26oC multiplied by the difference between 26oC and the actual temperature. This is a better indicator of the need for cooling than merely the hours over 26oC. For example, two houses might each total 10 hours over 26oC, but one is just one degree over on average, a total of 10 degree hours; the other being on average 4 degrees over would total 4 degrees times the 10 hours or 40 degree hours. Overheating hours will tend to be afternoon and evening hours in summer. The following tables show the number of overheating degree hours (above 26oC) in each of the houses – even when the windows are opened for natural ventilation cooling. The calculation models the windows being opened to allow ventilation when the temperature reaches 26oC. The ventilation rate achieved is dependent on the opening sizes of the windows and the amount of wind. Obviously if no one is home to open the windows the overheating problem will be much worse. Amount of overheating – degree hours above 26oC

Here the complex interaction of glass, thermal mass and insulation becomes clear. Increasing glass area facing north (left to right in each group) brings big increases in overheating degree hours. A doubling of the number of degree hours is approximately correlated with a doubling of the need for cooling energy (not accounted for in the energy consumption figures above). However, increasing the amount of available thermal mass within each insulation

64


“Increasing insulation and increasing mass in the house greatly reduces the temperature dropping below 16oC overnight.”

group – moving up from one row to the next in each group – results in very large decreases in overheating.

Overnight temperature drop A significant amount of energy can be saved by turning off the heating before going to bed for the night, but a major influence on the feeling of comfort in a house is how much the temperature in the house falls overnight. Underheating hours will tend to be pre-dawn hours in winter – they are based on how often the temperature drops below 16oC when the heaters are turned off at 11.00pm and turned on the next day at 7.00am. The following tables show how many degree hours below 16oC occur in each of these e-buildings. Amount of underheating – degree hours below 16oC

The benefit of mass and insulation are obvious in these tables. For all insulation groups, the underheating figures in the bottom row (low mass) are significantly worse than in the next two rows up (medium and high mass). Increasing the insulation – moving from left to right across the groups – also reduces underheating.

Purchased energy for heating Energy use is presented for just one heating schedule. You may, of course, operate a quite different heating schedule. The absolute energy use is less important than the comparison between different glass, mass and insulation options – with the same heating schedule. Many New Zealand homes are less well heated than the schedule presented and therefore energy use will be lower. As described earlier on page 49, heating for longer each day will increase your energy use, but not nearly as much as heating to a higher temperature (greater than the 20oC modelled). Energy cost can be estimated using roughly $200 per 1000kWh (at the time of writing). The following tables show purchased energy (x 1,000kWh) required to maintain a minimum temperature of 16oC in bedrooms and 20oC in living rooms between 7.00am and 11.00pm, 365 days a year (no heating 11.00pm-7.00am). Use of air-conditioning units to control overheating has not been modelled so overheating may still occur as control is by opening windows only. Use of air-conditioning units, such as heat pumps, to control overheating can increase energy consumption very significantly.

65


4 expected performance – Christchurch Heating energy consumption (x1,000 kWh)

The tables above demonstrate that improving insulation is by far the most effective way of reducing energy use. The set of e-buildings with code level insulation on the left have much higher annual energy use than those to the right with higher levels of insulation.

“Heating energy consumption decreases dramatically with increases in insulation.”

By looking at the energy use, overheating and underheating tables you can see that if you increase the amount of northfacing glazing, in conjunction with increased thermal mass, you generally get comfort benefits – and at better and best insulation levels, reduced energy consumption. When you are comparing specific glass, mass and insulation combinations, don't just look at one factor in isolation. It pays to look at the sparklines, overheating, underheating, energy use and heater capacity tables together to get a good overall picture of the likely performance you can expect.

Required heater size For each computer study, heating capacity required to meet peak demand on the coldest day is also presented for the 7.00am-11.00pm heating schedule. Typical domestic electric heaters have a capacity of 500W to 2.4kW, heat pumps 4-9kW, flued gas heaters 3-7kW and wood burners 8-15kW. Several of the e-buildings require less than 10kW heater capacity for the whole house. Required heater capacity (kW)

66


New Zealand Building Code requirements

5


5 New Zealand Building Code requirements Chapter 5: NZ Building Code Requirements Determining Insulation Values The first step in checking a house for compliance with the Building Code is to determine the insulation values for the various building elements. The insulation value is expressed as a thermal resistance, which is a measure of how efficient each element is in resisting the flow of heat. These thermal resistances are known as R-values. The greater the R-value, the better the resistance to heat flow (better insulation value). The R-value of a building component is essentially a combination of the R-values of the individual elements that make up that component. There is also a surface effect, both internally and externally, which adds a small amount to the overall R-value. For example, adding the R-value of a concrete masonry wall, the R-value of the insulation attached to that wall, and the R-values for the surface effects, gives an overall component R-value for the wall. This simple calculation becomes more complicated when the layers are not continuous. When there is thermal bridging, as with a timber-framed wall for example, calculations are required to allow for this bridging effect. NZS 4214:2006 Methods of Determining the Total Thermal Resistances of Parts of Buildings details the calculation methods and provides R-values for a wide range of generic building materials. Commercial suppliers of insulating materials will be able to provide R-values for their products. BRANZ also produces a house insulation guide which provides R-values for a range of floor, wall and roof construction systems.

Methods of Compliance Clause H1 of the New Zealand Building Code specifies the minimum performance requirements for the energy efficiency of houses. Clause H1 and its associated means of compliance can be downloaded free from www.dbh.govt.nz. NZS 4218:2004 Energy Efficiency – Small Building Envelope is referenced as a means of compliance with Clause H1 (but with significant modification). This means houses that comply with this New Zealand Standard (as modified by H1/ AS1) must be accepted by territorial authorities as code compliant. There are 4 ways to comply with H1: 1. Acceptable Solution • Schedule method . Here the design has to comply with minimum R-values for walls, roof, floor and glazing. This method can be used if the glazing does not exceed 30% of the external wall area.

68


Simple tables of the required R-Values are provided for both solid and non-solid construction. • Calculation method . This method allows lower insulation values in one building component (e.g. walls) to be traded off (via numerical calculation) against increased insulation in another component (e.g. roof), provided the overall efficiency of the house is not compromised. This method can be used if the glazing does not exceed 50% of the external wall area. The calculation method allows a mix of solid and non-solid construction. 2. Verification method • Modelling method . This option uses sophisticated computer modelling to calculate the energy consumption of a proposed design in a specific location. The proposed house must perform as well as a house insulated to the Schedule Method above. There are numerous modelling programmes available but a relatively easy to use ‘home grown’ option is AccuRateNZ (see www.energywise.govt.nz). 3. Building Performance Index (BPI) • The annual heating energy of a house is calculated using standard assumptions (appropriate software, for example, ALF or AccuRateNZ). The BPI is then calculated using the annual heating energy and must not exceed a limit set in the Building Code. 4. Alternative Solution • This approach allows the designer complete freedom to use any method to show compliance, provided the building consent authority (council) can be satisfied that the resulting design has adequate energy efficiency.

69


appendix

6


6 appendix Chapter 6: Appendices Appendix 1 – Two-Storey House Results A two-storey house with a similar floor area to the house on which Chapter Four is based was also investigated, to ensure that the trends demonstrated for the single-storey house were more generally applicable. This two-storey house has also been the basis for the studies on the effects of climate and orientation to the sun and on pages 43 and 45. These studies confirmed that the general trends demonstrated in this book (for a single-storey design) are applicable to a two-storey design. See Chapter Four for more details on how to interpret the information presented in this appendix.

The 'sparklines' in the following charts for the three main centres represent overheating and underheating potential of the various combinations of glass, mass and insulation. The horizontal axis of each chart represents the 365 days of the year. The red lines above the axis represent the house overheating – when the temperature is over 26oC in the living room. The blue lines below the axis represent the days when the living room temperature drops below 16oC overnight.

71


6 appendices As with all the data in this book the purpose of the following sparklines is to describe the trends. The sparklines show that the trends demonstrated for the single-storey house are also consistent for the two-storey house. These trends include: • increasing thermal mass, regardless of the insulation level, will reduce overheating • increasing insulation greatly reduces of the overnight drops in temperature (below 16°C) • increasing north-facing window area increases the temperature swings in the house. The heating energy use data in the tables that follow is also consistent with the trends demonstrated for the single-storey house in Chapter Four. These trends include: • Increasing insulation is the single biggest factor reducing heating energy consumption • Increasing north-facing window area generally decreases heating energy consumption, the decrease is greatest with better and best insulation levels combined with high levels of mass. For any specific glass, mass and insulation combinations that you want to compare don't just look at one factor in isolation, it pays to look at the sparklines, overheating, underheating and energy use tables that follow to ensure you get a good overall picture of the likely performance you can expect.

Auckland Temperature fluctuations

72


The following table provides further overheating and underheating data as well as heating energy consumption data for the two-storey house. Code insulation LOW glass

HIGH MASS

Degree hours MEDIUM MASS underheating

Better insulation

MED glass HIGH glass LOW glass

Best insulation

MED glass HIGH glass LOW glass

MED glass HIGH glass

0

0

0

0

0

0

0

0

0

1

4

3

0

0

0

0

0

0

LOW MASS

230

354

389

32

83

99

1

2

3

HIGH MASS

0

30

110

26

187

371

40

263

473

9

128

259

74

365

586

98

484

770

130

604

961

241

892

1,340

269

1,042

1,586

HIGH MASS 7.7 Energy consumption MEDIUM MASS 4.5 kWh x 1,000

6.2

5.2

3.8

2.9

2.3

2.2

1.2

0.7

4.0

3.9

2.9

2.5

2.5

1.6

1.2

1.1

4.2

4.3

3.0

3.0

3.1

1.7

1.6

1.6

Degree hours MEDIUM MASS overheating LOW MASS

LOW MASS

4.3

Wellington Temperature fluctuations

The following table provides further overheating and underheating data as well as heating energy consumption data for the two-storey house. Code insulation LOW glass

HIGH MASS

0

Degree hours MEDIUM MASS 101 underheating LOW MASS

1,244

HIGH MASS

Better insulation

MED glass HIGH glass LOW glass

Best insulation

MED glass HIGH glass LOW glass

MED glass HIGH glass

0

1

0

0

0

0

0

0

198

219

0

1

2

0

0

0

1,608

1,700

201

304

330

47

73

80

0

1

0

13

52

0

17

53

Degree hours MEDIUM MASS overheating

0 0

1

10

1

47

101

0

91

102

1

75

175

15

187

393

11

168

370

12.9

11.9

7.3

5.8

4.9

5.3

3.7

2.9

9.7

9.7

5.6

4.9

4.7

3.9

2.9

2.9

9.4

9.6

5.5

5.3

5.3

3.9

3.5

3.3

LOW MASS

HIGH MASS 14.4 Energy consumption MEDIUM MASS 10.2 kWh x 1,000 LOW MASS

9.3

73


6 appendices Christchurch Temperature fluctuations

The following table provides further overheating and underheating data as well as heating energy consumption data for the two-storey house. Code insulation LOW glass

Best insulation

MED glass HIGH glass LOW glass

MED glass HIGH glass

97

128

0

0

0

0

0

0

1,237

1,294

62

94

95

11

18

18

4,294

4,476

1,165

1,366

1,415

689

779

803

0

3

34

1

110

262

2

116

254

9

114

201

99

367

568

90

349

546

207

561

826

326

882

1,303

292

802

1,200

HIGH MASS 19.4 Energy consumption MEDIUM MASS 14.9 kWh x 1,000

18.2

17.2

10.8

9.0

7.9

8.5

6.7

5.6

14.7

14.8

8.4

7.5

7.2

6.5

5.4

5.1

13.7

14.1

8.2

7.8

7.8

6.2

5.7

5.6

HIGH MASS

18

Better insulation

MED glass HIGH glass LOW glass

Degree hours MEDIUM MASS 889 underheating LOW MASS

3,553

HIGH MASS

Degree hours MEDIUM MASS overheating LOW MASS

LOW MASS

74

13.4


Appendix 2 – Climate Zones To summarise the climate of New Zealand, selected locations throughout the country have been grouped into broad climate zones (see maps below). The maps below show the National Institute of Water and Atmospheric Research (NIWA) general climate regions and the legal definitions for the operation of the Building Code of the three climate zones for which there are different insulation requirements. The map on the right shows the locations of the weather stations (two letter codes) for which there are Typical Meteorological Year (TMY) weather files for energy performance purposes. The climate descriptions for the NIWA climate regions on the following pages have been kindly provided by NIWA and are available from their website (www.niwa.co.nz/educationand-training/schools/resources/climate/overview).

The map above shows the locations of the EECA Home Energy Rating Scheme weather files developed by NIWA and downloadable from the US Dept of Energy website http:// apps1.eere.energy.gov/buildings/energyplus/weatherdata_ sources.cfm. These weather files are the basis of the climate studies published on page 43. The weather data from Auckland, Wellington and Christchurch are the basis of all the analyses of energy performance in this book.

75


6 appendices TMY

Stations

Territorial Local Authorities

ZONE 1

Building Code plus NZS 4218

NL

Kaitaia

Far North, Whangarei, Kaipara

AK Auckland

Rodney, North Shore City, Waitakere City, Auckland City, Manukau City, Papakura, Franklin, Thames-Coromandel

ZONE 2

Building Code plus NZS 4218

HN

Ruakura / Hamilton Hauraki, Waikato, Matamata-Piako, Hamilton City, Waipa, aero Otorohanga, South Waikato, Waitomo

BP

Tauranga

Western Bay of Plenty, Tauranga, Whakatane, Kawerau, Opotiki

NP

New Plymouth

New Plymouth, Stratford, South Taranaki, Wanganui

EC

Napier

Gisborne, Wairoa, Hastings, Napier City, Central Hawke’s Bay

MW Paraparaumu

Southern Rangitikei, Manawatu, Palmerston North City, Horowhenua, Kapiti Coast

WI

Masterton

Tararua, Upper Hutt City, Masterton, Carterton, South Wairarapa

WN

Wellington

Porirua City, Hutt City, Wellington City

ZONE 3

Building Code plus NZS 4218

RR

Rotorua

Rotorua

TP

Turangi / Taupo

Taupo, Ruapehu, Northern Rangitikei

NM

Nelson

Tasman, Nelson City, Marlborough, Kaikoura

WC Hokitika

Buller, Grey, Westland

CC Christchurch Hurunui, Waimakariri, Christchurch City, Banks Peninsula, Selwyn, Ashburton, Timaru, Waimate QL

Queenstown

Queenstown-Lakes

OC

Lauder

Mackenzie, Western Waitaki, Central Otago

DN

Dunedin / aero

Eastern Waitaki, Dunedin City, Clutha

IN

Invercargill

Southland, Gore, Invercargill City

76


Northern New Zealand Kaitaia, Whangarei, Auckland, Tauranga KEY: Blue middle line = Average day temperature during allocated months Wider red area = Range of day temperatures during allocated months Green solid line = Average direct sunlight per day and month (W/m2) Green dotted line = Average diffuse sunlight per day and month (W/m2) Dark green bars = Comfortable temperature range for months

This is a sub-tropical climate zone, with warm humid summers and mild winters. Typical summer daytime maximum air temperatures range from 22°C to 26°C, but seldom exceed 30°C. Winter daytime maximum air temperatures range from 12°C to 17°C. Annual sunshine hours average about 2,000 in many areas. Tauranga is much sunnier with at least 2,200 hours. Southwesterly winds prevail for much of the year. Sea breezes often occur on warm summer days. Winter usually has more rain and is the most unsettled time of year. In summer and autumn, storms of tropical origin may bring high winds and heavy rainfall from the east or northeast.

Kaitaia

Auckland

Tauranga

77


6 appendices Central North Island Hamilton, Taupo, Rotorua As this region is sheltered by high country to the south and east, it has less wind than many other parts of New Zealand. Being inland, a wide range of temperature is experienced. Warm, dry and settled weather predominates during summer. Typical summer daytime maximum air temperatures range from 21°C to 26°C, rarely exceeding 30°C. Winters are cool and this is normally the most unsettled time of the year. Typical winter daytime maximum air temperatures range from 10°C to 14°C. Frosts occur in clear, calm conditions in winter. Sunshine hours average 2,000 to 2,100 in most places. Southwesterlies prevail. Lake breezes often occur in Taupo and Rotorua on warm summer days. Hamilton

Turangi

KEY: Blue middle line = Average day temperature during allocated months Wider red area = Range of day temperatures during allocated months Green solid line = Average direct sunlight per day and month (W/m2) Green dotted line = Average diffuse sunlight per day and month (W/m2) Dark green bars = Comfortable temperature range for months

78


South-West North Island New Plymouth, Wanganui, Palmerston North, Wellington Because of its exposure to disturbed weather systems from the Tasman Sea, this climate zone is often quite windy, but has few climate extremes. The most settled weather occurs during summer and early autumn. Summers are warm. Typical summer daytime maximum air temperatures range from 19°C to 24°C, seldom exceeding 30°C. Winters are relatively mild in New Plymouth and Wanganui, but cooler in Palmerston North and Wellington. This is normally the most unsettled time of the year. Typical winter daytime maximum air temperatures range from 10°C to 14°C. Frost occurs inland during clear, calm conditions in winter. Annual sunshine hours average about 2,000 hours, but inland at Palmerston North it is much cloudier. Northwesterly airflows prevail. Sea breezes occasionally occur along the coast during summer. New Plymouth

Wellington

KEY: Blue middle line = Average day temperature during allocated months Wider red area = Range of day temperatures during allocated months Green solid line = Average direct sunlight per day and month (W/m2) Green dotted line = Average diffuse sunlight per day and month (W/m2) Dark green bars = Comfortable temperature range for months

79


6 appendices Eastern North Island Gisborne, Napier, Masterton Sheltered by high country to the west, this zone enjoys a dry, sunny climate. Warm, dry settled weather predominates in summer. Frosts may occur in winter. Typical summer daytime maximum air temperatures range from 20°C to 28°C, occasionally rising above 30°C. High temperatures are frequent in summer, which may be accompanied by strong dry foehn1 winds from the northwest. Extreme temperatures as high as 39°C have been recorded. Winter is mild in the north of this region and cooler in the south. Typical winter daytime maximum air temperatures range from 10°C to 16°C. Annual hours of bright sunshine average about 2,200 in Gisborne and Napier. Heavy rainfall can occur from the east or southeast. Westerly winds prevail. Sea breezes often occur in coastal areas on warm summer days. Napier

Masterton

1

A foehn wind or föhn wind is a type of dry down-slope wind which occurs in the lee (downwind side) of a mountain range. KEY: Blue middle line = Average day temperature during allocated months Wider red area = Range of day temperatures during allocated months Green solid line = Average direct sunlight per day and month (W/m2) Green dotted line = Average diffuse sunlight per day and month (W/m2) Dark green bars = Comfortable temperature range for months

80


Northern South Island Nelson, Blenheim As much of this climate zone is sheltered by high country to the west, south and in some areas to the east, it is the sunniest region of New Zealand. Warm, dry and settled weather predominates during summer. Winter days often start with a frost, but are usually mild overall. Typical summer daytime maximum air temperatures range from 20°C to 26°C, but occasionally rise above 30°C. Late winter and early spring is normally the most unsettled time of the year. Typical winter daytime maximum air temperatures range from 10°C to 15°C. Annual hours of sunshine average at least 2,300 hours. Northnortheast winds prevail in Nelson, while southwesterlies prevail about Blenheim. Nelson has less wind than many other urban centres and its temperatures are often moderated by sea breezes. High temperatures are frequent in Blenheim and may be accompanied by foehn winds from the northwest. Nelson

KEY: Blue middle line = Average day temperature during allocated months Wider red area = Range of day temperatures during allocated months Green solid line = Average direct sunlight per day and month (W/m2) Green dotted line = Average diffuse sunlight per day and month (W/m2) Dark green bars = Comfortable temperature range for months

81


6 appendices Eastern South Island Kaikoura, Christchurch, Timaru The climate of this zone is greatly dependent on the lie of the massive Southern Alps to the west. Summer temperatures are warm, with highest temperatures occurring when hot, dry foehn northwesterlies blow over the Alps and plains. Mean annual rainfall is low, and long dry spells can occur, especially in summer. For much of the time summer temperatures are moderated by a cool northeasterly sea breeze. Typical summer daytime maximum air temperatures range from 18°C to 26°C, but may rise to more than 30°C. A temperature of 42°C has been recorded in Christchurch. Winters are cold with frequent frost. Typical winter daytime maximum air temperatures range from 7°C to 14°C. Northeasterlies prevail about the coast for much of the year. Southwesterlies are more frequent during winter. Christchurch

KEY: Blue middle line = Average day temperature during allocated months Wider red area = Range of day temperatures during allocated months Green solid line = Average direct sunlight per day and month (W/m2) Green dotted line = Average diffuse sunlight per day and month (W/m2) Dark green bars = Comfortable temperature range for months

82


Western South Island Wesport, Hokitika, Milford Sound The climate of this area is greatly dependent on its exposure to weather systems from the Tasman Sea and the lie of the Southern Alps to the east. Although mean annual rainfall is very high, dry spells do occur, especially in late summer and during winter. Heavy rainfall occurs from the northwest. Summers are mild. Typical summer daytime maximum air temperatures range from 17°C to 22°C and seldom exceed 25°C. Winter days often start with frost. Typical winter daytime maximum air temperatures range from 10°C to 14°C. Northnortheast winds prevail along the coast in Westport and Hokitika while southwesterlies prevail in coastal areas further south. Sea breezes can occur on warm summer days. Hokitika

KEY: Blue middle line = Average day temperature during allocated months Wider red area = Range of day temperatures during allocated months Green solid line = Average direct sunlight per day and month (W/m2) Green dotted line = Average diffuse sunlight per day and month (W/m2) Dark green bars = Comfortable temperature range for months

83


6 appendices Inland South Island Lake Tekapo, Queenstown, Alexandra, Manapouri The climate of this zone is largely dependent on the lie of the Southern Alps to the west, but many areas are also sheltered by high country to the south and east. Mean rainfall is low, and long dry spells can occur, especially in summer. Summer afternoons are very warm, with high temperatures occurring when hot, dry foehn northwesterlies blow over the Alps. Typical summer daytime maximum air temperatures range from 20°C to 26°C, occasionally rising above 30°C. Winters are very cold with frequent, often severe frosts, and occasional snowfalls. In severe cases, snow may lie for several days or longer. Typical winter daytime maximum air temperatures range from 3°C to 11°C. Wind flow is dependent on topography, however the strongest winds are often from the northwest. Queenstown

Lauder

KEY: Blue middle line = Average day temperature during allocated months Wider red area = Range of day temperatures during allocated months Green solid line = Average direct sunlight per day and month (W/m2) Green dotted line = Average diffuse sunlight per day and month (W/m2) Dark green bars = Comfortable temperature range for months

84


Southern New Zealand Dunedin, Invercargill Most of this climate zone is characterised by cool coastal breezes, and absence of shelter from the unsettled weather that moves over the sea from the south and southwest. Hot northwesterly conditions in summer can occasionally bring high temperatures. Typical summer daytime maximum air temperatures range from 16°C to 23°C, occasionally rising above 30°C. Winters are cold with infrequent snowfall and frequent frost. Typical winter daytime maximum air temperatures range from 8°C to 12°C. Hours of bright sunshine average about 1,600 hours annually and are often affected by low coastal cloud or by high cloud in foehn wind conditions. Southwesterlies prevail for much of the time about Southland, but northeasterlies are more frequent from Dunedin north. Dunedin

Invercargill

KEY: Blue middle line = Average day temperature during allocated months Wider red area = Range of day temperatures during allocated months Green solid line = Average direct sunlight per day and month (W/m2) Green dotted line = Average diffuse sunlight per day and month (W/m2) Dark green bars = Comfortable temperature range for months

85


bibliography Alcorn, J.A. (1996). Embodied energy coefficients of building materials Wellington: Victoria University of Wellington, Centre for Building Performance Research. Baird, G., Alcorn, A., & Haslam, P. (1997). The energy embodied in building materials – updated New Zealand coefficients and their significance. IPENZ Transactions, 24 (1), 46-54. Baird, G., & Chan, S.A. (1983). Energy cost of houses and light construction buildings (NZERDC Report No. 76). Auckland: University of Auckland, New Zealand Energy Research and Development Committee. Baird, G., Treleaven, C., & Storey, J.B. (1994). The embodiment of embodied energy. In C.J. Kibert (Ed.), Sustainable construction. Proceedings of the first international conference of CIB TG 16, November 6-9 (pp. 251-260). Gainesville, Fla.: University of Florida, Center for Construction and Environment. Bernhardt, J. (Ed.) (2008) A deeper shade of green – sustainable urban development, building and architecture in New Zealand. Balasoglou Books. Breuer, D.R. (1988). Energy and comfort performance monitoring of passive solar, energy efficient New Zealand residences (Ministry of Energy Report No. 171).Wellington: Ministry of Energy, New Zealand Energy Research and Development Committee. Breuer, D.R. (1994). Energy-wise design for the sun: Residential design guidelines for New Zealand. Wellington: Energy Efficiency and Conservation Authority (EECA). Burgess, S.M. (1988). The climate and weather of Manawatu and Horowhenua. Wellington: New Zealand Meteorological Service.

bibliography

Donn, M., & Van Der Werff, I. (1990). Design guidelines: passive solar in New Zealand (Ministry of Commerce Report RD 8831).Wellington: Ministry of Commerce, Energy and Resources Division.

86

Donn, M., Van Der Werff, I., & Miller, G. (1990). Construction issues: Passive solar in New Zealand (Ministry of Commerce Report RD 8832). Wellington: Ministry of Commerce, Energy and Resources Division. Isaacs, N., Camilleri, M. et. al. (2006) Energy use in New Zealand households, report on the year 10 analysis of the Household Energy End-use Project (HEEP). BRANZ Study Report SR155. Gjerde, M. (2000). Residential concrete: Detailing and specification guide. Wellington: Cement & Concrete Association of New Zealand (CCANZ).


Heschong, L. (1979). Thermal delight in architecture. Cambridge, Mass.: MIT Press. Isaacs, N., & Donn, M. (1994). Effect of thermal mass on house energy use and internal temperatures. Wellington: Victoria University of Wellington, Centre for Building Performance Research. Leslie, S.F. (1976). Annual heating energy demand of heavy domestic buildings (NZERDC Report No. 16). Auckland: University of Auckland, New Zealand Energy Research and Development Committee. Marsh, A. (1999). ECOTECT software. Architectural science software. Retrieved 24 January 2001 from the World Wide Web: http://fridge.arch.uwa.edu.au/software/index.html Maunder,W.J. (1974). Climate and climatic resources of the Waikato Coromandel King Country region. Wellington: New Zealand Meteorological Service. McPherson, E.G., Herrington, L.P., & Heisler, G.M. (1988). Impacts of vegetation on residential heating and cooling. Energy and Buildings, 12, 41-51. Robinette, G.O., & McClennon, C. (1983). Landscape planning for energy conservation. New York: Van Nostrand. Standards New Zealand. (2009). Thermal insulation – Housing and small buildings. NZS 4218:2009. Standards New Zealand. Energy Efficiency – Installing Insulation in Residential Buildings. NZS 4246:2006. Van Der Werff, I., Amor, R & Donn, M. (1990). Standard data files for computer thermal simulation of solar low energy non-residential buildings (Ministry of Commerce Report CRP53). Wellington: Victoria University of Wellington, Energy Research Group. Van Der Werff, I., & Trethowen, H. (1995). BRANZ house insulation guide. Wellington: Building Research Association of New Zealand (BRANZ). World Health Organisation. (1987). Health impact of low indoor temperatures (WHO Report No 16). Copenhagen: World Health Organisation. Wright, J., & Baines, J. (1988). Supply curves of conserved energy: The potential for conservation in New Zealand’s houses. Wellington: Ministry of Energy.

87


INFORMATION BULLETIN: IB 18 Architectural Surface Finishes Introduction Reinforced concrete is unique among the everincreasing range of building materials the designer can choose from. When used as a massive element in a building it can provide the required structural capacity, can define space and be seen as the architectural surface, all in one. It is also the only contemporary construction material that in the hands of the contractor passes through a plastic state that allows it to take on the shape of the formwork into which it is cast. Moreover, the process allows the surface to be rendered as the negative of the surface it is cast against.

can enhance a building in many ways, among them the architectural qualities. Concrete can be produced with a broad range of surface finishes, making it ever more attractive to architects and designers. With renewed interest in materials and surface finishes evident over the past decade designers are also exploring how concrete can affected as an architectural element. When concrete is exposed as the visible architectural surface it is most likely contributing to the: x

Cost efficiency of the initial building project by not requiring application of surface finishes costing time and money

x

Thermal and energy efficiency by allowing the density of the material to dampen temperature swings over the course of a day.

It is also likely that the exposed concrete will be more durable over its life than any other lightweight cladding or finish.

Objective of this I.B. To provide general information to specifiers and builders on the many various concrete surface finishes that can be achieved. This bulletin is not intended to provide all the technical information necessary to achieve these finishes nor is it possible to present all the various finishes that can be achieved. Many of the references given at the end of this bulletin are a useful source of further technical background.

Catholic Cathedral of Los Angeles. Coloured in-situ concrete. The appropriate use of exposed concrete elements

General Background The care exercised in the selection of the raw materials and in the shaping of the formwork will

IB 18: Architectural Surface Finishes

Page 1


be reflected in the quality of the final surface. It is therefore important before selecting the forms, materials or mixes to have a clear understanding of the different modes of treatment possible. The presentation of information in this bulletin is grouped under the three categories for finishes established by NZS 3114: 1987 Specification for Concrete Surface Finishes. These three categories are:

formwork is stripped. Such measures demand the following precautions be taken: 1.

Attention to detailing, with adequate provision for joints, edges, corners, drips and other weathering details. Adequate measures must also be taken to allow smooth form removal that does not lead to damage requiring remedial attention.

Type A:

Concrete surfaces that are produced by manipulating the surface of the form before casting the concrete.

2.

Clean, well maintained and watertight forms (See also Information Bulletins 29 and 41).

Type B:

Concrete surfaces that are produced by manipulating the surface of the fresh concrete before it has set.

3.

A concrete mix with adequate cement content, low water/cement ratio and high density.

4.

Adequate consolidation and uniform curing to help ensure uniformity of colour and texture.

5.

Protection to reduce the likelihood of chipping and damage after casting.

Type C :

Concrete surfaces that are produced by manipulating the surface of the hardened concrete.

These three methods of achieving the concrete surface can be applied to cast-in-situ or precast concrete construction. It would be difficult to represent the full range of surface finish possibilities in any one publication. The examples have been included to help illustrate the qualities of each surface finish. The examples are largely found in New Zealand, a fact that should give designers confidence in specifying these finishes. It is clear that all can be successfully manufactured by the local concrete industry. It is important that designers work with the contractors and manufacturers to achieve the desired results. We are very fortunate in New Zealand to have an industry that is approachable and willing to rise to any challenge. By working closely the designer will better understand the processes allowing him or her to work with or in some cases change the process to enable a better outcome. The manufacturer may enhance the outcomes with suggestions to the designer.

Steel or Plywood Sheet Formwork Sheet formwork can be used to achieve a concrete surface with minimal texture and minimal evidence of joints. The joints between steel sheets can in fact be welded and finished to be almost imperceptible in the concrete. A shortcoming with the use of sheet formwork that is highly impermeable is the likelihood of blowholes in the surface of the concrete. This will occur more often in concrete that is cast face down and arises from small pockets of air that are not eliminated through vibration. A great advantage of using impermeable formwork is the increased consistency of colour that can be achieved.

Type A Surface Finishes This is the most common, often being referred to as fairfaced concrete. The finish is produced by the pattern of the concrete form being mirrored on the concrete. It may be the most economical form of production provided that adequate measures ore taken to avoid the need for remedial work after the

St Paul’s Cathedral, Wellington. Cast in-situ concrete.

IB 18: Architectural Surface Finishes

Page 2


Board Formed Timber boarding has been one of the more common formwork materials throughout the history of concrete use. During the 1960’s in New Zealand architects began to exaggerate the imprint the timber would leave by lightly blasting the surface to raise the grain and by using a vee joint between T & G boards. Another method of creating desirable surface texture is to band saw the timber boards. Uniformity of colour can be enhanced with all porous formwork by thoroughly sealing the surface prior to the first use.

Lyons TGV Station, France. Cast in-situ concrete.

Mølster Museum, Voss, Norway. Board formed cast in-situ concrete.

Form Liners Concrete surfaces can be enlivened through texturing or modelling. This is also an effective way of disguising surface imperfections.

University of Cambridge, United Kingdom. Precast concrete.

Form liner materials include styrene foam, rigid plastics, fibreglass, polyurethane rubbers, silicone rubbers, profiled steel sheet and timber battens. The choice of the form liner material will be based on the complexity and depth of the modelled surface, and the number of reuses.

IB 18: Architectural Surface Finishes

Page 3


Cement hydration produces temperatures up to 60oC. High temperatures may degrade the form liner material.

Colouring Pigments Integrally coloured (or colour-through) concrete refers to colouration to the full depth of an in-situ or precast concrete element. The mineral oxide powder is added to the concrete mix and thoroughly dispersed. A monolithic topping is a layer of concrete that is placed on top of a prehardened structural slab or precast panel while it is still in its ‘plastic’ or workable state. This allows bonding of the two as they harden simultaneously, effectively producing a monolithic unit. The appearance can be the same as for integral colour, but of course the colour appears only on one side. There are, possibly, cost savings as a result of reducing the amount of oxide required.

St. Joseph’s Church, Wellington. Precast concrete using form liners.

Poetry Panels, Wellington. Precast concrete using form liners.

St Peter’s School, Auckland. Precast concrete. Eexposed aggregate and coloured concrete.

Plastic Rumpled Appearance – Lyon University. Cast in-situ concrete using form liners.

Lyons TGV Centre, France. Coloured cast in-situ concrete.

IB 18: Architectural Surface Finishes

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Barcelona Convention Centre, Spain. Cast in-situ coloured concrete.

Controlled Permeable Formwork Concrete is normally cast against impermeable formwork that leads to a relatively smooth concrete surface finish. Controlled permeable formwork (CPF) has been developed to improve surface durability of the cast concrete. Air and excess water that remain trapped at the formwork can result in surface imperfections in the concrete. CPF works by allowing air and water to be absorbed into the surface of the formwork. As a result cement grains pack more closely and the concrete surface is smoother, in some cases glass-like.

Christchurch Casino, Christchurch. Precast concrete. Exposed aggregate and polised concrete.

Type B Surface Finishes These effects result from special treatment of the concrete surface while still in its plastic state.

Exposed Aggregate – Water Washed One of the earliest and still most popular of the Type B techniques is that of exposed aggregate. Here the outer paste is removed through the application of water to reveal the aggregate within. The exposed stone may be the normal coarse aggregate or it may be a special material selected for its appearance. This technique requires skilled technicians to achieve the best results. Variables to be accounted for include weather conditions, mix design and geometry of the area to be treated. Careful thought must be given to the control of the runoff as indiscriminate release can cause environmental harm.

Wellington Public Library, Wellington. Precast concrete with exposed aggregate.

Set Retarders Printing set retarders on form liners to reproduce patterns or images in the surface of precast panels is another area of development.

IB 18: Architectural Surface Finishes

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Trials in Melbourne (ii) have successfully transferred large-scale digital images (up to 1.2 m x 2.5 m) onto precast concrete by first reproducing the reverse image on the plastic form liners in a concrete set-retarding medium. After hardening for 24 hours, the influence of the set retarder is washed from the face and the images emerge from the pixel-like dots etched 0.5 mm into the surface. The potential exists for creating increasingly sophisticated imagery and aesthetic effects.

consistent and uniform appearance to the concrete. This technique can only be achieved with unformed surfaces, that is those not cast against formwork

Trowelled in Colour Pigments Coloured topping products can be supplied as prebagged mixtures of mineral oxide, cement and sand. They can also contain a surface hardener to increase the strength of the concrete surface and consequently its resistance to abrasion.

Š Mixx 5, Aprril 20 000.

The method involves broadcasting the powder by hand onto the surface of prehardened concrete, following the evaporation of bleed water. The surface is floated and finished in the same way as general concrete. Curing requires care to avoid patchiness of colour. After hardening, a thin monolithic coloured layer results.

Pressed Surface Finishes Pressed surface finishes are made by altering the surface of the concrete after the mix has stiffened but before the concrete is fully hardened. The process for stamping is relatively simple but the timing of each stage is critical to the success and durability of the finish. Pressed surfaces can resemble traditional finishes such as stone or timber or can be abstract and capitalise on the plastic nature of concrete. The method and implements used to stamp the concrete surface is largely up to the ingenuity of the designer to achieve the desired appearance.

Pfaffenholz Sports Centre in Basel, Switzerland by Architects Herzog and De Muron.

Exposed Aggregates – Trowelled in Aggregates Another method of realising an exposed finish is to trowel selected aggregates into the still wet surface. This method allows the designer to specify a normal concrete mix. This method will give a

Residential Driveway. Cast in-situ with exposed aggregate.

IB 18: Architectural Surface Finishes

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Type C surface finishes Acid Etching Diluted acids are used to remove the surface skin of cement paste to reveal the underlying aggregates — usually sand and smaller stones. Concrete must be well-compacted, high density, free from cracks and have sufficient cover for reinforcement.

heavy blast. Sample panels are useful to make selections and become the basis for approvals. Brush blasting is a light surface texturing that feels like sandpaper. It does not reveal the coarse aggregates. The resulting colour is that of the cement paste. Brush blasting can be done any time after seven days.

Textures resembling fine sandpaper are commonly specified, although deeper etching that reveals coarse aggregate is possible. Etching involves controlled and deliberate action over small areas at any one time. Different personnel may produce slight variations in finish. Therefore results are improved if the same person works on the entire panel. Personnel should be coordinated to improve consistency between adjoining panels. Panels or elements are inclined during etching to prevent ponding, which should be avoided. After etching the surface must be thoroughly washed with water to remove any residual acid. Acid etching is often done to improve the colour uniformity of panels. However, during the manufacturing process different panels may be subjected to varying levels of ambient humidity. Initially, tonal variations in colour might be considered unsatisfactory, but are likely to moderate when the panels have balanced moisture content. The combination of etching and honing produces a surface characterised by flat coarse aggregate, which is slightly proud of the underlying matrix. Pavements are treated in this way to improve slip resistance.

Abrasive Blasting

St Paul’s Apartments, Wellington. Precast concrete using form liner.

Honed Finish

Abrasive blasting produces a cost effective finish with good weathering characteristics. The inherent appeal of the aggregates is revealed. Abrasive media include airborne or air/water borne sand, boiler slag and carborundum. The choice of medium is best left to the contractor to decide on the basis of the specified finish. Ensure good placement and compaction. Sandblasting reveals air voids from inadequate vibration (compaction) and aggregate segregation from uneven vibration. Sandblasting is followed by a light acid wash to clean the surface. Generally four grades of abrasion: brush blast, light, medium,

Honed or polished concrete surfaces are achieved by grinding the concrete surface and exposing the aggregates. Smoother surfaces (more polished) can be achieved through extended honing using progressively finer abrasives (finer grinding grit heads/pads). Alternatively, surface sealants may be employed to provide a surface lustre to the honed surface. Factors which affect the final appearance include: x

The colour and hardness of the coarse aggregate exposed through the grinding.

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x

The colour of the matrix.

x

The quality of the concrete.

x

The depth of grinding.

Louis XIV Bedroom, Versailles, France. Precast concrete – polished.

Te Papa, Wellington. Musee D’Orsay, France. Precast concrete – coloured and polished.

Polished Finish (Terrazzo) Polished finishes are an extension of honed finishes and are achieved by using very fine grinding media. Terrazzo floors may be slippery when wet. The layout of terrazzo floors must reflect the existing control joints in the substrate. Wellfinished terrazzo is extremely durable.

Burnished Finish Burnishing is a term applied to the finishing of concrete surfaces to provide a hardwearing, durable finish with a surface lustre. The application may incorporate integral or broadcast surface dry shake colourants, colouring dyes and or staining. By the nature of the process, burnishing results in

IB 18: Architectural Surface Finishes

Page 8


densification, and therefore darkening, of the surface from overworking.

broken on each face with a club hammer to expose the aggregate.

Floor waxes, liquid polishes and resin-based coating applications can also be used to produce a burnished finish. These are multi-layer applications which, after the recommended curing period, are burnished using polishing equipment. The polishing action produces friction, the heat from which melds the layers and induces the bond to the concrete surface. The degree of lustre achieved is dependent on the quality of the concrete (particularly the surface density), the quality of the particular product and the burnishing technique.

The geometry of the nib, the size and type of aggregate and the strength and colour of concrete will all influence the overall effect.

National Library of New Zealand, Wellington.

Te Papa Panel, Wellington.

Te Papa Floor, Wellington.

Broken Concrete Surfaces Broken concrete finishes provide the strongest texture of any discussed here. A popular technique has been to create thin fins in the surface that are

Christchurch Public Hospital, Christchurch.

IB 18: Architectural Surface Finishes

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Summary

References and Further Reading

Around the world architects, designers and building owners are looking to distinguish their projects with interesting and innovative material surface finishes.

x

Cement & Concrete Association of New Zealand. (2005) Specification and Production of Concrete Surface Finishes (Information Bulletin 33). Wellington: The Author.

Concrete has been experimented with more than most materials because it invites participation.

x

Cement & Concrete Association of Australia. (2003). Colour and texture in concrete walling (Briefing 03). St Leonards, N.S.W.: The Author.

x

Cement & Concrete Association of Australia. (2003). The specification of honed concrete finish (Data Sheet Oct). St Leonards, N.S.W.: The Author.

x

Soerensen, M.G. Draining concrete - controlled permeability formwork. Biennial conference (of the) Concrete Institute of Australia, Brisbane, 21, 871-880.

x

ACI Committee 303. (2004). ACI 303R-04. Guide to cast-in-place architectural concrete practice. [ACI Manual of Concrete Practice 2004]. Retrieved from MCP database (Microsoft Windows CD-ROM, 2004 release, Item ACI 303R_04.pdf).

Designers can easily engage with the manufacturing processes individually. Most of the successful processes have now become mainstream and can be reproduced locally by willing and capable tradespeople. Recent developments such as controlled permeability formwork and printed surface retardant combines with traditional methods such as form liners and exposed aggregate to give the industry an exciting range of surface finish possibilities. The range of finishes will continue to expand as new materials and processes combine with designers' imaginations.

ISSN 0114-8826 Š Revised December 2004. Cement & Concrete Association of New Zealand, Level 6, 142 Featherston Street, PO Box 448, Wellington, telephone (04) 499-8820, fax (04) 499-7760, e-mail admin@cca.org.nz, www.cca.org.nz. Since the information in the bulletin is for general guidance only and in no way replaces the services of professional consultants on particular projects, no liability can be accepted by the Association by its use.

IB 18: Architectural Surface Finishes

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INFORMATION BULLETIN: IB 33 Specification and Production of Concrete Surface Finishes CONTENTS Part 1: Commentary on Standard Specification

Part 2 continued Production of Concrete Surface Finishes

Introduction

2

Application of the Standard

2

Surface plane variations Colour variations Physical irregularities The “X” factor – (for exceptions) Sample Reference Panels (SRP)

Categories of Finish

2 2 2 2 3

3

Off-the-form surfaces Exposed aggregate surfaces Unformed surfaces

3 5 6

Materials and Workmanship

6

Part 2: Production of Concrete Surface Finishes General

8

Variations in colour and texture

8

Determination of Finish

9

Treatment before casting – Type A

9

Off-the-form finish Characteristics of form materials Surfacings applied in the mould Surfacings applied after casting Wet off-the-form finish

9 10 12 13 13

Treatment during setting – Type B

13

Face-down treatment Face-up treatment Coloured concrete surfaces

13 14 15

Treatment after casting – Type C Relatively smooth surfaces Relative rough textured surfaces

17 17 18

Cost of Finishes

20

Finishing Techniques

20

Tie rod holds Surface dressing Minor repairs/patching Cleaning

21 21 22 22

Summary

22

References

23

Appendix A:

23

Appendix B:

27

Blemishes in Concrete

Checklist of Specification, Design and Construction Matters. Structural detailing Formwork Release agents Cements Aggregates Mix design Preliminary contract work Supervision Weather conditions Batching Mixing Placing and compaction Striking Remedial work

IB 33: Specification and Production of Concrete Surface Finishes

27 27 27 27 27 27 28 28 28 28 28 28 28 28

Page 1


PART 1 COMMENTARY ON STANDARD SPECIFICATION

3.

Introduction

The specification provides guidance as to the physical characteristics that can be expected to affect the finish and defines limits for the various grades of finish.

This Bulletin was originally produced following the publication of New Zealand Standard 3114:1980 'Specification for Concrete Surface Finishes' to provide information on the background and use of this code, both by the specifier and by the contractor (see also Information Bulletin IB 18 for examples of finishes). NZS 3114, which was revised in 1987, provides the format which enables the statement of the concrete finishing requirements of the specifier to be translated, through contract documentation, to the contractor. The standard is divided into three parts: 1.

Off-the-form surfaces.

2.

Exposed aggregate surfaces.

3.

Floors, exterior pavements and inverts.

The characteristics that are covered by the specification are: •

Tolerance for other colour variation factors are not defined. SRPs are recommended where colour is important. Particular characteristics that cause common distinct problems are highlighted and it is recommended that “precautions be taken to minimise the effect”. •

2.

Exposed aggregate finishes, whether formed or otherwise are described in Part 2 - Exposed Aggregate Finishes. This section refers to its counterpart in Parts 1 and 3, using a suffix 'E' and also dictates additional parameters that are imposed because of the exposed aggregate nature of the finish.

Physical Irregularities Blowhole frequency and size limits are set by comparison with standard photographic references produced at full size. Tolerances of other physical defects are not set. SRPs are recommended to provide irregularities where physical irregularities are of importance.

Consideration of the method by which the surface is prepared will direct the user to one of the three parts of the specification. Finishes that are formed, and thus mirror the characteristics of the form are "F" finishes and are described in Part 1 – Off-the-form Finishes.

Colour Variation Inherent shade variations are limited by Sample Reference Panels (SRP) defining the standard and a photographic grey scale used to define variation limit.

Application of the Standard

1.

Surface Plane Variations Limited by standard measurement.

The appendix describes the various blemishes and their probable causes. The application of the standard permits appropriate qualities of finish to be assigned to all surfaces being constructed, and attention to be drawn to specific needs and requirements to be emphasised to the contractor.

Unformed surfaces are those which are generally laid horizontally, and generally incorporate screeding, floating or trowelling during their production. Such surfaces are described in Part 3 of the specification and are classified "U" finishes.

Particular physical characteristics are highlighted and “precaution taken to minimise” or “to prevent the effect” are recommended. •

The “X” Factor – (for Exceptions) The specification permits the specifier to define variations from the standard by using the “X” factor. Thus the finish will be as defined by the standard except as further

IB 33: Specification and Production of Concrete Surface Finishes

Page 2


defined by the specifier in a particular regard. An example would be an F5 finish where blowhole frequency was not important; the finish could be defined as “F5X – blowholes to be in range 1 to 4”. Unless the “X” factor is used, the code requirements apply to that finish. The quality of finish, and the value of the finish are to be assumed to be those outlined in the standard. •

Sample Reference Panels (SRP) To quantify tolerance limits of physical irregularities and colour variation, the specification stipulates that the specifier nominate an existing finish that is locally available for inspection (Cl. 104.4.1). Minimum size SRPs (650 x 650 mm) could be produced during the tender period if required by the specifier. The standard recommends that full size sample panels be produced following tender acceptance, and that acceptance of such panels should serve to establish a quality reference for the remainder of the job. The specifier and constructor are recommended to consider the checklists in Figures 1 and 2. Since the production of the SRP will be, unless otherwise specified, after the contract is awarded, it is important that the specifier clearly define the texture and any special effects he requires at the timer of tender. Such definition may be by reference to existing panels, the use of good quality photographs, including scale, or a combination of both. The constructor must be confident that the required finish can be produced and should incorporate in his tender price an allowance for all special measures that he considers necessary to achieve the required finish. When assessing SRPs for acceptance with respect to colour variation, the time from casting will be significant, and should be agreed. The constructor should use the SRP to demonstrate difficulties (e.g. formwork junctions and displacements, mix variation, colour variations due to pressure variation with height, and vibration. It is advisable to include construction joints, rebates, arrisses etc., that will be encountered in the job so

that particular features and finishing details can be resolved. Thus the SRP becomes the constructor's checklist for achieving the specified surface finish.

Categories of Finishes •

Off-the-form Surfaces This category covers the concrete surfaces that are primarily dependent on the formwork for texture and finish. As such the most effective results are gained by attention to detail before the concrete is cast. The formwork dimensions, rigidity, joint tightness and texture all become of increasing importance. It is commonly accepted that time spent before casting to ensure the exactness of all of the above is never wasted. Often short-cuts prove very troublesome and more costly in the long-term with significantly more hours, and money, being spent attempting to remedy defects resulting from such short cuts. The six classifications (F1 to F6) cover all qualities of formed finish. They range from hidden surfaces - (F1) (e.g. foundations, rear of retaining walls, lined surfaces, underwater dam faces), plaster surfaces (F2), exposed surfaces viewed from afar (F3), to architectural and high quality panels (F6). Table 1 outlines the range and requirements incorporated in the standard specification. Although there is a grey scale included in the Standard there are no specific limits set as to the variations accepted under each finish. It is up to the specifier to determine an acceptable range and to monitor this with a SRP. Any finish that has nominated colour range restriction must be designated with the X suffix and the range specified. The typical control is the restriction to a range of 2 or 3 shades. For example: Using the shade chart NZS 3114. The SRP sets the mean position of colour shade. In this example let it be shade 3. A specification calling for a range of three shades would permit panels ranging in colour from shade 2 to shade 4. The greatest contrast for two adjoining panels or areas is shade 2 compared to shade 4.

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THE SPECIFIER’S CHECKLIST

THE CONTRACTOR’S CHECKLIST

Decide on finish required.

Receive Contract Documents.

If non-standard – define. • Locate construction joints. • Locate sawcuts.

No

I Understand Finish.

SRP required.

Define texture special effects. Similar existing finish. Limits on form junctions. Limits on tie locations. Rebates weatherband details. Yes Exposed Aggregate. • • • •

Aggregate Size. Aggregate Colour. Aggregate Exposure. Bedding Matrix.

I Can Make Finish.

Make Trial Panel.

Price Tender. Acceptance of Tender. • Discuss SRP. • Mix, Orientation,

Rebates, Curing Method, Jointing, Sheet Laps, Ties. • Admixtures. • Patching.

Inspect SRP. Colour variation. Physical irregularities. Blowhole frequency size. Rebates joints fasteners. Defect treatment.

No

Consider: 1. Mix Design – Strength, Finish Workability, Availability. 2. Formwork – Rigidity Tightness Reuse. 3. Release Agents – Colour, Variation. 4. Retarders – Spread, Control. 5. Colouring – Aggregates Pigments. 6. Defects – Scour Grout Loss 7. Curing – Effectiveness Duration. 8. Stripping – Timing Release.

Accept Tender.

• • • • •

finish.

Yes

Tenders.

For SRP: 1. Casting orientation. 2. Curing method. 3. Details to include. 4. Timing of colour insp. 5. Aggregate required.

• Ask specifier. • Look at existing

Yes

• Size SRP. • Number of SRP. • Features in SRP. • • • • •

No

Make SRP. Accept SRP.

SRP Acceptance. Receive details of SRP. • Approve form sheet joints. • Approve form tie locations.

Receive: • Method of applying remedial action. • Mix design. • Curing method.

Figure 1: Specifier’s Checklist.

Submit SRP Details. Submit: • Intended Tie Bolt Locations. • Formwork Sheet Junctions. • Patching Method/Application. • Protection Required. Commence Production.

Figure 2: Contractor’s Checklist. IB 33: Specification and Production of Concrete Surface Finishes

Page 4


Table 1

Summary of specification requirements for formed finishes. Surface Plane Variation

Contamination

Dusting

Retardation

Efflorescence

Acceptable Shade Range*

Blowhole Limits

Grout Loss/Scour

Form Tie

Sheet Location

Scabbling

Chipping

Spalling

Filling Composition

Method

Action

P

P

P

P

*

2

2 mm 1/360

E

A

A

P

P

P

S

A

A

3

6

P

P

P

P

P

*

3

3 mm 1/270

P

A

A

P

P

P

S

A

F4

4

6

P

P

P

P

P

*

4

3 mm 1/270

P

A

A

P

P

P

S

A

F3

Exposed surfaces not Building and subjected to close engineering scrutiny. structures viewed from afar.

6

6

P

P

5

P

P

P

F2

Keying surfaces for plaster and other thick coatings.

Interior and exterior surfaces to be coated.

6

6

P

P

7

F1

Roughness permitted: Fill tieholes, defects. Colour variation permitted.

Concealed surfaces. Foundations, lined walls, upstream dam surfaces.

Architectural or feature panels. High velocity water channels.

R

Structural surfaces of importance. Frequent close scrutiny.

Walls, panels, columns, beams, piers, soffits, parapets, railings, offices, foyers, public areas.

R

Structural surfaces of Walls, panels, moderate importance columns, in observed frequently. secondary areas (e.g. basements, car parks).

R

R = Required

S = Specifier to Stipulate

1 3

Formwork Deflection

Discoloration P

Surface of high importance. Alignment, appearance very important.

Abrupt (mm)

Gradual (mm)

F5

Surface Dressings

Physical Irregularities

4

Sample reference panels required F6

Colour

P

A

7

P = Precautions to Minimise Effects

E = Prevent Occurrence

A = Approval Required

* If specified shade range required, the finish must be designated with X suffix.

•

Tighter control can only be exercised with a range of two shades which is difficult to administer since the concept is that the SRP sets a mean about which there can be lighter and darker shades. Consequently unless the SRP mean shade is literally "between" two shades, interpretation in a light/dark variation can be difficult for a range of two.

The primary extension relates to the selection and uniform end result of the aggregates to be exposed. In all cases SRPs are required to provide a means of compliance.

Exposed Aggregate Surfaces

The aggregate:

As defined, surfaces enter this category if they have exposed aggregate on their surface. The specification extends the classification from Parts 1 and 3 with an "E" suffix. Thus finish F5E is a formed finish to F5 tolerance limits with exposed aggregate surface texture.

1. 2. 3. 4. 5.

When using exposed aggregate surfaces, the specifier must consider and define the following:

Weathering and staining characteristics. The colour and mineral type. The source of the material. Exposure depth. Angular characteristics required.

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Page 5


The matrix: 1. Colour. 2. Texture. 3. Thickness. Because exposed aggregate finishes will only be used where the surface is visible, the formed finishes F4, F5, F6 are extended to accept the exposed aggregate standard of F4E, F5E, and F6E. Exposed aggregate may also be used in unformed surface, resulting in a shallow texture. Thus U5 finish may be applied to exposed aggregate unformed surfaces as U5E. •

Unformed Surfaces This category of concrete surface finish extends to all floors, pavings, slabs and inverts. These surfaces remain exposed when concrete casting is completed. The surface results from screed, float or trowel action, and texture sometimes provided by additional measures such as brooming, raking, grinding or scabbling. There are eleven standard finishes specified in the code. They relate primarily to the texture required for the surface to perform its intended function. The derivation of a particular class of finish frequently requires the surface to proceed through lesser classes (i.e. a U5 broomed finish is usually screeded to Class U1 and floated to Class U2 prior to the final texture being applied). The classifications for unformed finishes are shown in Table 2. The durability required of the slab often dictates the finish specified, with U3, U4 and U11 (trowelled, machine screeded and ground finishes) increasing the toughness of the surface. The specification tolerances with respect to colour and physical irregularities are tabulated and vary somewhat depending on

location and end use. Abrupt deviations are to be less than 3 mm in all finishes but should be avoided where carpets and thin tiles are to be used for floor coverings. Gradual deviations are within 5 mm over 3 m for most classes of finish. The problems of plastic cracking and crazing are more common with the large exposed surface areas involved. The specifier must stipulate the spacing and requirements of joints to minimise these effects.

Materials and Workmanship The standard requires that the selection of the material and composition of the concrete should take into account the surface finish required. The finish will depend on many factors including concrete grade, cement content, workability, formwork, release agents, placement technique, compaction, curing methods, protection, finishing method and dressing. When coloured aggregates or colour pigments are to be used, it is recommended that sufficient quantities be stockpiled from the outset of the work as variations in colour and composition are more apparent in this type of finish. NZS 3114 is a performance specification, and the constructor is responsible for determining the method to be used to produce the specified finish. The appendices of the specification are intended to provide some insight as to causes of defects of the surface. The constructor is advised to take precautions against particular defects in selected instances. The constructor is required to provide adequate protection for all surfaces from the time of casting, until the completion of the job. This should include handling during transportation, erection and all subsequent operations. Where units move beyond the control of the constructor, as would often be the case with precast panels, protective measures required should be detailed and undertaken by the recipient of the units.

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Page 6


Table 2

Classes of floor, exterior pavement and invert finishes.

Class

Finish

Technique

Examples

U1

Screeded

Hand sawing motion with straightedge or mechanical vibrating screed.

Finishes covered by backfill or concrete. Footpaths, yards and driveways. First stage for placement.

U2

Floated

Wood or bull float, or both. Generally manual but power driven equipment may be used.

As for U1 where a higher standard of finish is required. Floors to receive carpets with underlay or similar coverings. Inverts of syphons, flumes, floors of canal structures, spillways outlet works and stilling basins. Surfaces which are intended for use by ambulant or wheelchair-bound persons.

U3

Trowelled

Manual or mechanical steel trowelling of floated finish after concrete is sufficiently hardened, to prevent excess fine material and water being worked to the surface, may be done in one or two stages depending on degree of smoothness required.

Direct wearing floors such as in factories, warehouses and processing plants. Floors to receive thin sheet coverings, carpet and similar coverings. Inverts of water, tunnels and tunnel spillways. Not generally used for pedestrian or vehicular traffic where a smooth finish could be dangerous in icy or wet conditions. Is not suitable even when dry, for surfaces which are intended for use by ambulant disabled or wheelchair-bound persons. See U2.

U4

Machine

Vibrating or oscillating screed or vibrating plate, or both, which may be supplemented by long handled metal, wooden, or rubber floats.

Used for durability where resistance to erosion and cavitation under action of high velocity water is especially required: and as first and second stage finishing for roads and airfield pavements prior to texturing with U5, U6 or U8 finishes.

U5

Shallow Textured

Hard or soft bristled brooms.

Footpaths, yards, driveways, roads, pavements for aircraft.

U6

Deep Textured

Wire broom or rubber tyning.

Surface to receive a subsequent textured bonded concrete topping. Roads and runways where greater frictional resistances are required than can be obtained by U5 finish.

U7

Grooved

Saw cutting or flailing by mechanical means.

Treatment to existing roads and runways to provide frictional resistance and drainage paths for run-off to minimise aquaplaning.

U8

Grooved

Mechanical grooving the fresh concrete surface after compaction and surface screeding techniques.

Roads and runways.

U9

Scabbled

Mechanical hammering of hardened concrete.

Can be used on any pavement surface to produce a textured effect or to reduce high surfaces to the correct level or to rectify out-oftolerance pavements.

U10

Special Textured

The use of equipment to give special effects.

Architectural effects on pavements and slabs, produced by rollers with drums of expanded metal, or profiled tempers on screedboards, and the like.

U11

Ground Finish

Low speed coarse stone grinding to remove thin weak surface layers/minor ridges and to produce an even “glasspaper� textured surface, that is, not a polished surface. Used as a second state finish to U2, approximately 36 to 48 hours after laying.

Direct wearing floors such as in warehouse.

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Page 7


PART 2 PRODUCTION OF CONCRETE SURFACE FINISHES General Various types and uniformities of finish have been discussed in Part 1, with attention being given to the finish that is required. To achieve the defined finish it is essential that a systematic approach be adopted, using consistently good quality products. This includes good quality moulds, forms, compaction equipment and concrete. All finishes require care and attention during casting. Selected finishes require additional attention and treatment either before, during or after the concrete is cast. The classification relating to when the attention is required is used in this Bulletin as follows: Type A:

Before casting. The finish is the mirror of the mould.

Type B:

During casting/setting. The exposed surface is treated.

Type C:

After casting. The finish is obtained from the hardened surface.

Some methods apply to both insitu and precast work, whereas some cannot be obtained from insitu concrete.

Variations in Colour and Texture The primary characteristics of concrete that relate specifically to its surface are that of colour and texture. The New Zealand Standard NZS 3114 'Specification of Concrete Surface Finishes', provides the means of specifying what colour and texture variations are acceptable in particular circumstances. Common physical and colour related blemishes are itemised in the appendices of NZS 3114. The tables have been incorporated here in Appendix A. In addition Table 3 has been prepared to highlight the features that require particular attention when manufacturing concrete products, and possible defects that may result.

Table 3 Item

Feature

Defect

Formwork

Preparation Absorbency Roughness Cleanliness

Alignment, grout loss, joint stepping. Crazing, colour. Scaling, chipping, spalling. Discolouration.

Release Agents

Effectiveness Purity Compatibility

Scaling, chipping. Local discolouration, shade variability. Retardation.

Mix Design

Low strength Excess cement Proportions

Scour, scaling, chipping. Crazing. Blowholes.

Placement

Inadequate ventilation Excessive drops Excessive vibration Non-uniform

Air pockets, honeycomb. Segregation, steps. Crazing, laitance. Plastic cracking.

Curing

Impurities Inadequate Uneven Excessive

Contamination. Crazing, warping. Colour variation, efflorescence. Abrasion, scour.

IB 33: Specification and Production of Concrete Surface Finishes

Page 8


Figure 3: Hydration discolouration (half scale size).

Determination of Finish

5.

Treatment Before Casting – Type A •

Figure 4: Colour variations often associated with impermeable form face (half scale size).

Off-the-form Finish This finish is the most common, often being referred to as "fairfaced concrete". The finish is produced by the pattern of the concrete form being mirrored on to the concrete surface. It may be the most economical form of production, provided adequate measures are taken to avoid the need for remedial work after stripping. Such measures demand the following precautions: 1.

Attention to detailing, with adequate provision for joints, edges, corners, drips and other weathering details, and adequate measures to allow form release and removal;

2.

Clean, well maintained and watertight forms (see also IB 29 and 41);

3.

A concrete mix with adequate cement content, low water/cement ratio and high density;

4.

Adequate consolidation and uniform curing to ensure uniformity of colour and texture;

Protection to minimise chipping and damage subsequent to casting.

The finish may be flat smooth (i.e. formed from sealed wood, steel, sealed concrete, fibreglass etc.) or patterned smooth (i.e. fluted, sculptured or board finished. The patterned smooth finishes tend to mask many of the limitations of the flat smooth finish. They are however, more expensive to form, requiring additional treatment to the flat form finishes. Major blemishes in the concrete surface relating primarily to the composition of the form face are: •

Hydration Discolouration: This relates to the absorbency of the form face. Variations in absorbency within the material itself, e.g. springwood/ summerwood or variations caused by wet concrete pressure will result in hydration staining. A further problem relates to the use of materials that are completely impermeable such as steel and HDO plywoods. These tend to give dark polished areas caused by form face vibration during placing of concrete (Figures 3 and 4);

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Figure 5: Blowhole in concrete surface usually less than 10 m notional diameter (half scale size)

Figure 6: Crazing pattern of fine network of shallow cracking (full size)

Blowholes: Form faces which have an impermeable surface tend to have a higher incidence of surface blowholes. In this regard plastic faced ply whilst producing a smooth surface is likely to have a higher incidence of blowholes (Figure 5);

Crazing: Form faces which have a glazed smooth or polished impermeable surface can lead to fine cracking. As will be seen from a comparison of these factors, specific provisions to avoid blowholes may lead to hydration discolourations and vice versa (Figure 6).

tongues and plastic foam strips should be used. The tongues hold adjacent boards in alignment and the plastic foam strip prevents leakage at the joints which otherwise would form fins or discolouration accentuating the joint lines. The boards must be of uniform thickness so that there will be no offsets at the joints.

Characteristics of Form Materials The range of patterned and smooth textured finishes is considerable. Some examples of materials used to imprint patterns are discussed. •

Timber: Sand blasted to raise the grain, rough cut; bevelled or champhered for fluting; clapboard fashion for bold texture etc. Smooth board surfaces; For the smoothest possible board marked finish only dressed tongued and grooved boards or grooved boards with loose

Rough board surfaces; Where no joints between boards are to be emphasised the procedures are as above. Featured joints; Raised joints between adjacent boards can be emphasised by a chamfer of say 10 mm on a 25 mm board. Mechanical damage however is very likely with horizontal raised joints. A better feature therefore is produced at the joints between boards. The indent is produced by fixing a fillet on the board face at the joint position. Profiled surfaces; When deep profiled surfaces are to be produced, timber formers should have a draw of 1 in 4 for softwood and 1 in 6 for hardwood. General comments; To achieve maximum uniformity of colour, timber should be pre-treated by thorough oiling before the

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first use. Failure to effectively seal the first use will result in a lightening colour effect after each successive use. •

some blowholes are inevitable. A high standard of site care and maintenance of steel forms is necessary to avoid rust discolouration and distortion of the edges of pans and panels. The practice of painting steel forms to protect them from rust is not recommended because eventual failure of the paint causes unsightly scabbing. Because of the flexibility of sheet steel facing, special attention should be paid to jointing, to avoid high vibrator amplitudes and leakage during vibration, and to ensure that the steel sheet is of sufficient thickness to limit deflection between supports. The selection of a mould oil with rust inhibiting properties is of prime importance. Neat oils with surfactant are usually more suitable than mould cream emulsions.

Plywood: Plain construction plywood; textured plywood; HDO plywood. Exterior grade plywood should be used. Whilst sizes range from 3 mm to 22.5 mm, the most commonly used in sheeting are 9.6, 12.5, 17.5 and 22.5 mm. The advantages of plywood over timber sheeting are that it is rapidly fixed, can provide large surface areas without joints, has high resistance to impact, can be nailed close to the edge and is considerably more stable in relation to moisture shrinkage and swelling effects. For forming curved surfaces the typical radii that can be achieved with 6 mm plywood bending parallel to the grain is 600 mm, and across the grain 380 mm. Typically, 12.5 mm plywood can be bent to a radius of 2.4 m and 1.8 m respectively.

In the use of plywood it is extremely important to note that its strength relates to the direction of the grain of the outer plyface. Panels should normally be used with the grain parallel to the span of the sheet. Severe reductions in load capacity and increased deflections will occur if used with outer ply face grain running at right angles to the span. Surface coatings reduce the colour variations on the concrete face as well as extending the ply's use. In particular, colour variations due to concrete pressure are less marked. As the surface coating becomes more impermeable, such as a plastic faced sheet – HDO – then there tends to be an increase in the formation of blowholes and a possibility of crazing. Relative number of reuses is, however, increased. •

Steel: Steel forms produce concrete of uniform colour provided they are protected adequately from rusting and form face vibration can be reduced; however, because they are impermeable,

Oil tempered hardboard: Oil tempered hardboards are almost impermeable and provide concrete of reasonably uniform colour although some surface blowholes are inevitable. Their life is considerably shorter than that of most other linings. A recommended procedure is to wet the back of sheets and stack flat for 48 hours before use. Preferably the sheets should be centre pinned in order to reduce buckling tendencies. The material should be oiled before use, cleaning down should take place using a stiff brush and cold water before re-oiling for use.

Neoprene and rubber linings: Rubber sheet linings may be used to create textured or profiled surfaces. The surface is generally of uniform colour although having some blowholes. For fixing in vertical positions linings can be glued or tacked to the backing sheet. Thick sheets may be lightly tacked since the fluid pressure of the concrete is sufficient to expel any air between shutter face and rubber lining. Thin sheets should be stuck to the backing shuttering. Mineral oil based release agents must not be used since these soften the rubber. Castor oil or lanolin are suitable release

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shapes can be sprayed to form sheeting, which often has sufficient structural properties to require only the minimum of structural support from a backing system. The advantage of the material is that it allows a highly impermeable surface to be produced; cast face down avoids blowholes so the surface is very suitable for external decoration such as painting. The material is of thin section 6-12 mm usually, thus allowing full potential of insitu casting to provide the structural continuity needed in seismic design. As a low profile material it can be used without decoration. •

Figure 7: Use of cement board as formwork liner to produce an even coloured textured finish. agents. On shallow profiles no release agent is necessary. It is recommended that concrete be allowed to harden for 48 hours before demoulding when not using a release agent. The rubber liners should be cleaned down with water brushing after striking and then lightly oiled with vegetable or animal oil. •

Glass fibre reinforced plastic – GRP: Moulds of GRP produce low relief patterns with a smooth eggshell like finish. Blowholes may present problems and can be minimised by using mould oil. There is also a higher risk of producing panels where mottling and surface crazing are evident if the GRP surface is highly polished. Matt finishes of GRP give less colour variations and less risk of crazing. Formwork should be left for 48 hours before striking. The concrete will have a high gloss finish which slowly disappears with time due to carbonation. The GRP form should be wiped clean with damp or oily rags. Any stubborn concrete pieces left should be removed with a timber scrapper.

Glass fibre reinforced cement – GRC: GRC permanent formwork systems are now available in New Zealand. Low profiled

Special applications. Cement board such as Hardiflex has been successfully used to produce a textured finish with a high degree of colour control (Figure 7). Various other materials have been used to create special effects, e.g. rope, plaster casts, urethane rubber etc.

Surfacings Applied in the Mould (Restricted to Precast Products). The texture is created by material other than concrete (e.g. brick, glass, cobblestones, large aggregates etc.) being hand placed into the bottom of the mould. Generally a process known as sand-bedding is used. The bottom of a horizontal slab form is covered with a layer of sand, the depth depending on the size of aggregate to be used, and the amount of exposure. Large aggregate can be exposed as much as 50 mm. After the sand has been spread, coarse aggregate particles are hand-placed in the sand, the stone and sand gently sprayed with water to settle the sand, then the structural concrete is placed. When the concrete reaches the necessary strength, the unit is removed from the mould, raised to a vertical position, and vigorously washed with water to remove the loose sand and expose the stone. This method can be used for any size of aggregate, and is especially suitable for exposing the larger sizes (Figure 8). The technique can be applied in particular to tilt-up slab construction.

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attention to mix design (a low water and cement content) and slow, humidity controlled curing. It is highly desirable that samples be prepared, and behaviour tests undertaken to verity the behaviour of the composite unit. •

Wet Off-the-forrn Finish This method is not commonly applied in New Zealand. Its principal advantage is that the mould becomes rapidly available for re-use. The concrete is cast face down into the mould, a pallet is fastened on top of the mould which is inverted and removed leaving the concrete on the pallet to cure.

Treatment During Setting – Type B •

Figure 8: Sand bed technique for face-down special finish casting.

The finish is that of the facing material with the concrete providing strength and bond to the element (ceramic tile, brick, or stone).

This process involves the treatment of the mould with a chemical surface retarder which slows the setting process of the concrete which comes into contact with it while allowing the body of the concrete to gain strength. The slowing of the surface setting allows the form to be struck and the soft material to be removed by washing and/or brushing exposing the aggregate. Finishes vary from a light exposure (cement only removed and edges of closest coarse aggregate exposed) through a medium exposure (cement and surface sand removed) to a deep exposure (up to 12 mm surface removed, coarse aggregate is the predominant surface feature).

Attention must be paid to the compatibility of the texturing material with the concrete backing. Aspects requiring investigation include different thermal expansion characteristics, (especially for dark coloured materials), the effects of humidity, stability under atmospheric attack, and chemical compatibility with the concrete backing.

The shape of the aggregate, its position following consolidation and the depth of etch will determine the surface appearance. The appearance will therefore vary to some degree depending on orientation of the surface and on the aggregate shape. This should be taken into account for returns and exposed vertical sides of forms.

Where significant differences in movement are expected between the facing material and the concrete, a complete bondbreak can be incorporated, and the facing attached by mechanical fasteners. Recognition of the need for independent movement must be made. Usually, cut stone faces have little resistance to bowing, and chipping or cracking can readily occur. This necessitates careful

The retarder is usually in a liquid form. It must be applied uniformly to the formwork usually with a roller, although it may be spray applied.

The aggregate transfer method can be used for small areas of vertical casting. Aggregate is pre-selected and glued to a backing sheet which is placed in the mould and subsequently stripped off after casting has embedded the aggregate. •

Face-down Treatment

Surfacings Applied After Casting (Precast Only).

If the formwork has varying absorbency (e.g. timber or ply) this can influence the degree to which the retarder will be effective when it comes to exposing the aggregate. This effect can be reduced by sealing the formwork with a

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depth of etch required and the concrete mix used. Proper planning is required to ensure that the retarder remains operative sufficiently long to allow stripping and exposure to occur. Generally, a wash down with 10% hydrochloric acid is recommended at seven days to remove cement bloom, followed by a general surface wash down. •

Face-up Treatment Treatment of the exposed surface is most common in slabs, floors and inverts. It also applies to precast units which are cast horizontally. •

Figure 9: Hand test carried out to check when a concrete surface is ready for fine trowelling. The upper hand shows the ideal conditions.

Finishing should not be attempted where bleed water has accumulated on the surface, nor should these areas be dried by sprinkling with cement. If natural evaporation or absorption is too slow, the water should be removed by draining, mopping or by dragging a piece of hessian across the surface.

barrier paint before coating with the surface retarder. When the formwork is used for the first time two coats of a suitable retarder should be applied and for each subsequent use one application should be enough.

Trowelling should not take place until the surface is hard and dry enough for a hand not to imprint the surface or pick up a significant amount of cement paste. This timing varies very considerably with the temperature (Figure 9). In summer it may be only 1-2 hours, in winter it may take 5 or 6 hours. Techniques like vacuum dewatering, described in CCANZ Information Bulletin 01, help overcome the timing problem.

The time of year, and particularly the temperature of the concrete, will have an important effect on the time at which formwork should be removed and the surface treated. Experience suggests that the sooner the formwork can be stripped and exposure commenced the greater chance there will be of success. On no account must exposure of the aggregate be delayed after stripping otherwise the cement will set and harden. Care must be taken when casting vertical elements that the concrete does not discharge directly on to a retarder-treated surface, as this will both remove the retarder and contaminate the concrete mass. Similarly, vibrators should not be held in contact with the form surface as this will also remove the retarder. Rain may also remove the retarder before casting. The selection of which type of retarder to use will depend upon the time to stripping, the

Smooth flat: Obtained by screeding, floating and subsequent trowel finishing. Most common form of finish to floors and inverts. Timing the processes according to degree of set is very important.

It is possible to produce different textured finishes by stopping at the screeding stage or proceeding to the floating stage when, for example, a woodfloat finish is formed. Texturing is described in a later section. •

Exposed aggregate: The process primarily involves a brushing and washing method during the concrete setting process. Occasionally a retarder application and after-set washing may be used. The

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timing of the brushing and washing method to expose aggregate depends on the mix, the water/cement ratio, the size of the member, the type of cement and the time of year. With ordinary portland cement mixes it will usually be found that the most suitable time is between 2 to 6 hours after casting.

water has evaporated to achieve the best striations. A deeper striation can also be formed for greater frictional resistance. Two rows of spring steel tapes have been found to be the most suitable for the "bristles" of the broom. A suitably designed lawn rake with rubber tynes can also produce a deep texture. The tynes need to be curved with a minimum pitch of 12 mm, 15 mm being preferable and 18 mm excessive. It is essential that the tynes be so shaped as to induce aggregate into the ridges so formed rather than surface laitance only.

Good exposure of the aggregate is obtained from a gap-graded concrete, often where the 10–2.36 mm (3/8 in – No. 7) sizes have been omitted from the mix. When using a tilt-up mould the mould should be slightly tilted, with the water and brushing starting from the top. Different types of broom will give different depths of texture.

A twin roller with drums of expanded metal each about 125 mm diameter by 1m wide or a single pipe, 300 mm diameter x 3.5 m wide and weighing about 44 kg/m around which sheets of patterned rubber or expanded metal can be wrapped, can be used to give a satisfactory ribbed pattern of a texture of average depth 5 to 6 mm. General purpose diamond mesh with 300 mm x 12 mm apertures is considered to be satisfactory, but the protruding fins formed by the apertures tend to consist of weak mortar and would be quickly worn down by traffic.

Uniformity of the finish depends to a very great extent on the degree of supervision at all stages of the job and it cannot be over-emphasised that a high standard of workmanship is essential for an acceptable finish. A clean down using 10% hydrochloric acid is usually required to remove any cement bloom and the surface washed down. The resulting texture differs from the "Face-down" technique since the coarse particles tend to migrate to the bottom of the mould during consolidation.

Imprinted patterns can be formed by rollers or pressing in special formers into the wet concrete. Deep surface sculpture of exposed surfaces using polypropylene concrete is possible because the high air entrainment and fibres will support deep texturing at the time when the concrete is still in a very plastic state (Figures 10 and 11).

The exposed surface may be seeded with larger size aggregates. This should be done after consolidation and before washing if required. Control of the depth of aggregate exposure is possible by rolling the seeded particles into the surface. • •

Decorative/textured - broom or pressed finishes: A shallow texture finish can be produced by scoring the floated finish with the common bass broom with hard or soft bristles depending on the degree of frictional resistance needed. Transverse striations are produced by drawing the broom across the surface in a continuous movement so that the bristles trail the head of the broom. It is emphasised that this is done after bleed

Coloured Concrete Surfaces Permanent colouring of concrete surfaces is achieved by adding colouring pigments during the batching process. Another popular method of providing permanent colour to concrete surfaces is to use and expose coloured aggregate to the concrete surface. For economy, both methods are most commonly used as a surface topping (i.e. up to 50 mm from the surface) using both the "face-

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Figure 10: Polypropylene fibre concrete showing its ability to hold shape in its wet state.

Figure 11: Textures and patterns achieved using polypropylene concrete. in the concrete, pigment and water;

down" and "face-up" casting techniques (conventional concrete is employed as backing to such units). The use of the face down technique is limited to precast units. •

Pigmented concrete: The pigments are added to the concrete during batching and operate on the binder (i.e. the cement) while the aggregate particles remain unaffected. The use of coloured aggregates is not necessary although contrasting aggregate/binder colours can be used to good effect with exposed aggregate finishes. Care must be taken when selecting colouring pigments which must remain colour stable when exposed to sunlight and weather. Water soluble salts within the pigment may accentuate efflorescence and should be avoided. The pigments are most commonly derivatives of Iron Oxide (reds, browns, yellows and blacks), Chrome Oxides (greens and blues) and Titanium Dioxide (white). To achieve maximum uniformity of colour it is vitally important to have: 1.

Consistent batching of all materials

•

including

the

2.

Consistent mixing times;

3.

Consisting striking times for face formwork where used, or consistent trowelling techniques for horizontal surfaces. Different trowelling times or applications can give colour variations;

4.

Consistent curing methods used throughout job. Variation in curing can give rise to serious colour discrepancies.

Coloured aggregates: Both colour and texture can be added to concrete surfaces by using coloured aggregates which are exposed. The methods and depth of exposure are the same as those described elsewhere (i.e. retarder, brushed, sand embedded etc.). The significant differences between this type of colouring and pigmented concrete is that the surface usually has texture as well as colour. The exception is when the hardened surfaces are mechanically ground (see later section) thus exposing sections through the aggregate.

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It is important that the coloured aggregate used is of consistent colour and composition. It is recommended that sufficient coloured aggregate is stockpiled at the beginning of the job to ensure this consistency. A list of generally available coloured aggregate is given in IB 11.

depth of texture required, with the deeper texture being easier to attain. Light blasting, with a single cover depends heavily on the operator's consistent concentration. Variations in the surface such as airholes, joint lines, etc, are easily accentuated with blasting and extreme care is required. It is a common misconception that abrasive blasting will improve the appearance of poor quality concrete. It will remove many colour variations but may accentuate physical defects in the surface. It is important that realistic shapes be incorporated into the standard sample so that such effects can be recognised.

Treatment After Casting – Type C •

Relatively Smooth Surfaces •

Acid etching: The finish is achieved by washing the hardened concrete surface with an acid solution (10% hydrochloric acid). This will react with and soften the cement paste which is removed by washing. Features which require consideration when this technique is applied include stability of the aggregate under acid attack, the protection of hardware and the protection of surfaces not to be treated. The acid action is noticeably greater on poorly compacted concrete. Thus uniformity of compaction and mix are influential in attaining consistent texture. Although the depth of texture is dictated by the time that the acid is left on the surface, it is usual to expose the coarse aggregate (between 5 and 10 minutes) for best consistence of result. During this time the reaction gives off considerable fumes making ventilation important.

Grit or sand blasting should be recognised as having a dulling effect on the aggregate. It is however more stable than many alternative forms of treatment, the colour and texture remaining substantially constant during weathering. •

Light blasting: Blasting techniques involve the use of sand, or other abrasives, to remove the surface of the concrete. The abrasive is ejected by hose directly on to the surface, with the depth of exposure being dictated by the type of abrasive, the pressure used, the distance from the surface and the age of the concrete. On concrete less than 3 days old exposure rates of 3.75 m2 – 5.5 m2 per hour can be achieved. A serious consideration is the degree of clean-up of spent abrasive. This is minimised if air or water is used as the abrasive, which is possible for light blasting if it is undertaken early. The degree of uniformity is related to the

Honed or polished: Grinding of the concrete surfaces, usually with mechanical equipment, results in a honed finish. The surface of the aggregate is ground smooth and dominates the concrete surface. Continued grinding, with the addition of fine grit, can result in a highly polished surface. This technique is expensive and demands a high degree of craftsmanship. For economy, honed and polished surfaces are usually restricted to flat areas where access of the grinding equipment can be achieved. It is often used in conjunction with other techniques to provide very satisfying results. Recommended bay sizes are shown in CCANZ Information Bulletin IB 26. Since it is the aggregate itself being modified by this process, particular attention must be paid to the maximum size and hardness, which affect both the final appearance and the cost of the finish.

Painted: This process is for aesthetic reasons not being generally required for

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the concrete itself. It is often desirable to permit a lesser quality of finish, and cost savings can be made by painting exterior surfaces. Acceptable results can also be achieved by painting internal surfaces. •

Medium and heavy sand blasting: Continued blasting will produce any depth of exposure required. The surface will be dulled and rounded however, and this should be recognised. For deep exposure, retarder or face-up water washing may be used initially.

most satisfactory aggregates are those derived from crushed rocks as opposed to natural gravels, and the most suitable mixes are those in which the aggregate has not more than 10% of 10–5 mm (3/8– 3/16 in.) materials in the coarse fraction. Tooling produces a homogeneous surface in which the particles of coarse aggregate are not seen individually. By breaking particles of aggregate and removing the protective fine cement-sand from the face, it makes the concrete more absorbent. Therefore, additional cover to the reinforcement should always be provided.

Mechanically fractured surfaces: Mechanically fractured surfaces are the result of mechanically removing part of the off-the-form concrete surface by scaling, bush-hammering or tooling.

Tooling is not normally suitable for arrises, and these are frequently protected by battens during tooling. This leaves a plain margin to the bushhammered surface.

Removal of the skin of hardened cement paste from the face of the concrete reveals rather than masks any imperfections, whether they be from poor formwork design or lack of attention to mixing, placing and compaction of the concrete. This cannot be emphasised too strongly as the most common misconception is that tooling will improve the appearance of poor quality concrete.

Whilst tooling should not be commenced until the concrete has gained sufficient strength to resist serious spalling, it is possible to start after 1-2 days. The earlier the start obviously the greater the rate of production. By leaving the tooling to the latter stages of the job, the work takes considerably longer to execute but has of course the advantage of removing surface staining that might have occurred during construction at higher levels of the building.

Relatively Rough Textured Surfaces

In general, to produce a satisfactory tooled finish, it is first necessary to produce a good plain finish. It is important to obtain complete compaction and to avoid any segregation for when the mortar skin is removed these defects are noticeable to a greater depth than before. Colour variations on the mortar skin caused by the use of an absorbent lining are not important as this discolouration does not penetrate deeply. Consequently any type of form face material may be used as long as special attention is paid to rigidity at all joints and the avoidance of leakage through the formwork. The final finished appearance will depend upon the detailed design, the composition of the concrete and the method used to expose the aggregate. With all methods of bush hammering, the

Scaling is achieved by using a pneumatic scaler fitted with three piston-headed chisels that rotate and fracture the concrete surface. The result is a fine nibbled effect, rather than a deeply chipped texture. This method is more helpful towards minimising surface defects than say blasting, and is considerably cleaner than grit blasting. Bush-hammering is a similar process but the bush-hammer face has a deeply indented multi-pyramidal pattern. The hammer head is driven by a pneumatic, electric or hand hammer and the result is forgiving in that it can contribute to masking surface defects. A chiselled or pointed tool is used for jack-hammered surfaces. This system

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Figure 12: Tools used in creating finishes on hardened concrete: (1) and (2) – point tools: (3) – roller comb: (4) – bush hammer: (5) – comb chisel. relies on fracturing the mortar and coarse aggregates for good effect and should be done after the matrix of fine aggregates and cement has reached the strength of the coarse aggregate. If hammering is carried out at an earlier stage there is the risk of knocking out particles of coarse aggregate rather than breaking them. The objective is to reveal the coarse aggregate particles and not to produce holes where particles had been. Chiseltype tools are better for fracturing across aggregate particles, while pointed tools tend to dig into the matrix (Figures 12 and 13). Hammering of the nibs of a formed insitu or precast ribbed surface produces a robust vandal proof finish requiring little maintenance and having excellent weathering characteristics. The fractured ribs present an attractive, austere appearance with an emphasis on large scale texture (Figure 14). It is always desirable to construct a prototype to investigate profile, concrete mix design, release agent, stripping time and optimum time for hammering. When finalised the prototype can be the reference standard for the job.

Figure 13: Different textures available using bush hammering or tooling.

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time is a function of the gain of strength necessary to achieve fracture of aggregate when hammered and to prevent aggregate pop-out exposing only the matrix. After a 14 day curing period it is found that it makes little difference when hammering is executed, and it may be done at a contractor's convenience. Many techniques can be used, but to obtain uniformity it is important that the set instructions be followed by all employed on the job. The actual hammering technique employed should be determined by the designer. It is possible to hammer in bands or with a random pattern depending on the appearance required. Figure 14: Hammered nib finish being completed.

Generally, because of the labour content, hammered surface finishes are usually more expensive than chemically-retarded and abrasive-blasted surfaces.

Design considerations for this specialised finish are: 1.

2.

The selection of profile should be considered in relation to: readability at varying distances, the area of wall on which the finish is to be used in order to achieve the desired effect, the ability of the selected aggregate to penetrate the nib, stripping of forms, hammering by hand and unskilled labour as opposed to the use of pneumatic tools and skilled operators; Selection of concrete to meet structural and visual requirements: selection of sand and cement to matrix colour will dominate finish, selection of aggregate size and colour including the colour of the fractured aggregate, and mix design to ensure a cohesive nonsegregating mix with minimum bleed characteristics;

3.

Materials and construction watertight formwork;

of

4.

Form oil-release agent must be selected to suit colour control;

5.

Curing and stripping time. Curing

Cost of Finishes The cost will vary significantly throughout the country, and depend both on the plant set-up (for precast units), the skill of the operators and a variety of other factors. As a general guide the following list indicates a typical cost structure: (in ascending order of cost). 1.

Smooth off-the-form finish.

2.

Painted finish.

3.

Retarded or water wash exposed aggregate formed liners; sand blasted.

4.

Acid etched exposed aggregate; bushhammered; hammered rib (fractured); ceramic/tiled faced.

5.

Honed; polished; cut stone (veneered).

Finishing Techniques In a large expanse of wall it is generally not possible to completely avoid surface blemishes or

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a requirement for cleaning down. In addition on wall formwork, there is generally a need to deal specifically with form tie rod holes.

ramming with a steel rod or some other suitable tool. This mortar should be cured for at least three days if possible.

Tie Rod Holes

Surface Dressing

If tie rods are the type that are entirely removed from the wall they should be pulled toward the inside face to avoid spalling the concrete on the exposed surface. The holes should be filled as soon as possible after stripping of formwork.

A typical specification for bag rubbed surface dressing is as follows:

Tie holes should be filled solid with mortar using a grease gun of the plunger type such as those used on automobile transmissions. The flexible hose on the gun should be replaced by a short pipe for this purpose. Filling should be done from the inside of the wall. A piece of burlap or canvas should be held over the hole on the outside face and when the hole is completely filled the excess mortar should be wiped off with this cloth. No other finishing is necessary. Where tie holes are to be filled and there is no colour match requirement, then the holes should be filled with a mortar mix consisting of 1 part of cement to 1 to 2 parts of sand passing a 4.75 mm sieve. Appearance can be enhanced in many cases by stopping the mortar filling of form tie holes about 2 or 3 mm from the surface. This requires properly aligned tie bolts, but the resulting effect is worth the slight effort required in setting out and placing the tie bolts. This recessed filling also relieves problems of colour differences and of smearing the surface as could happen with a flush finish. Exact colour and texture matching for tie hole filling is virtually impossible to achieve. However, partial replacement of ordinary portland cement with white cement and the use of a light coloured sand can assist in reducing the colour differences between the concrete and mortar fill. Because of the colour/texture match problem it is recommended that holes be featured in some way such as described above. Tie-rod holes left by removing only the outer ends of the rod so as to leave no metal closer than 35 mm to the surface, should be filled with a small tool that will permit filling the hole solid with mortar beginning at the back of the hole. The mortar should be stiff enough to allow for

1.

The concrete surface should be thoroughly pre-wetted then permitted to approach a surface dry condition.

2.

The grout mix should consist of 1 part cement to 1½ to 2 parts fine sand. The sand should be clean and free of deleterious materials. White cement or white sand may be used in place of a proportion of the ordinary portland cement and sand. The grout should have the consistency of thick cream.

3.

To fill all small air holes the grout should be rubbed thoroughly in a circular motion over the area with clean burlap or sponge rubber pads.

4.

After the grout has stiffened sufficiently any surplus grout may be removed with a burlap or sponge rubber pad.

5.

When visibly dry (after 2 hours) the surface should have a final rubbing down as in (4).

Note: Brushed on cement washes are not normally standard practice. The sand should all pass a 600 Âľm sieve and not more than 10%' should pass a 150 Âľm sieve. If it is necessary to remove fins of mortar projecting at formwork joints, care should be taken to avoid damaging the surface. Excessive surface grinding can cause exposing of aggregate and the resulting change of texture may be unacceptable. Hand rubbing down to remove fins and rough patches using silicon carbide stones is recommended. Grade 36 stone is the most usual used but finer work can be achieved by finer stone grades. Final hand rubbing with a piece of marble or No. 80 carbide stone can often produce an even, smooth surface.

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Minor Repairs/Patching

patch by striking off the surface with a straightedge paralled to the direction of the marks.

Reference to the type of finish will indicate the requirements to match colour and texture of any repair in addition to the structural requirements of the filling or patch. During construction every effort should be made to obtain a finish that does not require patching; patching adds to the cost of finishing and usually becomes more conspicuous with age. If well-made formwork has been properly erected, and concrete of proper workability has been well compacted during placing, honeycombing should not occur and patching should not be needed. The extent to which it is safe to repair by patching depends upon the depth, position and extent of the honeycombing in relation to the size of the member. If reinforcement is exposed or the honeycombing occurs at vulnerable positions such as at the ends of beams or columns, it may be necessary to cut out the member completely, or in part, and reconstruct. A decision on the procedure to be adopted should be obtained from the engineer. If only patching is necessary, the defective concrete should be cut out to a depth of at least 25 mm or until solid concrete is reached, the edges being cut perpendicular to the surface, or if possible, with a small undercut. An area extending several centimetres beyond the edges of the patch should be saturated with water before making good. A grout of equal parts of cement and sand should be brushed well into the surface to be patched, followed immediately by the patching concrete which should be well compacted with a wooden float and left slightly proud of the surrounding surface. Then, after an hour or more, depending on the weather, it should be worked off flush with a wooden float. A smoother finish can be obtained by wiping with hessian, cheese cloth or a similar soft material. A steel trowel should not be used because the smoothness produced will show, even through paint. Rubbing with a piece of marble will produce a finish texture similar to ascast concrete. The mix for patching should be of the same materials as those used in the concrete. Some reduction in maximum size of coarse aggregate may be necessary, and the mix may need to be richer in consequence. The mix should be kept as dry as possible. Where the surface is boardmarked, this texture can be carried across the

Patches tend to be of a darker colour than the original concrete. Where this is of consequence, white portland cement should be substituted for some of the ordinary portland cement, the necessary quantity being determined by experiment, making comparisons when the samples have dried out. The proportion of white portland cement required varies from 10 to 30 percent of the total quantity of cement. The patched areas should be kept moist for several days and prevented from drying out too soon. This is particularly important with patches made to repair honeycombed areas. Structural repairs which are not covered in the scope of this bulletin are outlined in the CCANZ Information Bulletin IB 08.

Cleaning Following the surface dressing procedures for stoning or bagging, it may be necessary to consider the removal of other stains. Oil may be removed by using 5-10% solution of muriatic acid scrubbed onto the surface of a wetted concrete and subsequently well rinsed clean with water. There should be no fins or mortar projecting between form boards or panels of plywood unless a rough texture is desired, but if there should be an occasional small fin that is objectionable it may be broken off carefully with a hammer. Rough spots, stains and hardened mortar or grout can be removed by rubbing lightly with a fine abrasive stone (No. 36 or finer for a smooth finish) or hone. A hone used for sharpening tools will be satisfactory. Streaks caused by leakage from the lift of concrete above can often be removed by use of a hone. Plenty of water should be used, and rubbing should be sufficient only to remove the streaks without working up a lather of mortar or changing the texture of the concrete.

Summary The finishing of concrete surfaces usually reflects the general workmanship and soundness of the

IB 33: Specification and Production of Concrete Surface Finishes

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construction. Although no more or less important than other phases of concrete work, the finishing is of importance to a much greater cross section of people than the actual core of the job. Not only the people directly affected by the job but also any observer, casually, or interested in the project in a specific way, will judge and pass comment, based on the visual finishing. If the finishing of concrete surfaces is not correct in the first place remedial measures are few and expensive. Exposed concrete should have a high standard of finish, be it on floors, or walls, smooth or textured, but unfortunately this is not always the case. Exposed concrete surfaces can give a product that is almost maintenance free or maintenance intensive, that is profitable or costly, that causes satisfaction or argument, that gives pleasure or despair. The difference between good and bad concrete finishes is usually only a measure of proper specification, preparation, skill and care. Reference to Appendix B gives a summarised checklist which should prove to be of assistance to specifiers and constructors alike. Concrete can and should provide a long term maintenance free structure as well as a finishing material. Concrete is almost unique among building materials in meeting structural, protective and aesthetic requirements in the one product. However, good finishes do not just happen, consideration has to be given to a wide variety of aspects.

References •

NZS 3114 Specification for Concrete Surface Finishes SANZ 1980.

•

Control of Blemishes in Concrete. W. Monks, Cement & Concrete Association, UK, 1981. (now British Cement Association).

APPENDIX A Blemishes in Concrete Various types of blemish which can occur on concrete surfaces are described together with their probable causes in Tables A1, A2, A3 and A4 (from NZS 3114). It is important for the specifier when preparing the specification, and the constructor when considering the methods necessary to meet the specification, to consider the probable causes of blemishes and their possible elimination or reduction. A photographic definition of some of the blemishes is contained in the Cement and Concrete Association, U.K., publication "Control of Blemishes in Concrete".

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Table A1

Colour Variations (Early age of concrete)

Blemish

Description

Most Probable Causes

Inherent colour variation

Variation in the colour of the surface

Materials: Inconsistent grading, colour or source, aggregate transparency, material changes. Concrete: Incomplete mixing, segregation, or variation in proportions, ingredient omission.

Hydration discolouration due to moisture movement within or from the fresh concrete

Variation in shade of the surface

Formwork: Variable absorbency, through joints, variable vibration. Release agent: Uneven or inadequate application. Curing uneven.

Dye discolouration

Discolouration foreign to the constituents of the mix

Formwork: Stains, dyes or dirt on the form face. Release agent: Impure. Materials: Dirty.

Oil discolouration

Cream or brown discolouration

From construction plant. Release agent: Excessive; Impure (applied too late to the formwork). Timber or plywood inhibition.

Retardation

Matrix near the colour of sand and lacking in durability

Formwork: Retarder in or on form face; timber or plywood retardation. Release agent: Water soluble emulsion; cream or oil with excessive surfactant (surface active agent). Unstable cream; unsuitable or excessive chemical release agent.

Banding

Texture or colour variation showing in bands, generally in the horizontal planed in the members

Due to inconsistency in the concrete placement, stopstart methods in either conventional or slipforming concrete placing behind the forms, different hydration conditions.

Table A2

Colour Variations (Later ages of concrete)

Blemish

Description

Most Probable Causes

Drying discolouration

Variation in shade of surface from light to dark

Curing: Different conditions. Reinforcement: Inadequate cover.

Lime bloom or efflorescence

White powder or bloom on the surface

Design: Permitting uneven washing by rain. Leaching action. Release agent: Type. Curing: Uneven conditions.

Contamination

Discolouration foreign to the colour of constituent materials

Materials: Pyrites, clay or other impurities. Construction plant. Embedded steel: Inadequate cover, rust from steel above. Curing: Impure curing compounds, dirty covers.

Dusting

Light-coloured dusty surface, which may weather to expose aggregate.

Curing: Inadequate (very rapid drying). Vibration: Excessive vibration causing formation of laitance on surface. Excessive trowelling too early. Cement: Air-set. Release agent: Excessive application.

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Table A3

Physical irregularities (Early age of concrete)

Blemish

Description

Most Probable Causes

Honeycombing

Coarse stone surface with air voids and lacking fines

Concrete mix: Insufficient fines; workability too low. Formwork: Joints leaking. Placing methods: Segregation, compaction inadequate. Design: Highly congested reinforcement, section too narrow.

Blowholes

Individual cavities usually less than 12 mm diameter. Small cavities approximately semispherical. Larger cavities often bounded by stone particles

Formwork: Form face impermeable with poor wetting characteristics; Inclined; Too flexible. Release agent: neat oil without surfactant. Concrete mix: Too lean; Sand too coarse; Workability too low. Placing methods: Inadequate compaction; Rate of placing too fast: Ineffective external vibration.

Grout loss

Sand textured areas devoid of cement, usually associated with dark colour on adjoining surface

Formwork: Leaking at joints, tie holes, stop-ends, and similar defects.

Scouring

Irregular eroded areas and channels having exposed stone or sand particles.

Concrete mix: Excessively wet; Insufficient fine particles; Too lean. Placing methods: Water in formwork; Excessive vibration on wet mix; Low temperature when placing.

Steps

Step, wave or other deviation from the intended shape

Formwork: Damaged, deformed under load; Joints not tightly butted – poorly designed. Placing methods: To rapid or careless.

Plastic cracking

Short cracks often varying in width along their length

Concrete mix: High water cement ratio; Low sand content; Uneven moisture retention prior to curing. Compaction: Uneven compaction ambient conditions leading to high evaporation rate and moisture loss from concrete. Reflective cracking above reinforcement due to insufficient concrete c over. Movement of partially set concrete; sloping conditions.

Form scabbling

Parts of the form face, including barrier paint, adhering to the concrete

Formwork: Form face excessively rough, weak or damaged. Release agent: Ineffective, inadequate application or removed during subsequent operations. Striking time: Too late.

Laitance

Milkiness – surface accumulation of porous weak cement paste

Pacing methods: Excessive vibration; Premature floating. Concrete mix: Unsatisfactory or excessively wet, or both.

Ridges or waviness

Physical deviations from the intended shape

Sideforms: Lack or rigidity. Finishing methods: Insufficient care during floating and screeding operations.

Dishing

Noticeable slumping of parts of surface

Placing: Uneven compaction. Finishing: Screeding and power floating techniques. Sub-base: Insufficient preparation.

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Table A4

Physical Irregularities (Later ages of concrete)

Blemish

Description

Most Probable Causes

Scaling

Thin layer of hardened mortar removed from the concrete surface, exposing mortar or stone

Formwork: Relaxing after compaction; Form face excessively rough. Release agent: Ineffective application or removed during subsequent operations. Concrete: Low strength; Placing over vibration of high slump concrete. Striking time: Too early.

Spalling or chipping

Pieces of concrete removed from the hardened surface

Formwork: Difficult to strike. Release agent: Ineffective, inadequate application or removed during subsequent operations. Concrete: Low strength – aggregates susceptible to damage by frost or water. Striking time: Too early; Mechanical damage after striking. Weathering: Frost action – corrosion or reinforcement.

Deeper and usually more sever than scaling

Crazing

A network of fine cracks in random directions, breaking the surface into areas from about 6 mm to 75 mm across

Formwork: Form face of low absorbency, smooth, or polished. Concrete mix: To rich in cement, too high watercement ratio. Curing: Inadequate. Striking time: Too early, especially in cold weather. Compaction; Over vibration.

Scouring and abrasion

Surface material washed away by fluid action and surface material removed by rubbing action of solid bodies

Curing: Inadequate protection (water cure too severe, rainwater access). Concrete mix: Aggregates with insufficient abrasion resistance; lack of adhesion in mix; Segregation; Surface hardness treatment insufficient for purpose.

Holes

Irregular cavities

Concrete mix: Presence of soft, light materials such as wood and seedpods.

Warping

Deviation from the intended shape

Curing: Temperature and shrinkage differentials, and latter due to variation in water retention.

Shrinkage cracks

Usually transverse cracks, partly or wholly across slabs.

Concrete mix design: Water/cement ratio, aggregate/ cement ratio; Incorrect design of slabs; Slabs unable to slide on sub-base due to excessive frictional resistance during curing; Saw cutting joints to late. Excessive moisture loss through surface or into subbase. Inadequate protection during hydration and hardening.

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APPENDIX B A Checklist of Specification, Design and Construction Matters Structural Detailing 1.

Cracking can be minimised by specifying more, smaller diameter bars rather than fewer, thicker bars to provide the same crosssectional area of steel reinforcement.

2.

The reinforcement should be wired securely together or welded to form a rigid cage that will not be displaced during concreting.

3.

The correct cover should always be provided. For ease of placing, it should be at least 1½ times the maximum size of the coarse aggregate.

4.

The cover should be maintained by bar spacers, secured at regular intervals, or by battens that are withdrawn as placing proceeds.

5.

All ends of wire ties should be turned inwards away from the face of the concrete. All loose ends should be removed.

5.

When the primary requirement is for a concrete surface free from blowholes, formwork made from unsealed timber or plywood, hardboard or a water-absorbent lining is recommended.

6.

When the primary requirement is for uniformity of colour of the concrete surface, it should be borne in mind that the absorptivity of the above-mentioned formwork materials will reduce with each successive use. Nonabsorbent form materials such as steel can give concrete of uniform colour, but it is important to avoid the use of shiny, polished surfaces as these can produce variations in the colour of the concrete.

Release Agents 1.

Release agents should be applied only to clean form faces. Clean brushes, cloths or sprays should be used.

2.

The covering should be complete, uniform and very thin.

Formwork

Cements

1.

The formwork should be watertight and be capable of resisting the pressures generated during placing.

1.

2.

The formwork should be designed to limit any deflection. It should be rigid enough to prevent high-amplitude vibration during compaction. Variations in stiffness should be avoided so as to prevent differences in vibration across the form face.

Aggregates

3.

4.

All joints between sections of formwork and between formwork and hardened concrete must be carefully sealed. The use of tape or foamed plastic strips is recommended. Formwork ties should be arranged in a regular pattern. They should be positioned to facilitate securing the formwork against leakage at construction joints.

All the cement for one job should preferably be from the same consignment; it should certainly be from the same works.

1.

The sand should be uniform in colour and grading throughout the contract.

2.

The coarse aggregate should be obtained in separate sizes and recombined in the required proportions.

Mix Design 1.

To obtain concrete with few blowholes, the sand content of the mix should be no higher than is necessary to avoid segregation and bleeding.

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2.

When the main requirement is for concrete of uniform colour, a somewhat higher sand content should be used.

2.

Segregation and drying out must not be allowed to occur in transit.

3.

Segregation must also be avoided during placing, which should continue without interruption from start to completion of a section. Walls, abutments and the like will have to be placed in layers but there should be no delay between layers.

4.

The rate of placing should be uniform. It should exceed 2 m/h in vertical sections if possible.

5.

Vibration must be continuous and begin at the bottom of each section of concrete as it is placed.

6.

Internal (poker) vibrators are preferred.

Preliminary Contract Work 1.

Trial mixes are essential.

2.

Construction samples are necessary for verification of any untried details, and are valuable for 'training' and as an example.

Supervision 1.

The quality of the finished work will be dependent upon the experience and the calibre of the supervisory personnel.

Weather Conditions 1.

Striking

Extremes of temperatures may have an untoward effect on the concrete.

1.

The top of the concrete should remain covered until striking.

2.

Striking times should be the same wherever possible - the target time for all vertical faces is two days.

3.

After the formwork has been removed, the concrete should be protected from accidental damage.

Mixing

4.

All exposed surfaces should be covered with polythene sheeting to prevent drying out.

1.

Efficient mixing is essential. For visual concrete, longer mixing than is normal in ordinary concrete work may be necessary.

5.

Rust from projecting reinforcement should be prevented from washing over the face of finished work.

2.

The workability of the concrete must be checked frequently.

Batching 1.

All materials except the mixing water should be batched by weight.

2.

Due allowance should be made for the weight of water in the aggregates.

1.

Placing and Compaction 1.

Remedial Work

Equipment used for transporting the concrete must be clean.

Remedial work is seldom entirely successful; the need for repairs should be avoided by taking greater care during construction.

ISSN 0114-8826 Š December 1989. Cement & Concrete Association of New Zealand, Level 6, 142 Featherston Street, PO Box 448, Wellington, telephone (04) 4998820, fax (04) 499-7760, e-mail admin@cca.org.nz, www.cca.org.nz. Since the information in the bulletin is for general guidance only and in no way replaces the services of professional consultants on particular projects, no liability can be accepted by the Association by its use.

IB 33: Specification and Production of Concrete Surface Finishes

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INFORMATION BULLETIN: IB 37 Weathering of Concrete Buildings Introduction

3.

It is pleasing to note the increase in variety of concrete surface finishes in recent years and improvements in the quality of those finishes. But some finishes that are excellent in themselves when new, become stained and unattractive in just a few years through the process of weathering. All buildings weather, but some better than others. Dirt is deposited on them mainly when it is not raining, and most of the natural cleansing is provided by rainwater. Although rainwater is an effective wash when it first hits a building, it can contribute to weather staining of expansive surfaces if allowed to run over them at slow speeds and deposit or spread dirt in the process. Wind flow over a facade influences the depositing and buildup of dirt and the flow of cleansing rainwater. The problem of weathering manifests itself most when a dirt-laden surface is only partially cleansed by rainwater, thereby leaving lighter coloured areas contrasted by darker dirt-covered patches. Weather staining can be minimised, if not eliminated, by full consideration being given at the design stage to the mass and form of the building, its location and micro-climate, its elements and its materials. Such consideration should include prediction of how rainwater will flow or be blown over the facades of the building. Thought should be given to how that rainwater flow could be controlled to produce desirable cleansing actions and minimum staining.

Incorporating design features to prevent rainfall flowing freely over surfaces.

All of these methods have the objective of allowing each section of a facade that can be cleaned by direct rainwater to be cleaned, and then for the water to be led along preferred lines of flow or to be taken away by drainage. Surfaces that cannot be cleaned by direct rainfall are likely to be only partially cleaned, with the consequent result of streaky or blotchy staining. In such cases it might be preferable to exclude rainfall from the surface completely and to allow dirt to accumulate more or less evenly over the surface. Horizontal or slightly sloped surfaces such as window sills and parapet cappings, tend to collect dirt to a greater extent than vertical or steep surfaces and care should be taken to avoid that deposited dirt being carried onto cleaner surfaces by the flow of rainwater. Similarly, rainwater flowing from relatively clean vertical surfaces directly onto dirtier lower surfaces could cause streaking of those lower areas unless the flow was controlled in a way that would prevent such disfigurement. The same applies to windows. 1

Rainwater flow can be controlled and utilised in several ways. 1.

Shaping of surfaces and textures to create preferred lines of flow.

2.

Arranging surfaces so that they present themselves to direct rainfall.

IB 37: Weathering of Concrete Buildings

Page 1


2

3

5

4

1.

Modelling and fenestration related to preferred lines of water flow.

2.

Partial cleansing by rainwater causes streaking.

3.

Vertical modelling controls waterflow but absence of collection at beam leads to staining.

4.

Corners do not collect as much dirt and are more fully washed than the main body of large walls.

5.

Exposed aggregate collects dirt and emphasises need for even overall rainwater flow.

6.

Water flow on rounded spandrels is unpredictable. Staining results.

7.

Horizontal textures spread stains rather than prevent them.

8.

Vertical textures attractively resolve more problems than just weathering.

IB 37: Weathering of Concrete Buildings

Page 2


made of local buildings to assess the extent of dirt accumulation, rainfall, wind eddies and sunshine and their influence on weathering.

6

Part and parcel of the prediction of rainwater flow is the detailing of surfaces and modelling of the facades. Every situation will require individual consideration but the following notes have wide application in controlling weather-staining of buildings.

The Drip The drip is a traditional feature of the building industry and is usually found as a groove running the length of, and near the outer edge of, a horizontal projection such as a sill course, window lintel or exterior beam.

7

In some cases the drip is formed by a rebate in the soffit of the projection, but where the projection runs into a vertical element (e.g. junction of window lintel and reveal) it is recommended that a groove be used. A drip grove or rebate will stop the flow of water across the underside of a projection, while the projection will check the rate of flow down the facade. Where a projection checks water flow and has an associated drip groove or rebate on its soffit to even out the flow onto lower surfaces, it is essential that the outer lip of the drip be true and dead level. If the drip runs one way or the other, water will run to the lower end and will have to be handled at that point by means of a vertical groove or other feature. Not to do so would be to risk streaking on the vertical reveal or column face.

8

Dirt washed from windows is still dirt, and could cause staining of sills or lighter coloured spandrel panels if the form and texture of those surfaces were not self-cleansing by rainfall, or somehow controlled the flow of cleaning water. In order that the effect of weathering can be foreseen it is important that prediction be made at the design stage of water flow over the whole building, bearing in mind the frequency and quantity of rainfall and the micro-climate. It is strongly recommended that close study be

The consequence of horizontally-channelled rainwater meeting vertical surfaces cannot be overemphasised. Full attention should be given to tracing the path of rainwater from the time it hits the building until it reaches the ground or is drained away.

Plain Walls Although simple and straight-forward in themselves, plain walls are perhaps the most unpredictable of surfaces in the matter of weather staining. A large high plain building facade may be well washed on the side of prevailing rain, whereas

IB 37: Weathering of Concrete Buildings

Page 3


a similar wall on the sheltered side of the same building might receive little rain and therefore spasmodic or uneven washing. Dirt on the latter side will not be removed completely or evenly and the result will be weathered staining in the form of random light and dark streaks. An interesting point is that such dark streaks rarely run down the outer edges or corners of tall facades. Observation indicates that wind eddies around the comers of buildings minimise the accumulation of dirt at those points. Furthermore, rain flow over a tall plain facade seems to be towards the outer edges, thereby providing more cleansing there than in the main body of the wall - hence relatively clean edges to many plain walls that are otherwise marred by staining. It is suggested that the moulding of more vertical "edges" into a facade would limit the transverse flow of rainwater and thereby produce a more even and predictable result. The use of vertically-striated finishes has proved to be very successful in limiting or controlling weathering of large expanses of concrete. Many types of surface finishes having vertical grooves are available and some are described in CCANZ Information Bulletin IB 18. Exposed aggregate surfaces spread the flow of rainwater through the channels formed between the aggregate particles, but it must be borne in mind that dirt will readily lodge in those same crevices. It is therefore important that exposed aggregate surfaces be well exposed to cleansing rainwater or be sheltered from it. Very few horizontal surface treatments are successful from a weathering point of view and should be limited to boarded-formwork finishes and then only when they will be fully rain-washed over the whole surface. Precast concrete cladding panels require regular vertical joints and these help in channelling water, provided the joint is not pointed flush with a sealant or gasket. The concentration of water at such joints requires careful detailing so as to prevent leaking.

Parapets and Roofs Parapets should be such that the run-off from them is towards the roof and not over the building facade. The edges of flat roofs should be such that

they fall back towards the roof. However, it is not always possible to avoid some run-off from parapets or roof edges, and in those cases the outer lip of the parapet should be well sloped and narrow to minimise dirt accumulation and maximise washing by rainwater. Roof edges and flashings should be finished with a drip groove or edge at least 25 mm out from the lower surface, and this drip must be dead level to ensure even distribution of water falling therefrom.

Openings Openings in facades, such as windows and doorways require special attention but the principles outlined before still apply. In most cases rainwater flow should be encouraged to pass over windows, sills and spandrels as evenly and freely as possible. Window frames should be of materials that do not stain easily, and sills should be well sloped and smooth so as to minimise dirt accumulation. Many recent buildings have used concrete spandrel panels and windows in more or less the same plane, without sill ledges or projections, and they have weathered well without staining. This method seems to be at best when the spandrels are of a darker colour. Again, the path of flow must be anticipated and provision made to collect and drain away the water in due course. The use of projecting sill courses has had mixed success from a weathering point of view. It is therefore recommended that sill courses be omitted in favour of the "in-plane" method mentioned above. If strong modelling of the facade requires the use of recessed windows and their associated deep sills, it is recommended that the sills be designed to check and arrest rainwater and direct it to intentional run-off channels in reveals or spandrels or to a drainage system.

Conclusion It would not be possible in an article such as this to contemplate all the forms, textures and situations that arise in concrete structures of all shapes and sizes. But in designing all those structures the principles of rainwater flow must be applied and solutions designed as part of the building fabric.

IB 37: Weathering of Concrete Buildings

Page 4


Not to do so is to risk uncontrolled and unsightly weathered staining that would give displeasure to many. It must be stressed that the many concrete buildings that have weathered well have been the subject of careful design and detail as much as of good workmanship. The most excellently formed, placed and finished concrete will not be spared from weather staining unless the design itself is efficient.

Further Reading •

Weathering: Design of concrete buildings, John Partridge; "Concrete" November 1975.

Weathering: Appearance of concrete structures, W.L. Monks; "Concrete" May 1975.

Weathering: Cleaning and restoration of concrete structures, Ian Clayton; "Concrete" April 1975.

Design for Weathering of Buildings using Architectural Precast Concrete: Prestressed Concrete Institute, Chicago, 1978.

Reports on "The Weathering of Concrete Symposium" London; "Concrete" February and March 1971.

ISSN 0114-8826 © June 1987. Cement & Concrete Association of New Zealand, Level 6, 142 Featherston Street, PO Box 448, Wellington, telephone (04) 499-8820, fax (04) 499-7760, e-mail admin@cca.org.nz, www.cca.org.nz. Since the information in the bulletin is for general guidance only and in no way replaces the services of professional consultants on particular projects, no liability can be accepted by the Association by its use.

IB 37: Weathering of Concrete Buildings

Page 5


INFORMATION BULLETIN: IB 46 Vibration of Concrete Introduction The correct placing and compaction of fresh concrete are probably the most important parts of the whole sequence of concreting operations. Success relies on careful planning, the right manpower and internal equipment. This information bulletin discusses various aspects of the compaction process. It is pertinent to remember that the mixing process for concrete entraps air within the mix. For each 1% of voids left within the concrete the strength is reduced by approximately 5-6%. Air entrapped in the concrete leaving the mixer typically may vary from 5-20%. Compaction is vital to achieve: Maximum strength of the placed concrete.

2.

Maximum durability.

3.

Adequate bond and protection reinforcement in the concrete.

4.

Avoidance or reduction of visual blemishes, such as honeycombing and blowholes on the surface of form cast concrete.

for

The ease with which optimum compaction can be achieved by vibration techniques is related to:

2. 3.

Compactability refers to the ease with which a concrete can be compacted properly with efficient removal of entrapped air and the repositioning of constituent particles into a denser state. Mobility of mix related to aspects of flow. Internal cohesion due to frictional effects, surface forces and the like is an important factor here. Stability of a mix refers to its resistance to segregation effects during transporting, handling, placing and compacting.

1.

1.

There are three inter-related properties that may influence the behaviour of a concrete mix during vibration. These are known as compactibility, mobility and stability. Each is affected by changes in the physical make-up of the mix, and can control the degree to which efficient consolidation of the particles is possible.

Physical properties of the fresh concrete which in turn depend on the type of aggregate, constituent particle shapes, and relative mix proportions. Harsh mixes are more difficult to consolidate. Mixes high in fines or cement are "sticky" and may also present problems of compaction; Types of vibrators, associated characteristics and vibration patterns through the concrete; Techniques in handling vibrators, in particular spacing and duration of vibration.

Segregation. A significant separation of the course and fine fractions is highly detrimental to concrete quality. The object in vibrating concrete is to mobilise it sufficiently, so that it becomes plastic enough to enable air voids to be removed and the aggregate particles to gravitate together to form a homogeneous mass. The stiffer the mix and the larger the aggregate particle sizes, the greater will be the force required to energise the mix. Lower water cement ratio concrete has a lower workability, but becomes a much stronger compacted concrete. A high degree of compaction with harsh mixes requires very efficient vibration both in terms of effectiveness of the applied poker vibrator and the number of insertions made.

Vibration Mechanisms The equipment that is used in compacting concrete

IB 46: Vibration of Concrete

Page 1


develops its vibrations by a form of eccentric rotation. Because of this, the vibrations are generated in a steady flow of cycles, and are transmitted into and through the medium in contact with the vibrator.

.. cycle is given by x = a sin (2Ď€ft) where the maximum acceleration is given by a = 4Ď€2f2s metres per second2 (figure 1).

The cycle of vibrations travel through the concrete, transferring their energy to the particles in the mix. Eventually, at some distance from their source, the vibrations lose their effectiveness. As the vibrations pass a certain point, the mix at that location moves back and forward about its original point of rest. As this occurs, the entrapped air is released and moves the surface while individual particles oscillate about and settle down into the mix. The components of the vibration cycle are amplitude, frequency and acceleration, and these terms are used to describe the performance characteristics of vibration equipment. See Table 1.

Table 1:

Vibration Method

Recommended accelerations and frequencies of concrete vibration Recommended Recommended Acceleration Frequency (without concrete load) g

Internal

Hz

vib/min

100-200

150-250

9,000-15,000

Form

5-10

50-200

3,000-12,000

Surface

5-10

50-100

3,000-6,000

Table

5-10

50-100

3,000-6,000

Amplitude is the maximum departure for a point of rest during a displacement cycle under vibration. Most concrete vibrators operate with an amplitude of 0.5 mm to 2.0 mm. Frequency (f) is usually described by the number of vibrations per unit time. 1 Hertz (hz) = 1 vibration per second, or 60 vibrations per minute. Therefore 200 Hz refers to 12,000 vibrations per minute. The displacement at any time during a simple sine wave oscillation is given by the formula x = s sin (2Ď€ft) where s denotes the amplitude. Similarly, the acceleration (which is the rate at which the velocity is changing) at any time in the

Figure 1: Sinusoidal vibratory motion. The maximum acceleration during a vibratory motion is often expressed as a multiple of the acceleration due to gravity, g; for example 5 g (50 m/sec2) for table vibration. From research conducted by Dr L. Forssblad of the Dynapac organization in Sweden, the interactions of concrete of properties, frequency and amplitude of internal vibration are shown in graphs of radius of action versus frequency, for various amplitudes and times of operation with a constant mix design. The studies indicated that there was an optimum combination of vibratory conditions for the response of the concrete mix (figure 2, page 3). During the vibration process the concrete undergoes three different stages. The first is the initial rapid collapse of the uncompacted mix. This requires a large energy usage. If the vibration effort is too low, the internal resistance of the mix dampens the motion and the concrete absorbs the energy without any plastic deformation occurring. As the force is increased, the mechanical properties of the mix and its resistance to the compaction effort falls until the material is transformed into a liquid. The mass then begins to flow. As the concrete then liquefies, de-aeration begins and most of the entrapped air is released. Finally, as the number of air bubbles being liberated

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Figure 2: Graphs showing the correlation between radius of action, frequency, and amplitude for a 60 mm internal vibrator. ceases, little energy is required to overcome the internal friction and damping effect of the concrete as the mix is behaving nearly as an ideal fluid, and its surface begins to acquire a glistening smooth appearance.

Types of Vibrators The four most commonly used systems for compacting concrete are internal vibration, table vibration and surface vibration. With each of these the mechanism of vibration and the effect of the formwork on the concrete mix is different.

Internal Vibrators Internal or poker vibrators are available with a

selection of power sources and types of vibrating mechanisms. The power source is either electric, pneumatic, petrol or diesel based. The vibrating mechanism in the poker head can be driven by a flexible shaft, motor-in-head or pneumatically. Pneumatic poker vibrators that operate a rotating mechanism within the head, are used in areas where it is convenient to have compressed air available and when it would be dangerous to use other types of machines. Whatever the form of vibrator, the rotating member in the head produces an eccentric motion that generates the vibrations. Circular compression waves are produced in rapid succession. These travel away from their source and through the concrete. The further they travel through the concrete, the amplitude of vibration imparted to the particles that are met reduces, due not only to

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the damping effect at the vibrator itself and in the concrete, but also to the increased length around the circular wave (figure 3).

head. The diameter of the rotor is smaller than the inside diameter of this rolling ring, and since the inside of the tube is scrupulously clean, the rotor ‘grips and skids’ inside the ring four times for every revolution of the flexible shaft. This system effectively gears up the 3,000 rpm to produce 12,000 vibrations per minute at the nose cap end. Since the maximum amplitude is at the nose cap, the pendulum vibrator when withdrawn from the concrete compacts the upper surface without leaving holes or voids. Developments to the principle have been made over the years to produce longer lasting and cooler running vibrators with improved efficiency of vibration. These features, coupled with the availability of waterproof joint extension shafts to make the flexible shaft up to 11 m long and rubber covered nose caps to protect formwork, have made the pendulum vibrator a popular choice for concrete compaction.

Figure 3: Principle of internal vibration.

Flexible Shaft Poker Vibrators These vibrators employ two sections for generating their vibratory output. They are known as “parallel” or “pendulum” vibrators. The parallel design embodies an eccentric shaft rotating between bearings at both ends, whilst the pendulum design involves the use of a suspended rotor with a self aligning bearing at the drive end, with the lower end being allowed to freely orbit when rotated within the housing. The vibratory characteristics of the two types are different, in as much as the vibratory output from the parallel machine gives a force of equal power over the length of the tube, while with the pendulum design the power is at its maximum at the nose cap end of the vibrator. The parallel vibrator historically was the preferred system, but it was found with harsh mixes that although it effectively compacted the mix, it left a hole when the poker head was withdrawn. The pendulum system developed in Sweden in 1936 overcame this problem. In this design the flexible shaft is driven at 3,000 rpm and is screwed (via an end shank) to the top end of the solid steel rotor. The self aligning bearing at this end allows the other bottom end to float inside a hard steel ring which is permanently fixed inside the tube

Pneumatic Poker Vibrators These vibrators generally have an integral oil bottle and throttle control and a compressed air hose inside a large diameter exhaust hose to allow used air to escape by the oil bottle. The poker heads comprise four basic types. The oldest style uses an airmotor inside the tube driving an eccentric shaft between two bearings. Another type uses an airblown ball bearing in a race to produce the vibrations. The most common two types in use are the rotary vane vibrator and the helical rotor vibrator. The helical rotor vibrator was a development from the rotary vane to primarily reduce the weight of the vibrator which was required in the vane operation. The spinning rotor is forced outwards by a series of discretely located airflow paths to produce the vibration. This process is repeated over 20,000 times a minute which reduces to 12,000 times when placed in the concrete, producing the characteristic rise and fall droning noise of an air vibrator.

External Vibrator The selection and application of external vibrators requires careful consideration. The units are available in varying output powers, that are defined

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either by the centrifugal force developed or the wattage of the motor. The transfer of vibratory power though the formwork must be considered as the nature of the mix and density of any reinforcement within the section (figure 4).

frequencies used range between 3,000 and 12,000 vibrations per minute. The high frequency use tends to give a better surface appearance. Large contracts benefit by the use of external vibration with regard to a lower manpower and reduction of human error. Far stiffer mixes can also be used.

Vibrating Screeds Surface vibration is usually accomplished by comparatively light single or double vibrating screeds which can compact up to 200 mm thick layers of flowing to plastic concrete mixtures. For such screeds, a frequency range of 3,000 to 6,000 vibrations per minute and accelerations to 5-10 g are customary. The amplitude distribution along the screed should be reasonably uniform (figure 6).

Figure 4: Principle of form vibration. Generally, the external vibrator consists of an electric motor with an unbalanced member to create the vibration (figure 5).

Figure 6: Principle of surface vibration.

Roller and Laser Screeds

Figure 5: An external vibrator clamped to a form. The best frequency of vibration depends mainly on the design of the formwork with high vertical forms usually requiring the high frequency option. However, very stiff mixes respond better to high amplitude and lower frequency. Generally, the

The use of these two methods represents the most recent advances in the placement and compaction of concrete. It is important to note that additional vibration will still be necessary when using these methods to screed and finish concrete as the amount of vibration imparted into the concrete by these two methods may not be enough to achieve total compaction. •

Roller Screeds Roller screeds are sometimes used as a placement and compaction tool in its own right, but this is usually only in relatively thin

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slabs, and with the use of immersion vibrators around the perimeter forms, where additional compaction is usually required. Manufacturers of these screeds claim that the placement of concrete using roller screeds leaves more large aggregate at or near the surface, which enhances the performance of the slab under harsh operation conditions (such as is found in warehouses for instance). •

Laser Screeds Laser screeds are used primarily in large floor pours where slab flatness is of prime concern. While thinner slabs will only require supplemental vibration around the slab perimeter, thicker slabs are generally placed using a combination of immersion vibration and the vibrating laser screed. (This approach is the recommended method to follow).

Table vibrators can give less consistent results even with careful operation. The compaction effect is determined by the acceleration of the table. Accelerations of about 5-10 g before the forms are placed on the table, and 2-4 g during vibration, are required. For table vibration the optimum frequency range is fairly low, 3,000-6,000 vibrations per minute. Comparatively large amplitudes are generally needed for efficient and rapid consolidation. The location of the vibrators and direction of rotation is important since it effects the primary direction of the vibration which may be a rotational motion or uni-directional.

Compaction Methods

Table Vibration

The characteristics of concrete, effects of vibration and equipment available, have been discussed in the previous sections. This section deals specifically in turn with the practical consideration in the workplace of using vibrators. Often the cause of many problems of faults in concrete is directly traceable to the failure to ensure adequate vibration.

Vibrating table techniques are usually restricted to precasting operations. On a vibrating table, the forms as well as the concrete can move during vibration and resonance may occur. Also reflection of the pressure waves against the concrete surface will influence the amplitude distribution (figure 7).

The main feature of construction work tends to be a lack of sufficient vibration to the concrete in terms of providing manpower and equipment to match the placing rate of the concrete. When placement is by concrete pump considerable resources are needed if full compaction is to be achieved.

Both methods will produce a slab with surface levelness and flatness tolerances that are much better than free screeding techniques.

Internal Vibrators

Figure 7: Principle of table vibration.

Most concrete is compacted by means of immersion or poker vibrators. This method is considered the most satisfactory because the poker works directly on the concrete and can be moved from one position to another easily and quickly. For most reinforced concrete work, pokers of diameters from 25 mm up to 75 mm are used. Diameters up to 100 and 150 mm are available, but their use is mainly restricted to mass concrete in heavy civil engineering works like dam construction. Due to their weight, these large pokers usually need two people to handle and operate them. For efficient compaction, the largest diameter that the complexity of formwork and reinforcement will allow should be used. Table 2 gives an indication of poker sizes and applications.

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Although the table indicates the radius of action for various poker diameters, the actual effectiveness of a particular poker in a specific situation depends on the workability of the concrete and the characteristics of the poker itself. Generally, the larger the diameter and the higher the frequency, the greater will be the radius of action, but in practice it is best to judge by eye the actual radius for a particular situation. This radius will determine the spacing and pattern of insertions of the poker. For example, if the radius of action is about 200 mm, insertions will need to be about 300 mm apart and to a predetermined pattern if all the concrete is to be fully compacted. As a guide, a spacing of about 450 mm (250 mm radius of action) may be assumed for a 60 mm diameter poker with concrete of medium workability.

from a number of sites have shown that they are often running wastefully, or at a reduced efficiency, for about 70% of their operating time: • • •

This means that the poker is doing useful work for only 30% of the time, which is why it is necessary to plan the compaction, placing method and technique in advance, so that both operations are carried out as economically and quickly as possible. The following guidelines are helpful to ensure a well compacted mix (see also figures 8, 9 and 10): 1.

Make sure the operator can see the concrete surface.

2.

When inserting the poker, allow it to penetrate to the bottom of the layer as quickly as possible under its own weight. If done slowly, the top part of the layer will be compacted first, making it more difficult for the entrapped air in the lower part to escape the surface.

3.

Leave the poker in the concrete for about 10 seconds and withdraw it slowly ensuring that the hole made by the poker is closed up. If a hole is left (and it is often difficult to prevent if the concrete is very stiff), replace the poker near enough to the hole for the next spell of vibration to close it up. For the final insertion, withdraw the poker even more slowly and wiggle it about to ensure that the hole closes up properly.

Length of Head Because it is only the head itself which is vibrating, the concrete layer should not be deeper than the head length, otherwise there is a danger that the top part will not be fully compacted. For most pokers within the range of diameters given in table 2, the poker head is likely to be between 350 and 600 mm long.

Using a Poker Vibrator Pokers are often used inefficiently. Observations

15% out of the concrete and running, 35% wrongly positioned in the concrete, 20% vibrating already compacted concrete.

Table 2: Poker sizes and applications Diameter of head (mm)

Radius of action (mm)

Appropriate rate of compaction, assuming rapid placing (m3/h)

20-30 (Needle)

80-150

0.8-2

50 mm slump and above in very thin sections and confined places. May be needed in conjunction with larger vibrators where reinforcement, ducts and other obstructions cause congestion.

35-40

130-250

2-4

50 mm slump and above in thin columns and walls and confined places.

50-75

180-350

3-8

25 mm slump and above in general construction free from restrictions and congestion.

Application

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4. 5.

Replace the poker in the concrete to correct spacing. Avoid touching the formwork face with the poker as this will leave a ‘poker burn’ on the formwork and a resulting mark will be left on the finished concrete surface. To be on the safe side, keep the vibrator about 75-100 mm away from the formwork. Avoid touching the reinforcement with the poker, although, provided that all the concrete is still fresh, vibrating the reinforcement should not do any harm and could improve the bond. The danger lies in the vibrations in the reinforcement being transmitted into parts of the section where the concrete may have stiffened, in which case the bond may be affected.

there is a risk of the bearings overheating. 6.

Avoid sharp bends in flexible drives and do not move the vibrator by pulling on the flexible drive.

7.

Remember that where finish is important, a little extra vibration can reduce the number of blowholes.

8.

Make sure the driver motor will not vibrate itself off the stagings, and when finished clean all the equipment thoroughly.

Avoid using the poker to make the concrete flow and never use it to flatten a heap. Instead, insert the poker carefully around the perimeter which will avoid segregation, remembering that compaction starts only after the heap has been flattened. 7.

Make sure that the poker extends about 150 mm into any previous layer of concrete and put the whole length of the poker head into the concrete. This is essential to keep the bearings cool. Avoid leaving the poker running when it is not in the concrete, otherwise

Figure 8: Diagram showing incorrect and correct placing of poker in concrete.

Figure 9: Use of poker vibrator.

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1.

Length of Time Required for Full Compaction The length of time a poker has to be in the concrete at any one position in order to fully compact the surrounding concrete cannot be precisely stated since it depends both on the workability of the mix and on the size of the poker itself. The duration will vary between 5 and 15 seconds for concrete with a slump of 25-75 mm, so practically, a time of around 10 seconds in the concrete should be satisfactory. Being able to tell when concrete is fully compacted is a matter of experience. With a poker, one soon gets the feel of it and can judge the right amount of vibration to give. The following will help: 1.

Initial consolidation is rapid and the level of the concrete drops quickly but the entrapped air has still to be removed.

2.

As the concrete is vibrated, air bubbles come to the surface. When the bubbles stop, it can be taken as a sign that not much more useful work can be done on the concrete. The distance of the bubbles from the poker is also a useful guide to its radius of action.

3.

Sometimes the sound can be a helpful guide. When the poker is inserted there is usually a dropping off in frequency, and when the pitch (whine) becomes constant the concrete is free from entrapped air.

4.

The surface appearance also gives an indication of whether or not compaction is complete. A thin film of glistening mortar on the surface is a sign that the concrete is compacted, as is cement paste showing at the junction of the concrete and formwork.

In any case, the dangers from under-compaction are far greater than those from over-compaction, so if there is any doubt don’t be in a hurry to stop vibrating. Too much is better than too little, since it is virtually impossible to over-vibrate a properly designed mix. Figure 10: Sequence of the stages that occur during vibration of a heap of concrete. The photographs show the spacings of the vibrator insertions and the glistening appearance that is given to the surface.

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The result of over-vibrating badly designed mixes, such as those prone to segregation and lacking cohesiveness or containing too much water, is at the worst, only likely to cause an excess of laitance on the surface, and it is better to have to remove this laitance than risk under-vibrating the mix. With columns and wall tops, this removal is not difficult and usually has to be done before the next lift is placed. However with slabs, laitance removal is impossible, and it is therefore essential to make sure that the mix is designed to reduce bleeding to a minimum, and that the surface is not overworked. Concrete can be placed and compacted at any time after mixing provided that it is still workable by the compacting method available, even if some loss of workability has taken place. For example, if a poker will sink into the concrete under its own weight and the hole closes up as the poker is withdrawn, then that concrete can still be compacted. No fixed time limit can be applied to all concreting operations because the actual time will depend on the stiffening of the mix which in turn depends on the richness, on the temperature (both ambient and of the concrete itself), and on whether a retarder has been used. On cool, damp days, most concrete is still workable 3-4 hours after mixing, whereas on warm dry days, and especially with rich mixes, 30 minutes may be the limit.

Revibration Provided that it is still workable, compacted concrete will not be harmed if it is revibrated. In fact, tests have shown that the strength is increased slightly if it is revibrated some time after the initial compaction. On columns and walls where surface finish is of importance, there is sometimes a tendency for blowholes to occur in the top 600 mm of a lift; because unlike the lower layers, this top layer does not have the advantage of the weight of additional concrete on top to increase the compaction. It can often help to revibrate the top 600 mm or so some thirty minutes to one hour after the initial compaction. In thick sections of slabs and beams, and particularly with mixes that are prone to bleeding, there is a danger of plastic settlement cracks appearing over the line of top reinforcement. These

cracks generally form about 1-2 hours after compaction and if they are noticed within this time, and provided the concrete is still workable, revibration of the top 75-100 mm can close them up again.

Care and Maintenance of Poker Vibrators Whatever the type of vibrator, it must be treated with care and properly maintained if breakdowns are to be avoided. Obtain the manufacturer’s instruction booklet and follow its recommendations for both operation and maintenance. Some general points of care and maintenance are given below: 1.

With electrically operated machines, check the voltage and frequency before connection to any power supply, ensure that the equipment has a good earth connection and see that all joints are adequately protected.

2.

With a petrol or diesel engine, periodically check that it is running at the speed recommended by the vibrator manufacturer. If it isn’t, the frequency developed in the poker head won’t be correct either, and compaction of the concrete won’t be as quick and efficient as it should be.

3.

Always avoid sharp bends in drive shafts, particularly when in use.

4.

Regularly check all equipment for signs of wear and get any faults seen to.

5.

Never engage a poker drive to a motor that is running. Many accidents have happened because the operator didn’t bother to switch off the motor or, if it was fitted with a centrifugal clutch, didn’t throttle it back.

6.

Ensure there is enough grease in the bearings, for example, the vibrator tube may start to twist and jump about. If this happens, stop the vibrator, examine the bearings, and grease them if necessary.

7.

Avoid leaving pokers in the same place for long periods when vibrating concrete.

8.

Don’t leave pokers running while waiting for fresh supplies of concrete.

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9.

If a pendulum-type poker fails to vibrate when switched on, it can often be started by rattling the head and giving the nose cap a smart rap (but don’t bang it hard). If this doesn’t work, switch it off and check the motor coupling. Don’t go on using the machine if it is still faulty.

2.

With shaft driven machines, the drive shaft or drive pin may have failed. With electric machines, it could be a switch, fuse or a break in the wiring; it could even be a complete motor burn-out.

Make sure that the vibrators are firmly clamped or bolted to the brackets, and keep a constant eye on them during use to see that they don’t loosen; otherwise the full vibrations won’t be transmitted to the formwork and the concrete.

3.

Feed the concrete into the section in small quantities so that it is placed uniformly in layers about 150 mm thick. This will prevent air being trapped as the lift is built up.

4.

Keep a continuous watch on all fixing (which should be screwed rather than nailed), especially on nuts of through-bolts which can easily work loose under intense vibration. Also watch out for grout loss, plugging leaks whenever you can.

5.

If possible, compact the top 600 mm of concrete in a wall or column with a poker. If this isn’t feasible, compact the top 600 mm by hand-rodding and spading down the face of the formwork. External vibrators tend to create a gap between the formwork and the concrete. In the lower lifts this gap is closed by the weight of the subsequent layers of concrete, but in the open layer it can remain to disfigure the surface.

10. When using a pneumatically driven vibrator, clear the air line of moisture before coupling it up. Also check that there are no leaking lines or connections otherwise the vibrator will not be operating at full power.

External or Clamp-on Vibrators

and grout will find its way through the smallest of openings.

External vibration systems are available with different frequencies and centrifugal forces. The external or clamp-on vibrator consists of an electric motor with an unbalanced member. It is fixed to the formwork so that the vibrations are transmitted through the formwork into the concrete. Although their use is mainly in precast concrete, they may sometimes be necessary for insitu construction when it is not possible to insert a poker, as in very narrow sections or where there is congested reinforcement. They will only compact concrete in sections up to 400 mm thick. Where it is possible to fit vibrators on either side of formwork even greater thicknesses of concrete can be compacted. When external vibrators are used, the formwork has to be designed and constructed to stand up to the repeated reversals of stress, and to be capable of spreading the vibrations uniformly over a considerable area. Specially designed brackets must be fixed to the formwork to hold the vibrators. Since vibrators are usually moved up or along as the forms are filled, the number of brackets may be greater than the number of vibrators available.

Numbers and Spacing of External Vibrators Because of the variables involved, such as rigidity of the formwork, the quality of the concrete and the effective range of vibrators available, there are no hard and fast rules about the number of vibrators required and their most suitable arrangement. The following points are suggested as guides. 1.

The positions should generally be not more than 1.0 m apart in any direction when using small external vibrators with low centrifugal force. In some instances, they may need to be closer. More powerful vibrators can be spaced up to 2.0 m apart.

2.

At intersections and angles, the distance over which they are effective is reduced; they should therefore be positioned about 0.5 m

The following points should be noted: 1.

Ensure that all joints, both within and between panels, are tight and sealed. The formwork moves more than it does with poker vibration

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from corners and intersections. 3.

For walls and columns no more than about 1.0 m high, a single row of vibrating positions about mid-height will usually be sufficient.

4.

For heights greater than 1.0 m, the lowest row should be fixed about 0.5 m above the bottom, with subsequent rows at 1.0 m spacings vertically. Once each 1.0 m lift of concrete has been placed and compacted, the lower row of vibrators can be switched off, the next higher row being switched on until the next layer has been compacted, and so on. If there aren’t enough vibrators for the full height, the vibrators will have to be raised as concrete progresses. With modern equipment it is possible to have quick release systems. This allows the movement of vibrators either along or up a shutter as the pour progresses. Many concrete works use only three or four units over a much larger number of bracket mounts.

5.

Before concreting begins, the effectiveness of the arrangement of vibrators can be roughly checked by switching them on and moving a hand over the formwork to feel the vibrations and see whether there are distinct strong, weak or ‘dead’ areas. It may be necessary to adjust the positions of the vibrators to obtain uniform vibrations over the whole area.

4.

Make sure however that the beam itself is riding on the side forms and not riding up on the concrete forced on to the side.

5.

Keep beams moving evenly when the vibrator is running.

6.

Turn vibrator off every time the beam stops.

Table Vibration This requires special design consideration since every application is likely to be different.

Summary

Vibrating Screed These can be used for compacting slabs up to 200 mm in thickness. The following points should be noted. 1.

The vibrating beams should be run over as long a length of slab as possible in one pass. One well controlled pass of a double beam should be adequate. A second faster pass of the double beam may be necessary in some cases to improve the finish on the concrete.

2.

Too many passes of the beam will bring unwanted excess mortar to the surface.

3.

Figure 11: The roll of concrete maintained in front of leading beam of double vibrating beam.

A surcharge of concrete is required to be maintained ahead of the beam (see figure 11).

Optimum compaction of concrete must be achieved if the concrete is going to achieve its strength and durability requirements. Modern day methods of mechanical vibration provide the most economical means of compacting concrete in most construction situations. They cannot however make up for human deficiencies in the handling of the equipment which usually relates to having insufficient manpower and equipment available to match the speed of concrete placing that can be achieved.

Further Reading Cable, J.K., McDaniel, L., Schlorholtz, S., Redmond,

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D., & Rabe, K. (2000). Evaluation of vibrator performance vs. concrete consolidation & air void system (Research and Development Information 2398). Skokie, Ill.: Portland Cement Association. Chan, Y-W., Chen, Y-G., & Liu, Y-S. (2003). Effect of consolidation on bond of reinforcement in concrete of different workabilities. ACI Materials Journal, 100(4), 294-301. Compaction of concrete using immersion and surface vibrators (Current Practice Note 33). (2002). North Sydney, N.S.W.: Concrete Institute of Australia. Ford, J.H. (2003). Internal or external vibration. Concrete Construction. [Online]. Retrieved April 1, 2005 from ftp://imgs.ebuild.com/woc/C03A084.pdf Forssblad, Lars.

Rheology and mechanism of

concrete vibration – Solna: Dynpac Research 1980 – (Research Bulletin No. 8023 Eng. February 1980). Harding, M.A. (1995). Vibrating concrete in wall forms: use proper internal vibrating techniques to ensure adequate consolidation. Concrete Construction. [Online]. Retrieved April 1, 2005 from ftp://imgs.ebuild.com/woc/C950180.pdf. Koski, J.A. (1994). Using Internal concrete vibrators. Concrete Producer. [Online]. Retrieved April 1, 2005 from ftp://imgs.ebuild.com/woc/J941010.pdf. New technologies for improving the consolidation of concrete (Technical Report CPAR-SL 97-2). (1997). Vicksberg, Miss: United States Army Corps of Engineers. Pneumatic external vibrators. (1997). Concrete Producer [Online]. Retrieved April 1, 2005 from ftp://imgs.ebuild.com/woc/J970690.pdf.

ISSN 0114-8826 © Revised Edition March 2005. Cement & Concrete Association of New Zealand, Level 6, 142 Featherston Street, PO Box 448, Wellington, telephone (04) 499-8820, fax (04) 499-7760, e-mail admin@cca.org.nz, www.cca.org.nz. Since the information in the bulletin is for general guidance only and in no way replaces the services of professional consultants on particular projects, no liability can be accepted by the Association by its use.

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INFORMATION BULLETIN: IB 93 Fire Performance of Concrete and Concrete Masonry them to exit the building quickly and safely. Secondly, the structure must be designed to allow enough time for fire fighters to safely carry out any search and rescue operations, along with firefighting operations. Thirdly, there are requirements to protect other property under the New Zealand Building Code (NZBC), these include preventing the fire from spreading as well as preventing hazardous materials at the fire site entering waterways.

CONTENTS Introduction

1

Principles of Fire Protection

1

Active Versus Passive Fire Protection

2

Concrete Performance in Fire

2

Basis of Fire Design

3

NZBC Fire Safety Requirements

4

Structural Fire Design

5

Insurance and Fire Damage

6

Conclusions

7

Sources and Further Reading

7

Concrete is commonly used to provide stable firecells in large industrial or multi-storey buildings as a means to contain a fire and prevent it spreading to the whole building. This is also called fire separation or compartmentation. Concrete walls reduce the spread of fire horizontally and concrete floors vertically. Concrete provides the opportunity to install safe separating structures in a reliable and economical way.

INTRODUCTION Concrete is generally considered to have good fire resistance since it is non-combustible (i.e. it does not burn), absorbs heat only slowly, and does not give off toxic fumes or smoke. As it is a poor conductor of heat and has a high heat capacity, concrete is used to protect other construction materials such as steel and timber from fire. In addition, it is this slow heat absorption which enables concrete to act as an effective fire shield to protect adjacent spaces and contents, as well as itself from internal fire damage.

Fire performance is the ability of a particular structural element (as opposed to any particular building material) to fulfill its designed function for a period of time in the event of a fire. The three functions of Stability (R), Integrity (E) and Insulation (I) are universally recognised to define fire protection. Time periods (fire ratings) are attributed to each of these functions to designate the level of fire performance. The overall Fire Resisting Rating of an element is termed FRR, thus a FRR of 90/90/90 requires a 90 minute rating for each of stability, integrity, and insulation.

These inherent properties, combined with the appropriate design of structural elements, ensure concrete performs well in fire.

Stability

However, there are some issues surrounding concrete’s performance in fire which require careful consideration. This bulletin outlines these issues, while providing general guidance to designers and specifiers on the design of concrete structures against fire.

Stability is the load bearing capacity provided by the primary elements within a firecell and includes elements which are part of the structural frame as well as those providing support to other fire rated elements. The Stability fire rating (R) is based upon the time an element can withstand a standard fire test and retain its loadbearing capacity while allowing for a level of superimposed load.

PRINCIPLES OF FIRE PROTECTION

Integrity Integrity is the flame arresting separation typically provided by secondary elements e.g. internal walls, to protect people and goods from flames, harmful smoke and hot gases. Primary elements, along with secondary elements, are also rated for integrity. The

The first and most important objective in fire protection is to safeguard the lives of any people who are in the structure which is on fire, and enable

IB 93

1

Fire Performance of Concrete and Masonry


time during which an element’s fire separation capability is maintained is determined by the tightness of joints to limit smoke and gas penetration.

blast furnace slag have lower quantities of free calcium hydroxide which can give reduced hydration loss on heating, and consequently lower strength loss.

Insulation

The fire rating of a concrete is also influenced by the aggregate type. This results partly from the coefficient of thermal expansion between the aggregate and the cement paste being different, particularly at higher temperatures. The thermal conductivity of concrete depends on the nature of the aggregate, porosity and moisture content. As water is driven from the concrete in a fire, the conductivity of the ‘dry’ concrete is more relevant. Lightweight aggregate concretes in particular, have very good fire performance in ‘dry’ building fires because they have a thermal expansion closer to cement paste. They also have good aggregate bond and high aggregate temperature stability. Limestone has an additional advantage in that it breaks down at temperatures over 660oC giving off carbon dioxide which provides a blanketing effect against heat penetration.

Insulation is the heat shielding capability provided by either primary or secondary elements. It is applied to fire separations where the transmission of heat may endanger occupants on the non-exposed side or cause fire to spread to other fire compartments. The fire rating is the time defined by a maximum permitted rise of temperature on the non-exposed side.

ACTIVE VERSES PASSIVE FIRE PROTECTION Concrete’s inherent fire resistance provides a robust passive protection system that usually requires no additional fireproof linings or coatings. Fire protection for lightweight construction often relies on active protection systems such as sprinklers. However, the robustness of sprinkler systems following an earthquake has been questioned in light of the vulnerability of reservoir water supply and the significant risk of a post-earthquake fire.

The effect of aggregate type on fire resistance is demonstrated in the table below. Based on minimum effective slab and wall thicknesses the table shows a range of insulation fire ratings (I) for three different aggregate types. Fire Resistance rating (minutes)

The integrity of fire linings following an earthquake has also been brought into question by BRANZ research, particularly where dislodged plaster filling at joints, resulting from seismic shaking, compromised the integrity by 40%. In addition, it has also been found that poor workmanship in retrofitting of structures after installation of services through lightweight fire rated elements has compromised subsequent levels of fire protection.

CONCRETE PERFORMANCE IN FIRE At temperatures of 150OC upwards there is some loss of water from the silicate hydrates in concrete, while temperatures above 300OC result in the loss of bound water, and in turn strength. While concrete may undergo strength loss at temperatures 300OC and above, the main losses are seen until 500 OC upwards. Even though flame temperatures are up to double 500 OC, the temperature of the internal concrete remains relatively low as a result of concrete’s slow heat absorption. Therefore, only intense fires of long duration may cause any weakening of concrete structures.

Type A aggregate

Type B aggregate

Type C aggregate

30

50

45

40

60

75

70

55

90

95

90

70

120

110

105

80

180

140

135

105

240

165

160

120

Note: Aggregate types: A - quartz, greywacke, basalt and all others not listed B - dacite, phonolite, andesite, rhyolite, limestone C - pumice and selected lightweight aggregates

Cement type can have some influence on strength loss. Cements with fly ash and ground granulated IB 93

Effective thickness (mm) for different aggregate types

Source: NZS4230: 2044 2

Fire Performance of Concrete and Masonry


Spalling of the surface concrete is a phenomenon which may occur in certain circumstances where the surface concrete breaks away at high temperatures. This is more common in higher strength concrete, where moisture content and reinforcement cover are more significant. The spalling is caused by internal moisture turning to steam during a fire with a resultant build-up of pressure in the pores of the concrete which cannot escape. Spalling can have a progressive effect on fire performance as it exposes the internal concrete and reinforcement to the heat of the fire. As the use of silica fume in concrete reduces the porosity, this has the potential to increase the risk of spalling.

The hydrocarbon load in a tunnel can be considerable, which includes not only vehicles but also the bituminous road surface. As a result, the use of concrete roads in new tunnels is now recommended. Figure 2 represents a standard furnace time temperature curve for a building fire taken from AS 1530.4-05 2005 Methods for Fire Tests on Building Materials, Components and Structures (Part 4: Fire-Resistance Tests of Elements of Building Construction).

Fortunately there is a fairly simple solution, which involves adding monofilament polypropylene fibres, at 2kg/m3, to the concrete. This provides for steam release via the fissures formed when the fibres melt at elevated temperatures. BS EN 1992-1-2 General – Structural Fire Design states that precautions need to be taken where the concrete strength is above 55 MPa, with additional precautions required where the cover is greater than 70mm or the silica fume content is greater than 6% by weight of cement. The code also gives the critical concrete moisture content above which ‘explosive spalling’ can occur. In this instance a deeper analysis is required involving the type of aggregate, permeability of the concrete and heating rate.

Figure 1: Standard fire curves for three scenarios – tunnels, hydrocarbons and buildings Source: Concrete and fire safety. UK Concrete Centre (2008)

The NZS 3101:2006 Concrete Structures Standard and the NZS 4230:2004 Design of Reinforced Concrete Masonry Structures cite AS 1530.4-05 2005 as the compliance code for carrying out fire tests on building components or assemblies. This code gives a standard time-temperature curve. This will differ from the time temperature relationship in an actual fire as controlled by a number of factors – fuel, fuel geometry, ventilation and restraint provided on members from adjacent areas of the building which are unaffected by the fire.

Reinforcing steel loses strength at elevated temperatures – there is a 15% loss from 350 OC up to 50% at around 600 OC, and an 80% loss at 750 OC. However, concrete’s low thermal conductivity protects reinforcing steel from significant temperature gain provided it has sufficient cover. Thus, the specification of minimum cover to reinforcement has to meet both durability and fire performance requirements.

BASIS OF FIRE DESIGN Standard test methods are used to determine the fire performance of materials or structural elements. These tests may either be at a small scale with a component of a building in an oven or furnace, or at full scale in a mock-up of a fully assembled building subjected to a fire regime. Standard fire time temperature curves have evolved to represent typical fires experienced in practice. The curves for fires representing three scenarios for building fires, hydrocarbon fires and tunnel fires are shown in Figure 1. These curves are different for the different scenarios. For instance, the temperature of a building fire rises much more slowly and peaks at a lower temperature than a hydrocarbon fire from burning vehicles as there is less combustible material present. Tunnel fires have a significantly higher peak temperature owing to the confinement of the fire. IB 93

Figure 2: Standard furnace temperature-time curve Source: AS 1530.4-05 2005 3

Fire Performance of Concrete and Masonry


The increasing sophistication of computer modelling techniques has enabled data from standard fire tests on building components to be interpolated into the predicted fire behaviour of building assemblies and whole buildings. This has had the effect of reducing the need for comprehensive whole assembly fire tests of buildings.

passage of fire. The specific requirements are given by their F (firecell) or S (structural endurance) rating. The F rating of a specific construction element is designed to prevent the spread of fire to another firecell. F ratings apply to both loadbearing and non loadbearing elements in a firecell (walls, floors and their supports). The S rating is to prevent fire spread or structural collapse for the complete burnout of the firecell. It usually applies to a structural member on or near a boundary where there is a requirement that a wall or floor does not collapse as a result of a fire. The collapse of any part of the building must not cause the collapse of the S rated wall or floor during the fire’s duration. Thus an S rating is usually more stringent than an F rating.

NZBC FIRE SAFETY REQUIREMENTS NZBC Compliance Document Clause C Fire Safety sets out four objectives for meeting fire safety requirements. These are: ƒ

C1: Outbreak of fire - Safeguard people from illness or injury caused by fire.

ƒ

C2: Means of escape - Safeguard people from illness or injury whilst escaping and facilitate fire rescue operations.

ƒ

C3: Spread of fire – Protect adjacent dwellings and other property from the effects of fire and safeguard the environment from the effects of fire.

For a building design (excluding boundary protection measures) the highest fire safety rating required by the Acceptable Solutions is F90 and is for buildings over 58m high (unless a specific design is being used, in which case the fire rating could be higher). The most common rating is F60 for two or more floors of a building without automatic fire sprinklers. The F rating is required between levels and for protection of escape routes. With automatic fire sprinklers fitted the F rating can be halved in some cases. Fire Hazard Category (FHC) is used to classify purpose groups or activities having similar fire hazard, and where fully developed fires are likely to have a similar impact on the structural stability of the building. As examples, FHC 1 applies to low risks, such as ground floor structures manufacturing noncombustible materials, whilst FHC 4 applies to chemical manufacturing plants. Table 5.1 of Acceptable Solution C/AS1 sets out the required S rating for buildings up to FHC 3, which is dependent on the ventilation of the building for a given FHC i.e. the fire load. A well ventilated building will burn faster and hence the S rating is lower than that required for a building with little or no ventilation. Note that glazed windows are considered as open vents as they generally fail early in a fire.

C4: Structural stability – Safeguard people and adjacent dwellings and property from structural instability caused by fire.

ƒ

In clause C2 the functional requirement for means of escape is as follows: Buildings shall be provided with means of escape from fire which: (a)

Give people adequate time to reach a safe place without being overcome by the effects of fire and

(b)

Give fire service personnel adequate time to undertake rescue operations.

FHC 4 buildings require specific design to determine the duration of the fire burn and hence the S rating.

The NZBC does not set the requirements for a specific FRR of a building or other fire safety features as can be seen from the description of the functional requirement for means of escape given above. These are however, outlined in Acceptable Solution C/AS1, which is prescriptive in terms of the fire safety requirements. The FRR applicable to a particular situation is typically chosen based on the purpose group, the height of the building, the occupant load and the fire hazard category. As an acceptable solution this is a ‘deemed to comply’ solution, other specific design solutions can be submitted but require verification.

Most S rated boundary walls utilise concrete for its superior toughness, good fire rating and being structurally sound, as well as having good Spread of Flame Index (SFI) and Smoke Developed Index (SDI) properties, which are satisfactory for the worst case scenario. High-rise apartments are generally concrete structures and the fire escapes (deemed safe places) are concrete enclosed, usually bare, to comply with the need to have no combustibles within the space. In the design of a multi-level building, each level is a separate firecell. Hence penetrations through the floor must be protected against the passage of fire

The material used for structural and separating elements has to be designed to resist the effects or IB 93

4

Fire Performance of Concrete and Masonry


by the installation of a suitable fire stopping mechanism. The most common need for floor penetrations is to distribute services up the building. Services on each level do not require any further fire protection unless there is a special case to warrant it. Another alternative is to provide a fire rated shaft running up the building with all services in it. This requires the services taken from the shaft onto each level to be protected with a suitable fire stopping mechanism.

a

=

the required axis distance,

b

=

the wall width, and

ƞfi =

the ratio of the factored design axial load under fire conditions (n*t) divided by the axial load capacity at normal temperature (Nu).

NZS 3106: 2006 also refers to the use of either simplified or advanced calculation methods detailed in Eurocode 2: Design of Concrete Structures Part 12: General Rules-Structural Fire Design BS EN 19921-2:2004. Further guidance on these methods is provided by the UK Concrete Centre publication How to Design Concrete Structures Using Eurocode 2 – Structural Fire Design.

In non-sprinkler protected buildings, walls and ceilings require limitations on the surface finishes for SFI and SDI indexes. These are dependent on the purpose group and location within the building. The purpose of these indices is twofold: a) Stop the rapid spread of flame across a surface

FRR for Insulation (minutes)

b) When the combusted amount of smoke generated is controlled and not likely to reach untenable conditions during the time of escape. Surface finish requirements apply also to roof underlays when exposed to a fire, to floor coverings in certain instances, and to HVAC ducting for both internal and the exterior surfaces.

Effective Thickness (mm)

30

60

60

75

90

95

120

110

180

140

240

165

Source: NZS 3101:2006. Table 4.3 Fire resistance criteria for insulation for slabs

STRUCTURAL FIRE DESIGN Concrete NZS 3101:2006 The Concrete Structures Standard sets out design requirements for determining the fire resistance ratings of concrete elements required by the NZBC. Fire design is based on the Tabular method which gives minimum dimensions for beams, columns, walls and slabs for structural adequacy and insulation. Also included is the minimum reinforcement depth for fire rating, which is referred to as the axis distance based on a calculated average distance to the centroid of the main reinforcement. The following tables are extracted from Section 4 of NZS 3101:2006 for floor slabs and load bearing walls. In the case of load bearing walls, as the axial load as a proportion of the load capacity increases, the required wall thickness increases. The axis distance is also given. This ensures that the steel has adequate protection from the heat of a fire by cover concrete.

Wall exposed to fire on one side ηfi = 0.35

ηfi = 0.7

30

b a

100 10

120 10

60

b a

110 10

130 10

90

b a

120 20

140 25

120

b a

150 25

160 35

180

b a

180 40

210 50

240

b a

230 55

270 60

2

3

4

Column 1 Note:

(1) ηfi = N*t/Nu see 4.6.2.

Table 4.3 of NZS 3101: 2006 gives effective slab thickness based on FRR for insulation, which also applies to partition fire rated walls. Table 4.9 of NZS 3106: 2006 is based on FRR for structural adequacy of load bearing walls where:

IB 93

Minimum dimensions (mm)

Fire resistance rating (minutes)

(2) For prestressing tendons the increase in axis distance given in 4.3.3 shall be noted. Source: NZS 3101:2006. Table 4.9 Fire resistance for structural adequacy for load-bearing walls

5

Fire Performance of Concrete and Masonry


The wall has the potential to collapse when the actions on the wall due to thermal bowing and Pdelta effect can lead to the wall’s capacity being exceeded effect – see Figure 3. Such a collapse into adjoining property risks placing fire crews or neighbours in danger. A base-cantilever-resisting mechanism is usually required to prevent collapse.

Concrete Masonry NZS 4230:2004 sets out design requirements for concrete masonry. These are based on British and European documents published by BSI and CEB/FIP. It gives minimum dimensions for walls, beams and columns based on structural adequacy and insulation. The effective thickness of partially filled masonry walls needs to be adjusted downward by dividing the net cross-sectional area of the wall by the length of the wall. Also, the cover depth for masonry walls has to be taken from the inside of the faceshell.

A wall connected to a very weak or flexible roof structure will need to be designed with a cantilever base connection. The design of the unprotected mild steel connections needs to be based on 30% of the yield strength of the exposed steel in ambient conditions. Components made from other types of steel shall use mechanical properties of the steel at 680oC. Details for FRR ratings and fixing of proprietary inserts are given in the standard. Adhesive (glued) anchors are have been found to behave poorly at elevated temperatures and need to be protected from fire.

However, it is over 6-years since NZS 4230 was published and more up to date material is available in Eurocode 6: Design of masonry structures Part 12: General rules-Structural fire design BS EN 1996 -12:2005. This standard is based on a tabular method for masonry structures. In the same way as Eurocode 2, the required wall thickness increases as the axial load increases. In addition, plastering of a masonry wall increases the effective fire rating.

Structural Fire Engineering The specialist discipline of structural fire engineering involves the knowledge of fire load, fire behaviour, heat transfer and the structural response of a proposed building structure. The application of structural fire engineering allows the use of a performance based approach using advanced calculation methods which lead to more economical, robust and innovative concrete buildings.

Figure 3: Deformation profile caused by heating one side of the wall

Analytical computer based modelling of whole buildings utilise the interaction between building elements which can result in structures being safer than calculated in design based on individual structural elements. For example, when a concrete slab expands under high temperatures to push outwards against its supports, a mechanical arching effect takes place in the slab. The compression generated in the bottom of the slab can greatly increase the load capacity.

Recent research has been carried out on slender panels by BRANZ and the University of Auckland owing to a concern of the high slenderness ratios of on-site and off-site precast panels being used in practice. A range of slenderness ratios from 30 to 75 were investigated. NZS 3101:2006 places a slenderness ratio limit of 75. Other maximum slenderness ratios have been proposed.

External Walls

INSURANCE AND FIRE DAMAGE

Section 4.8 of NZS 3101: 2006 gives particular requirements to prevent collapsing external walls outwards in a fire. The loadings code requires free standing external walls to be designed to resist a face load of 0.5 kPa in the after fire condition. When a fire occurs inside a building, the interior face of the wall heats up and expands while the exterior face remains relatively cool. Coincidentally the eccentricity of axial load on the wall causes additional deflections due to the P-delta. IB 93

A recent, independent European investigation on the cost of fire damage in relation to the building material from which houses are constructed used statistics from the Insurance Association in Sweden (Forsakrings Forbundet). The study was on large fires in multi-storey buildings in which the value of the structure insured exceeded €150k. The sample set was 125 fires which occurred between 1995 and 2004. The results showed that: 6

Fire Performance of Concrete and Masonry


ƒ

ƒ

The average insurance payout per fire and per apartment in concrete/masonry houses is around one fifth that of fires involving other materials (approx €10,000 compared with €50,000)

2.

Concrete and fire exposure. Bob Cather, Advanced Concrete Technology, Concrete Properties JB Newman, BS Choo (2003).

3.

A major fire is less than one tenth as likely to develop in a concrete/masonry house than one built in other materials

Post earthquake performance of passive fire protection systems. BRANZ study report SR147. BRANZ, Wellington (2005).

4.

Introduction to passive fire protection. BRANZ Bulletin 510. BRANZ, Wellington. (2008).

5.

Slender precast concrete panels with low axial load BRANZ design guide BRANZ, Wellington. (2007).

6.

Report to Department of Building and Housing – Review of design and construction of slender precast concrete walls. R Poole, DBH (2005).

7.

Eurocode 2: Design of concrete structures Part 1-2: General rules-Structural fire design BS EN 1992-1-2:2004, British Standards Association, UK.

8.

Eurocode 6: Design of masonry structures Part 1-2: General rules-Structural fire design BS EN 1996 -1-2:2005, British Standards Association, UK.

9.

NZS 3101:2006 Concrete structures standard. Standards New Zealand, Wellington.

Of the concrete houses that burned only nine per cent needed to be demolished whereas 50 per cent of houses built from other materials had to be demolished

ƒ

The time taken to repair a building after a fire is important in terms of downtime for commercial businesses. Concrete and concrete masonry buildings are generally easier and quicker to repair. In buildings subject to arson attack such as schools, the loss of contents and repair time is also critical. These losses can be significantly less in concrete and concrete masonry buildings. In the UK there have been a disproportionate number of fires in timber structures under construction. The fire load of a timber building being constructed is significant, and cannot be contained effectively until compartmentation is completed. In a concrete and concrete masonry structure the fire load during construction is significantly less.

10. NZS 4230: 2004 Design of reinforced concrete masonry structures. Standards New Zealand, Wellington.

CONCLUSIONS The excellent performance of concrete and concrete masonry structures in fire is widely accepted. The role of concrete in providing passive fire protection gives a significant advantage over steel and timber structures and provides a more robust solution to fire protection. The behaviour of concrete in fire is well understood, and is substantiated by a wealth of fire testing research data.

11. How to design concrete structures using Eurocode 2 – 12. Structural fire design. 12. AS 1530.4-05 2005 Methods for fire tests on building materials, components and structures (Part 4: Fire-resistance tests of elements of building construction). Standards Australia, Sydney, Australia.

Concrete design standards have historically been based on prescriptive data generated from fire tests. Eurocode 2 outlines an alternative approach based on computer simulation and performance based firesafety engineering. This allows a greater degree of flexibility in terms of sizing concrete elements for fire safety and will lead to the more efficient design of concrete and concrete masonry structures.

13. Resistance to fire and high temperatures. Portland Cement Association, Skokie, Illinois, USA.

ISSN 0114-8826 © September 2011. Cement & Concrete Association of New Zealand, Level 6, 142 Featherston Street, PO Box 448, Wellington, telephone (04) 499-8820, fax (04) 499-7760, e-mail admin@ccanz.org.nz, www.ccanz.org.nz.

SOURCES AND FURTHER READING 1.

Since the information in the bulletin is for general guidance only and in no way replaces the services of professional consultants on particular projects, no liability can be accepted by the Association by its use.

Concrete and fire safety. Concrete Centre, Camberley, Surrey, UK (2008).

IB 93

7

Fire Performance of Concrete and Masonry


Concrete

3

Economic, Social, Environmental

Concrete in Sustainable Development www.sustainableconcrete.org.nz


Contents 1

Introduction

2-

Cementing Our Future

6-

A Sustainable Life Cycle

10-1

Concrete and the New Zealand Economy

14-1

Concrete and You

18-1

Supporting Renewable Energy

20

Summary

21

References

Sustainable development implies meeting the needs of the present without compromising the ability of future generations to meet their own needs. 1987 Brundtland report of the World Commission on Environment and Development


Introduction Concrete is the most widely used construction material on earth. In many developed countries, concrete infrastructure comprises about 60% of the built environment.1 Concrete has shaped civilizations from as far back as Ancient Egypt and the Greek and Roman Empires. Today, it is indispensable in the development of infrastructure, industry and housing. Without concrete, the built environment would fail to accommodate our modern and demanding lifestyles. Given our reliance on concrete, it will inevitably play a major role in New Zealand’s ability to pursue sustainable development. The importance of sustainable development is currently dominating headlines, and as a concept is frequently defined as the practice of meeting present needs without compromising the ability of future generations to meet their own needs. The quest for sustainability has been compared with New Zealand’s nuclear free stance in the 1980s, and politicians have been enthusiastically pledging their support to make New Zealand the “first nation to be truly sustainable”.2 There is no question that sustainable development has been adopted as the philosophy to direct New Zealand’s way forward, and as a means to find solutions that provide the best economic, social and environmental outcomes. Produced from readily available raw materials, concrete’s strength, durability and versatility ensure it provides solutions for the built environment that

help achieve sustainable development. At its most basic, concrete is a mixture of aggregates and paste. The aggregates are sand and gravel or crushed stone; the paste is water and Portland cement. Portland cement is the generic term for the type of cement used in virtually all concrete. Cement comprises from 10 to 15% of the concrete mix, by volume. Through a process called hydration, the cement and water harden and bind the aggregates into a rock-like mass. With appropriate mix design, concrete can be tailored for any construction requirement. As outlined in the following sections, major efficiencies and innovations in the manufacture of cement and the production of concrete have been achieved over the past decades, while the CO2 absorption capabilities of concrete are beginning to be fully understood. The reuse of concrete structural elements is becoming more commonplace, along with the recycling of concrete as aggregate. Furthermore, concrete’s durability, thermal efficiency, acoustic performance, fire resistance and roading and stormwater management applications, will ensure that its contribution to a sustainable New Zealand construction industry continues to be significant. This publication seeks to demonstrate how concrete contributes to both this and future generations’ sustainable development, and will be of interest to architects, engineers, policy makers, contractors and clients, as well as others involved with the design, construction or operation of buildings and infrastructure.

Sustainable Development Triple Bottom Line

1


Cementing Our Future Over recent decades, there has been a significant drive towards sustainable practices in the cement sector. Production efficiencies have been introduced, along with the use of cement additives and alternative fuels. The development of new cements enabling depolluting and ultra-high strength concretes is ongoing, along with research into the CO2 absorption properties of concrete.

Industrial Ecology Considerable reductions in energy use (and therefore CO2 emissions) in New Zealand have been realised by improving the efficiency of the cement kiln operation, a significant energy user.

2

Alternative Fuels Cement manufacturers in New Zealand use alternative waste fuels for a substantial part of their operations, and are continually examining the practicalities of increased supplementation as part of their strategic operations. The environmental benefits of using alternative fuels in cement production are numerous. The need to use non-renewable fossil fuels such as coal is reduced. Using alternative fuels also maximises the recovery of energy from waste, reduces methane emissions, and saves landfill space by using a product that would otherwise not have an outlet.

Golden Bay Cement’s Portland cement plant near Whangarei is operating at world’s best practice for emissions management (Case Study 1). Further energy efficiencies and emissions control in cement manufacture are ongoing, as demonstrated by Holcim New Zealand’s use of used oil as an alternative fuel in kiln operation (Case Study 2).

Golden Bay Cement uses wood waste along with standard coal to fuel its Portland kiln. Wood waste is a cleaner burning fuel than coal, and has the potential for greater production efficiencies while at the same time decreasing carbon emissions. This is also a much more environmentally friendly way to dispose of wood waste, which would otherwise be sent to landfills.

The increasing use of supplementary cementitious materials (SCMs) to replace cement and therefore directly reduce embodied CO2 makes sound ecological sense. SCMs are derived from lower embodied energy, industrial by-products or waste materials, and can result in environmental benefits, improved concrete performance, and long-term cost advantages.

Golden Bay Cement has recently completed a partial redesign and technology upgrade to accommodate the change to mixed fuel use. Initially, wood waste fuel will account for some 10-20% of the company’s production energy needs. With further work planned at the plant, it is likely there will be an even greater replacement of coal as the prime energy source.

As the global cement industry seeks to reduce CO2 emissions per unit product produced, there has been a steady growth in the use of blended Portland cements containing SCMs. The most commonly used SCMs are amorphous silica, selected limestone, ground granulated blast furnace slag (waste from steel manufacture) and fly ash (waste from coal combustion).

Up to 20% of the total thermal energy requirement at Holcim New Zealand’s Westport Works has been routinely replaced by used oil, making possible a very significant reduction in the consumption of non-renewable coal. During 2006, about 13,300 tonnes of used oil, provided through the government-approved Used Oil Recovery Programme, was consumed in the kilns.


Case Study 1

Golden Bay Cement Portland Plant Redevelopment

September 2006 saw the completion of a four-year project to improve Golden Bay Cement’s Portland cement plant (near Whangarei). The redevelopment started in 2003, first by upgrading the kiln firing system, and then improving the clinker cooling and raw materials handling systems and installing closed circuit cement milling. The major upgrade programme has resulted in an increased capacity to meet the current and future cement demand of the local market. Clinker making capacity has risen from 1750 tonnes per day to 2600 tonnes per day, with an overall production capacity close to one million tonnes. This increased capacity will also offer the ability to look at developing further export opportunities, while ensuring the quality and consistency of cement manufactured at the Portland plant. The upgrade programme was also undertaken to improve health and safety at the plant through the introduction of new work practices using modern technology. As part of the improvement process, a team of occupational experts was commissioned to systematically document all the plant’s standard operating procedures. A careful analysis of the collected data has greatly assisted in establishing best practice. The plant is now performing to a more competitive level in terms of reliability and operational stability. The maintenance carried out will improve the collection of fugitive dust and reduce housekeeping requirements on site. The gas handling capacity of the kiln has been improved to reduce the visibility and volume of any adverse emissions affecting the environment, as well as improving the production process efficiency and minimising plant disruption. Golden Bay Cement has reduced the cement plant’s environmental impact, and is making a product with many sustainable advantages in its end use. The upgraded plant has fewer emissions and is more fuel-efficient: – a step in the right direction Towards Zero Harm.

World’s Best Practice – Golden Bay Cement’s Portland cement plant.




Cementing Our Future Depolluting (Photocatalytic) Concrete Depollution means the removal of contaminants and impurities from the environment. The newest tool for achieving depollution is a photocatalyst.

possess a unique combination of superior strength (compressive and flexural), ductility, aesthetic properties and durability. This enables the equivalent mechanical and load-bearing performance of conventionally built structures to be achieved, whilst requiring less raw material and primary energy, and generating fewer CO2 emissions.4

Photocatalysts accelerate the chemical reaction whereby strong sunlight or ultraviolet light decomposes organic materials in a slow, natural process.3

CO2 Absorption

When used on or in a concrete structure, photocatalysts decompose organic materials, biological organisms, and airborne pollutants. Dirt, soot, mould, bacteria and chemicals that cause odours are among the many substances that are decomposed by photocatalytic concrete. These compounds break down to have a minimal impact on the environment. Titanium oxide (TiO2), a white pigment, is the primary catalytic ingredient, and can be incorporated in the cement manufacturing process. When activated by the energy in light, the white pigment creates a charge that disperses on the surface of the photocatalyst, and reacts with external substances to decompose organic compounds. Photocatalytic concrete has other environmental benefits, such as reflecting much of the sun’s heat and reducing the heat gain associated with dark construction materials. This keeps cities cooler, reduces the need for air-conditioning and reduces smog. Designing projects with photocatalytic precast concrete also helps to promote aesthetic endurance, keeping the structure looking like new over time.

Ultra-high Strength Cementitious Materials Recent developments in ultra-high strength cement materials have enabled the realisation of slender and more elegant forms, more visually appealing surface finishes, and lighter and more durable materials with longer service lives and lower maintenance costs. Construction materials developed using ultra-high strength cement

4

Recent research confirms that the carbonation of concrete is a mechanism that counters much of the CO2 emissions resulting from the original manufacture of cement.5 Upon exposure to air, concrete and concrete masonry have the potential to absorb (sequester) atmospheric CO2. Concrete’s absorption of CO2 can occur either through the use of CO2 curing technologies in the manufacture of pre-cast concrete products, or as a natural carbonation process that takes place over time. In both cases, the fundamental mechanism for CO2 absorption is carbonation, which occurs during the service life of a structure and particularly after demolition. Even highly durable concrete with low permeability will sequester CO2 rapidly when the structure is eventually demolished and recycled. Traditionally, the carbonation of concrete has been associated with negative issues such as alkalinity loss and corrosion of reinforcement. However, these issues can be easily dealt with by appropriate design. As carbonation has the potential to reduce the net CO2 emissions of cement-based materials, it should be considered in life cycle analyses, and will also have a significant effect on the criteria for environmental labeling of cement-based materials. Further international and New Zealand-based study is still required to accurately quantify the carbonation of concrete as a mechanism to mitigate CO2 emissions. However, the concept that the world’s concrete infrastructure could provide the single largest human-made carbon sink has genuine scientific merit.


Case Study 2

Holcim New Zealand Environmental Initiatives

Holcim New Zealand is firmly committed to the principles of sustainable development in its use of natural resources, and has made a significant effort towards achieving the highest possible level of environmental performance. The following initiatives demonstrate this commitment, and were integral in Holcim New Zealand recently being awarded ISO 14001 certification – an international standard specifying the requirements for an effective environmental management system.

Westport Works – CO2 Reduction Using Alternative Fuels Ten years of environmental monitoring data was recently reviewed by Holcim New Zealand. Emissions test data for the kilns operating with coal alone was compared with emissions data from the kiln where used oil is co-processed with coal.6 The results confirmed that co-processing of used oil has helped reduce the emissions of CO2 at Westport Works when compared with using only coal for process heat. Furthermore, it had little other effect on kiln stack emissions, which were well within international limits.

Westport Quarry - Long-Term Rehabilitation Holcim New Zealand’s Westport quarry recently won the 2007 Aggregate and Quarry Association’s Environmental Excellence Award for quarry rehabilitation.

Environmental Monitoring at Holcim (New Zealand) Ltd Westport Works. The rehabilitation concept is based on four key sustainable principles: 1) Rehabilitation should mimic natural forest regeneration; 2) Direct human contact is to be minimised; 3) Rehabilitation will be concurrent with quarrying operations; and 4) Cost must be well managed. The land being restored has been divided into zones based on their specific ecological make-up. The most ecologically sensitive of these is the coastal restoration zone adjacent to the endangered New Zealand fur seal and little blue penguin colonies.

The project reflects Holcim New Zealand’s long-term commitment to environmental performance, and was initially designed in the 1980s to mitigate the visual impact of quarry operations. However, its objectives quickly grew to incorporate biodiversity aspects of the quarry and its surroundings – these include indigenous forest, a lake within the area of the quarry workings and adjacent wetlands.

The project has had scientific input from its earliest stages through the School of Forestry at Canterbury University. The university supervised projects assessing the re-establishment of native species in the quarry environs and has presented reports on the success of the quarry so far. This work will form the basis for ongoing monitoring work to provide a long-term understanding of the results of the programme and hopefully establish the site as an important example of rehabilitation.

The overall goal of the rehabilitation is to restore a mosaic of indigenous forest and wetlands, with 60ha of the total 100ha area so far converted into regenerating and rehabilitated growth.

The additional resources provided and commitment of Holcim employees over the past 20 years has been an example of dedication and continuing effort.




A Sustainable Life Cycle As with other construction materials, concrete has a life cycle that begins with its creation. However, as a result of its durability, the service life of a concrete structure is prolonged, and once the structure is no longer needed, it can be recycled as aggregate or its structural elements reused.

Recycling The ready mixed concrete industry is reducing its environmental loading through a series of initiatives and process efficiencies. Many ready mixed concrete producers use recycled water, extracted from their production operations. Additionally, the extensive use of water-reducing admixtures typically enables water reductions of around 10% and a corresponding reduction in the use of cementitious material. With enhanced understanding of the impact of water and waste disposal, there has been considerable progress in reducing wastewater discharge across the industry’s production facilities. It is now common practice to use chemical wash waste systems and aggregate reclaimers to minimise wash waste and water from the cleaning of truck-mixer bowls and plant. In some New Zealand urban markets, most notably Auckland, the supply of virgin aggregate is becoming limited.7 As a result it is now viable to establish recycled concrete aggregate facilities in these regions. These plants are able to accept, process and on-sell recycled concrete aggregate. Recycled concrete aggregate is separated from its recyclable reinforcing steel, and can be processed into specific aggregate sizes. The New Zealand Green Building Council has recently launched Green Star NZ, an environmental rating system for buildings. Green Star NZ awards points within its environmental impact categories for the incorporation of recycled materials in construction projects. As such, when a concrete structure is eventually demolished (most probably as it has no further use

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rather than failure due to age), the demand for recycled concrete as an aggregate source for structural concrete will increase from those seeking maximum Green Star NZ certification.

Reuse and Deconstruction Potentially, the greatest recovery of the energy and material resources embedded in a building can be derived from the reuse of the complete structure.8 Adaptive reuse means that the building is fit for a new use after it is no longer needed for its original use. Concrete buildings, especially those that employ frame structural systems, are well suited to this type of conversion. In most cases, the concrete structure will not require secondary fireproofing or acoustic treatment. If a concrete building cannot be used in its complete form at the end of its life, then it can be deconstructed. Deconstruction is the partial or complete disassembly of an existing building and elements within it, to be reused in another building. It differs from demolition in that the building components are still in their original component parts.

Self-compacting Concrete (SCC) SCC is defined as “a concrete that is able to flow under its own weight and completely fill the formwork, while maintaining homogeneity even in the presence of congested reinforcement, and then consolidate without the need for vibrating compaction�.9 The noise associated with the compaction of conventional concrete can be significant. SCC affords quiet casting and the environmental loadings from noise are therefore reduced. It also eliminates the issue of blood circulatory problems caused by the vibration of concrete. SCC affords the designer greater flexibility in designing complex shapes. It is independent of the quality of mechanical vibration and therefore provides homogeneity leading to improved durability and potential for reuse.


Case Study 3

Golf Links Road, Christchurch New Zealand’s First Recycled Road

Internationally, recycled roading materials are widely used. Previously regarded as waste products, the new trend has demonstrated that certain recycled materials, particularly crushed concrete basecourse, are cost-effective and can outperform natural materials. In late 2003, Fulton Hogan sought the support of Christchurch City Council to help showcase the attributes of recycled materials in New Zealand. The objective was to minimise environmental impacts and encourage sustainable outcomes in the roading industry. A 300m-long stretch on Golf Links Road in Christchurch was chosen as the site for New Zealand’s first “green” road, using 100% recycled materials. Golf Links Road is a busy section of road behind a shopping mall, with high numbers of heavy service vehicles. Using recycled materials on this road has provided a true test of their constructability and durability. After extensive research, crushed concrete and recycled asphalt were chosen as the most appropriate materials to use in construction of the road – both readily available and commonly used in other parts of the world. The road was completed in June 2005 and is made up of 3000m3 of concrete, including a sub-base of AP65 crushed concrete, and a base of AP40 crushed concrete. The top layer was made of recycled asphalt, using material from the millings of other job sites that was reheated and constituted into 15mm-thick asphalt. One of the major challenges the Fulton Hogan team faced was ensuring that the concrete was substantially free from contamination by other building products, such as plastic, brick and timber. The Golf Links Road project offered significant environmental and economic benefits. It proved recycling can deliver a huge reduction in the dumping of used concrete and asphalt, as the materials can be used repeatedly as roads are replaced. Significant cost savings can also be achieved. In addition, the use of recycled materials saves on non-renewable natural resources, such as quarry aggregate and petroleum-based bitumen.

Golf Links Road, New Zealand’s first recycled road in development. Recycled materials also offer performance benefits, as the residual cement content of the crushed concrete means it may have higher strength and can perform better than natural aggregate. In addition, the extra water required for compacting crushed concrete means it is well suited to winter construction, when the weather is not suitable for other materials. When comparing the cost of materials used in isolation using recycled materials for the project had a small additional cost compared with the cost of using conventional materials. However, this does not take into account a whole of life consideration for the disposal of the materials involved, which would significantly increase the overall cost of using conventional materials. The Golf Links Road project shows that the use of recycled crushed concrete and reclaimed asphalt product offer a high-strength solution, together with the additional benefits of cost reduction, higher performance, and suitability for winter construction.




A Sustainable Life Cycle Cement Stabilisation Stabilisation is the improvement of a soil or pavement material usually through the addition of a binder or additive. The use of stabilisation means that a wider range of soils can be improved for bulk fill applications and for construction purposes. The most common method of stabilisation involves the incorporation of small quantities of binders, such as cement, to the aggregate. Stabilisation is used widely in both the construction of new roads and the rehabilitation or recycling of existing roads worldwide. It is used partly as a response to increasing traffic volumes and axle loadings that contribute to premature pavement failures, and partly where other roading materials are unavailable or the cost of material cartage is prohibitive. The advantages of using in situ stabilisation techniques to upgrade or recycle existing materials in deteriorated pavements include cost savings of between 30 and 50%, faster rehabilitation, maximisation of materials, and reduced noise and dust pollution.10 Compared to other rehabilitation alternatives, in situ stabilisation also saves on landfill space as excavated materials do not need to be disposed of, and minimises the quarrying of replacement materials, which are finite resources. The other benefits of using cement stabilised roading include reduced rutting, the ability to produce smoother and longer lasting riding surfaces which result in lower fuel usage for transportation, a reduction in the layer thickness and lower maintenance. Recent applications of cement stabilisation in New Zealand have taken place on SH16 in Rodney, and between Hicks and Poverty Bays on SH35. By allowing premium aggregate to be preserved, and by using marginal aggregate, cement stabilisation’s ability to prolong the service life of

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New Zealand’s roading network is completely in tune with the principles of sustainable development.

Reinforcing Steel Pacific Steel, New Zealand’s only reinforcing steel manufacturer, is the primary user of recycled scrap metal in New Zealand, converting more than 280,000 tonnes every year into reinforcing elements for the construction industry. This equates to approximately 265,000m3 of saved landfill space. Every year some 90,000 car bodies that would otherwise have been left to rust away, polluting the environment, are recycled. The carbon in end-of-life tyres is also utilised by Pacific Steel. Carbon is an important ingredient in steel making, and the opportunity exists to substitute carbon from pulverised coal with tyre-derived carbon. Historically, end-of-life tyres end up in landfills or littering the landscape. Therefore, by using the carbon in about 3000 tonnes of tyres annually, Pacific Steel’s steel-making process is helping to eliminate a problematic source of waste. Water, air, energy and storm-water controls are also in place at Pacific Steel. It is interesting to note that the Stubbles Report, an independent body of work commissioned jointly by Fletcher Building and the New Zealand Climate Change Office, recognises that Pacific Steel’s operation converts scrap metal to reinforcing products as efficiently as any similar international mill. These recycling initiatives and environmental controls not only reduce waste, but the local production also eradicates the CO2 emissions that would arise from importing reinforcing steel into New Zealand. Pacific Steel’s operation is an example of the potential synergies between manufacturing industries and the sustainable use of natural and physical resources.


Case Study 4

Precast Concrete Car Park Building Designed for Deconstruction and Reuse

Worldwide Parking Group Ltd has developed an innovative precast concrete system for car parking buildings around New Zealand that offers a range of benefits, from design versatility and speed of assembly through to the potential for reuse on other sites. The precast concrete system’s most striking feature is the patented demountable connections, which mean that at any given point in time, the structure’s standard components can be dismantled and removed from the site for storage or re-erection on another site. The technology refines established multi-storey, precast concrete technology by incorporating patented seismic connections and foundation systems, and new concrete mix designs, reinforcement and casting techniques. Rationalising component sizes has also led to efficiencies in cost and planning. The system uses standardised precast concrete structural components that are assembled without the need for poured or welded connections, utilising patented reinforcement and connections. Innovation in the design of services, structural framework, fixtures, fittings and equipment, also make it possible to achieve rapid and orderly construction. The precast concrete system was used in the construction of the Nuffield Street car parking building in Newmarket, Auckland. The building has four levels, with provision to add more car parks through the addition of another floor. The car parking building has about 320 components, manufactured offsite by Stahlton Prestressed Concretes, Wilco Precast Ltd and Stresscrete. The components include columns, spandrels (which support the floors and act as handrails), and 18-tonne double-T floor pieces, measuring 2.5m wide and 16.7m long. The simple design involves placing the spandrels in rebates on the columns, with the double-T beams sitting over, and being bolted to the spandrels.

Assembly of the car parking building at Auckland Airport. The Nuffield Street car parking building is the third Worldwide Parking Group system project completed in New Zealand, following the construction of two domestic terminal car parking structures at Auckland International Airport. The airport was seen as an ideal location to showcase the system’s advantages as the buildings can be dismantled and re-erected as the airport’s plans require. The first domestic terminal car parking building was completed in April 2004 after a three-month construction period and is a single storey structure for 300 car parking spaces. The first building has performed well and has led to significant developments in the precast concrete system, which have been adopted in the construction of the second domestic terminal car parking building. These innovative structures will become a more familiar sight as specifiers become aware of precast concrete’s lifecycle cost advantages. Pre-engineered standardised concrete components ensure a low cost outlay, fast assembly, early occupation, minimal maintenance and potential reuse – all benefits which are attractive in a construction environment concerned with sustainability.




Concrete and the NZ Economy The cement and concrete industry plays a substantial role within the New Zealand construction sector, which itself is crucial to the country’s overall economic wellbeing. During 2005 and 2006 the economy, as measured by GDP, grew by an average of 2.05%. The value of all New Zealand building consents issued in 2006 was $11.18 billion, an increase of 2.2% over the previous year. As the New Zealand economy grows, so too does the construction industry, and in turn the demand for concrete. Concrete’s whole-of-life cost advantages, based on its inherent properties, also contribute considerably to New Zealand’s sustainable economic development.

Local Reources The cement and concrete industry has impressive credentials in terms of its use of materials that are extracted and manufactured within New Zealand. This is in line with the increased demand for building materials (and products) that are sourced and processed locally, thereby creating jobs and reducing the environmental impacts resulting from transportation. New Zealand is virtually self-sufficient in concrete, and the associated materials required for its production. Along with the fact that ready mixed concrete is generally produced within close proximity to where it is cast, this means that concrete more than meets the sustainable development principle of products being consumed near to the place of their production.

Household Economy The thermal capacity of concrete and concrete masonry, often referred to as its thermal mass, enables it to absorb, store and later radiate heat. Exposed concrete can absorb heat during the daytime, reducing temperatures by 3° to 4°C, and delaying peaks in temperature by up to six hours.11 During the night, natural ventilation is used to cool the concrete, priming it for the next day.

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Some 90% of the total energy used in buildings is for heating, cooling and lighting. Employing the thermal mass of concrete can reduce or even eradicate energy-intensive airconditioning, while maintaining a comfortable temperature for occupants. To optimise concrete’s thermal mass, it must be used in conjunction with higher thermal insulation, window placement for good solar gains and natural ventilation as part of an integrated and sustainable passive design. There has been extensive research modelling the performance of thermal mass in residential housing under New Zealand environmental conditions.12 Thermal mass can also be effectively used in the commercial sector, with the Maths and Computer Science Building at Canterbury University an excellent example. The use of concrete and concrete masonry in homes enables reduced energy consumption for heating through improved air-tightness. Further financial savings can be achieved as a result of concrete’s ability to reflect natural light and therefore reduce the need for artificial lighting.

Building Rating Systems The New Zealand Green Building Council’s Green Star NZ rating system is used to assess the environmental impact of offices against eight environmental impact categories, plus innovation. Within each category, points are awarded for initiatives that demonstrate a project has met sustainable development objectives during the different phases of a building’s development (design, fit-out and operation). Points are then weighted and an overall score is calculated, determining the project’s Green Star NZ rating – 4 Star = Best Practice, 5 Star = New Zealand Excellence, and 6 Star = World Leadership. Although a relatively new initiative, Green Star NZ is being widely recognised and accepted by the construction industry. Owners, operators, and their clients and tenants are being driven by the desire for “green certification” of a building, which will provide opportunities for the sustainable attributes of cement and concrete to be recognised.


Case Study 5

Meridian Energy Building – Wellington Waterfront Concrete Core to Sustainable Building Design

In December 2004, Meridian Energy identified the need for larger premises, and initiated a project to develop office accommodation that met its immediate and long-term operational needs, and reflected its commitment to renewable energy and sustainability. The construction project adopted Ecologically Sustainable Design (ESD) objectives to ensure the Meridian building would respond to and utilise external environmental conditions. To help achieve the ESD objectives, designers referred to the Australian Green Star office building rating tool. The designers’ efforts to optimise energy use and year-round comfort included extensive use of natural light and ventilation, as well as insulation. In the building, solar gains are controlled by active shading systems, while the natural air supply is sourced entirely from the outdoors. These innovative features have been integrated into an overall passive design through the thermal mass properties of the building’s concrete shear wall core and other exposed concrete surfaces. The designers of the Meridian building were aware that concrete walls, columns and floors have the capacity to store and release heat. This function has the effect of regulating the internal environment by reducing and delaying the onset of peak temperatures, to create healthy working environments for the occupants and reduce energy consumption costs for building tenants and owners. This can also be cost-effective if the concrete utilised is already part of the building’s structural components. The use of exposed concrete as part of an integrated passive design to achieve low energy thermal comfort has been widely used in commercial offices throughout the UK and Europe. The Meridian building’s focus on ESD, and its profile at the forefront of sustainable building design, should increase the understanding and appreciation of concrete’s thermal mass properties within New Zealand.

Meridian Energy building on the Wellington waterfront. The Meridian building’s ESD credentials have also been increased by the use of Holcim New Zealand’s Duracem. Duracem is blended cement with an iron blastfurnace slag content of around 65%. The decision to utilise concrete containing a supplementary cementious material enabled a reduction in the Portland cement content and therefore an increase in the building’s “green” rating. Used in the Meridian building’s jump-formed concrete shear core and the external precast elements, Duracem’s unique blend reduced the permeability of the concrete, inhibiting chloride ions from reaching and corroding the reinforcing steel, and therefore preventing any resulting expansion, cracking and spalling of the concrete. Duracem cement was also used in the Meridian building’s concrete piles, which are submerged to a depth of around 18m. The Meridian building has created a new environmental performance benchmark for New Zealand’s commercial buildings. To help realise the objectives of their sustainable design philosophy, the building’s planners have looked towards concrete’s thermal mass properties and the benefits of concrete incorporating an SCM, such as blastfurnace slag.

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Concrete and the NZ Economy Concrete Roads Roads play a very important part in any nation’s infrastructure. Their construction and maintenance, and the vehicles that travel over them, consume large amounts of energy. This energy use results in atmospheric emissions, the reduction of a non-renewable resource, and other environmental impacts. Any reduction of the lifetime energy use associated with roading, even if only by a small percentage, will have significantly positive implications for sustainable development. Concrete roads are durable and safe. They are considerably less prone to wear and tear defects like rutting, cracking, stripping, loss of texture, and potholes that can occur with flexible pavement surfaces. This low maintenance requirement is one of the principal advantages of concrete pavements. There are well-designed concrete pavements that have required little or no maintenance well beyond their 40-year design lives. Less maintenance also means fewer traffic delays, a huge advantage on some of our already congested highways. Fuel consumption is a major factor in the economics of roading, with the rolling resistance of the pavement being an important contributor to the fuel consumption and the corresponding CO2 production. Rolling resistance can be attributed in part to a lack of pavement rigidity. In the case of a heavily loaded truck, energy is consumed in deflecting a nonrigid pavement and sub-grade. Using rigid concrete pavement will result in less fuel consumption, and a decrease in associated emissions.13 In New Zealand, concrete pavement, such as the Peanut Roundabout near the Port of Napier (Case Study 6), is currently restricted to areas requiring high-strength roading components. This is mainly as a result of first-cost rather than a whole-of-life cost approach. The lifetime costs of concrete roads are, however, lower than asphalt.

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Another benefit of using concrete as opposed to alternative flexible pavements is a reduced need for street lighting, due to higher surface reflectivity after dark. Better light reflection on the brighter surface could potentially result in electricity savings of about 30% for lamps, lampposts and signs.14 However, the largest savings from higher surface reflectivity are to be gained from a reduction in accidents, and the associated loss of life and serious injury.

Concrete Road Barriers The benefits of concrete road barriers make them a suitable and affordable alternative to wire median barriers. Concrete road barriers can easily meet the performance criteria required for New Zealand’s roading infrastructure, as evidenced by recent developments from overseas. Developed in the Netherlands, the Concrete Step Barrier (CSB) has proven successful in preventing dangerous motorway accidents where the central barriers have failed to restrain a crashing vehicle from crossing over into the face of oncoming traffic.15 Their profile design minimises injury by redirecting the vehicle along the direction of the flow of traffic. Concrete barriers also require less working width in the central reserve than other barrier systems, allowing motorway lanes to be increased in number without major planning and traffic disruption. A whole-of-life cost analysis carried out by the UK Highways Agency, which has recently specified CSB, concluded that the it offered substantial benefits in terms of safety and cost. CSB is designed to achieve an essentially maintenance free serviceable life of not less than 50 years.


Case Study 6

Peanut Roundabout – Port of Napier Concrete Roads for Low Speed, High Stress Applications16

Concrete is often used on industrial pavement sites within New Zealand that have high volumes of heavy traffic. However, the initial cost to the public roading network of using concrete has meant that bitumen-bound materials have been preferred. Even so, short sections of concrete pavements in high-stress areas can provide a long-term solution with minimal maintenance. Therefore, Transit New Zealand is now trialling short concrete road sections to take advantage of the superior strength and robustness of concrete. The Peanut Roundabout in Napier is an example of a trial site that is part of Transit New Zealand’s programme. This section of SH50 carries most of the fully laden trucks bound for the Port of Napier and has a history of surfacing distress due to the tight curvature and high volumes of heavy vehicle traffic. The brief for the project was to design and construct a sound and rigid concrete pavement that provided adequate skid resistance for the traffic environment. In addition, construction of the road had to be finished with minimal delays to the travelling public. Construction of the roundabout was completed in just five days. On the first day, the existing pavement was removed and stockpiled, the subgrade prepared and the proof rolled. On day two, the stockpiled pavement was stabilised and the surface prepared for concrete. On day three, the road was concreted and cured. Concrete with a compressive strength of 30MPa was used along with mixed grades of sealing chip and crushed aggregates. Polypropylene and structural synthetic fibres were used to reduce plastic shrinkage and increase flexural strength. The concrete was screeded by hand, delivered at 60mm to 80mm slump, and superplasticised to around 110mm in order to achieve the desired workability. Poorly designed and constructed joints can lead to differential

Peanut Roundabout – Port of Napier. settlement. To overcome this, dowelled joints at 200mm centres were employed at regular 5m intervals transversely along the road to suit the road geometry. The concrete was poured directly up to the cut edges, with no local thickenings or slab anchors used. On day four the joints were saw-cut, and on day five the line marking was completed, and the road opened once adequate concrete strength was confirmed. Since the roundabout was completed, the pavement has performed well – no cracking is visible and no differential settlement is evident. Expected wearing of the surface has occurred in the running path, while in the low-speed environment skid resistance is not compromised. The use of concrete in road pavements is a practical way of providing a long-term durable solution for highly stressed local sections of roads. As demonstrated by this trial site, a sound pavement structure, adequate surface texture, and constructability during a short time period can all be achieved with the use of concrete.

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Concrete and You As daily life becomes more hectic with increasing demands placed on our time, we all crave a peaceful home environment as respite from the outside world. Concrete’s inherent properties of durability, strength, thermal mass, fire and acoustic performance, along with its suitability for storm-water management applications, make it an ideal construction material to keep our families safe, secure, warm and dry.

Durability and Longevity Concrete and concrete masonry endures. As a highly durable construction material with low maintenance requirements, well-designed concrete structures can be expected to exceed their minimum service life as specified in the New Zealand Building Code, and in some cases last for centuries (Case Study 7). Over recent decades, technological advances have led to high performance concrete that can be engineered to suit the most demanding specifications. Concrete’s long life means it is more likely that a concrete building will come to the end of its life because no further use can be found for it (social or economic obsolescence), rather than the concrete having failed due to age. As such, concrete’s durability allows for the chance to repeatedly strip the building back to its structural framework for redesign and refurbishment, after the initial use of the space has passed. Concrete foundation elements from one building can also be reused for another application in a new building. Concrete also has the ability to resist extreme weather events such as flooding, which is predicted to become a more common occurrence in New Zealand as a result of climate change. Concrete’s water resistance makes quick re-occupancy possible as cleaning, drying and repair are minimised. This has economic as well as social and environmental benefits.

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Comfort The World Health Organisation recommends a minimum indoor temperature of 16ºC to reduce the risk of respiratory infections.17 Concrete’s thermal mass helps maintain temperatures above this level. In a concrete structure, temperatures are less likely to drop below 9ºC, a level where there is an increased risk of dust mites and allergens. Concrete walls also tend to remain at a more stable temperature, reducing condensation and thereby minimising mould and fungi growth.

Fire Performance Concrete structural elements are known to have good inherent fire performance. Concrete is non-flammable, noncombustible, and more robust in fire than other structural systems as it can absorb a greater amount of heat before reaching critical overload. Concrete simply cannot be set on fire. As it does not burn, concrete does not emit any environmentally hazardous smoke, gases or toxic fumes. In addition, unlike some plastics and metals, concrete will not drip dangerous molten particles. Concrete also acts as an effective fire shield as its mass confers a high heat storage capacity while its porous structure provides a low rate of temperature rise. The majority of concrete structures are not destroyed in a fire, and can therefore be repaired easily, minimising inconvenience and cost. Everyone from private owners and insurance companies, to local and national authorities, share the economic benefits of fire safety, and its contribution to the sustainable upkeep of critical infrastructure. Concrete’s superior fire performance also ensures that buildings remain stable during fire. This enables occupants to survive and escape, while also allowing emergency services to work safely.


Case Study 7

The Pantheon – Rome Built to Last Millennia

Almost 2000 years old and virtually intact, the Pantheon in Rome stands as testament not only to the engineering skill of an Empire that accelerated the development and application of concrete, but also to the durability of concrete as a sustainable construction material. The Pantheon (“Temple of all the Gods”) was originally built as a temple to the seven deities of the seven planets in the state religion of Ancient Rome. Built of concrete, it has been in continuous use throughout its history, and is the best preserved of all Roman buildings. The Pantheon’s massive portico, consisting of three rows of eight columns, leads to the rotunda, upon which rests the building’s most distinctive feature – its 43.2m-domed concrete roof. In order to support the dome, eight-barrel vaults in the massively thick 6.4m rotunda wall carry its downward thrust. In the absence of steel reinforcing, the dome’s weight was minimised through several design features. The dome is configured as five rows of 28 square coffers that diminish in size as they approach the central 8.7m diameter opening (oculus) at the top of the dome. The coffers not only enhance the aesthetic of the building, but more importantly they reduce the thickness and therefore the weight of the concrete dome. At its base the concrete dome is more than 6m thick, but diminishes to about 1.2m at the edge of the oculus. Also crucial to the dome’s reduced weight are the variances in the type of concrete. Towards the oculus, unglazed to further reduce the dome’s weight, a much less dense concrete mix was used containing a relatively light pumice aggregate. While the Romans cannot be credited with the invention of concrete, an honour belonging to the Egyptians, they were certainly instrumental in its large-scale uptake. This adoption is based upon the use of volcanic ash from near Pozzuoli, which when combined with lime resulted in a concrete far stronger than anything previously produced.

Pantheon - Rome. Pozzolanic cement, as the material became known, quickly established itself as a core construction material in all large-scale Roman construction projects. The theatre at Pompeii, built in 75 BC relied heavily on concrete, as did the Colosseum, built around AD 82. As the largest and most iconic of Roman amphitheatres, the Colosseum made use of dense concrete in its foundations, as well as lightweight concrete in its numerous arches and vaults. Hundreds of examples of Roman structures made using concrete still stand today, ranging from magnificent temples and sporting arenas, to functional bridges, aqueducts, reservoirs and sewers. There are even instances of the underwater use of concrete in Roman breakwaters. Their continued existence today embodies not only the enterprise and innovation of their creators, but also the long-term durability of concrete. Concrete technology has undoubtedly developed over the centuries, but it is not a coincidence that the designers of Te Papa, New Zealand’s national museum, chose concrete as its structural material to achieve a 350-year expected life without significant maintenance.

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Concrete and You Robust and Secure

Storm-water Management

Concrete will not rot, rust or corrode. In fact, concrete actually gets stronger throughout its life. Reinforced concrete, with its capacity to accommodate alternative load paths, is ideally suited to New Zealand’s seismic conditions.

There are many opportunities where concrete products can be used to improve storm-water control. The amount of impermeable land is increasing, and as it grows so too does the amount of storm-water that flows along its surface as run-off.

Concrete’s high resistance to wear means less maintenance, which is particularly important as the consequences of global warming have led to more extreme weather patterns. In certain regions of the world, concrete’s ability to withstand increasingly severe storm events has led to a surge in concrete construction.

How storm-water is managed has a tremendous effect on pollution levels in streams, rivers and lakes as it contains sediment that strips nutrients from the land, and pollutants such as pesticides from agricultural land, bacteria from livestock wastes, and fuels and oils from vehicles. Excessive storm-water also reduces groundwater recharge and therefore diminishes aquifer supplies.18

In the path of unpredictable and violent climatic conditions, concrete buildings offer their inhabitants added security from debris. Concrete’s virtual impenetrability also contributes to community and personal safety, as it can withstand willful damage and resist arson.

Acoustic Performance The sound insulation and acoustic performance of buildings has grown in importance over the past decades due to the trend for inner-city apartment living and multi-unit housing complexes. The proliferation of high-powered entertainment systems has also placed unprecedented demands on housing in terms of its acoustic performance. Due to its high-density, concrete has advantages over lightweight construction materials in various aspects of acoustic performance, specifically reducing airborne noise transmission, reducing noise from exterior sources and providing sound separation between adjoining rooms. While exposed concrete may heighten impact sound, various integrated design solutions have been developed to address the problem of incorporating an adequate degree of acoustic absorbency without reducing the thermal functionality of an exposed concrete surface. The overall sustainability implications of concrete’s acoustic absorption properties lie in the potential to enhance building occupants’ productivity, health and wellbeing.

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The use of pervious (also referred to as permeable) concrete and pervious concrete pavers can play an important role in an overarching management strategy to mitigate the environmental impacts of storm-water. This role is based on their ability to allow rainwater to drain through the paved surface in a controlled way into the ground before being released into sewers or waterways. Their applications can be as diverse as drives, paths, general landscaping or other hard surface requirements. Low impact design is an approach for site development that protects and incorporates natural site features into erosion and sediment control and storm-water management plans. This new approach contrasts with the conventional approach of discharging storm-water directly to large scale piped systems. These systems mimic natural drainage regimes and improve visual and amenity forms. Whether of the conventional type or the turf block type, pervious concrete is a simple and effective means of reducing the amount of storm-water. Its use may reduce the necessity for other more expensive storm-water reduction measures, thus contributing towards sustainability, both environmentally and economically.


Case Study 8

Kaikoura’s Lyell Creek - Flood Protection System Functional and Aesthetic

Designed to protect Kaikoura from flooding, the Lyell Creek floodwall utilises the durability and versatility of concrete to create a piece of town infrastructure that is both effective and aesthetically pleasing. Kaikoura has been flooded 16 times since 1923, including the devastating Christmas Eve flood of 1993 that caused $12 million in damage and prompted a review of the town’s flood protection. After careful assessment of available reinstatement options, it was decided to provide a channel with the capacity to convey all the floodwater that could flow under the SH1 bridge to the sea. The challenge was to provide a flood channel through the backyards of shops and the most frequently used tourist area in the township. Given the very limited space available, and the requirement for increased flood capacity, a new continuous protective concrete wall was selected as the only practical solution to address flooding issues. Construction began in 2004 and was completed two years later. The project is the culmination of 10 years’ work by Environment Canterbury to provide better flood protection further upstream. The 400m-long wall has been designed to keep floodwaters out of the town. While the floodwall can contain a 160m3 per second flood, the foundations were designed to allow the height of the floodwall to be increased to match any future growth in flood capacity that could result if the state highway bridge was raised. The floodwall has numerous innovative features, such as a section with an adjustable weir installed, which will allow fine-tuning during floods to maximize flood capacity. Removable stop logs have also been incorporated to allow town floodwater back into Lyell Creek in the event that water gets into the town upstream at the state highway bridge. Where possible, the position of the wall has been adjusted to improve car parking and access to buildings. A wavy wall top was incorporated into the precast concrete panels, which along with an

Kaikoura’s Lyell Creek - Flood Protection System. exposed concrete aggregate surface decoration enhances the visual appeal and evokes the nearby seascape. With co-operation from Kaikoura District Council, the finished work also incorporates a concrete amphitheatre and a new concrete footbridge to the beachfront, which are well used by locals and tourists alike. Inviting the locals to choose the wording that would be cast into the concrete contributed to community ownership of the project. After consideration, the local runanga suggestion was adopted: “KI UTA KI TAI - The Conservation and Protection of the Mountains to the Sea”. Extensive consultation during the project revealed opportunities for associated community enhancements. The result is an innovative, flexible, cost-effective and aesthetically acceptable piece of infrastructure that relies heavily upon concrete to not only mitigate flooding, but also to foster civic beautification and social inclusion.

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Supporting Renewable Energy Supporting Renewable Energy As New Zealand’s population and economy grows, so too does its demand for electricity. With diminishing fossil fuels and an increased awareness of their environmental impact, the spotlight has fallen on renewable energy sources. Wind power is increasingly looked to as the renewable energy source of the future. The inherent properties of concrete can maximise production capacity through innovative and robust foundation design, as well as facilitating the construction of taller and stronger wind towers.19

Wind Farm – Concrete Foundations Concrete is well suited for use in a range of foundation types for both onshore and offshore wind towers. As turbines become larger, foundation costs become a significant proportion of the total cost of wind farm development and influence the overall cost of energy. Foundation design and selection of materials is therefore critical. Concrete foundations can be designed in a range of sizes, shapes and densities to optimise tower stiffness, foundation pressures, and reinforcement and formwork requirements. They can be designed as ground bearing or as a pile cap and can incorporate excavated material from site to maximise foundation stability and eliminate site waste.

Concrete Wind Towers With the anticipated growth in wind farms throughout New Zealand, increased emphasis will be placed on higher power outputs. To meet this demand, wind towers will have to become taller and stronger in order to gain access to more powerful wind currents and accommodate larger turbines and rotor spans. These requirements mean that concrete is the ideal construction material.

18

Depending on site conditions and accessibility, both in situ and precast methods of construction are suitable for concrete wind towers. In situ construction can assist to overcome a problematic site, while also requiring minimal form and space. Precast techniques enable high quality sections to be produced efficiently under controlled conditions. Flexibility of construction methods means concrete is suitable for demanding offshore installations. Gravity foundations can be constructed onshore and delivered for assembly using existing flat top barges. A similar procedure can be followed for the delivery of individual precast concrete sections of the pylon. Concrete’s high dampening properties can help reduce noise emissions and structural fatigue in wind towers. The use of concrete in gravity foundations also improves dynamic response, while the wind towers in-service performance can be optimised further through pre-stressing. Concrete wind towers may incur a greater initial investment than using alternative materials, but could prove extremely economical over their prolonged life due to durability and higher power generation potential. Pre-stressed concrete wind towers can also accommodate multiple futuregeneration turbine retrofits, thereby increasing service life. When constructing concrete wind towers, the levels of embodied energy and CO2 are significantly reduced in comparison with other materials, as is the period of operational time required to offset the energy consumed during their construction. As a durable and versatile construction material, concrete can facilitate taller and stronger wind towers which can help New Zealand meet its current renewable energy supply targets and in so doing contribute to sustainable development.


Case Study 9

Te Apiti Wind Farm Turbine Foundations - Design and Construction20

Te Apiti was Meridian Energy’s first New Zealand wind farm and is the largest in the Southern Hemisphere. The wind farm’s total installed capacity of 90MW generates enough clean, sustainable electricity to meet the electricity needs of approximately 45,000 homes. These large structures are now a striking feature on the local landscape. What is not so obvious is the concrete foundation that supports each structure. Prior to the construction of the wind farm, a comprehensive geotechnical investigation was undertaken by Opus International Consultants Ltd to determine the ultimate foundation bearing capacity and soil shear modulus. Foundations for wind turbines are low-frequency machine loaded structures subjected to coupled horizontal-rocking vibrations. Therefore, extreme loads, production loads and fatigue loads were all analysed during the design phase. To optimise the diameter and thickness of the pad, preliminary design studies were also undertaken with a simple rigid disk model.

Te Apiti Wind Farm.

Forces on the foundation pad were analysed using a model that indicated large variations in both bending moment and shear force across the width of the pad and these were averaged for design. Grade 500E reinforcement was used to provide the necessary flexural strength and to maximise fatigue resistance. The transfer of vertical forces from the tower steel shell into the concrete foundation via embedment of the cylinder was also resolved.

Due to the thickness of the foundations (2.55m maximum), they contain a huge volume of concrete. As such, there was a risk that large temperature rises associated with heat-of-hydration effects could result in thermal gradients across the depth of the pad sufficient to cause thermal cracking. The concrete supplier, Higgins Concrete Ltd, therefore designed a concrete mix to control temperature rises. This was achieved primarily by the partial substitution of the highly reactive Type GP cement with fly ash. The use of a larger 30mm aggregate also enhanced the strength properties of the concrete, and minimised thermal gradients.

Following the exhaustive design process, engineers selected a shallow gravity pad foundation as the most appropriate design for each of the 55 turbine structures at Te Apiti to rest upon. These concrete pad foundations are suitable for most ground conditions. The pads are a 16m wide octagonal shape with depths varying from 2.55m at the centre to 1.5m at the edges. Each pad contains 375m3 of 30MPa concrete and 28 tonnes of reinforcing steel. This is a total of 22,000m3 of concrete for the wind farm.

Te Apiti wind farm embodies a sustainable approach to the construction of infrastructure on many levels. It generates renewable electricity without producing greenhouse gases and therefore protects the environment. Concrete foundations guarantee long-term durability within a demanding environment, while the use of a supplementary cementitious material has reduced the Portland cement content of the concrete and further enhanced the project’s contribution to sustainable development.

19


Summary The need to strive for sustainable development is now recognised as a global imperative. Strategies that encompass economic, social and environmental solutions within an overarching holistic approach are required to ensure that future generations are not disadvantaged by current consumption patterns. Recognising the importance of immediate action, the cement and concrete industry of New Zealand has fully committed to the quest for sustainable development. Efficiencies and innovations during concrete’s manufacture, along with its inherent properties in a range of applications, ensure that concrete provides solutions to the built environment that help New Zealand achieve sustainable development. The question should not be, how sustainable is concrete? But rather, how sustainable is a world without concrete?

20

Wellington Writers Walkway.


References Mak, S.L. (1999). Sustainable use of concrete through carbon abatement and sequestration. Proceedings of the Int. Power & Energy Conf., Churchill, Victoria, Australia, 1999. 1

Young, S. Turnbull, S. & Russell, A. (2002). What LCA can tell us about the cement industry? An independent study commissioned by the WBCSD. 14

15

Rt. Hon Helen Clark. Speech notes for address to Buddle Findlay Sustainability Seminar. Wellington. (8/05/2007). Retrieved August 2007 from www.beehive.govt. nziPrint/PrintDocument.asDx?DocumentlD=29235 2

Chusid. Michael. (2006) Words you should know: depollution, photocatalysis photocatalysts keep concrete clean and depollute the air we breathe, Precast Solutions, Fall 2006.

Munn, C. (2006). Concrete road barriers key to safety on roads. Concrete, 50(1), 4.

Hart, Gordon & Johnson, Richard. (2006) Concrete roads for high stress applications. Proceedings of the Transportation and the Pursuit of Excellence, NZIHT & Transit NZ 8th Annual Conference. Auckland, New Zealand. 16

3

Lukasik, J.Damtoft, J. S., Herfort, D., Sorrentino, D. & Gartner, E.M. (2007). Sustainable development and climate change initiatives, Proceedings of the 12th International Congress on the Chemistry of Cement (ICCC). Montreal, Canada. 2007. 4

Danish Technological Institute. CO2 uptake during the concrete life cycle. (2006). Retrieved August 2007 from http://www.danishtechnology.dk/building/14460

Designing comfortable homes: guidelines on the use of glass, mass and insulation for energy efficiency. (2001). Wellington, New Zealand. Cement and Concrete Association of New Zealand. 17

Environmental Building News. (1994). Stormwater management – environmentally sound approaches. 3(5). 1-18. 18

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5

Halliday, L. Slaughter, G. Rynne, M & Bluett, J. (2007). Ten years of the New Zealand used oil recovery programme, Proceedings of the 14th World Clean Air and Environmental Protection Congress (IUAPPA). Brisbane, Australia. 2007. 6

Park, Stuart. (1999). Recycled concrete construction rubble as aggregate for new concrete. BRANZ SR 86. Porirua. 7

Gjerde, Morten. (2003). Deconstruction: helping to foster a sustainable concrete industry. Proceedings of the New Zealand Concrete Industry Conference. Taupo, New Zealand. 8

Self compacting concrete: a review. (Technical Report 62). (2005). Surrey, England: Concrete Society. 9

Wilmont, T. D. (1991). The recycling opportunities in the effective management of road pavements. Proceedings of the Local Government Engineering Conference, Hobart, Australia. 10

Designing comfortable homes: guidelines on the use of glass, mass and insulation for energy efficiency. (2001). Wellington, New Zealand. Cement and Concrete Association of New Zealand. 11

Gjerde, M. & Munn, C. (2003). A comparison of cost and thermal performance of concrete and lightweight housing systems In New Zealand, Proceedings of the 21st Biennial Conference of the Concrete Institute of Australia. Brisbane, Australia. 2003. 12

Jamieson, N.J. & Cenek, P.D. (1999). Effects of pavement construction on the fuel consumption of trucks. Options for a post millennium pavements symposium. New Plymouth. New Zealand Institute of Highway Technology. 1999. 13

Concrete wind towers. (2005). Surrey, England: Concrete Centre.

Davey, R. & Green, R. (2006). Te Apiti wind farm turbine foundations: design and construction. Proceedings of The New Zealand Concrete Industry Conference. Christchurch, New Zealand. 20

Further Reading Concrete Thinker (www.concretethinker.com) Sustainable Concrete (www.sustainableconcrete.org.uk) Concrete through the ages: from 7000 BC to AD 2000. (1999). Berkshire, England: British Cement Association.

Acknowledgements Golden Bay Cement (www.goldenbay.co.nz) Holcim (New Zealand) Ltd (www.holcim.com/nz) Pacific Steel (www.pacificsteel.co.nz) British In-situ Concrete Paving Association - Britpave (www.britpave.org.uk) Environment Canterbury (www.ecan.govt.nz) Fulton Hogan (www.fh.co.nz) Higgins Concrete Ltd (www.higgins.co.nz) Hiway Stabilizers (www.hiwaystab.co.nz) Meridian Energy (www.meridianenergy.co.nz) New Zealand Green Building Council (www.nzgbc.org.nz) Opus International Consultants (www.opus.co.nz) Worldwide Parking Group (www.worldwideparkinggroup.com)

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“We have not inherited the world from our forefathers - we have borrowed it from our children.� Kashmiri proverb

Cement & Concrete Association of New Zealand Level 6, 142 Featherston Street, Wellington, New Zealand ISBN: 978-0-908956-19-7 (paperback) First published 2007 ALL RIGHTS RESERVED. This document is entitled to the full protection given by the Copyright Act 1994 to the holders of the copyright. Reproduction of any substantial passage from the book, except for review or the educational purposes therein specified, is a breach of copyright of the author and or publisher. This copyright extends to all forms of photocopying and any storing of material in any kind of information retrieval system. All applications for reproduction in any form should be made to CCANZ, PO Box 448, Wellington, New Zealand. Since the information in this publication is for general guidance only and in no way replaces the services of professional consultants on particular projects, no liability can be accepted by the association from its use. Made with paper from a sustainable forest

www.sustainableconcrete.org.nz


RESIDENTIAL Floor Slabs Introduction Producing a good concrete floor slab is very easy if some simple rules are followed. Concrete used in residential slabs is often the most abused material we come across. This information is intended to assist builders produce a high-quality product at little additional cost to the prevalent practices which at present give disappointing results. The cost of rework is very high. Follow these suggestions and save money and time.

Questions are regularly asked about the use of concrete for residential flooring and this information answers some of the more commonly asked questions and gives guidance on good practice. It is not intended to replace the use of NZS 3604, or any other related Standard.

What concrete strength should I use for the slab? • NZS 3604:1999 refers to slabs on grade in Section 7 of the Standard. • Section 4 of NZS 3604:1999 explains the various zones that comprise the exposure maps for New Zealand. • Most of the country’s population is based in Exposure Zone 1, which requires reinforced concrete with 50mm cover to the steel to have a 20 MPa strength “when exposed to weather”. • The alternative approach allowed by NZS 3101:1995 is to use 17.5 MPa concrete with 65mm cover to the steel. • NZS 3604 requires a concrete strength of 17.5 MPa for all concrete used in residential housing work in Zone 2 and 3. • All concrete within 500 metres of high tide, and in certain coastal zones on the west coast of the South Island and a band on the west coast north of Auckland require 25 MPa concrete when exposed to weather. As a general rule, we recommend using 20 MPa or 25 MPa concrete for improved performance at little additional cost, especially if the concrete is to be exposed in use, in areas such as garage floors and areas to be tiled.

Do I need to extend the damp-proof membrane (DPM) under the perimeter footings? • The use of DPM is mandatory under all living areas. We also recommend it be used for the garage area. • The role of the DPM is to stop the passage of water vapour from the sub-base into the slab, where increased moisture will damage base plates of walls, floor coverings, etc. • Granular fill material is required under the DPM to prevent ground water being drawn up to the underside of the slab by capillary action. • Polythene DPM needs to be carefully placed on a layer of sand or on a layer of building paper to prevent accidental puncturing of the membrane. • All penetrations and laps need to be taped or sealed to prevent unintended moisture ingress.

Figure 1: Damp-proof membrane stopped at foot of foundation wall 2/D10 bars

Figure 2: Additional reinforcing at bays or insets

• On well-drained sites the DPM can terminate at the outer edge of the footing (the risk of moisture migrating in from the untreated outer face of the footing is low). See Figure 1. Bulletin 333 from BRANZ gives more detailed guidance on this. • In damp sites with high water tables the DPM must be extended under the footing and up the outside face of the perimeter beam.

What are the reinforcement requirements for slabs on grade? • NZS 3604 covers reinforcement detailing in Section 7.

BUILDING ON KNOWLEDGE


• It is important to place the correct number of bars as detailed in the plan: - ensure that they are placed with the correct amount of cover - ensure the steel is well tied to prevent accidental displacement during the concrete placing operation. • NZS 3604 permits slabs to be either unreinforced, fibre reinforced or steel reinforced, usually with mesh. Careful selection of the type of reinforcement is necessary otherwise excessive cracking of the slab may occur. Even slabs described as “unreinforced” require steel reinforcing to be installed at internal corners (see Figure 7:17 in NZS 3604:1999 for details) and will require control joints. • Two-storey houses must have a reinforced ground slab. The common practice of not chairing the mesh but simply lifting the mesh as the concrete is placed means much of the steel is in the wrong position or simply ends up back on the bottom. Mesh with a 300mm grid is preferable to standing on mesh with a smaller grid.

Reinforced or unreinforced – which is the best option for me? Reinforcing in most residential slab-on-ground is there to control crack widths and to allow for a slightly larger spacing of the joints. Reinforcing mesh allows bay sizes to extend to 6m. Polypropylene fibre extends bay sizes to 4m and unreinforced slabs cannot exceed 3m. Two-storey structures must have a reinforced slab on grade. Crack control is primarily catered for by the use of control joints. The choice of mesh type and control-joint location should be detailed on the drawings. Any decisions that have to be made on site on these items should be discussed with the designer first.

Unreinforced slabs with separate reinforced perimeter foundation • If the presence of construction joints on a 3m-grid is acceptable then unreinforced slabs will be satisfactory. This is certainly the case when the slab is to be completely covered with carpet. • The maximum plan dimension between construction or shrinkage joints for unreinforced slabs must not exceed 3m, with maximum bay dimensions of length:width (aspect ratio) not exceeding 1.3:1. • Internal corners need additional reinforcing bars (2 No. D10’s, each 1.2m long) see Figure 2. The additional steel must not cross shrinkage-control joints. Where they would cross shrinkage-control joints, leave them out.

Fibre-reinforced slabs with separate reinforced perimeter foundation • Polypropylene fibre, (added at the rate of not less than

0.7 kg /m3) permits the maximum plan dimension between construction or shrinkage joints for unreinforced slabs to be increased to 4m, with maximum bay dimensions of length:width: width (aspect ratio) not exceeding 1.5:1. • Additional steel is needed for internal corners as covered in the unreinforced slab section. Where they would cross shrinkage-control joints, leave them out.

Steel reinforced slabs on grade with thickened edges • The use of steel reinforcing mesh permits the maximum plan dimension between construction or shrinkage joints to be increased to 6m, with maximum aspect ratio being 2:1. (CCANZ recommends that bay sizes are no larger in any dimension than 5m, and should not exceed 6m under any circumstance). Internal corners need additional reinforcing bars (2 No. D10’s, each 1.2m long.) The additional steel must not cross shrinkage-control joints. Where they would cross shrinkage-control joints, leave them out. • Reinforcing mesh needs to be placed in the top portion of the slab with a minimum cover to the top surface of 30mm. The mesh requirement is 2.27kg/m2. • It needs to be well supported on reinforcement chairs that will not puncture the DPM when the concrete is being placed and compacted. • If the mesh is not well supported in the top section of the slab it will be ineffective in controlling shrinkage. • Where tiles or other special finishes are being applied, consider reducing bay sizes to a 1:1 ratio. Specific engineering design is recommended for these applications to minimise the risk of uncontrolled cracking. • It is important to accommodate the additional stresses brought about by perimeter restraint when reinforced slabs are tied into the perimeter foundation, especially where visible floor areas can be up to 6m or more in each direction. Edge restraint will almost certainly guarantee cracks developing unless the bay is divided in two in both directions. Consider using proprietary crack inducers to isolate garages and in areas to be tiled.

Masonry walls • For walls that are non-retaining, starter bars should be placed in the centre of the wall and at 800 mm centres along the length of the wall, but you need to set out the position of doorways and windows. • The starting point for the first bar at a corner is 100 mm. • Starter bars are needed on each side of every window opening, even if the window is not at slab level. • The finishing point for the last bar will always be 100 mm from the corner. • If the wall is a retaining wall, you must check the position of the bars both for position within the

BUILDING ON KNOWLEDGE


thickness of the wall and for centres along the wall because they may be set out at 200, 400 or 600mm. The starting and finishing point remains at 100mm from the edge of the corner. If in doubt, get a registered structural mason to set out the starter bars (see Figure 3).

600 100

800 100

1200 100

800 100

100

Should I tie the slab into the perimeter foundation? Won’t this restraint increase the probability of cracking? • Tying steel, connecting the perimeter footing, and localised thickenings to the slab all increase the likelihood of early-age thermal cracking and restrained shrinkage. For single-storey construction, no tying steel is needed from the slab to the foundation perimeter, provided the detail shown in Figure 4 is used.

Elevation – showing vertical steel.

How can I minimise the risk of cracking? Granular fill • The granular fill should be well compacted and level. An uneven surface will restrict slab shrinkage movement.

100

Joint layout

100

• Shrinkage-control joints need to be positioned to coincide with major changes in plan. • Square bays are less prone to shrinkage cracking. • Sensible layout of the joints will greatly reduce the chance of random cracking. • The layout of joints should be shown on the construction drawings and strictly followed by the builder. • More flexibility for bay layout is possible when the slab is steel reinforced because of the maximum dimension between joints of 6m. • Remember that you cannot have a slab dimension greater than 18m without having a free control joint which has no steel going through it (i.e. you can only have three bays of 6m that are tied). • When planning the joint layout, first look for internal corners. These increase the stress in the slab, and are the most common position that cracks propagate from. It is almost possible to provide a guarantee that a crack will form at this location, so you ignore them at your peril (see Figure 5). • Think carefully about penetrations and box-outs. If square shaped, these can create sharp re-entrant corners that trigger cracks. • Circular blockouts reduce the risks of cracks developing. • Wrap compressible materials, such as polystyrene or semi-rigid foam, around cast-in formers to minimise the risk of restrained shrinkage cracking developing. • Crack control needs to be considered if areas of the slab are to be tiled or covered with thin floor coverings, such as vinyl, and in uncovered garage floors. In instances such as these the careful layout of saw cuts is essential. Saw cuts need to be positioned to ensure that any movement occurs beyond the areas to be covered with vinyl or tiles. • Consider locating these saw cuts under internal walls where they will be hidden from view.

100 400

Actual

800

100 800

800

100 1,000

800

800

100 1,000

800

Theoretical Plan – showing position of vertical steel.

recess for masonry

95 mm for 20 series 70 mm for 15 series floor level

20-50

foundation

Section – position of vertical steel in relation to edge.

Figure 3: Layout of vertical steel for concrete masonry

Mesh reinforcing D12

D12 Figure 4: Slab confined by foundation wall

BUILDING ON KNOWLEDGE


The concrete Major crack

Major crack

• The risk and extent of cracking occurring can be minimised by ensuring a low-water content mix is used. • Use a 19mm structural mix rather than a 12mm pump mix. • The second option is to use a superplasticiser which significantly reduces water content. Seek advice from your readymix supplier on this. • There will be far less bleeding when using a superplasticiser. Watch for plastic cracking with this type of mix. • Adding water on site to increase slump for the ease of the placer and pump operator will increase the chances of shrinkage.

Additional control joints depending on slab size

Control joints Major crack

Additional control joints depending on slab size Control joint

Plastic cracking • Plastic cracks normally appear on the day the concrete is being placed. • To avoid these cracks the concrete must be protected from evaporation of the bleed water from the moment it is screeded until it is hard enough to finish and cure. This is when it is most at risk. • This is best achieved by using either a water mist or alcohol based membranes (antivaps) sprayed on the screeded concrete at the rate specified by the manufacturer. These membranes may require re-application on windy days. If you do not maintain a damp look to the surface it will dry out. This can be achieved by using a water blaster aimed above the slab. • If the concrete does not appear to be bleeding you are at risk of plastic cracking occurring. If it’s a good day to get washing dry then beware of plastic cracking!

Figure 5: Positioning of crack control joints Former is inserted while concrete is wet and the surface floated over

Induced crack

Pressed M.S. crack inducer Reinforcing steel

Early-age thermal movements • Temperature changes in the freshly placed concrete mean many slabs crack overnight. • To significantly reduce the risk of an early-age thermal crack developing, all joints should be in position before the first night. • This entails the use of crack inducers (see Figure 6), tooled joints or early-age saws. • Many cracks will be seen within the first 48 hours. (These cracks look exactly like a drying shrinkage crack.) • Sawcutting has been the traditional technique for forming control joints. Sawcutting of the slab to initiate shrinkage-induced movement should be carried out as soon as the concrete can withstand the process and within 24 hours. • Carry out any sawcutting within 12 to 18 hours using traditional sawcutting equipment, particularly where the slab is exposed to high temperature changes or drying winds. • Consider the use of early-entry saws (within the first few hours of placing the concrete). However, this option may not be available in all locations. • Failure to carry out sawcutting of the joints within this timeframe significantly increases the probability of uncontrolled cracking in the slab.

Figure 6: Crack inducer (for reinforced or unreinforced slabs)

Drying shrinkage • Drying shrinkage becomes noticeable after two weeks at the earliest and will continue to widen for several months • Shrinkage cracking is controlled by the correct positioning of control joints.

Do I need to vibrate the concrete? Yes. This is very important. • Poorly compacted concrete, with air voids within it, will be significantly weaker and could result in expensive call-backs and remedial work. • Even pump mixes, which appear to be very easily moved and compacted by the screeding process, must be vibrated. • Special attention needs to be paid to compacting concrete in locally thickened regions, such as perimeter beams (see Figure 7).

BUILDING ON KNOWLEDGE


What are the concrete placement options? • It is becoming the norm for the concrete to be pumped into residential slabs. Though this is quick and easy, the shrinkage potential for these pump mixes is higher than a conventional mix. • For critical areas, consider using a structural concrete mix with a 19mm aggregate, rather than the 13mm maximum aggregate pump mixes usually supplied for residential slabs.

D E

What is the effect of water addition on site? • Increasing the water content of a concrete mix will reduce the potential strength that the concrete will be able to achieve. If you require 120mm slump for placing then order it so that a mix designed for the higher slump is delivered. • It will also increase the shrinkage movement that it will undergo as it finally dries out after the curing process is completed. • Water added to the mix without the approval of the readymix supplier places the onus of responsibility for all aspects of the performance of the concrete on the person adding the water. • It also transfers liability for any financial consequences for this action to that person.

E= D=

The effective range of the immersion vibrator. 180mm to 360 mm The distance between immersion is approx 150 mm

Do not add any water to the concrete mix unless the readymix supplier approves it. The driver should carry out the water addition, but only on the instructions of the batcher.

How should I finish the slab? • Section D1/AS1 of the Building Code describes acceptable finishes for different applications. Wet areas, such as driveways, should not be steel-trowel finished (Class U3, NZS 3114:1987 specification for concrete surface finishes) as this process produces slabs with a poor skid resistance. This may also be a consideration in areas subjected to intermittent wetting, such as garage floors. • Finishing operations must not begin until the slab has stopped bleeding and has taken on a dull grey appearance, with no visible surface moisture. It will be stiff enough to walk on and only leave a foot imprint of 2mm to 3mm (see Figure 8). • Finishing operations must be timed to ensure that the surface can be worked without the addition of water or cement to the surface to improve the ease of finishing. Either technique will lead to a dusting surface, or one that will delaminate as the slab dries after wet curing. • In winter, be prepared for significant delays between placing and finishing.

Stage 1. The form is surcharged with concrete.

Liquification of the concrete. It slumps and fills the form (3-5 seconds.)

Stage 2. Trapped air is expelled.

7-15 seconds.

Total time for both stages, 10-20 seconds.

Figure 7: Centres for insertion of poker vibrator and the process of compaction

The common practice of squeegeeing the bleed water from a slab presents two problems. First, if the day has any wind this bleed is protecting the slab from plastic cracking. Second, if the removal process mixes any water into the remaining paste then this paste will be severely weakened. Correct finishing procedures will produce a very hard, long-lasting surface. For more details on correct finishing procedures contact CCANZ.

How should the concrete be cured? It is very important that concrete is not allowed to dry out in its early life. Apply the curing as soon as the concrete can withstand the

BUILDING ON KNOWLEDGE


process. The most effective method for curing concrete is by water spraying or ponding (see Figure 9). Plastic sheeting is very good, as long as it is held in place and does not permit any wind to get between the slab and the plastic sheet. Curing membranes, if complying with NZS 3109:1997 (typically only wax-based membranes and some acrylics meet the standard), and applied at the correct rate, can also be effective. Improperly applied membranes, and membranes that do not meet the Standard, are usually ineffective. Membranes, however, are not suitable if tiles or vinyl are to be placed on the floor. Points to remember: • Poor curing of floor slabs can reduce concrete strength by 50%, resulting in greater risk of random shrinkage-induced cracking, despite control joints being saw cut. • Effective curing will improve the durability and the abrasion resistance of the concrete. • The curing period should be at least three days. Longer is better, and can be accommodated with good planning.

Figure 8: Power floating

What you should see happening on site if you are using a specialist subcontractor There are 9 key steps that are important if a good quality slab is to be produced. These are: 1. Sub-base correctly formed and compacted. 2. Sub-base blinded with sand then DPC carefully installed and taped. 3. Steel reinforcing (where used) placed, tied and spaced to within 30mm of top surface of slab with trimmer bars placed at all reentrant corners; crack inducers (if used) positioned and fixed together with any starter reinforcement for masonry walls. 4. Concrete of correct specified strength delivered to site in accordance with NZS 3604:1999 Section 4.8 (No water added without the permission of the supplier). Concrete placed and compacted with the use of immersion vibrators. 5. Concrete finished only after all bleed water has evaporated from the surface. 6. Antivap sprays used (applied more than once if necessary) to control evaporation rate to prevent plastic shrinkage cracking. 7. Curing process started immediately finishing operations are completed. 8. Joints cut immediately (using early-entry saws) or within 12 to 18 hours if using traditional sawcutting equipment. 9. Wet curing or covering the concrete with black plastic sheeting continued for three to seven days if a membrane system is not used.

Figure 9: Curing concrete using a sprinkler

Where can I get more information? New Zealand Ready Mixed Concrete Association (www.nzrmca.org.nz). New Zealand Registered Structural Masons (www.mtrb.org.nz)

A coloured concrete floor with cut joints

Cement and Concrete Association of New Zealand has produced two floor design guides that are an excellent source of more detailed information. Visit the website (www.cca.org.nz) or phone on 04 4998820. BRANZ Bulletin 333: June 1995. Damp-proof membranes to concrete slabs. BRANZ Good Concrete Floors and Basements Practice, October 2002. Visit BRANZ website (www.branz.co.nz) or phone 0800 80 80 85.

This document was prepared by the Cement and Concrete Association of New Zealand, on behalf of the New Zealand Ready Mixed Concrete Association.

BUILDING ON KNOWLEDGE

August 2003


Discussion Document on Building Sustainable Urban Communities

Consultation Feedback from the Cement & Concrete Association of New Zealand on Building Sustainable Urban Communities

24 September 2008


24 September 2008 Sustainable Urban Development Unit Department of Internal Affairs PO Box 805 WELLINGTON 6011 Dear Sir/Madam COMMENTS ON BUILDING DISCUSSION DOCUMENT

SUSTAINABLE

URBAN

COMMUNITIES

Thank you for the opportunity to comment on the Building Sustainable Urban Communities discussion document. This submission has been prepared by the Cement and Concrete Association of New Zealand (CCANZ). CCANZ is at the forefront of the building industry in New Zealand, and is well placed to comment on the proposals contained within the discussion document. We represent in excess of 300 corporate and individual members who collectively account for over 90% of the concrete industry in New Zealand and approximately $2.8 billion in annual turnover. Part of our mandate within industry is to liaise with industry sector groups in the preparation of this submission. Our detailed submission is attached. Should you have any queries please do not hesitate to contact me. Yours faithfully

Patrick V McGuire CHIEF EXECUTIVE OFFICER


Discussion Document on

Building Sustainable Urban Communities 1.0

INTRODUCTION

1.1

The Submission In August 2008 the Department of Internal Affairs (DIA) published a public discussion paper entitled, ‘Building sustainable urban communities”. The DIA invited interested parties to express their views on the proposals canvassed in the document. This submission responds to that invitation.

1.2

The Association The Cement and Concrete Association of New Zealand (CCANZ) is at the forefront of the building industry in New Zealand, and is well qualified to comment on this proposal. We represent in excess of 300 corporate and individual members who collectively account for over 90% of the concrete industry in New Zealand and approximately $2.8 billion in annual turnover (or 1.8% of New Zealand’s 2006 GDP1). Approximately 24,300 people find employment either directly or indirectly within the wider concrete industry2.

1.3

Knowledge Organisation In addition to its primary representational role, CCANZ seeks to inform a broad construction industry audience including architects, designers, engineers, building contractors and inspectors of the technical benefits of concrete as a construction material. This knowledge role focuses on issues at the heart of the regulatory debate – how building owners and occupiers can be assured their buildings are safe, healthy, comfortable, durable and environmentally sustainable. Groups with whom we have discussed this amendment include the New Zealand Concrete Masonry Association, and Precast New Zealand. It is against this background that CCANZ makes the following submission.

2.0

GENERAL COMMENTS

2.1

Government Initiative CCANZ fully supports the Government’s desire to encourage all future development to achieve sustainable urban communities. Key to achieving this is a radical change in the valuation of infrastructure and construction methodologies in conjunction with careful design of our urban environments.

1 2

Cement and Concrete Production – Economic Impact Assessment, NZIER, May 2008 Ibid. P 17

Building Sustainable Urban Communities Discussion Document

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CCANZ Submission


3.0

SPECIFIC COMMENTS

3.1

General Questions In asking what options would be effective in encouraging sustainable urban development the key word here is ‘encouragement’. Currently the tendency is to control development by a legislative ‘stick’ using rules. CCANZ proposes a different means of creating sustainable urban environments using incentives as a ‘carrot’ for developers to provide quality. Where a development has a given density, a higher density would be permitted if, for example, all housing units are designed using passive solar principles and construction, exterior hard surfaces are permeable paving, construction is durable and designed for a minimum 100 year lifecycle (rather than the 50 years permitted by the NZ Building Code). The idea would be to create such incentives so that it is economically unviable for developers not to provide high quality and sustainable urban environments.

4.0

SPECIFIC QUESTIONS Numbering follows the numbering on the DIA document.

4.1

Barriers and Development

Implementation

Difficulties

in

Sustainable

Urban

The time and cost of Resource Consenting is a significant impediment to any form of development, sustainable or otherwise. That parties not directly affected by a development can make submissions driven by commercial or political interests can add unnecessary costs and cause significant delays to projects. CCANZ submits that the Resource Management Act requires significant overhaul to enable efficient and fair processing of applications. The Act should also provide mechanisms to promote sustainable development. With regard to public resistance to urban intensification the key issue is the quality of the proposed developments. This must be assessed not only in terms of design but also the durability and quality of the construction materials. CCANZ believes that the use of Urban Design Panels such as Auckland City’s provides an effective vehicle to critique buildings within their urban context and to continually strive for the design of better living environments. This model could be established within regional councils to evaluate developments in a wider context. One must recognise however, that for smaller councils there is likely to be a lack of suitably qualified professionals to establish such panels. That the current New Zealand Building Code (NZBC) requires only a design life of 50 years for buildings (and only 15 years for exterior claddings) is simply unsustainable. Indeed it is almost ludicrous that a building can be designed to have its cladding replaced three times during its design life. Frankly this represents poor stewardship of materials and resources.

Building Sustainable Urban Communities Discussion Document

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CCANZ Submission


New Zealand also needs to change its attitude to the construction quality of infrastructure, particularly roading. The continued construction of highmaintenance asphaltic roading needs to be questioned when studies prove that in terms of life cycle costing, concrete roads are much more sustainable both from a straight cost perspective and improved fuel usage by motor vehicles. Other infrastructure using more durable construction materials may have initially a slightly higher cost but long term will reap benefits for future users. Use of pervious concrete pavements, for example, can assist in control of peak stormwater events while treating the water before it is discharged into stormwater systems. In regard to street lighting, the greater reflectivity of such pavements mean that lighting power demands can be reduced with no loss of visual amenity. 4.2

Strengthening Existing Tools and Ways of Working While regional councils are able to provide broader ‘oversight’ of development of land and regional infrastructure, often what happens with developments is that duplication then occurs with affected local councils resulting in delays and costs. Streamlining in this area would be of great assistance to cost efficient sustainable practice. Additionally there often seems to be a ‘disconnect’ between regional and local councils, providing a mechanism to control this would also save time and costs. Many of the great urban experiences worldwide are the result of centuries of evolution creating ‘character’ often derived from regional influences. CCANZ also believes there needs to be options for innovative developments to achieve such places in New Zealand. Current planning practices and policies would often prevent such intensification and to achieve innovative designs it is necessary to undertake various legal avenues at great cost. If we are to achieve sustainable urban environments mechanisms need to be established to encourage them.

4.3

The Role of Government in Sustainable Urban Development CCANZ believes the government has a vital role in ‘leading from the front’ by providing a strategic vision and enacting legislation to make it easier for sustainably responsible development to prosper. That said, history would show that where government policy is established costs follow soon after. One of the difficulties with policies like the Urban Design Protocol is that when projects are evaluated against it, the basis of judgement tends to be rather subjective, often the opinion of the town planner. Also the opinions of panel members or town planners can add significant cost to project with little opportunity for developers to appeal. A formal evaluation mechanism would improve this from both the regulator’s and developer’s perspective.

Building Sustainable Urban Communities Discussion Document

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CCANZ Submission


4.4

Improving Co-ordination and Integration CCANZ believes that at the regional level issues of transport and services infrastructure should be governed while specific future development should be managed at local authority level. In regard to infrastructure CCANZ believes that the roading discount rate should be amended to reflect a true life cycle cost. In this way a more sustainable model for funding can be achieved.

4.5

Funding Ideally costs associated with developments should be borne by the developers themselves and is predominantly the current situation. The difficulty with this is that developers are then put into a position of attempting to recover their costs as quickly as possible. This tends to lead to use of less durable construction materials in the interests of speed of construction. This is a false economy as the ongoing maintenance of the infrastructure will then fall on the rate payer.

5.0

CONCLUDING COMMENTS Building sustainable urban communities is obviously in the best interests of all New Zealanders, now and in the future. CCANZ believes that key to this is a comprehensive overhaul of the Resource Management Act concentrating on simplifying and streamlining processes while at the same time expanding ‘sustainability’ principles with in it. Secondly, and in association with the overhaul of the RMA, must come a reevaluation of the design life times of all developments; urban environments and their supporting infrastructure. Clearly a 50 year design life is not sustainable and in fact is a poor use of resources. Life cycle costing of development should be undertaken using true costs and without discounting. While this could mean that up-front costs are be slightly higher, future generations will enjoy the benefits of far-sighted decisions made decades earlier. The prime concerns must be good design, quality development and long term durability.

If you require further information or assistance from us please do not hesitate to contact the undersigned. Yours faithfully

Patrick V McGuire CHIEF EXECUTIVE OFFICER Building Sustainable Urban Communities Discussion Document

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CCANZ Submission


TM 34 Tilt-up Technical Manual


Special Acknowledgement

Special Acknowledgement

Tilt-up Technical Manual

The late W.J. (Bill) Lovell-Smith, former consulting engineer in Christchurch, made a significant contribution to the use of tilt-up construction. By his influence, the system was consistently in use in Christchurch during the late 1950’s.

Revised and Reprinted June 2004. Cement & Concrete Association of New Zealand, Level 6, 142 Featherston Street, Wellington. © Cement & Concrete Association of New Zealand

From this developed an ever-widening use and versatility of design for tilt-up. Bill LovellSmith was involved with the design of structures in New Zealand and Australia. One particular structure in New Zealand, the Queen Elizabeth Park Stadium in Christchurch, built for the 1974 Commonwealth Games, saw the extent to which Lovell-Smith had developed the art of tilt-up from two dimensional to three dimensional structural forms. In papers he presented about his work he commented:

This edition of the Tilt-Up Technical Manual was compiled by D.H. Chisholm, B.E. (Hons) MIPENZ. Apart from any fair dealing for the purposes of private study, research, criticism or review, no part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording or otherwise without written permission.

“It is perhaps unfortunate that one of the most versatile and adaptable of modern concrete building methods got stuck with a popular name that typecasts it in most people’s minds with a certain rather limited type of building. ‘Tilt-up’ buildings evoke pictures of rather plain stereotype single storey factories or warehouses without much to redeem them aesthetically. A surely more accurate name for the technique would be ‘site precasting’ as distinct from ‘factory precasting’ or ‘casting insitu’.” This publication, which attempts to encapsulate today’s practice from Australia, the United States and New Zealand, wishes also to record the former works of W.J. (Bill) Lovell-Smith, which led to the significant developments of technique in New Zealand.

TECHNICAL MANUAL 34 (TM 34)

The Cement & Concrete Association of New Zealand acknowledges the use of material from the Tilt-Up manual published by the Cement and Concrete Association of Australia in this publication.

TM 34

ISSN:

1171-0748

ISBN:

0908956002

Cover picture and copyright permission provided by the Portland Cement Company (USA).

1

Tilt-up Technical Manual


Contents

Tilt-up Technical Manual Contents FOREWORD

PAGE 3

1

APPLICATIONS

PAGE 4

2

PLANNING FOR TILT-UP

PAGE 6

3

STRUCTURAL DESIGN

PAGE 8

4

DETAILING

PAGE 17

5

CONSTRUCTION

PAGE 23

6

SURFACE TREATMENTS

PAGE 34

7

COSTS

PAGE 37

8

SAFETY CHECKLIST

PAGE 38

REFERENCES

TM 34

PAGE 39

2

Tilt-up Technical Manual


Foreword

Foreword The tilt-up construction technique was pioneered in the USA around 1908 but it was not until the late 1950’s that it was practiced in New Zealand. The concept was mainly confined to flat panels in commercial buildings where aesthetics was not of importance, however, in more recent times, universally, the growth of tilt-up has run parallel with the developments in architectural tiltup. The system now offers designers a diversity of aesthetically pleasing structures at economic advantage compared to other building systems. Use of the term tilt-up is sometimes restricted to wall panels cast on a horizontal surface and requiring only to be tilted into their final location. However many of the principles applying to this equally apply to the broader concept of site precasting of columns, beams and plane frames, which after being cast horizontally are lifted by crane and moved to their final location. Thus, although this manual is written around the construction of tilt-up wall panels, it does have a wider application. Where tilt-up and off site precasting are being considered as alternative construction methods, the restriction of precast panel size, as dictated by road transport, with the consequential extra joints and panel numbers may lead to increased erection and finishing cost compared to tilt-up. However, where high quality architectural finishes are being considered, this skilled work is easier to achieve in factory type conditions. The ultimate solution in these special requirements may be a combination of off site precast and tilt-up. As with any precast method of building, the best results using tilt-up are achieved when there is close collaboration from the outset between all members of the design and construction team. To foster such an approach, this manual covers all aspects of tilt-up construction from planning through to finishing. Safety aspects during lifting and temporary propping are matters of concern to authorities. Handling large panels can be done safely provided that simple rules on equipment and procedures are followed. This aspect is also covered in this manual.

TM 34

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Tilt-up Technical Manual


Applications

1. Applications Tilt-up is a construction method which allows a great deal of flexibility and innovation. The use of concrete as a construction material offers the designer structural capacity, fire resistance, acoustic capacity, thermal capacity, aesthetic qualities and durability. Initially tilt-up panels were often used simply as cladding panels continuously supported on strip footings. Today most tilt panels span between pad footings and have the potential to carry the roof load and provide transverse load resistance in shear. Figure 1.

the associated office accommodation (the prestigious ‘front’ of the building) was carried out using a different form of construction. Current detailing and finishing approaches have made tilt-up walls suitable for use throughout the project.

Tilt-up construction has the potential to realise the following advantages over alternative building systems: •

Lower Cost – lower costs can arise from faster construction and a simpler structural form than alternative concrete systems.

Speed of Construction – tilt-up panels are often erected and in place within a few weeks of access to site. Finishing trades can then commence resulting in earlier occupancy.

Design Versatility – tilt-up is a structural form in itself and columns and concrete encased portal legs can often be eliminated. Panels can provide a wide range of integral architectural treatments.

Weatherproofing – panels do not require any protective treatment to provide weatherproofing to the structure and will remain durable over the life of the structure.

Robust Material – maintenance costs are reduced because reinforced concrete by its rugged nature is able to withstand the heavy wear imposed by commercial and industrial applications.

Since 1980, the availability of specialist tilt-up hardware has increased the scope for development of tilt-up. This and the improved appearance of tilt-up have largely been responsible for increasing the range of applications for the method in recent years, particularly in Australia and USA.(1-4) The diversity of applications allows for broad

Fire Rating – tilt-up panels have inherent fire rating capabilities.

In many early tilt-up industrial developments

TM 34

4

Tilt-up Technical Manual


Applications developments as office or industrial parks using tilt-up in Commercial, Recreational and Residential construction.

• • •

The following list illustrates the diversity of applications:

Recreational Construction • • •

Commercial/Industrial Construction • • • • • • • • •

Warehouses. Automotive workshops. Storage units. Offices. Factories. Motels. Hotels. Restaurants. Shopping complexes.

• • •

Houses. 2-3 storey flats. Town houses.

Other Construction • • • • • • •

Farm sheds. Piggeries. Dairies. Tanks.

TM 34

Squash courts. Indoor cricket facilities. Gymnasiums.

Residential Construction

Rural Construction • • • •

Drainage systems. Grain storage bunkers. Settlement tanks.

5

Churches. Community halls. Schools. Colleges. Motorway sound barriers. Retaining walls. Reservoirs.

Tilt-up Technical Manual


Planning for Tilt-up

2. Planning for Tilt-up The planning phase of a tilt-up project is one of the most crucial for its success. During this phase the entire design and construction procedure for the building should be worked out. Time spent in thorough planning can be repaid in full by a problem-free construction period. At the planning stage the various alternatives for each aspect of the project can be calmly evaluated; once construction is underway, proper evaluation may not be possible since expediency could be the overriding consideration.

It is important that each member of the team is aware of the constraints of the method and of the broad implications of any planning decision. Compromise will often be necessary; the participation of all members of the team in all decision making is therefore required if the best solution is to be found, particularly for the casting and erection sequences. Changes should be made during construction only after careful consideration since many decisions depend on or affect other operations. Reversing one decision may start a chain reaction, which could necessitate the reconsideration of all subsequent decisions.

Two aspects of planning for tilt-up are worthy of particular mention; firstly, the need for the continuous involvement of every member of the design/construction team; secondly, the need to design the building specifically for the method.

The benefits of the tilt-up method are optimised when the building is designed for tilt-up. Adapting a design based on the use of a different form of construction can be difficult and will often result in the tilt-up panels serving only as cladding, size being dictated by grids and frame spacings selected to suit other considerations.

The co-operation of the whole team is necessary if the advantages and versatility of tilt-up are to be fully exploited and if cost benefits are to be maximised. It should begin at the planning stage and continue through to the completion of the project. The team involves the designer, contractor, specialist sub-contractor and crane operator. The crane operator is vital to any successful job and should be included in the deliberations and planning as early as possible.

FIGURE 2

TM 34

The following points should be considered at the early planning stage in order to exploit the benefits of tilt-up:

Site-Utilisation Advantages of Tilt-Up

6

Make use of as many of the panel’s attributes as possible (structural, acoustic, thermal, fire resistance, etc.).

Decide where access is to be provided onto site for concrete supply and cranes.

Establish the broad approach to the casting and erection procedures. As the floor slab often acts as the casting surface and the erection platform, early access to site for casting of the slab becomes critical. Consideration of the positioning of the shrinkage control joints in the floor slab and the finishing which reflects in the forming of the tilt-up panels needs to be given. If the available room on site is minimal, stack casting will need to be considered. Other factors which are relevant at this stage are crane size

Tilt-up Technical Manual


Planning for Tilt-up It is important to realise the scope of the project at this stage and a scale model of the building and site can be very useful. Figure 2.

availability which will determine the maximum panel size, special surface finish requirements, positioning of panel props and time available for casting and erection.

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Tilt-up Technical Manual


Structural Design

3. Structural Design 3.1

to other types. Table 1 lists some of the broad considerations to be evaluated when selecting the type of construction.

GENERAL

The same structural principles apply to the design of tilt-up panels as to normal insitu concrete construction. It is necessary, in their design, to satisfy a number of independent criteria. Wall panels must be designed for not only the loadings and conditions to be experienced in the final structure, but also for construction loads during erection, and when temporarily braced. Account should be taken of the volumetric effects of shrinkage and temperature.

Table 1:

Type of Construction Reinforced (Normal-Weight)

Fibre reinforced (steel fibres)

Materials and labour readily available

Permits thinner panels and/or longer spans

Disadvantages Panels reasonably heavy Dimensional limitations imposed by lifting considerations and lifting stresses Restricted availability Thinner panels may warp Higher cost

Design for lifting (tilting) is frequently the most critical design state and will dictate the design of the panel for a majority of situations. Design for lifting is normally based on uncracked design whereas ‘in service’ loadings are based on cracked design.

Prestressed

Permits thinner panels and/or longer spans

Requires the introduction of special skills

Reinforced (lightweight

Lower density may permit the use of smaller cranes or larger panels

Lightweight aggregate available only in certain areas

Better insulation and fire resistance

Throughout the design phase there should be a conscious striving for ‘buildability’. A check of the design details should be carried out to ensure that they are practicable. The designer must also anticipate the construction practices and allow for realistic tolerances. See Section 5.12.

Concrete tensile strength could be lower

Information in this manual is for normal-weight reinforced concrete. Some of this data will be directly applicable to other types of construction. If adapted for this purpose then the designer must satisfy himself as to the validity of the data.

PRELIMINARY CONSIDERATIONS

Secondly, consideration must be given to the implications of particular details for the total design, joint and connection details, for example. The New Zealand loadings code NZS 4203(5) stipulates that depending on the earthquake risk zone and the height of the building, the building can be classed as ductile or non-ductile. This will influence the connection details adopted between panels and the magnitude of the design lateral forces. Similarly, connection details will determine whether volumetric changes need to be considered over the total length of the building or not.

Before embarking on detailed structural design, two broad questions need to be answered: Firstly, the type of concrete construction, e.g. reinforced concrete or prestressed concrete, normal-weight or light-weight to be used. Reinforced concrete will usually be favoured because the constituent materials and construction skills are readily available. Nevertheless, consideration should be given

TM 34

Advantages

Skills readily available

Durability and fire-resistance requirements for the panels need to be established. These considerations may control some aspect of the design.

3.2

Comparison of Concrete Construction Types for Tilt-up

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Tilt-up Technical Manual


Structural Design

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Tilt-up Technical Manual


Structural Design may dictate the specified strength of the concrete supplied.

3.3 CONSTRUCTION LOADINGS

The analysis of stresses during lifting of the panel can be complicated. Figure 3 shows an analysis for a double row lift or two high lift. Computer programmes are now available which will detail the lifting insert positions after analysing the lifting stresses. The programmes are particularly useful for irregular shaped panels with multiple

Two situations are usually considered in design:

3.3.1 Lifting Probably the most severe loading experienced by the panel will be that to which it is subjected during lifting. The design loading must allow for the self weight of the panel, the ‘suction’ between the panel and the casting surface, and the dynamic loading which will occur when the panel is separated from the casting surface and as the panel is lifted by the crane. The effect of these forces must be considered firstly on the panel and secondly on the lifting inserts (see Clause 4.1). For the typical tilt-up panel, the reinforcement will normally be central in the panel acting as shrinkage and temperature control steel (See Clause 3.6). This is different to normal reinforced concrete design, where the reinforcing steel situated near to an outside surface carries the tensile loads. For the tilt up lifting operation the tensile strength of the concrete itself is required to resist these loads. The tensile stresses imposed during lifting will depend on the panel thickness and the lifting configuration. The concrete tensile strength must be sufficient such that the section remains ‘uncracked’ during lifting. As concrete is specified and tested for compressive strength, it is convenient to express the tensile strength of concrete in terms of compressive strength. The ACI figure for flexural cracking strength is 0.75√ fc and for tilt-up design purposes the allowable tensile stress is limited to 0.41√ fc allowing for a factor of safety. The lifting of tilt-up panels is a critical operation. A cracked panel resulting from lifting too early may be expensive to repair or may not be acceptable aesthetically. On the other hand having the panels on the ground when they could be erected defeats the time saving aspects of the construction method. Thus, because the concrete strength at lifting is so critical, it should be specified by the designer. This early strength requirement TM 34

10

Tilt-up Technical Manual


Structural Design openings. The programme will also give details on lifting anchor design and rigging requirements. For panels with large openings it may not be feasible to lift the panel without some cracking at critical sections. In this circumstance additional reinforcing steel should be placed locally on the tension face to ensure the cracks remain closed. The computer will calculate this steel. An advisory computer design service is available in New Zealand.(6)

happens that this moment is similar to that in Table 2 using the similar method. For the edge lift or single row lift Table 2 will be conservative. In the vertical direction the bending moments are assumed to be uniform over the full width of the panel and calculations are based on a typical one metre width. For panels which are wider than they are high, transverse bending moments can be critical and are calculated on notional beams through the lifting points. The assumed width of these beams is shown in Figure 5.

Figure 4 shows some of the simple tilt-up rigging configurations. The position of the lifting points as shown, result in an equal positive and negative bending moment for rectangular panels with no openings.

Table 2:

Tilt-up Maximum Tensile Stress (MPa)

Flexural

EDGE LIFT Panel Thickness

Panel Height (m) = H 2.5

3.0

3.5

100 mm

1.58 2.27

120 mm

1.31 1.89 2.57

4.0

4.5

150 mm

1.05 1.51 2.06 2.69

175 mm

0.90 1.30 1.76 2.30 2.91

200 mm

0.79 1.13 1.54 2.01 2.55

SINGLE ROW FACE LIFT (2pt or 4 pt) Panel Thickness

Panel Height (m) = H 4.0

4.5

5.0

5.5

6.0

6.5

7.0

7.5

100 mm

1.36 1.72 2.12 2.56

120 mm

1.13 1.43 1.77 2.14 2.54

150 mm

0.90 1.14 1.41 1.71 2.03 2.39 2.77

175 mm

0.78 0.98 1.21 1.46 1.74 2.05 2.37 2.72

200 mm

0.68 0.86 1.06 1.28 1.53 1.79 2.08 2.39

Panels up to 15 m high or up to 10 m wide can be lifted but the optimum size must be determined in conjunction with the crane to be used. As panel size goes up, rigging becomes more complicated. A larger crane is required which will take up more room and take longer to move around the site. For overall efficiency the optimum maximum panel width is around 6 m and weight 20-25 tonnes.

DOUBLE ROW FACE LIFT Panel Thickness

Panel Height (m) = H 6.5

7.0

7.5

8.0

8.5

9.0

9.5 10.0 10.5 11.0

100 mm

1.60 1.86 2.13 2.42

120 mm

1.33 1.55 1.78 2.02 2.28 2.56

150 mm

1.07 1.24 1.42 1.62 1.83 2.05 2.28 2.53

175 mm

0.91 1.06 1.22 1.39 1.56 1.75 1.95 2.16 2.39

200 mm

0.80 0.93 1.07 1.21 1.37 1.53 1.71 1.90 2.09 2.30

Odd-shaped, elongated panels, or those with large or multiple openings can be strengthened for lifting by the addition of strongbacks. Figure 6. The designer should indicate whether a strongback is required for lifting purposes and include its mass in all lifting calculations. Where possible, strongbacks should be avoided as their use can considerably increase the erection time of panels. Computer analysis will often show

For estimating purposes Table 2 shows maximum tensile stresses resulting from various lifting configurations against panel thickness and height. This table is based on a simplified analysis by multiplying the selfweight of the panel by 1.4 and calculating the bending moments at 0o tilt. For the double row lift the actual maximum moment in the panel occurs at between 25o and 30o of tilt. It TM 34

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Tilt-up Technical Manual


Structural Design that careful placements of multiple lifting anchors can remove the need for strongbacks.

Grooving, profiling, texturing, or any mechanical treatment of the surface will reduce the net section available for structural design and cover to the reinforcement. The thickness of the panel must be increased to compensate for this.

The braces should be fixed to the upper half of the panel and the optimum brace angle is 45o with the normal range 45o - 60o. Braces should be of one continuous length and designed to take the axial load with a factor of safety of 2.0.

3.3.2 Bracing

The wind loading on a panel can be considerable. Standard falsework props are neither long enough or of sufficient strength for panels over 5 meters high. Special heavy duty adjustable braces should be used and the detailing of these braces should be carried out as part of the structural design.

It is unusual for the temporary bracing loading condition on the panel to control its design. However, the loading needs to be determined so that the bracing and inserts can be checked to adequacy, thus ensuring stability of the panel. It is recommended that bracing should be designed for accidental loadings of 1% of vertical load or 1.5 kN/m applied horizontally to the top of the panel and wind loading. Loads due to wind are calculated as indicated in Figure 7. Note that the braces themselves may require bracing to prevent buckling under the full rated compression load. Two braces per panel should be used to provide stability against the panel twisting.

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3.4

IN SERVICE LOADINGS

The design loadings for the erected situation will depend on the building type, how the element is used, the support and fixings adopted, and other conditions. While the general design requirements of NZS 3101(7) must be satisfied, frequently tilt-up walls will fall outside the specific situations for which

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Tilt-up Technical Manual


Structural Design

FIGURE 8 Transverse Load Resistance

between the units and the footings must be designed to carry the induced forces.

design guidance is given. It is not feasible to provide detailed design advice within this manual covering the many and varied situations. However, some broad comment is made on the following aspects.

Where tilt-up wall panels supporting a roof rafter replace a portal frame design, the size of the roof rafter will generally be heavier than the portal rafter it replaces. If the height of the panels is high relative to the roof span, the weight of eliminated columns will be substantially more than the increase in rafter weight. For longer spans the weight of additional roof bracing may make a column/portal frame support system more economic.

3.4.1 Transverse Loads One of the main economic benefits of tilt-up is the elimination of columns. Where the walls are being used as load bearing elements, it is important that they provide sufficient restraint for the applied lateral loads due to wind or earthquake. For panels up to approximately 6 metres, loads can be taken at ground level by cantilever action alone. Beyond this height the roof can be designed to function as a diaphragm to carry the lateral load applied to one set of walls to those at right angles. The latter can act as shear walls to resist the applied loads. Figure 8. The panels in this wall resist the loading as illustrated in Figure 9. The connections and fixings between the units and TM 34

3.4.2 Vertical Loads Wall panels can be used to carry roofs, intermediate floor loads and light gantries. This can be done by providing a connection on the face of the panel. Figure 10. For specific situations encountered in tilt-up panels reference can be made to Weiler and Nathan(8) and Kripanarayanan(9) for recommended design approaches. 13

Tilt-up Technical Manual


Structural Design of wall and excess restraint of this movement will cause fixings to fail.

3.5

FLOOR LOADINGS

In most tilt-up construction the panels will be erected with the crane positioned on the floor slab. Loads from the crane outriggers can be considerable and will usually be distributed by the use of heavy timber bearers. However, these loadings may need to be considered at the design stage. Edge thickening of the slab could be appropriate or alternatively a thicker compacted sub-base may be all that is required.

3.6

REINFORCEMENT IN PANELS

Reinforcement in the panel is usually determined from consideration of loading acting on the panel in the long term, see section 3.4. A single layer of reinforcement placed at the mid-depth of the section will usually suffice. Two layers of reinforcement may be necessary in thick panels, or where items such as crane rails impose severe loads. Placing a single layer of reinforcement offcentre to resist the bending moments during lifting is not recommended, nor is draping the reinforcement since it is difficult to maintain the desired draped profile. Furthermore, the panel may warp due to the non-uniform restraint of concrete shrinkage. Improved durability is also provided when the reinforcement is placed centrally. Either mesh or bar reinforcement may be used. Bars may provide greater flexibility in adjusting cross-sectional areas, especially in irregularly shaped panels. On the other hand mesh costs less to place and fix and can be purpose made to specific designs.

3.4.3 Volumetric Movements Panels should not be rigidly fixed together to form a long wall as concrete shrinkage and normal thermal movements will invariably lead to cracking. Long walls should be broken up by the introduction of movement joints and/or connections that will permit some movement to take place.

Steel-fibre reinforcement may be used to increase tensile forces due to lifting loads as well as those arising in the erected situation. Nevertheless, as noted below, it will need to be complemented by some bar reinforcement.

A typical shrinkage figure is 8 mm/10 m length

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Tilt-up Technical Manual


Structural Design The control of temperature and shrinkage cracking in tilt-up panels should be carried out in accordance with NZS 3101. Recommended minimum areas of reinforcement are given in Table 3.

Table 3:

concrete with a specified 28-day strength of 40 MPa are as follows: A1 A2 B1 B2

Minimum Shrinkage and Temperature Reinforcement

Specified yield stress of reinforcement (MPa)

Ratio of area of reinforcement to gross area of concrete

Mesh

.0014

Grade 300 bar

.0020

Grade 430 bar

.0018

Interior Exterior Coastal Zone Coastal Frontage

20 mm 25 mm 30 mm 40 mm

The precise definitions of environmental zones are contained in NZS 3101.

3.7

SAFETY

While tilt-up panels are routinely tilted, lifted, handled and braced without incident, the safety of these operations must be taken into account during design. The Australian Standard for tilt-up construction AS 3850(10) is specifically aimed at this aspect of the process. See also Section 8 of this manual. One aspect which needs to be emphasised is that of the choice of inserts. Lifting and bracing inserts should be purpose-made. Drilled-in expansion anchors must not be used for lifting and should be used with care when used as fixing inserts for braces. Frequently, drilled-in expansion anchors are used to fix the braces to the floor because the fixing positions are located under casting positions. As 3850 places special requirements for anchors used for this situation. Section 4.1.2.

Extra reinforcement is recommended both at edges and around openings in a panel to control shrinkage stresses and possible cracking even in fibre-reinforced panels. Diagonal bars D12, or D16 in thick panels, should be used across re-entrant corners if the panel thickness can accommodate the extra bar and provide required cover. Figure 11.

3.8

DURABILITY

Durability as a design criterion is frequently overlooked, as concrete when well made from sound ingredients is inherently a durable material. NZS 3101 provides guidance on concrete quality and cover for reinforcement for a range of environmental conditions. In general terms these will not greatly influence the design of tilt-up panels but they should be adhered to strictly. They may demand a concrete quality higher than that required for lifting design. The minimum cover durability requirements are set out in NZS 3101 Section 5. The thickness of cover varies with the quality of the concrete chosen and the environment the panels will be placed in.

3.9

NZS 1900 Chapter 5(11) gives the fire rating requirements for walls depending on the type of occupancy and the building location.

For example the cover requirements for a TM 34

FIRE RESISTANCE

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Structural Design MP9(12) gives the fire resistance ratings (FRR) for different thickness of wall, which are summarised in Table 4.

Table 4:

Wall Thickness Fire Rating Requirements (from MP9)

FFR (min)

Minimum equivalent thickness

60

75 mm

(75)

90

100 mm

(95)

120

120 mm

(110)

180

150 mm

(140)

240

175 mm

(165)

a thickness of ceramic fibre blanket to be provided on the inside of the joint. The thickness requirements vary with the panel thickness and joint width. Reference(13) is a useful design aid. Lower risk occupancy areas require no additional joint protection. The performance of panel structures in an actual fire is of concern to fire protection agencies. It is recommended that the design provide details such that the panels, during the fire rated period will remain standing as a cantilever or a box, and after that will tend to collapse into the building envelope. This will affect the type of connection details used for panels. Except in low risk areas, every external boundary wall in a fire compartment shall extend at least 450 mm above its adjoining roofline to form a parapet.

These figures are based on concrete with siliceous aggregates. Required thicknesses for pumice or limestone panels are reduced.

Apart from the panels themselves, the joints between panels may need additional protection to satisfy the appropriate FRR. In high risk occupancy areas, boundary walls where all openings must be fire rated, require

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Recent, as yet unpublished, fire testing work by BRANZ, indicates that the wall thickness tabulated in Table 4 could be amended to those in brackets. Formal acceptance from SANZ MP9 is being sought.

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Detailing

4. Detailing 4.1

some angle. The loading on the insert being either direct tension, shear or a combination of the two. Figure 12. Note that failure may occur in either the steel anchor or in the concrete anchorage, both should be checked.

INSERTS

4.1.1 Lifting The use of proprietary lifting inserts specifically designed for lifting and carrying panels is recommended. Each manufacturer will normally supply test data giving the capacity of the insert under various types of loads. AS 3850 sets out requirements for testing inserts and the procedure for calculating the load capacity. The critical loading condition for the insert may occur when the panel is either horizontal or tilted at

Some inserts require reinforcing steel to be threaded through the insert to achieve their load capacity. Where concrete anchorage for direct pull relies on the shear cone, the capacity is reduced by inadequate edge distances or low concrete strength. When edge lifting, reinforcement may need to be provided above the insert to prevent spalling. These details should be sought from the manufacturer. Where it is necessary to replace a defective lifting insert in a panel either a drilled through bolt fixing or an undercut anchor should be used designed with a 50% impact factor on static load.

4.1.2 Bracing Cast in inserts should be used for bracing connections where practical. The dynamic loading on bracing caused by wind will cause some types of drilled in expansion anchors to work loose at less than their rated loading. For this reason the allowable load capacity for bracing inserts should be based on the load at which the insert first slips in the hole. AS 3850 defined first slip load as the load causing the insert to move 0.1 mm. It then limits the applied load to 0.65 times this value. Where used, their first slip capacity should be checked carefully, the construction procedure supervised thoroughly and regular checks made to ensure the fastening does not tend to loosen. Standard sleeve anchors and expansion anchors have a low first slip rating and are generally not suitable for use as propping inserts. Note that chemical anchors are very dependent on depth and cleanliness of the hole and thus AS 3850 prohibits their use unless each fixing is individually proof tested TM 34

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Detailing to the working load limit. The Reid Anchorage design guide(14) is a useful reference on concrete anchorages.

4.2

bending of the casting steel and not by weld failure or fixing pullout. Permanent fixings, especially those exposed to the external environment, should be protected against corrosion. This can be achieved by using stainless steel or by protective coatings, e.g. epoxy or rustproof paint. Any protective coating should be applied over the entire fixing, including those parts to be cast into concrete.

FIXINGS

General criteria to be considered when specifying fixings for tilt-up panels are: •

For stability the panels may require more than one level of fixings.

Panels should be supported on seatings in direct bearing. See Section 4.3.

The wall should be carried at one level by two (no more, no less) seatings.

Fixings should be designed to accommodate the permitted dimensional inaccuracies of both panels and structure.

Fixings may have to be protected against fire if heat will adversely affect their performance. In general this can be achieved by recessing the parts in a pocket and filling with concrete or mortar. The Portland Cement Association (USA) publication ‘Connections for Tilt-up Wall Construction’ is a useful reference.(15)

4.3

SEATINGS

Welded connections are sometimes preferred but care must be taken to avoid locking the joints up, thus preventing movement. Bolted systems will generally permit such movement to occur. Figure 13.

Various types of seating are illustrated in Figure 14. Design for vertical loads on these connections is based on the bearing strength of the various material, e.g. concrete. Friction should not be considered to carry any of the horizontal forces imposed on the panel at the base. Footing should be detailed to provide an easily accessible area to land wall panels and complete seatings.

To reduce the possibility of a brittle failure, the failure mechanism should be in tension or

Rigid plastic shims (levelling pads) should be used to locate the panel at the design height and level. Steel shims should not be used for erection and left in place after the base of the wall is grouted as they can cause spalling due

Fixings should allow flex/move under conditions.

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the panel to environmental

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Detailing to the disparity of the moduli of elasticity and may corrode. Spalling may occur if shims are located too close to the end of the panel, 300 mm is the recommended minimum distance. The size of the shims used should be determined by the load-carrying capacity of the shims and the bearing capacity of the concrete panel. They should not exceed 40 mm in height and should be not less than the width of the panel or 100 mm, whichever is less. Other typical fixing and seating details are shown in Figures 15 and 16.

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Detailing

4.4

Table 5:

JOINTS

The importance of joint detailing in respect of the cost, appearance and performance of a lift-up building cannot be over-emphasised. Joint details must be compatible with the structural design assumptions, the erection procedures, the fixing details and the construction tolerances. The aspects of joint design which must be considered are:

Joint Type Face-sealed

Comparison of Joints Advantages Simple edge profile (no grooves necessary) Completed joints easy to inspect

Effectiveness of seal totally dependent on continued adhesion and performance of sealant. Access necessary to front of panel after erection To ensure good adhesion, condition of concrete surface critical, i.e. must be clean, smooth, dense, dry

4.3.1 Appearance The number of joints should be kept to a minimum. If a small-panel appearance is desired then this can be achieved by the use of false joints (grooves) in the panel surface.

Sealant exposed to major deteriorating influences, e.g. UV light and weather Open-drained

It is usually desirable to express the joints, not to try to hide them. The use of a recess or a dark band of paint on either side will help mask any variation in the width of a joint. It will also minimise the effects of any variable weathering at the joint line. In certain circumstances, e.g. with heavily ribbed panels, it may be possible to conceal the joints in the overall texture of the wall.

Basic sealing mechanism dependent on geometry not on adhesion Will tolerate larger construction variations and subsequent movements Installation during wet weather possible Air seal protected from UV light and weather

Gasket

Require complex edge formwork Profiled edge prone to damage Installation of baffle is difficult The drumming of baffle under wind conditions may be objectionable

Maximum construction width tolerance Âą 4 mm

Simple edge profile Quick to install

Bevels at the edges of panels are desirable to reduce the vulnerability to damage during handling.

Completed joints easy to inspect

Corners of tilt-up buildings demand special consideration. Oversail joints are preferred where it is acceptable to show a panel edge on one facade (its prominence will depend on the finish used on the face of the panels). Mitred joints allow a uniform surface treatment of both walls, but they do impose greater restrictions on erection tolerances and are not recommended, see Section 5.3.

Limited movement capability

At a corner joint the situation is different. The movement of the joint will include some shearing as well as tension and compression so the criteria will be different for the selection of the joint-sealing material. Flashing details at the top of the wall and roof need to be matched to that adopted for the joints. In all situations the use of a cap flashing is recommended. Figure 18. Such cappings must be securely fixed to prevent wind uplift.

4.3.2 Weathertightness and Maintenance

4.3.3 Joint Width and Sealants

Joints between wall panels will usually need to be weathertight. Face-sealed joints or Gasket Joints are usually preferred between panels, although more expensive open-drained joints can be used for exposed situations. Figure 17. The advantages and disadvantages of the three types of joint are summarised in Table 5.

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Disadvantages

Joints must be able to accommodate rotation and the variations in width caused by construction and erection practices. They must also allow the panels to move relative to each other as the environment changes, e.g. changes in temperature or humidity.

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Detailing •

Joint widths should be in the range 12 to 25 mm.

To maintain specified joint widths, erection procedures should allow cumulative tolerances to be absorbed at corners or openings, see Section 5.12.

The design of the seal joints is complex and involves the consideration of a number of factors, e.g. expected movement, type of sealant, width-to-depth ratio of sealant. A full discussion of all factors is outside the scope of this manual, detailed evaluations can be found in the ACI ‘Guide to Joint Sealants for Concrete Structures’(16) and the BRANZ publications ‘Sealed Joints in External Claddings: 1 Joint Design’(20) and ‘Sealed Joints in External Claddings: 2 Sealants’(21). The following general points should be noted:

For tilt-up construction, it is recommended that:

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21

Wide joints lower the strain due to volume movements and are preferred. Figure 19.

Preferred sealant cross-section dimensions have an aspect ratio of 1:2 as these also help to limit stresses due to movement. Figure 19.

Sealants should be bonded only on the two sides faces. Backup rods which do not bond to the sealant are available to control the depth and profile of the sealant.

The concrete faces at the joint should be dense, smooth, clean and dry to enable a good bond to be made with the sealant. The compatibility of the form-release agent and any curing compound with the adhesion of the chosen sealant should be checked.

The extension and compression capacities of mastic sealants will be inadequate for most tilt-up structures.

The effect of aging and exposure on the sealant must be considered. Most tilt-up buildings are not tall and therefore access to the joints for maintenance or repair may be neither difficult nor costly.

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Detailing •

provides some general guidelines for panel shape.(17)

The removal of a failed sealant can be difficult and the cleaning of the joint surfaces to permit the installation of a new seal may not be easy. Thus for low maintenance costs a resistant sealant (not the cheapest available), shielded where possible from direct exposure to sunlight and weathering, is desirable.

4.4

OTHER PANEL DETAILS

Greatest economy is achieved by repetition of shapes and details. This particularly applies where panels need to be stack cast. Openings in panels can provide considerable variation but joints should be located such that the width of panel segments alongside openings is not too narrow. Figure 20

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Construction

5. Construction 5.1

All-weather access to the casting locations and for erection will be required if construction is to proceed with the minimum of interruption. Consideration should be given to providing temporary construction roads around the building area, or the early construction of final and car parking area bases.

PROGRAMME

The dual aspects of construction and programming should be anticipated during the planning and design stages and not regarded as a problem solely for the builder. As well as considering the physical aspects of how the building is to be constructed, thought must be given to the requirements for labour, time for construction, and the sequence and timing of the construction.

Having checked the requirements for access during construction, those for erection need to be examined. Usually the crane will be operated off the floor and at point of access, the ground will need to be built up outside the slab to ensure that the edge of the slab is not overloaded with crane movements.

The size of the workforce needed to complete the job in the required time will depend (amongst other things) on the level of experience with tilt-up. The learning period need not be long, particularly if there is a high level of standardisation, but allowance for this must be included.

Where the crane operates on construction roads or on the ground within the building perimeter, it is important to ensure the ground is adequate to take the loads from the crane wheels, track and/or outriggers. These loads are more severe than those imposed by general construction traffic. Where panels have to be ‘walked’, the preparation of the ground must be examined extremely carefully.

As much work as possible should be carried out on panels when they are on the ground rather than when they are, or are being, erected. For example, fixings (both temporary and permanent) and preparation for jointing.

5.2

It is desirable that crane operation is restricted as little as possible by other construction operations or by the building itself. For example, even with a steel-frame building where the tilt-up wall panel are being used only as cladding, the panels should be erected as soon as possible. Depending on the type of column-base connections, the panels may be erected and braced before or after the columns. The roof beams can then be erected inside this shell. This is preferable to the crane having to operate in the restricted area between the already erected frames.

ACCESS

Access to and around the site greatly influences the construction and erection processes. Two aspects have to be considered: access for construction of the tiltup panels and access for their erection. It is desirable for the builder, in conjunction with the crane operator, to prepare a site plan showing the casting layout, vehicular access and lifting-point locations for crane as well as the erection sequence and bracing layout.

The position of overhead services should be established so that clearances during erection can be checked.

The locations for casting the panels should allow easy access for concrete trucks and the discharge of the concrete, preferably directly from the truck. If truck access to the casting areas is not possible then other methods, such as pumping or crane/bucket will need to be considered.

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The position of underground services should also be determined and the path of any required connections to them plotted. Operating a mobile crane over or near recently backfilled trenches is always

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Construction To assist in this planning a crane radius/rating transparency can be used, produced to the scale of the layout drawings. Figure 21. Alternatively cardboard cutouts of the panels can be used in conjunction with the layout drawings.

dangerous; particularly when carrying a large, heavy wall panel.

5.3

LAYOUT AND CASTING METHOD

The choice of surface finish will determine whether the panels are cast face-up or facedown. Erection procedures will influence both the decision whether to cast singly over a large area or to stack cast, and the choice of casting locations. The advantages and disadvantages of the two methods are summarised in Table 6.

Table 6:

Single and Stack Casting Advantages

Single Casting

No separate casting pads required Simple edge formwork Full range of surface finishes possible* Easy set-out of patterns in walls and panels

Disadvantages Surface finish of floor and location of construction joints must suit required panel finish and dimensions Floor may require repair after fixings removed Conflict at corners requires resolution

Units close to final position Stack Casting

Can proceed independently of floor

Requires separate casting pads

Permits greater programming flexibility

Limited range of finishes*

In determining the casting locations it should be remembered that the lifting operation should always, where possible, take place so that the driver can view the lifting and bracing connections during the entire erection operation. Also with the crane operating inside the building it may be necessary to omit the last panel, move the crane out, and then erect this panel from outside to complete the envelope.

No damage to floor

* See Table 8.

Panels should be cast as close to their final position as possible to avoid double handling and to keep the erection time as short as possible. The layout and casting order should be planned around the proposed erection procedure. It is critical that the crane position for each panel lift has been planned so that there is sufficient room for the crane including outriggers, the lifting can take place within the crane’s capacity, the panel can be located in its final position and propped without interference from other panels or site operations. Sometimes on a narrow restricted site where the floor is being used as the casting bed, it may be necessary for the crane to move across, or set up on top of the cast panels. TM 34

In general, large panels will require a higher lifting strength then smaller panels. Thus the casting of smaller panels can be left until last consistent with placing order. When stack casting is adopted, the casting order should reflect the erection order to avoid double handling the panels, or having to erect one between those already placed. Figure 22. Casting-stacks should be sited to allow 24

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Construction room for the crane to be set up in positions such that double handling of panels is avoided and the number of set-up positions is kept to the minimum. The number of panels in the stack is controlled by the number which can be erected without double handling, and by concrete placing and finishing considerations. A limit of 900 mm high is suggested. Parking areas and access roads can be used as casting beds if they are cast in concrete.

Joint details may also influence layout and erection sequence. If oversail corner joints are adopted, the erection sequence should enable any accumulation of erection tolerances to be absorbed in the oversail. Figures 23 and 32. Mitre joints do not impose any restraints on erection sequence. However, they do require more stringent control of erection tolerances, are very prone to construction damage and are best avoided. Figure 24. After erection, the panels will require temporary bracing until the final fixings can be made. If the panels are to be cast on the floor slab, the braces will restrict the choice of casting locations of corner panels and movement of the crane. Various ways of overcoming this problem are shown in Figure 25. The alternative is to use external bracing in conjunction with purpose-made ‘dead-men’, e.g. bored piers.

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5.4

FORMWORK

Formwork for tilt-up construction is at its simplest limited to perimeter framing of the panel. However, the extent and sophistication of the formwork and form lining will depend on the amount of modelling or texturing of the

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Construction close the opening temporarily. The coat of concrete can be knocked out after the panels have been tilted. An alternative system is to form up the opening using formply or polystyrene and place a 20 mm coat of concrete over the formed surface.

external surface. The choice of materials for formwork and the accuracy of its construction, play a vital part in ensuring that the erection process goes smoothly and efficiently.

If temporary bracings are to be fixed to the casting surface, fixings which require predrilling or casting-in should be evaluated carefully since they may read on the face of the completed panel. The use of a floor as a casting surface may dictate tighter tolerances on construction and surface finish for the whole floor than would be required for its subsequent use. For a narrow site a floor surface may need to be used many times if stack casting is not an option, e.g. once for each perimeter wall and once for party walls. Formwork to provide recessed areas in the panel face should be robust enough to remain plane under the application of concrete and associated construction loadings.

5.4.2 Edge Formwork With planar units, edge formwork is all that is required. Figure 26. For floor-casting, timber formwork robust enough to withstand the rigours of construction is normal. The size of edge-formwork members and the spacing of the supports needs to be related to the tolerances of construction and construction methods.

5.4.1 Casting Surface When one concrete surface is cast on another it reflects all the imperfections and blemishes of the latter. Special care is thus required to control the tolerances and finish of all surfaces which are to have another cast directly against them. If possible no joints should be included in an area of floor which is to have a panel with a smooth finish cast against it, or the joints should be filled prior to casting. When openings must be left in the floor for pipes, utilities, or the erection of interior columns or walls at a later date, a 20 mm coat of concrete over a sand fill can be used to TM 34

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Construction A straight and true bottom edge to a panel may be particularly important if this surface is relied upon for the panel to be erected plumb on prelevelled shims. If a gasket type seal is to be used in the panel joints, the side forms will need to be more accurate to meet the tighter joint width tolerance.

As with all formwork, great care must be taken at the joints, e.g. at corners and between the edge forms and casting surface, to form a tight seal to prevent leakage of fines and mortar which could lead to honeycombing, weakened edges and severe discolouration. Edge forms should be coated with form release agents to permit easy stripping.

Proprietary aluminium angle forms are available which are robust and stiff. These also have the advantage that they can be fixed at wide spacings. The fixing of formwork to the floor becomes important depending on the floor’s subsequent serviceability requirements or if that part of the floor is to be subsequently used for panel casting. The use of explosive fastenings may lead to spalling of the floor.

5.4.3 Blockouts Blockouts for major openings can be treated in similar fashion to edge forms. They should be securely fixed to the base slab to avoid displacement during concreting. However, the blockout formwork must be released as early as possible to avoid shrinkage cracks developing.

The use of chamfers on the edges has many benefits. They reduce spalling on the edges during removal of the side forms or due to handling. They also mask visually any variations in joint width and make installation of joint sealants easier.

5.4.4 Grooves, Rebates

Indents

and

Grooves, indents and rebates are most easily formed on the face-down surface as mentioned previously. Timber strips for forming grooves should be splayed as shown in Figure 28 and sealed to prevent swelling. These can be fixed with double-sided adhesive tape. Polystyrene can be used for single casts.

One efficient method of casting a long line of panels is to form up and cast every second panel and then to cast the panels in between. The sides are formed by glueing polystyrene, the thickness of the panel joint width to the previously cast panels, and the end forms being just moved along by one panel width. For stack-cast panels more sophisticated edge formwork will be required. Figure 27.

5.5

BOND BREAKERS

Coatings used to prevent bond between the casting surface, typically concrete, and the panel cast on it are known as bond breakers. Their performance is probably the single most crucial element in the tilt-up process. The moment of truth for any tilt-up project is at lifting. Will the panel separate or not? A

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Construction single captive panel can disenchant all associated with the project. Thus the choice and application of the bond breaker is crucial to the success of any project.

The compound should be applied uniformly, with particular care being taken at the perimeter of the panel adjacent to edge forms. Puddles should not be left on the surface.

If the surface is rained on prior to the bond breaker drying, a recoat may be necessary.

When applying over fine textured surfaces, a heavier application will be required than on smooth trowelled surfaces.

If spraying over old concrete, e.g. dry absorbent surfaces, dampening the surface prior to spraying is recommended, as well as a heavier application, to limit and compensate for absorption.

No traffic should be allowed on the coated surface before the coating is dry.

An excessive delay in casting after coating, say one week, may affect the performance of the bond breaker.

Before casting the panel, questionable areas, e.g. those with light or dull colour, should be checked by sprinkling on to the surface a few drops of water which should bead, not be absorbed into it. If necessary, the doubtful areas should be recoated and allowed to dry before casting. Reinforcement should be protected from contamination by the bond breaker as it will impair the bond.

The functions of bond breakers are: •

To permit clean complete separation of the tilt-up panel from the casting surface.

To minimise the dynamic loading caused by suction at the time of separation.

Some bond breakers also function as a curing compound for the casting surface.

The residue of the compound on the panel or the casting surface should not discolour or interfere with the adhesion or performance of any applied coatings or coverings or cause discolouration of the concrete. It is important to stress that release agents used to facilitate the stripping of formwork in insitu concrete construction are not suitable for use as bond breakers for tilt-up construction. A number of satisfactory bond breakers are, however, available and it is essential that one of these be used. If the bond breaker is not doubling as a curing compound, then the compatibility of the two must be checked. When applying particular compounds, the manufacturer’s recommendations should be followed. However, the following points are offered as a general guide: •

The bond breaker should be applied in two coats each in two applications at right angles to each other.

5.6

When the first coat is being used for curing it is usually applied immediately after the concrete surface has received its final trowelling and when the moisture has just disappeared from the surface. The second coat is applied after the formwork is in position.

The amount of tension to be applied to free a panel should never exceed the panel weight. Otherwise the bouncing which will result when the panel springs free may damage either the crane or the panel or both. If the panel has not released under panel weight, the sides should be vibrated by hammering and steel wedges driven in at the top edge and at the lifting insert positions in an effort to slowly peel

Prior to spraying the compound, the surface should be clean and free from dirt, debris, sawdust, etc.

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SEPARATION OF CAPTIVE PANELS

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Construction Secondly, the compatibility of the chosen compound with the bond breaker and its effect on subsequent surface treatments needs to be evaluated, e.g. wax emulsion will impair the bond of future surface coatings.

it off. This method will probably damage the edges of the panel and the casting surface. Alternatively, a hydraulic jack giving a sideways push between panels can also be effective. Where, however, the problem results from the use of a completely ineffective bond breaker, these methods may not be effective. It is therefore a golden rule to test the bond breaking compound prior to casting.

5.7

5.8

The concrete strength of vital importance is that achieved at the time of lifting. The 28 day strength must comply with requirements for durability and the designer’s requirements for the final structure, but it is common for the lifting strength to control what is ordered. In general, lifting strengths, depending on the design, will be in excess of 15 MPa. To achieve this strength at a few days after casting will usually require a 28 day characteristic strength greater than that required for other reasons. These requirements should be discussed with the concrete supplier.

PLACING, COMPACTING AND CURING

In general, normal practices for placing, compacting and curing should be followed. The concrete should be placed, compacted, levelled and screeded as promptly as possible. Use of vibrating screed is good practice. Care should be exercised around fixings, at corners and edges where steel congestion may prevent easy compaction. No final finishing should be attempted until the bleed water has disappeared from the surface. No driers should be used.

As accurate prediction of lifting strengths is important, it is appropriate for a set of test cylinders to be cast for site curing. These could be made on site or by the readymix supplier and delivered to site to be stored in the same curing regime as the panel. At low temperatures, the reduction in strength compared to standard cured cylinders could be considerable.

In hot, dry conditions the top surface of the concrete should be protected against rapid drying by shielding the surface from winds, shading from the sun and timing the placement to avoid the worst conditions. Spraying aliphatic alcohols onto the surface will also help control evaporation from the surface and the risk of plastic cracking. Plastic cracking could cause a significant reduction in the tensile capacity of a tilt-up panel.

The tensile splitting test as an alternative to the compression test will generally result in a more accurate prediction of flexural tensile strength. Concrete mixes using crushed aggregate rather than rounded gravels will have a higher tensile strength for a given compressive strength, which will be reflected in the tensile splitting test.

Tilt-up panels should be cured properly to ensure that the full potential concrete strength is developed. Lack of curing may reduce the tensile strength of the concrete by up to one third.

5.9

As with bond breakers, two further points need to be stressed. Firstly, to be effective the curing compound needs to be properly applied to give uniform and complete coverage to the concrete surface. This application should take place just when the sheen of surface moisture has disappeared but the concrete is still damp.

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CONCRETE

CRANES

The rating of a crane is the maximum load that can be carried at its minimum radius. The radius is measured from the centre of rotation of the crane. The greater the radius, the lesser the load, for example a crane rated at 35 tonnes will carry 35 tonnes at its shortest reach but at 6 metres radius will lift only 20 tonnes. Figure 29. For this size crane, the

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Construction reasonable level (10T/m2 for a 125 mm thick slab). Crawler-mounted cranes impose lower bearing stresses on the ground and can be useful when erection from outside the building is possible.

lowest operational radius is in fact around 6 metres but this will increase for larger cranes.

The lifting limitations (height, reach and load capacity) of the chosen crane should be carefully examined. As a rough rule of thumb, crane capacity should be two to three times the maximum panel weight. Dismantling, moving and setting up in a fresh location takes considerable time and is completely unproductive. Therefore, the more panels which a crane can erect from a given position the more efficient the operation. When moving the crane on cast walls still to be lifted, tyre marks will result which are difficult to remove. If this is critical the running surface should be protected with newspaper. All rigging, lifting beams, shackles, etc., may be available from the crane supplier, but this should be checked. With modern quickrelease inserts it is common to use only one set of rigging/lifting gear and there seems to be no great speed advantage in using multiple sets.

Many factors come into the selection of crane size and this should have been determined at the planning stage along with panel sizes and casting layout. The crane operator should be involved at this early stage.

Rate of erection will vary with the size of the panels, layout, complexity of bracing, etc. As a guide, competent contractors aim to erect one panel every half hour and frequently manage a 15-20 minute cycle.

When assessing panel working radius, 1.5 metres should be added to the final panel position to allow for the tilt of the panel when on the hook. Figure 30. Also the weight of rigging gear and any strongbacks need to be added to the weight of the panel when evaluating crane capacity. The use of a larger crane with fewer number of panels will not always be economical. The additional crane costs need to be balanced against the reduced casting costs. A larger crane will take longer to set up and move between lifts. A large crane will generally not be able to get as close to a panel and also rigging of large panels will be more complicated. Certainly a larger crane required for only a few larger panels in a contract is an uneconomical solution. High point loads will be imposed on a slab from the outriggers or a mobile crane. This load should be spread into the slab by using timber bearers to keep bearing stresses to a TM 34

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Construction shimming, cleaning out inserts, etc. and all rigging and bracing gear to be checked and at hand. Delays during the erection operation can be very costly.

5.10 RIGGING AND BRACING HARDWARE The erection of panels on a boundary against an existing wall can often be difficult. Face lifted panels will always hang slightly off vertical (3o to 5o). Edge lifted panels will hang vertical. However this lifting configuration is not economical for panels over 3-4 metres high. One solution is to use an extra set of inserts in the top edge for face lifted panels. The load can be transferred to these using a second crane or alternatively the panel could be temporarily propped off vertical and relifted off the top edge. Alternatively offset lifting brackets can be used or trigger mechanisms which lock the lifting ropes against the top of the panel when the panel is near vertical. These operations need to be planned beforehand and should only be carried out by an experienced crane operator.

Where possible the crane should be on the same side of the panel as the bracing so that the driver can see the erection operation. The lifting inserts must be placed symmetrically about the centre of gravity in the horizontal direction so that the panel will lift level, and above the centre of gravity in the vertical so that the panel will tilt. Centres of gravity for each panel should be calculated as shown in Figure 31, or by computer, and marked on the drawings.

The use of remote release lifting inserts is preferable as this reduces erection time and is safer than climbing up the panel to release the rigging. Braces should be connected to the panel prior to lifting and these should be positioned clear of lifting inserts and rigging. Purpose-made adjustable braces are available and these speed the erection process as final plumbing of a panel can be carried out using these braces. Braces should have the maximum safe working load displayed at zero, and maximum extension and should have stops to avoid over extension. The layout of the lifting inserts should also be clearly shown. Very tall panels, or those with thin legs of multiple or large openings may need to be strengthened by strongbacks before lifting.

The rigging must not be released until the panel is adequately braced. Lateral bracing where required should be fixed immediately so that it is not more than one panel behind the last panel erected. All braces should be checked at regular intervals for tightness and security.

5.11 LIFTING

Lifting should be carried out so that the panel rotates about the bottom edge. Any damage to this edge can be hidden by appropriate joint detailing. Bottom-edge chamfers are normally used to reduce this risk.

Prior to the crane coming on to site all preparatory work should be completed – panel

Care should be taken to avoid sliding or dragging panels across the finished floor

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Construction oversail corner of doorway. Figure 32.

because of the risk of damage to panel, casting slab, personnel and equipment. With stack-cast panels, more care is needed to prevent the panels sliding off the stack and damaging the face of the lower panel. If, after heavy rain, water is lying against a panel, lifting should be not attempted since suction forces will be substantially increased. The accurate erection of the first few panels is critical. Extra time spent in plumbing these in both directions and establishing the correct line will repay itself in quicker erection of succeeding panels. Extra time should also be allowed on the first panels for the erection team to become familiar with the procedure. Panels must be moved smoothly at all times to avoid shock loading which may induce cracking or possibly damage the crane. Panels should not be lifted in high winds or adverse weather conditions. Putting a panel back down again after lifting will almost certainly result in a cracked panel.

If tilt-up panels are being used in conjunction with insitu construction then the tolerances for tilt-up panels should not be used to absorb the construction errors of the insitu work.

Final fixings should be completed as soon as practicable after the panels have been temporarily braced. Safety considerations will usually dictate a hour interval between the two operations.

5.12.1 Panel Tolerances These can have a marked effect on all aspects of the construction. Suggested tolerances are given in Table 7. Tighter tolerances will be expensive to achieve.

The importance of safety during the lifting operation cannot be over emphasised. Do not take any dangerous short cuts. Packers and spacers should never be placed in position under the suspended panel. All personnel must stay clear of the line of fall of the panel and crane hook. The lines of communication with the crane operator should be clearly established using correct hand signals as necessary, prior to lifting.

5.12.2 Insert Tolerances Some are more critical than others. are given in Table 7.

These

5.12.3 Joint Tolerances

5.12 TOLERANCES

Joint tolerances are important for the weatherproofing performance of joints. Gasket joints have movement capabilities of Âą20% whilst flexible joint sealants are capable of around Âą25%.

It is of the utmost importance that the specified panel and joint tolerances are realistic. Once established they must be maintained. In general, both will lead to a growth in overall wall length. Depending on the size, joint details may be used to absorb these variations either progressively at each joint or collectively at one location, e.g.

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Maintenance of the nominated width of joint as per Figure 32 is the preferred option, with dimensional variations taken out at doorways and/or oversail corners.

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Construction Table 7:

Recommended Tolerances (Table 3.7.1 of AS 3850) PANEL TOLERANCE (mm)

Panel Size <3 ≤ 3<6 ≤6

Width +0, +0, +0,

1

Height

Planeness

Squareness

± 5 ±10 ±10

±5 ±5 ±5

± 5 ±15 ±15

- 5 -10 -12

2

Edge Straightness

3

Thickness

± 5 ± 7 ±10

±10 ±10 ±10

1

Deviation of any point on the face from the intended line. Measured as tolerance in length of diagonal. 3 Provided that in any 3 m, the deviation from the intended line does not exceed 5 mm. 2

INSERT TOLERANCE (mm) Face Lifting Inserts Edge Lifting Inserts – Longitudinal – Thickness Bracing Inserts Fixing Inserts Strongback Inserts

±20 ±20 ± 5 ±50 ± 5 ± 5

PANEL LOCATION Deviation of panel from the specified final position in the structure

5 mm

(iv) Fixing inserts, and if required

5.13 CONSTRUCTION PLANS

(v)

Strongback inserts.

Construction plans should include details of the following:

(e) The concrete grade specified strength.

(a) Panel dimensions.

(f)

(a) Structural reinforcement.

and

minimum

The required concrete compressive strength at the time of lifting. fcm.

(g) The mass of each panel.

(b) The location orientation and depth of embedment of inserts and size, configuration and cover of any component reinforcement required.

(h) The surface finish of each panel, and where appropriate surface finish tolerances.

(c) The size, configuration and cover of any additional reinforcement required for lifting of panel. (d) Where applicable, the make, type and capacity of technical specifications of:

(i)

Any architectural features.

(j)

The rigging configuration and minimum sling length.

(k) Strongbacks, if applicable.

(i)

Panel braces,

(l)

(ii)

Lifting inserts,

The orientation of the panels on the plans should be the same as the proposed casting orientation.

(iii) Bracing inserts,

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Bracing size and configuration.

Tilt-up Technical Manual


Surface Treatments

6. Surface Treatments over surface finish that is normal in a precasting factory.

A major factor in the acceptance and therefore the increased use of tilt-up overseas has been improved appearance in recent years. A wide range of treatments and finishes, most of which are easy to achieve and some for which specialist skills are available, have been developed. This move has been assisted greatly by the development of a wide range of paints and textured applied coatings. These afford versatility and variety in appearance at reasonable cost.

Coatings can be used to provide strong visual effects, to mask colour changes and reduce the visual prominence of accidental variations in texture. Grooves should be used to break up the scale of panels and to separate different finishes or colours. Such grooves should never be more than 20 mm deep, frequently 10 mm is adequate. If these grooves are to be painted then they should be wide enough to accept a small-size standard paint roller.

The increase in the use of tilt-up can be attributed to the promotion of architectural tiltup and expansion into the more prestigious building market. Apart from the use of shapes and outlines to achieve the desired effect, improved appearance of tilt-up building stems largely from sensitive detailing of panels, small changes in panel shape and size, and an almost limitless range of colours, patterns and textures, breaking up the monotony of long walls of large uniform panels. Often tiltup can be made to look impressive by contrasting different surface finishes within a panel or line of panels. Examples of these are: •

Picture frame effect – exposed aggregate panel with a border of fairface concrete around the edges.

Use of broad band of contrasting high build paint. This band could either be recessed in the panel or alternatively defined by edge rebates.

Use of rebates in exposed aggregate or contrasting paint to display company logos.

Use of formliners contrasted with painted fairface concrete.

6.1

The compatibility of the bond breaker with the desired surface finish should be checked, by test panel if necessary. This should establish any risk of surface staining and the effect on any subsequent paint film to be applied to the surface. Concrete mix design should take account of the quality of surface finish desired. It should be cohesive and be rich enough to reproduce any fine textures which may have been specified. To ensure uniform colour on concrete surfaces it will be necessary to maintain a consistent supply of cement, aggregates and sand. Good mix design (including control of water-cement ratio and minimum cement contents), uniformity of casting-surface absorption and curing conditions are also imperative. (Note that these considerations rather than structural considerations may control the specification of the concrete). The use of test panels for special finishes/ treatments is strongly recommended. They should be large enough to be representative of the specified technique, approval should be related to the entire panel, not just sections of it.

GENERAL PRINCIPLES

6.2

Simplicity of finish should be the primary objective. It is not generally possible to achieve on the site the same degree of control

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IMPLICATIONS OF SURFACE TREATMENT

Each face of a tilt-up panel can be given a

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Tilt-up Technical Manual


Surface Treatments Table 8: Methods of Achieving Various Types of Finish by Both Face-up and Face-down Approaches

special finish but it is usual to confine special finishes to the external face. The internal face is normally given only a plain smooth finish. Finishes are described as being provided ‘face-up’ or ‘face-down’, depending on the position (at the time of casting) of the face receiving the finish.

Type of Finish

Table 8 provides a list of the types of surface finishes and how they can be achieved on face-up and face-down surfaces. From the comments included it can be seen that facedown is preferable for most types of finishes. This approach has the further advantages that the panels can be stack cast, and that the lifting inserts are on what becomes the back of the panel, where the subsequent filling will usually be least objectionable.

Rebates, grooves and patterns

Hammer form into top surface (Position and depth difficult to control)

Fix form to base slab (Position and depth easy to maintain)

Plain, smooth surfaces

Finish panel with bull float and trowel (Common paving technique)

Finish off floor or casting pad (Reproduces all imperfections of that surface)

Exposed Aggregate

Water washed (Special aggregates and patterns difficult to control)

Sand embedment (Different aggregates and patterns easy to achieve, independent of concrete mix)

Fine Textures

Broomed, Combed, Imprinted, Rolled

Timber forms, Formliners Timber forms, Profiled steel sheeting, Polythene over stones, Formliners.

* See Table 6

Solvent removal is frequently unsatisfactory due to the residue it leaves on the surface. Various applications may be used, both highbuild or thin film are suitable. High-build applications can be used to mask unwanted surface texturing. Surface preparation will depend on the type, the recommendations of the manufacturer should be followed. Application may be by spray or by roller, depending on the paint type and desired texture of the coating.(18)

PARTICULAR SURFACE TREATMENTS

6.3.1 Coatings Coatings are the easiest way of improving the appearance of smooth-finished surfaces. They can also be used on textured surfaces although application becomes more difficult as the coarseness of the texture increases. Recently developed coatings are available which give a range of textures. They have the advantage of masking minor imperfections and colour variations in the base surface but will not conceal major imperfections. Further, they offer the advantage of being easily reinstated after despoiling (accidental or intentional) and are easy to maintain and change to give a new image to a building following change in ownership/tenancy.

6.3.2 Form Liners These are applicable only to cast-down faces but can be used in either stack-cast or floorcast approaches. A wide range of patterns and textures is available overseas. They can be made of a number of materials: rubber, thermoplastics, fibreglass-reinforced plastics, timber and metal decking. Disposable formliner from lightweight polystyrene plastic are glued to the casting bed, with debonding taking place at tilt-up. Reusable formliners need to be fixed more permanently and with reasonable care, 5-10 re-uses can be expected.

The effect of the bond breaker and of the curing process on the adhesion of the coating needs to be checked, see Clause 5.5. If an incompatible material has been used it must be removed by lightly sandblasting, by grinding or high pressure water blasting. TM 34

Face-down (single or stack casting*)

Coarse Textures

An early decision on the finishes to be used and, more importantly, whether a face-up or face-down approach will be adopted is important since it can influence the whole casting procedure – location, sequence, etc.

6.3

Face-up (single casting*)

Use of formliners can eliminate the need for extra care in preparing the casting bed so that 35

Tilt-up Technical Manual


Surface Treatments Chemical retarders should be specialist architectural retarders which are available in varying degrees of etch. For face-down application care needs to be taken with the application of the retarder and the placing and vibration of the concrete. It is not possible to obtain the same degree of exposure with faceup retarded panels although it can be improved by seeding. In both cases it is likely that there will need to be a modification to the structural concrete mix to obtain effective exposure. Care needs to be taken in removal of the retarded surface to ensure uniformity of finish. This is normally achieved with a high pressure water blaster.

joints, column blockouts, etc., will not be reflected in the panel. Depending on the texture, liner sections can be lapped or butt joined and filled with a silicone sealant. Formliners need specialist release agents, these are usually recommended by or available from the manufacturer. Where not supplied by the formliner manufacturer, testing will be necessary.

6.3.3 Dimple Finish This finish is achieved by placing two sheets of polythene (6 mils) over a layer of stones and placing the concrete directly over this. This imparts a â&#x20AC;&#x2DC;dimpledâ&#x20AC;&#x2122; effect and gives the concrete a very smooth glossy texture. The effect can be varied with the size, shape and grading of aggregate used from 20 mm to boulder size. It is widely used in the USA owing to its relatively low cost, it masks any imperfections in the casting surface and eliminates the need for a bond breaker.

Retarders in the form of chemically impregnated paper rather than paint form are now available. These are a recent innovation from Europe and trial would need to be carried out prior to full scale use. They would be suitable for use in small areas of a panel to be used to break up a fairface finish. The use of retarders requires specialist skills and trial panels should be used to obtain the required finish. One option is use specialist labour from a precast manufacturer under subcontract, they should be experienced in this type of work.

6.3.4 Rebates and Grooves Rebate strips made of timber or polystyrene can be glued to the casting bed. The strips must have sufficient taper to ease demoulding and any fixings used to join the strips must be plastered over smooth to avoid spalling on demoulding. It is important to avoid a mismatch of rebate alignment between panels.

Face-up exposure of panels can also be achieved by water washing the face some hours after casting. The sand bed method allows the hand placing of uniform size aggregate into a sand bed, over which the concrete is poured. This method is preferred in the USA because of its versatility.(19)

6.3.5 Exposed Aggregate Surfaces There are four common methods of exposing aggregate in tilt-up construction. These include the use of chemical retarders, either face-up or face-down, sand blasting, sand bed casting face-down, and seeding of aggregate on the face-up surface finish. The general method is therefore suitable for either floor or stack casting.

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Sandblasting â&#x20AC;&#x201C; As tilt-up is some days old when lifted, only light or medium sandblasting textures can be used. Sandblasting without the use of retarders can give a softening effect to the normally shiny surface of a panel.

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Costs

7. Costs erection costs in particular will ‘blow out’ if site efficiency is disrupted. The following unit costs based on panels 6 m high by 5 m wide and 120 mm thick are based on 1991 prices.

Tilt-up construction has proven to provide significant cost advantage over alternative heavyweight cladding systems such as concrete blockwork, brickwork or offsite precast panels in many low rise construction projects. The scope for cost savings depends on the extent to which the advantages of tiltup, as outlined in Chapter 1, are incorporated into the design, e.g. elimination of columns, architectural features, etc. Lightweight cladding systems may compete with tilt-up on a straight cost basis, however do not provide the fire rating, security, long term durability or robustness which tilt-up provides.

2

Tilt-up construction has the potential to provide benefits in three vital areas of development feasibility: 1.

Space: Total maximum area of lettable floor space that can be economically constructed on the site. Tilt-up can be built up to the boundary and the elimination of columns means there is greater flexibility or internal fit-out.

2.

Cost: Differential contract sums of up to 30% when compared to concrete blockwork have been realised.

3.

Construction Time: Savings in construction time not only reduce the contract sum as a result of lower P and G (Preliminary and General) costs but also additional rental income can be realised from earlier occupancy. Industrial and commercial buildings in tilt-up construction can often be constructed 2030% faster than buildings in alternative heavyweight systems.

Material supply rate

m rate

%

Reinforcing Steel – Supply and place

$11.90

19

$2685/T

Concrete – Supply and place

$20.30

33

$140/m

Formwork hire

$ 1.94

3

Inserts, Fixings, Bondbreaker

$ 2.70

5

Labour – Set up Panels

$10.00

16

Propping hire

$ 2.00

3

Cranage and erection

$11.00

18

Jointing

$ 1.56 Total

3

3

$8/m

2

$61.40/m of Panel

Once the decision has been made to use tiltup construction, the building should be designed as tilt-up rather than adapting a design based on a different form of construction. Minimising the costs for construction and erection of tilt-up panels relies on good planning. Many of the costs are fixed but the

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Safety Checklist

8. Safety Checklist The following list, which is not exhaustive, gives some of the areas of responsibility that each party has in safety:

Tilt-up construction involves the handling of large, heavy concrete elements and requires careful planning and proper execution by experienced personnel using good quality equipment to proceed in a safe manner. The majority of work follows good practice and shows that the method is safe. This requires a good team-approach as safety is a job involving the designer, contractor, and lifting operator. They each have a role and must each know what is being done and agree/ accept that procedure.

Designer • • • • • • • • • • • •

Overall building stability. Panel lift design. Insert selection. Insert location. Bracing design. Bracing type. Reinforcement. Concrete strength. Fire performance. Lifting procedures. Load design of floor/pavement. Communication of all aspects via drawings and documentation to the builder.

Contractor • • • • • • • • • • • • • • • •

Panel size/shape/tolerance. Access for crane/trucks. Preparation of pavement. Reinforcement location. Insert selection. Insert location. Brace-point location. Fixings. Bond breaker type. Bond breaker application. Concrete quality. Compaction of concrete. Concrete curing. Casting sequence. Erection sequence. Workshop drawings and casting and erection drawings – essential forms of communication.

Erector • • • • • • • • • •

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Safe working environment/procedures. Crane access. Crane position. Erection procedure. Crane/panel weight ratio. Strongbacks. Rigging gear. Correct lifting eyes. Concrete strength. Fixing bracing.

Tilt-up Technical Manual


References

References 1.

‘This is Tilt-Up’, Australian Constructional Review, Vol. 57, No. 1, February 1984, pp. 49-64.

13. ‘Design for Fire Resistance of Precast Prestressed Concrete’, MNL 124-89, Portland Cement Association, 1989.

2.

‘Tilt-Up Today’, October 1989, G67, C & CA Australia.

14. ‘Anchorage Design Guide’ – Reid Construction Systems Publication 170/1.

3.

‘Tilt-Up Construction’ Compilation No. 7.

15. ‘Connections for Tilt-up Wall Construction’, BE 110.OID, Portland Cement Association, 1987.

4.

‘Tilt-Up Concrete Buildings’, 1989, PA 079.02B, Portland Cement Association.

ACI

5.

NZS 4203: 1984, ‘General Structural Design and Design Loadings for Buildings’. SANZ.

6.

‘Aries Tilt-Up Design Computer Programme’. Alan H Reid Engineering Limited.

7.

NZS 3101: 1982, ‘Design of Concrete Structures’. SANZ.

8.

Weiler, G. and Nathan, N.D., ‘Design of Tilt-Up Concrete Wall Panels’, The University of British Columbia and Canadian Portland Cement Association, April 1979.

9.

16. ACI 504R-77, ‘Guide to Joint Sealants for Concrete Structures’, ACI Manual of Concrete Practice, Part 5, American Concrete Institute, Detroit 1990. 17. ‘Some Practical Tips in the Architectural Design of Tilt-Up’ – Ref. 3. 18. ‘Painting of Tilt-Up Panels’, Construction Note, C & CA, Australia. 19. ‘Exposed Aggregate Tilt-up Panels by Sand Embedment’, Construction Note, C & CA, Australia. 20. ‘Sealed Joints in External Claddings: 1 Joint Design’, Building Research Association of New Zealand, Judgeford, 1984, (Building Information Bulletin 238).

Kripanarayanan, K.M., ‘Tilt-Up LoadBearing Walls: A Design Aid’, BE 074.OID, Portland Cement Association, 1974.

21. ‘Sealed Joints in External Claddings: 2 Sealants’, Building Research Association of New Zealand, Judgeford, 1984, (Building Information Bulletin 239).

10. AS 3850, ‘Tilt-up Concrete and Precast Concrete Building Elements; Part 1; Safety Requirements; Part 2: Guide to Design, Casting and Erection of Tiltup Panels; Part 3: Guide to Erection of Precast Concrete Members’. SAA. 11. NZS 1900 Ch. 5: 1988. ‘Fire Resisting Construction and Means of Egress’. SANZ. 12. MP9: 1989. ‘Fire Properties of Building Materials and Elements of Structure’. SANZ.

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The Cement & Concrete Association of New Zealand is an independent, non-profit organisation whose mission is to promote the competitive, safe and innovative use of cement and concrete products.

Since the information provided in this manual is intended for general guidance only and in no way replaces the service of professional consultants on particular products, no liability can be accepted by the associations for its use.


residential concrete d e ta i l i n g a n d s p e c i f i c at i o n g u i d e


residential concrete d e ta i l i n g a n d s p e c i f i c at i o n g u i d e


preface This technical manual is published by the Cement & Concrete Association of New Zealand with funding assistance from the New Zealand Concrete Masonry Association. The construction details contained within this manual have been developed based on extensive research both locally and internationally. They are designed to give examples representative of good practice, rather than a complete range of possible alternatives. The manual is written by Morten Gjerde, Lecturer and CCANZ Fellow at Victoria University of Wellington, School of Architecture. Heartfelt thanks to the following people, without whose assistance this would not have been possible:

Research assistance: Rachel Chan Peter Lough Oliver Markham Nancy Bakker Grant Taylor Peer review: Daniel Bagust Philip Blair Ross Cato John Gibbons Derek Lawley Nigel Marshall Andy Wilton Typing: Tricia Hawkins Editing: Grant Thomas Dene Cook

Waterproof with us Resene X-200 Acrylic Waterproofing Membrane occupies pride of place in the Resene range of waterproofing products. With Resene X-200, most surfaces can be waterproofed and weatherproofed with a two-coat system*. Application costs are therefore similar to any two coats of conventional paint, combined with the benefits of multi coat high build systems. Resene X-200 uniquely combines low viscosity with high build ensuring excellent penetration into cracks and pores, resulting in superb adhesion. Resene X-200 high build properties allow the development of a tough, durable and continuous membrane, while non-

asbestos fibre reinforcement increases tensile strength. Resene also manufactures and sells a full range of textured coatings and specialist finishes to give you and your client the finish you desire. From high builds to aggregate textured coatings, we have the range to suit every taste. To find out more and obtain copies of the X-200 Data Sheet (D62) or textured coatings and specialist finishes specifications (21e/i), call 0800 RESENE (737 363), see your nearest Resene ColorShop, or visit the Resene website at www.resene.co.nz

* An additional coat of X-200 may be required on concrete block due to regional variations in standards.

3


contents General Information . . . . . . . . . . . . .7 Concrete Masonry . . . . . . . . . . . . . . .13 Insulating Concrete Formwork . . . . . .35 Precast Concrete . . . . . . . . . . . . . . . .55 Concrete Cast In-Situ . . . . . . . . . . . .77 References . . . . . . . . . . . . . . . . . . . .95

ISBN 0-908956-12-6 TM36 Cement & Concrete Association of New Zealand Level 6, 142 Featherston St, Wellington. P O Box 448, Wellington. Tel: (04) 499 8820, Fax: (04) 499 7760. Email: admin@cca.org.nz

Š Cement & Concrete Association of New Zealand 2000 Except where the Copyright Act allows, no part of this publication may be reproduced, stored in any retrieval system in any form, or transmitted by any means, without the prior permission in writing of the Cement & Concrete Association of New Zealand. The information provided in this manual has been prepared with all due care; however the Cement & Concrete Association of New Zealand accepts no liability arising from its use.

5


r e s i d e nt i a l co n c r e te d e ta i l i n g a n d s p e c i f i c at i o n g u i d e

Mann House in Auckland by Ian Juriss.

6


G e n e ra l I n f o r m a t i o n

General Information introduction Concrete is well known to many New Zealanders as a building material. Being a country of â&#x20AC;&#x2DC;doersâ&#x20AC;&#x2122; has meant that not only are we familiar with concrete but also many have had personal experience with it. Footpaths, garden walls, garages and sculptures stand as testament to this hands-on experience. In the construction industry, concrete is the most widely used material both here and overseas. Commercial structures from single to multi-storey continue to be built in concrete. Most residential construction is based on the concrete ground floor slab and our infrastructure, from underground pipes to bridges, is largely constructed of the material. The building industry in New Zealand is well resourced to construct in concrete. Raw materials are readily available throughout the country. The techniques for constructing formwork, placing concrete, erecting precast elements and building in masonry are to a very high standard internationally. The design of concrete structures by local engineers lead the world in many areas. The existence of several quality suppliers of precast structural systems and other proprietary elements in the marketplace allow designers and builders competitive pricing, extensive system choice and excellent technical support. For all that, New Zealanders continue to favour timber framing for the construction of their houses. It is not unusual to see a design modelled on the massive homes of the Mediterranean, built using spaced timber studs with a thin cladding of stucco or acrylic plaster on rigid board. Many designers and homeowners in this country prefer to continue to use systems and techniques with which they are familiar. Concrete construction has been widely used for housing throughout Europe and to a lesser extent in the United States. It would be difficult to think of the work by

Le Corbusier, Adolf Loos and more recently Herzog and deMuron without conjuring up images of concrete. Market research has been carried out in an effort to identify why concrete is not used more readily in the residential construction sector in New Zealand. These results indicates that there is inadequate information for those wanting to design and build concrete houses. There is also a lack of builders who are comfortable building concrete walls and suspended floors in the domestic context. The processes involved in building in concrete are different to those employed in timber framing and cladding. Builders comfortable with concrete have tended to become established in commercial construction. While the research pointed to an enthusiasm for concrete homes, designers and builders tend to stay with familiar materials and processes.

The raw materials for concrete are readily available.

This publication seeks to bridge the knowledge gap for designers and builders of concrete homes. It does not however claim to fulfil all their information needs. It has been structured to give an overview of the principles and highlight the critical issues facing designers and builders. The construction industry has been widely consulted and research has been carried out both locally and internationally. The details have been prepared to present a broad range of construction scenarios. The designer or the builder using this manual may find the need to change relationships or sizes shown to suit their own purposes. The intention has been to present a starting point from which specific details can be developed. The details shown here have been checked for suitability for New Zealand conditions. Provided the detailing principles are adhered to, others should perform equally well.

7


r e s i d e nt i a l co n c r e te d e ta i l i n g a n d s p e c i f i c at i o n g u i d e

scope This document has been prepared as a general guide to the design and construction of the single family house and projects of similar scale in New Zealand. Although this manual does not specifically address fire resistance and sound transmission ratings, the adjacent table demonstrates the values that can be achieved with appropriate detailing. It presents materials and systems that are commonly available in New Zealand. Some, such as timber joinery and concrete itself, have been in use for several generations. Others have recently come into the local market and industry experience with some of these may be limited. On the other hand, building products not available in New Zealand have not been incorporated. To do so would inaccurately present the range of materials available here. The construction, specification and detailing issues are presented in the New Zealand context. We have specific and often unique ways of doing things. The New Zealand environmental conditions are also unique.

Recessed timber door & sill Butyl rubber sill flashing

Non structural conc. veneer Insulation

Floor coverings Reinforced conc. slab

This book is principally concerned with design and construction issues. While it does touch upon topics such as thermal performance and structural engineering, it is not meant to serve as a guide in these areas. Structural design is still best left to the professionals except in those areas where non-specific design standards are available. Concrete masonry is one such format with NZS 4229 having been revised in 1999. The Cement & Concrete Association of New Zealand produces a range of other publications that may be of interest to the designers and builders of concrete homes. Further information is available at www.cca.org.nz.

Paving level Structural conc. panel

SILL DETAIL

Panel Thickness

Fire Rating

Sound Transmission Class (STC) rating

100 mm

90 minutes

44

120 mm

120 minutes

48

150 mm

180 minutes

55

200 mm

>240 minutes

58

Typical fire and sound transmission ratings that can be achieved with concrete systems when appropriately detailed.

8


detailing considerations Objectives

Successful architectural detailing requires attention to many factors. As with most aspects of building, it is often necessary to think laterally to achieve results that are both poetic and satisfy pragmatic goals. First off, it is important to be able to clearly identify the detailing objectives. These may come under headings such as: •

cost

appearance and aesthetics

buildability

materials usage

routine maintenance

All successful design and detailing efforts will consider these factors. The designer may make value judgments through the process, placing the importance of one aspect above another. The critical thing is to be aware of these considerations and to understand the consequences of favouring any one over the other. Environment

It is also important to consider the specific environment that the details are to exist in. It is critical to acknowledge and design for: •

prevailing winds and wind patterns created by the landscape or other buildings

Grigg House by Miles Warren.

quickly see mould and other organic growth develop, even with regular cleaning. If inappropriate materials are used or poor detailing choices are made, the building appearance can deteriorate quickly. Material properties

Concrete has a number of special and unique qualities that make it an ideal construction medium, particularly in domestic applications. These include: •

high durability

rain and other weather that can be expected

thermal mass benefits when used appropriately

UV exposure

ability to form and shape

dust and pollutants that may be in the air and settle on the building

enclosure of space and structure in one material

corrosive elements in the air such as salt spray

ability to form integral surface finishes and colour

moisture, either rising from the ground, or as general humidity

relatively inert and compatible with most other buildings materials

excellent acoustic and fire resistant properties

Specific environments can vary from site to site and even on different faces of the same building. While exposed concrete masonry may be appropriate on the sunny north face of a house, its use on the south side of a damp site could

Frank Lloyd Wright was an innovator with concrete.

Along with these qualities are some inherent limitations that the designer should bear in mind:

9


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â&#x20AC;˘

once cast it is difficult to change

â&#x20AC;˘

not sufficiently waterproof on its own

â&#x20AC;˘

sharp corners or edges can be vulnerable to mechanical damage

Once the decision to use a concrete structure in residential projects is made, the designer and the builder must find ways of optimising the positive attributes while minimising the negative aspects of concrete. The best way of ensuring this is through adequate and considered planning. This Guide is one resource to help with this planning. Maintenance

Planning for routine maintenance of the building, and in particular of the details, must be borne in mind. All materials and details perform better when they are maintained. Such maintenance may include washing, replacement of seals and sealants and re-application of waterproofing coatings.

Sargent House in Auckland by Ron Sang

Decisions made by the builder or designer may place high demands on the homeowner to maintain certain details. Often the homeowner is not consulted or considered at the time, a point that is particularly true of homes built speculatively. Homeowners, where appropriate, should be consulted with over maintenance issues. In all cases, they should be made aware of routine maintenance requirements. The lifetime success of the project will benefit.

An example of exposed aggregate finish. 10


G e n e ra l I n f o r m a t i o n

moisture control Concrete, although used in the construction of water tanks, is not generally considered to be sufficiently waterproof for housing without supplementary waterproofing systems. Not only is concrete water permeable, it also contains excess water from the construction process that must be allowed to escape. This moisture can, if not dealt with, continue to plague the homeowner. As a rule of thumb concrete requires one month per 25 mm of thickness to dry (from each exposed face) assuming dry conditions. This means that under ideal conditions a 100 mm thick concrete wall will require two months drying time if both faces are left exposed for that period. Finishes that are applied to exterior surfaces of concrete which have not dried adequately, may be affected by the tendency of water to escape to the warm side. This could lead to bubbling of the surface finish. The external moisture clauses of the New Zealand Building Code are increasingly being complied with through the use of painted membrane systems. These systems are continuing to develop and there are a number that have proven records in New Zealand conditions. Their use has increased the options for designers but at the same time designers must ensure that sound detailing and building principles are not ignored. If a strategy of reliance on painted membrane systems has been adopted, it is advisable to thoroughly investigate the systems under consideration. Speak to those who have applied the products and have experience of their performance. Also obtain test results and manufacturerâ&#x20AC;&#x2122;s guarantees of performance.

This house will be left unpainted until all construction moisture has escaped.

Internal moisture control is often not considered by designers but is critical to the comfort and enjoyment of the home. The best method of assuring that the concrete home performs well in this regard is to insulate well and to specify appropriate finishes in those rooms where high moisture levels can be anticipated. The enjoyment of a well designed concrete home will be enhanced by the designer considering the environment, material properties and sound detailing principles.

thermal performance and insultation Thermal mass within the building envelope can provide significant benefits in terms of both energy efficiency and comfort. Maximising the thermal mass benefits of concrete requires consideration of a number of issues including: site and building location and orientation, insulation placement, glazing placement and orientation, and usage patterns, to mention a few. This manual does not attempt to cover issues which need to be considered in maximising the benefits of thermal mass. Designers wishing to check thermal properties of concrete homes for code compliance should refer to two New Zealand standards: NZS 4214 provides the means of calculating the thermal resistance of building elements, and NZS 4218 defines minimum requirements for the various elements of a house (ie walls, roof, floor).

A contemporary concrete house.

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C o n c re t e M a s o n r y

Concrete Masonry

General . . . . . . . . . . . . . . . . . . .15 Design Issues . . . . . . . . . . . . . .16 Specification . . . . . . . . . . . . . .19 Construction . . . . . . . . . . . . . . .21 Details . . . . . . . . . . . . . . . . . . .22

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C o n c re t e M a s o n r y

Broderick House by Warren & Mahoney

oncrete masonry or blockwork has a long association with residential construction in New Zealand. As well as offering all the positive attributes of the other forms of concrete it is an easy format to use.

C

The use of concrete masonry has been well supported by the block manufacturers throughout the country. Special profiles are available to suit all the detailing conditions that can be anticipated. The range of products continues to be expanded as blocks with special surface finishes, sizes and thermal characteristics are put to the market. In effect concrete masonry is a type of permanent formwork for concrete. The grout fill working in conjunction with the reinforcing steel provides the structural strength. New research carried out by New Zealand universities has lead to a reduction in the amount of horizontal reinforcing steel and grout fill required. 140 mm wide (15 Series) concrete masonry has also been shown to be structurally appropriate for most residential projects. These changes have been incorporated into the recently released update of NZS 4229:1999, the Standard for non-specific concrete masonry design. Advantages of concrete masonry • economy – particularly when the construction module is fully exploited • does not require special or costly equipment to install • modular units are relatively easy to handle and can be delivered to most buildings sites • stop and start of construction is easy to incorporate structurally and architecturally • range of profiles allowing for most detailing requirements • interesting architectural scale and surface textures The qualities and advantages of concrete masonry certainly make it an appealing material to consider for residential construction.

Until the nineteen -seventies New Zealand houses built of blockwork used cavity wall construction techniques. Concrete masonry is more porous than most other forms of concrete. The blocks themselves are permeable, particularly when they are manufactured using the lightweight pumice aggregate typical of the upper half of the North Island. It is however the mortar joints which are the real culprit. As the mortar dries and shrinks, cracks develop against adjoining blocks. Traditional cavity wall construction assumes moisture will be able to penetrate the outer skin, but then drop to the bottom of the cavity and out through weep holes without affecting the inner skin. The outer skin of the wall also serves to conceal the waterproofing membrane on the outer surface of the inner skin. Time pressures and increases in the cost of construction have meant that this effective traditional method of construction has generally been replaced by the single skin masonry wall. As has been discussed earlier in this guide the change has been justified through the development of new materials which effectively seal the external surfaces while also serving as paint or plaster finishes. This is often in conjunction with rigid insulation. NZS 4229: 1999 has adopted the use of acrylic membranes as appropriate waterproofing solutions. 15


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design issues Modular setout Common mortar joint profiles

raked

flush

While other forms of concrete construction allow freedom of shape and size, the modular nature of blockwork directs many design considerations. For reasons of economy and ease of construction, the modular height of units â&#x20AC;&#x201C; typically 100 mm or 200 mm â&#x20AC;&#x201C; should be adhered to. This applies to overall heights of walls as well as openings within walls. Sticking to a running module of 200 mm will provide economy, however, the length of units can be easily cut. If the module is seen, the designer may wish to specify the position of the cut units. Joints

struck

vee

weathered

concave

The mortar joint between blocks has a number of functions. Its primary function is to bond adjoining blocks together. This is a permanent requirement for those blocks that are not to have filled cores. The grout fill will otherwise take over as the bonding mechanism. Another function of the joint is to take up construction or manufacturing tolerances as slight variations in block sizes may occur. Finally the joint contributes significantly to the appearance of the concrete masonry wall. The industry norm of a 10 mm joint is generally considered to be a good proportion when compared to the individual masonry unit. This width can be varied by the designer to suit particular requirements. When blockwork is designed to be left exposed, the colour of the joint is a consideration. It is, however, the profile which offers the designer the greatest number of variations to suit aesthetic or weathering requirements. Profiles of typical joints that can be specified are shown in the illustration to the left. Combining joint profiles, such as alternating flush with struck to suggest a different module, or raked horizontals and flush vertical joints can be effective. Bonding patterns

The way in which the concrete blocks are laid presents another opportunity to affect the overall appearance of a wall. The traditional bonding pattern for concrete masonry is the ashlar or running bond. Another option is the stacked bond. Beyond these

Running bond

16

Stacked bond


C o n c re t e M a s o n r y

15 series structural concrete masonry

it is over to the designerâ&#x20AC;&#x2122;s imagination to consider the surface patterns and textures that can be achieved. Mario Botta, a Swiss architect, is renowned for combining blocks of various colour, texture, height and laying position to create wonderful patterns that become an integral part of his architecture. Note that the bracing values for partial filled concrete masonry in NZS 4229 are based on the running bond. Partially filling a stacked bond wall at 800 mm centres will leave every second block unbound which then becomes vulnerable under earthquake loading. It is therefore recommended to fill cells at 400 mm centres or closer when using stack bonded concrete masonry.

veneer tie

concrete masonry veneer

insulation in cavity

Non-structural applications

water proofing membrane

Concrete masonry is generally used in a structural capacity, for which it is ideally suited. It can also be used as an external veneer cladding in conjunction with other structural systems. The most common is timber framing but combining structural and veneer masonry with a cavity between will allow the designer to take full advantage of the external appearance, durability and thermal mass benefits. Method of insulation

Appearance requirements and thermal mass objectives must be considered at the same time as the insulation strategies. The most common method of insulating a concrete masonry wall is to strap and line the internal face, fitting insulation between the strapping. An alternative approach is to fix insulation externally either in the form of rigid polystyrene sheet fixed in place with an external coating or by strapping and cladding with insulation between.

weep hole 10 series concrete masonry veneer over 15 series structural wall. Cavity should be insulated.

Proprietary self-insulating concrete block systems are available in New Zealand. Such systems allow both faces of the concrete masonry. This is achieved through the use of a biscuit of polystyrene fixed in a cavity near the exterior surface of the block. Concrete masonry built using the cavity method allows for effective use of insulation, thermal mass and the blockwork aesthetic. Insulation was often not included in the traditional cavity blockwork which gave these houses the reputation of being cold. While cavity construction allows insulation to be installed in the cavity, the detailing should ensure that the cavity will allow free drainage and that the type of insulation specified is capable of withstanding moisture. 17


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Waterproofing

The considerations for choice of waterproofing system are set out in the General Section. It is most important to consider appropriate and effective waterproofing strategies for concrete masonry due to its porosity. Cracks that develop between the mortar and blocks are also areas of vulnerability that the waterproofing system must be capable of bridging.

horizontal reinforcing steel

vertical reinforcing steel

sealant both faces

Plan view of bond beam at control joint

shrinkage central joint

debonded bar

vertical reinforcing

Shrinkage control joint

bond beam

full height shrinkage control joint

Unpainted and unsealed blockwork is an option in some circumstances such as when using veneer construction or in garages and uninhabited basements. It is important nevertheless to bear in mind the affect water can have on the masonry. Water can bring salts to the surface in the form of efflorescence, leaving an unsightly and unpredictable white pattern on the surface.

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C o n c re t e M a s o n r y

Shrinkage control joints

Shrinkage control joints are necessary to ensure that shrinkage cracking occurs in a controlled manner and allows movement due to thermal changes. NZS 4229 specifies requirements for control joints. These should occur at approximately six metre centres and will affect the appearance of the project when the masonry is to be left exposed or painted. Applied finishes such as stucco plaster should also acknowledge the control joint to avoid consequential cracking. The designer should take charge of the control joint setout and carry out detailing as illustrated on the previous page to avoid any surprises on site.

specification There are several New Zealand Standards that may be relevant to the written specification. These include the following: NZS 4229:1999 Concrete masonry buildings not requiring specific engineering design NZS 4230:1990 Code of practice for the design of masonry structures NZS 4210:1989 Code of practice for masonry construction: materials and workmanship

AS/NZS 4548 Guide to long-life coatings for concrete and masonry NZS 4251:1974 Code of practice for solid plastering NZS 3604:1999 Non specific design â&#x20AC;&#x201C; Light timber frame buildings Materials

All materials should be procured from a dependable source. Where appropriate, ensure that quality records are obtained and kept for easy retrieval, should they be required. Concrete blocks should be dry and remain so until they are used. Manufacture must comply with AS/NZS 4455 Excess moisture in any of the materials can reduce structural quality and require the blocks to have to dry longer before surface finishes can be applied. Steel reinforcing should be maintained free of dirt and organic material. Mortar mixing ratio (cement/sand/lime/water) to comply with NZS 4210 To provide a compressive strength of not less than 12.5 MPa.

Concrete blocks stacked on pallets. 19


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20 series Grout mixing ratio to comply with NZS 4210. To provide a compressive strength of not less that 17.5 MPa. Spread value 450 â&#x20AC;&#x201C; 530 mm Sand chloride levels should not exceed 0.04% by dry weight of sand Water one of the most important yet overlooked components of high quality concrete. Water must be clean and free from excess alkali, salt, silt and organic matter. Workmanship

Concrete masonry work should ideally be carried out by qualified tradesmen. As a minimum, tradesmen should have experience in the required areas of construction. In some instances, such as detailed structural work, it is desirable to employ a Registered Mason.

15 series

All concrete masonry work should be carried out under adequate supervision. Grout all cells that 1. contain reinforcing 2. are required to be filled as part of the design requirements Grouting should follow the procedures set out in NZS 4210. Form construction joints in accordance with NZS 4210 between grout pours and between the blockwork and any hardened concrete. The block layer must coordinate his work with the work of other trades. Coordination should take place well in advance of the work being done. The block layer must build in all elements including fixings, bolts, ties and any service requirements as called for, and/or necessary for the completion of the job. Once concrete masonry work is complete all block work must be cleaned.

20

10 series

A selection of concrete masonry profiles that are available. Consult with manufacturers to determine the full range.


C o n c re t e M a s o n r y

construction Planning the job

One of the most important activities when building in concrete masonry is planning the project. The economy of concrete masonry block work can only be maximised with proper planning. Consider the module. Try to minimise the number of cut units and to maximise the sizes of any units to be cut. Doing so will also serve to keep costs to a minimum. Check with the designer who may have specified the placement of any cut units. Plan the sequence of activities carefully. This is especially important with respect to services that will occur in masonry walls. Setting out

Reinforcing steel must be set out at foundation levels to fall within the planned location of cells. Normally the concrete masonry requires a vertical steel setout of 800 mm centre to centre spacing. Note that foundation stirrups typically occur at 600 mm centres meaning that only one in every four stirrups can be extended as vertical steel. Setting out of foundations to suit the specific requirements of the design is also critical. These include • allowing for any specified overhangs of concrete block or veneer • allowing for set downs or insets at door openings. Builders should take extra care when setting out services that will be concealed in masonry walls. This requires full coordination between trades such as plumbers or electricians and the reinforcing steel trade. Weather conditions

It is necessary to coordinate reinforcing placement with block setout.

Provided the blocks are not too dry the curing of the mortar and grout does not require special care. If strong hot winds or direct sunlight in the middle of the summer are anticipated it would be prudent to ensure the mortar and block surfaces are kept moist for the first three to four days after being placed. Protection

Builders should take care to protect finished concrete masonry from damage which could arise through the building process. This is particularly important with blockwork and veneer that has been designed to be left exposed. While in most cases it will be impractical to erect full protection for the masonry it should be possible to anticipate work that will create risks to the completed walls. Plywood sheets serve as an excellent form of protection.

Wet weather can cause build up of water in the blocks, as they are relatively porous. Excess water can reduce the strength of grout. This is particularly of concern where water is retained at the bottom of, or between lifts of, grouted cells. Rain onto fresh mortar can erode its surface, affecting the appearance and possibly the structural strength of the mortar joints. Cold conditions will not allow the mortar or grout to set properly. Concrete masonry and grout should not be placed in temperatures less than 4°C. Hot weather conditions are generally not a problem for concrete masonry in New Zealand. However, prolonged dry conditions may warrant attention when laying or grouting the masonry. Overly dry blocks will draw moisture out of the grout or mortar too quickly thereby affecting the bond with the blocks. It is therefore recommended that the blocks be wet lightly on those surfaces which will be against the mortar or grout.

Kew House by Melling Morse Architects

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Internally insulated wall section

Roofing on building paper on wire netting Timber trusses

This wall section presents: • single wythe 15 series concrete masonry Fascia Ceiling lining on battens Continuous timber plate on DPC

Bond beam in accordance with NZS 4229

Cast in bolt fixings External waterproofing system

• building paper on the inside face of the masonry acting as a second line of defence against moisture penetration • strapping and lining on the interior • insulation between strapping

15 series conc. masonry

• concrete masonry foundation wall acting as permanent formwork for concrete slab on grade.

WALL TO ROOF Insulation External waterproofing system ° acrylic plaster & paint ° acrylic paint system ° sand/cement plaster system & paint

MDF skirting Particle board flooring

Bolt connection to bond beam per NZS 4229 Joist hanger

° sealer Bond beam at floor level

Continuous boundary joist on DPC Internal linings on timber strapping

INTERMEDIATE FLOOR

15 series conc. masonry vertical & horizontal reinforcing per NZS 4229

Internal lining Insulation Building paper continuous Timber strapping

Waterproofing system extend min 50 below floor level

100 x 50 on DPC

100 MIN

150 MIN

Reinforced concrete slab

Paved G.L.

Unpaved G.L. 15 series conc. masonry foundation wall. Starter bars at required spacing.

DPC over 25mm sand blinding Compacted granular hardfill Reinforced concrete footing

WALL TO FLOOR 22

These details separate the thermal mass of the concrete masonry from the interior space. It also allows the concrete masonry to be expressed as an architectural finish externally.


C o n c re t e M a s o n r y D e t a i l s

Externally insulated wall section This wall section presents

FALL

External insulation system

• single wythe 15 series concrete masonry • exterior insulation and waterproofing system

Extend insulation and waterproofing over butyl with sealant bead Butyl as upstand dressed & sealed into chase in mortar joint Butyl on plywood on insulation on DPC

Acrylic plaster waterproofing system

• concrete roof system • concrete intermediate floor system • reinforced concrete slab with thickened edge perimeter foundation.

Bond beam

This construction allows full advantage to be taken of the thermal mass in the house. The texture/finish of concrete masonry can be expressed internally.

WALL TO ROOF

Concete floor system

Proprietary external insulation system

Suspended ceiling system for services & lighting

Proprietary concrete floor system

Acrylic plaster system

Bond beam

Suspended ceiling system for services & lighting

INTERMEDIATE FLOOR Internal finishes ° paint system ° plaster system ° none

Proprietary external insulation system Acrylic plaster system

Fix skirting & other elements by plug & screw on DPC

50 MIN

100 MIN

150 MIN

Reinforced conc. slab

Paved G.L.

Unpaved G.L. Reinforced concrete perimeter edge beam

Sand blinding on compacted hardfill DPC

WALL TO FLOOR

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Concrete masonry veneer

Roofing on building paper on wire netting Timber trusses

Fascia Continuous 10mm gap for ventilation

Ceiling lining on battens

Concrete masonry veneer has been widely used in New Zealand house construction. The principle of a ventilated cavity can give a greater source of security to the homeowner and designer alike.

10

As with all masonry, it is important to consider the modular height in setting out openings and heights of walls. This example shows the veneer stopping short of the soffit lining as a way of expressing the nature of the masonry on a veneer. This also stops the lining from meeting the masonry off the height module.

Masonry ties. Material to suit environment

Ventilated cavity 10 series conc. block veneer

WALL TO ROOF

75 max 40 min

Ventilated cavity Building paper continuous 10 series conc. block veneer Masonry ties in accordance with NZS 4229 Waterproofing on sloped plaster

100mm insulation Internal lining Bottom plate bolted to foundation Skirting Reinforced conc. slab

50 MIN

100 MIN

150 MIN

75mm high weep holes @ 800 centres

Paved G.L.

Unpaved G.L. Sand blinding on compacted hardfill DPC

WALL TO FLOOR

24

Note the requirements in NZS 4229 and NZS 3604 for the base material and protection for masonry ties in certain exposures.


C o n c re t e M a s o n r y D e t a i l s

Externally insulated wall Insulation

Timber strapping fixed to solid filled cells over DPC

Cement/sand plaster or acrylic plaster internal finish Fix skirting & other elements by plug & screw on DPC

50 MIN

Reinforced conc. slab 100 MIN

The internal finish should be applied directly to concrete masonry to allow the full advantage of thermal mass.

External cladding fixed over building paper

150 MIN

This system is designed to allow a traditional external appearance. Almost any external cladding can be chosen. Timber weatherboards are illustrated here.

15 series conc. masonry

Paved G.L.

Unpaved G.L. Perimeter edge beam

Sand blinding on compacted hardfill DPC

WALL TO FLOOR

Foundation crawl space

Internal finish Timber skirting

This construction detail is ideally suited to a sloping site. The use of concrete masonry as a foundation footing can be both economical and time saving, particularly on sloping sites or those with limited access.

External waterproofing and insulation system

Particle board flooring

Bond beam Timber stringer on DPC

M16 bolt to comply with NZS 4229

15 series conc. masonry

Sisalation or under floor insulation

Openings in wall for ventilation to comply with NZS 3604

20 series reinforced conc. masonry footing on concrete bed

RAISED GROUND FLOOR

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Timber window details External waterproofing system

Interior lining Insulation Building paper

15 series lintel block Timber strapping

The details illustrated here indicate an appropriate method for doing so.

Sealant over backing rod Architrave Timber frame on packing. Plug and screw to masonry

Timber reveal Glazing in timber window frame

HEAD DETAIL

TImber reveal

Galvanised metal flashing

Architrave

Extend waterproofing over plaster screed to falls and under sill generally

Interior lining External waterproofing system Insulation 15 series conc. masonry

SILL DETAIL 26

Timber joinery is still the preference for many homeowners. Modern timber windows are well made and draft free. It is important to build these windows units in to ensure weathertightness.

Timber strapping Building paper


C o n c re t e M a s o n r y D e t a i l s

Aluminium window details 20 series rebated lintel block

Aluminium is the most common material for exterior door and window frames in residential construction. These details demonstrate the use of aluminium window frames in 20 series blockwork using rebated blocks. The rebated block allows a positive step for the frame to fit against. When using an exterior membrane system be sure to extend it under the window frames prior to their installation. DPC should lap onto membrane and over building paper.

Interior lining Building paper Insulation

Timber strapping A Build up waterproofing membrane and form drip

DPC over waterproofing membrane and over building paper

Continuous sealant bead

HEAD DETAIL Timber reveal

Note the requirement by some window manufacturers to fit an angle (note A) in high wind areas to relieve the pressures on the sealant joint.

Continuous sealant bead A

Waterproofing system

Timber strapping

Interior lining Building paper Insulation 20 series rebated block. Reinforce per NZS 4229

JAMB DETAIL

Timber reveal

It is quite common to remove the projecting profile from the sill block to achieve a more flush appearance. Note that this may cause staining under windows as dirt that has settled on the sill gets washed down by rain.

Position frame to allow drainage from within Run waterproofing up under reveal

Timber strapping

Waterproofing system Remove projecting sill

DPC over waterproofing membrane and over building paper Interior lining Building paper Insulation 20 series rebated sill block.

SILL DETAIL 27


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Timber door details Acrylic interior plaster system. Neatly finish to timber frame

External Insulating Finishing System (EIFS)

DPC

15 series lintel block

Timber packing

Timber door head and bead

Sealant Continuous head flashing

Glazed timber door

HEAD DETAIL

Acrylic interior plaster system. Neatly finished to timber frame

External Insulating Finishing System (EIFS) 15 series lintel block on end

DPC

Timber packing

Sealant

Timber door jamb Timber bead

Glazed timber door

JAMB DETAIL

EIFS beyond Timber door sill

Timber angle fillet

DPC

Glazed timber door Rebate slab for timber sill

Fairface concrete foundation beyond

Conc. slab Form recess at openings

SILL DETAIL 28

The external ridgid insulation system allows the concrete masonry to be left exposed, or receive a thin finish as illustrated here. There may be thermal benefits to the home owner in adopting this strategy. The timber frame is supported on timber packing which is continuous and plastered over. The plaster system should be reinforced across this piece. Sealant is applied between the timber frame and the insulation system as a weather seal.


C o n c re t e M a s o n r y D e t a i l s

Aluminium door details Sand/cement plaster system

These details show the aluminium door frame set in 15 series blockwork not using the rebated profile. This presents greater flexibility for the designer to position frame in depth of block. It may be preferable to use rebated block profiles in openings as this gives maximum weathering protection.

Express control joint

External Insulating Finishing System (EIFS) 15 series lintel block

DPC Sealant bead. Leave 50mm high gap at bottoms of jambs for water to escape

Details show that the thermal mass is fully available to the interior space as the insulation is placed externally. Glazed hinged door in aluminium frame

HEAD DETAIL Sand/cement plaster system Express control joint

External Insulating Finishing System (EIFS) 15 series block

DPC Sealant bead. Leave 50mm high gap at bottoms of jambs for water to escape Glazed hinged door in aluminium frame

JAMB DETAIL The detail shows that the upstand leg from the sill frame across the threshold has been removed. This prevents it being damaged by being walked over.

EIFS

Aluminium door frame with weather strip on botttom edge Shaped timber threshold

Aluminium door sill frame Bring DPC over leading edge of slab

Concrete slab Form recess at openings

Fairface conc. foundation beyond Paving level

SILL DETAIL 29


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Masonry ties in accordance with NZS 4229

Interior lining

Masonry ties in accordance with NZS 4229

Insulation

Insulation Lap building paper over M.S. angle lintel

Lap building paper over M.S. angle lintel

Weep holes

Weep holes Timber Lintel per NZS 3604

125 x 125 x 8mm Hot dipped galvanised M.S. angle lintel fixed back to framing

Timber Lintel per NZS 3604 Architrave

Galvanised metal head flashing.

Sealant

Interior lining

Timber window frame

Aluminium frame with timber reveal

Veneer window details HEAD DETAIL

The position of window frames in a DETAIL Timber window frames, on the other HEAD hand, may require framing support in the veneered wall is critical to ensure cavity, as shown. adequate closure of the gap while ensuring adequate fixing for the frame. Units fabricated in the factory, before timber and aluminium may be able to Most aluminium window frames for span across the sill without fixings. residential use are delivered to the site with reveals fixed in the factory. Fixing through the reveal, as shown, will allow the frame to bridge the cavity.

Galvanised metal sill flashing. Lap over sill tile

Sealant between aluminium window frame and sill tile

Timber window sill

Sill tiles on plaster

Building paper

Masonry ties in accordance with NZS 4229

10 series masonry veneer

SILL DETAIL

30

Timber window frame Architrave

Timber framing with insulation between

Sill tiles on plaster

Interior lining

Masonry ties in accordance with NZS 4229 10 series masonry veneer

SILL DETAIL

Continuous support for timber sill. Fix over building paper Interior lining

Insulation


C o n c re t e M a s o n r y D e t a i l s

Roof details The use of sand/cement plaster allows a smooth uniform texture finish using a material similar in nature to concrete masonry.

Timber purlins/rafters (cantilevered verge) Metal roofing on building paper Metal flashing

Solid blocking

Care must be taken to: â&#x20AC;˘ ensure adequate bond of sand/ cement plaster to concrete masonry â&#x20AC;˘ follow control joints in masonry through sand/cement plaster A suitable paint finish will provide weatherproofing.

Soffit Casement bead

Ceiling lining on battens

Bond beam Internal linings over 50mm timber strapping Sand/cement plaster system (19mm textured surface)

Insulation Building paper

ROOF VERGE FALL

Bond beam Proprietary external insulation system

Metal flashing dressed & sealed into chase in mortar joint

Acrylic plaster system

Metal roofing to falls Furring to falls

Bond beam

Internal linings on ceiling joists/rafters

PARAPET / METAL ROOF FALL

The use of an internal gutter suits many of the contemporary expressions of architectural design. Dimensions of such a gutter should be to suit the expected rainwater flow, but in no case should it be less than 600 mm for ease of cleaning. Provide secondary overflow capacity to ensure rainwater does not back up inside house.

Bond beam Proprietary external insulation system Acrylic plaster system Gutter overflow. Opening size to match downpipe. Position below gutter freeboard height.

Butyl as upstand dressed & sealed into chase in mortar joint Butyl on plywood on 75x40 furring to falls Metal roofing to falls Furring to falls

Bond beam

15 series conc. masonry

Insulation Internal linings on ceiling joists/rafters

PARAPET / METAL ROOF 31


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Suspended floor details Insulation

Flooring

A hybrid form of construction with concrete masonry ground floor structure and a lightweight structure above. The durability aspects and appearance of concrete masonry is continued with 10 series veneer over the timber framing.

째 sand/cement plaster system & paint

Timber floor joist

째 sealer

Ceiling on timber strapping

Suspended deck details are critical to get right particularly if they sit above interior spaces.

10 series concrete block veneer

Blocking

External waterproofing system 째 acrylic plaster & paint 째 acrylic paint system

25 series bond beam 20 series concrete block

Timber plate bolted to bond beam on DPC

When the concrete block module is seen from outside, it is critical to ensure the full module carries through floor level and that the detailing reflects this.

Internal linings on timber strapping on building paper

BLOCK WALL / VENEER JUNCTION

Services details As with most forms of concrete construction, it is critical to plan for appropriate services reticulation when detailing in concrete masonry. When using masonry veneer construction it is tempting to reticulate services in the cavity but this is specifically prohibited in NZS 4229. When using partial fill concrete masonry, dropping services from ceiling level in an empty cell can make the job much easier, particularly as a retrofit. It is advisable to cast sleeves into the bond beam to allow these services to be reticulated easily. Casting in additional sleeves to anticipate future alterations is also recommended.

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C o n c re t e M a s o n r y D e t a i l s

33


I n s u l a t i n g C o n c re t e Fo r mwo r k

Insulating Concrete Formwork

General . . . . . . . . . . . . . . . . . . .37 Design Issues . . . . . . . . . . . . . .38 Specification . . . . . . . . . . . . . .39 Construction . . . . . . . . . . . . . . .41 Details . . . . . . . . . . . . . . . . . . .43

35


I n s u l a t i n g C o n c re t e Fo r mwo r k

nsulating concrete formwork (ICF) is a proprietary formwork system for concrete that is left in place to become part of the building. ICF systems have been available in New Zealand for the last 10 years and during that time have been increasingly used for both commercial and residential construction. ICF construction has been used for some 30 years in Europe, where concrete residential construction is quite common.

I

A contemporary house built using insulated concrete formwork.

Block systems are widely available in New Zealand. Plank and panel systems are available internationally but not currently in New Zealand. The forms are typically made of expanded polystyrene, a closed cell polymer. The reinforced concrete core provides all the structural capacity of the wall. The main advantages of these systems are: • excellent insulation properties • low levels of air infiltration • blocks are easy to lay and fill • relatively easy to run services concealed in polystyrene layer. This is true of both new construction and refitting work. • long life expectancy

37


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design issues Although the principle of ICF construction is similar to that of concrete masonry, there are some important differences for the designer to consider. Module

The modular height of systems available in New Zealand is typically 300 mm. As with concrete masonry, it will be more economical to work to the modular height for openings and wall heights. Most systems mechanically lock together along top and bottom edges. ICF systems are available in widths of 200, 250 and 300 mm. Unit widths correspond to different concrete thicknesses. The wider blocks offer increased structural capacity, little if any insulating increase and potentially reduce the interior floor space. The greater thickness will give greater reveal depth at openings which is often sought after by designers. ICF blocks are relatively long, in the order of 1000 to 1500 mm with many bridges between the faces. This allows the blocks to be easily cut to length without compromising the structural qualities. With block sizes like these, it is easy to see how these systems can be laid so quickly. Proprietary systems

This part of the guide has been prepared with information obtained from the suppliers of ICF blocks in New Zealand. As much as possible, it has been the intention of the writers to present this information in a generic manner, thereby not favouring any one supplier.

Typical ICF block format. Confirm the dimensions with the selected supplier.

As soon as a particular system is adopted it is advisable that the designer confirm all details with the particular supplier. Applied finishes

ICF systems comply with NZBC durability requirements, provided the blocks are appropriately finished or clad for protection from the effects of UV radiation and weather. Most ICF suppliers require that claddings or finishes are approved for use with their system. Modified acrylic plaster and paint systems, timber strapping with weatherboards, concrete masonry and stone veneers are examples of external claddings that ICF suppliers have recommended for use. Modified acrylic plasters, plasterboard or fibre cement sheet are typically used as internal linings. ICF suppliers will give guidance to the methods of fixing linings using adhesives and screws.

38


I n s u l a t i n g C o n c re t e Fo r mwo r k

Detailing – fixings

One of the most important detailing considerations with ICF systems is that of fixings. This includes fixings for both structural and architectural elements. The formwork units, as they are made of polystyrene, offer limited fixing capacity. To make allowances for timber skirtings to be secured, the fixing of windows into openings and joinery fittings to be positioned, it is necessary to cast in timber fixing blocks. These are typically 150 mm long and are secured into the concrete core by pairs of nails that protrude off the back face. This apparently low technology detail is very effective, provided the necessary planning has allowed them to be in the right places. Structural elements such as concrete flooring systems can be accommodated and are installed after the concrete has been cast to the soffit level. The seating depth can vary between 50 and 75 mm. The method for fixing timber floor framing to ICF walls is to secure a stringer on fixings cast into the concrete core.

specification It should be the objective of the specification writer to structure the documents in such a way as to encourage competitive pricing. Fortunately there are several suppliers of the forms in most parts of New Zealand. Once a system has been selected it is advisable to confirm all details and other design issues with the selected manufacturer. This includes wall thicknesses, building in details, steel reinforcing requirements and construction requirements. It is desirable to structure the ICF sub-contract on the basis of engineering design and supply. It may also be possible to include the erection of the system in that subcontract.

Timber inserts facilitate fixing of door frames, skirtings and other joinery items.

A Producer Statement: Design, or some other evidence of structural capacity should be required by the specification. This will assist the Territorial Authority in approving its use. Manufacturer’s literature and guarantees should also be required by the specification. Standards referred to:

NZS 3101: 1995 The design of concrete structures NZS 3104: 1991 Specification for concrete production – high grade and special grade NZS 3109: 1997 Concrete construction NZS 3402: 1989 Steel bars for the reinforcement of concrete Materials

There is at present no New Zealand Standard for the manufacture of ICF units. Accordingly the designer should reserve the right to approve the supplier.

39


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ICF Blocks should be made of fire retardant materials. In situations where fire resistance ratings are required. These must be specified as not all ICF blocks provide adequate fire resistance. Concrete infill to achieve a minimum compressive strength of 20 MPa. Maximum aggregate size to be 14 mm. Concrete slump should comply with the ICF manufacturerâ&#x20AC;&#x2122;s requirements. A 100 mm slump is typical. Expansive additives must not be used in any circumstances as these can blow out the forms. Steel reinforcing to comply with NZS 3402. Workmanship

Erection and filling of the system should be carried out either by the ICF supplier or by a firm approved by them. The installation should be carried out by persons with experience in this type of work. All necessary and appropriate equipment and construction techniques to be employed.

Concrete floor systems can be easily accommodated in ICF construction.

The blocks are fitted together and propped in place before filling with concrete. Temporary wire ties may be necessary to prevent the blocks floating on the concrete fill. These should be installed every four courses. Allow to build in all fixings and services as detailed and required by various trades. Typically, such fixings are supplied by the relevant trade or by the builder, to ensure they are correct. The ICF trade must coordinate with all other trades. Allow to locate and form construction joints in accordance with NZS 3109. Before placing concrete, ensure all cells are clean and reinforcing is secured in place. Consolidate concrete with a max 25 mm diameter poker vibrator or by rodding. Vibration should ensure that all cells are filled with well compacted concrete. Extent and height of lifts to be in accordance with ICF manufacturerâ&#x20AC;&#x2122;s recommendations. Significant construction tolerances for ICF are to be expected given the nature of the material. It is prudent to limit tolerances and to ensure subcontractors are aware of them so they can make appropriate allowances. Recommended limits are as follows: Deviation from plan location Deviation from vertical within a storey

Diagram showing ICF components.

40

Relative displacement between load bearing walls in adjacent stories intended to be in vertical alignment

20 mm 10 mm per 3 m 5 mm

Deviation from line to plan Any length up to 10 metres Any length over 10 metres

5 mm 10 mm

Deviation from horizontal Any length up to 10 metres Any length over 10 metres

5 mm 10 mm


I n s u l a t i n g C o n c re t e Fo r mwo r k

construction Planning the job

Due to the speed with which ICF systems can be erected, it is important to plan well ahead. Follow the manufacturerâ&#x20AC;&#x2122;s recommendations for the height of each lift. ICF blocks are easy to cut, allowing opportunities to deviate from the block module. It is important to consider, from a construction viewpoint, that the ICF walls have no structural capacity until the concrete core is cast. Therefore it is important to provide adequate propping and support for these elements until the concrete has achieved the appropriate structural strength. Setting out

As with other systems covered in this guide, it is important to set out reinforcing to suit the ICF block width. This must be confirmed prior to casting of foundations.

The ICF forms can be used for internal and external walls.

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Weather conditions

Due to its insulating qualities, in theory concrete can be placed in colder conditions than it can into other types of formwork. However, this is rarely a factor in New Zealand conditions. The forms themselves can be placed in most weather conditions, although the unfilled forms are susceptible to displacement in high winds. Concrete can be placed in the forms when it is raining provided measures are taken to remove water in the bottom of the forms, which if left will mix with the concrete thereby reducing its strength. Curing and drying

ICF systems enhance concrete curing by slowing water evaporation. This effect can increase concrete strengths. Obtain, and comply with the ICF and coating manufacturerâ&#x20AC;&#x2122;s recommendations for drying times prior to the application of surface finishes. Protection

ICF is vulnerable to mechanical damage particularly before claddings are applied. Protection, such as plywood sheeting, should be considered in areas of high risk during construction.

It is important to prop ICF units appropriately until concrete has set.

At exposed corners and edges PVC protection is recommended as part of the cladding system. Prolonged exposure to sunlight can cause surface deterioration of the polystyrene. If the surface becomes scaly after a period of exposure, this scaliness must be removed prior to the application of surface finishes. The minor deterioration that may occur will have no effect on the structure of the wall. Some reduction of the insulation properties may occur, depending on the depth of deterioration.

Stone and other veneers can be used to give the house a traditional appearance. 42


I n s u l a t i n g C o n c re t e Fo r mwo r k D e t a i l s

The roof details indicate a concrete floor slab system with topping formed to falls. With all parapet conditions it is important to make allowance for overflow in case primary drain becomes blocked. Insulation is shown on top of roof slab to allow thermal mass to help moderate indoor temperatures and to prevent condensation that may develop in certain conditions. Suspended floor detail indicates precast beam and infill system. A suspended ceiling can be included to conceal services and the soffit of the flooring system. With appropriate planning and good workmanship, it is possible to leave these surfaces exposed, thereby saving the cost of the ceiling, enjoying greater floor/ceiling heights and the thermal mass benefits of the concrete. ICF can be used as permanent formwork for foundations.

External plaster finish

FALL

Fix Butyl into chase cut into wall. fix 90째 PVC angle cap to Butyl edge and seal in place. Plaster down onto PVC angle Butyl on Plywood base Insulation over DPM

Reinforcing mesh

Concrete topping to falls

Construction joint

ICF block system

Concrete slab. Prop in place until conc. is cured

Reinforcing Metal frame suspended ceiling

CONCRETE ROOF Internal finish External plaster finish Reinforcing mesh Rough broomed surface to ensure good key

Skirting fixed to intermittent timber block cast into conc. Reinforced conc. topping

Construction joint TImber formwork

ICF block system

Reinforcing

Conc. beam & timber infill floor system Cut hole in block at each conc. beam

Metal frame suspended ceiling Internal finish

CONCRETE FLOOR

ICF block system External finish

Internal finish Reinforced conc. slab

PVC starter strip, forming a drip edge 100

These details indicate how the ICF construction system can be combined with various concrete floor systems.

Reinforce corners of plaster systems

150

Wall section

Paved G.L.

Unpaved G.L.

Reinforced concrete footing

WALL / SLAB

DPC Sand blinding Compacted granular hardfill

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Roofing

Wall section

Building paper & timber purlin Timber truss

The details on this page indicate a traditional sloping roof with overhang. Planning is required to cast in appropriate fixings for structural and architectural elements, as ICF will not support or transfer any loads.

Connection plate between top plate and truss Top plate fixed @ 750max ctrs with cast in bolts

Ceiling battens Insulation

Gutter Fascia board

DPC Soffit lining Internal lining Timber stringer, fixed @ 750max ctrs. with cast in bolt

ROOF OVERHANG

External finish

ICF block wall

Skirting fixed to intermittent timber block cast into conc. Flooring Timber joists

Malthoid strip between timber and concrete or use H3 treated timber

ICF block system

Joist hanger Continuous slot cut in block wall for stringer

TIMBER FLOOR

ICF block system External plaster finish. Extend to ground level

Skirting Reinforced concrete slab

100

PVC channel

150

Internal finish

Paved G.L.

Unpaved G.L. DPC Extend insulation down to bottom of foundation

Compacted sand blinding Granular hardfill

WALL / SLAB

44

The suspended timber floor must be securely anchored to the wall to transfer vertical and lateral loads. This should also coincide with a horizontal bond beam. As the intermediate floor acts as a diaphragm in this case, only one horizontal bar is required in the bond beam. The timber frame floor/ceiling assembly allows electrical services to be easily reticulated, but acoustic performance is somewhat compromised in comparison with a concrete system. The concrete slab on grade forms a perfect base for the insulated concrete formwork system. It is important to coordinate reinforcing steel starter bars and fixings for skirtings and the like.


I n s u l a t i n g C o n c re t e Fo r mwo r k D e t a i l s

Aluminium window details ICF block system

The key to fitting doors and windows into openings in ICF partitions is to plan for, and cast in, appropriate fixings. These fixings must be H3 treated or higher, as they are generally in full contact with concrete. These fixings are intermittent, about 150 mm long at 450 mm centre spacings. The nails on back help anchor the timber to the concrete. These details also make use of aluminium flashings and sealant to ensure a weathertight opening. The flashings must be compatible with the exterior finishing systems and fixed in a manner that will not cause the acrylic plaster system to break down.

External plaster finish.

Intermittent H3 timber blocks. Fix galv. nails skew nailed to timber & cast in concrete infill.

Corner strip Internal finish Form drip edge PVC flashing Sealant bead

Timber reveals Aluminium window section

HEAD DETAIL

Aluminium window section

Timber reveals

PVC flashing Sealant Corner strip

Internal finish

Timber packer

External plaster finish.

Intermittent H3 timber blocks. Fix galv. nails skew nailed to timber & cast in concrete infill.

ICF block system

JAMB DETAIL Timber reveals

Aluminium flashing External plaster finish

Timber plate

Corner reinforcing

Internal finish

ICF block system

Intermittent H3 timber blocks. Fix galv. nails skew nailed to timber & cast in concrete infill.

SILL DETAIL 45


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Timber window details ICF block system

Modified acrylic plaster. Return at reveal

Corner strip Corner protection Form drip edge

Sealant

Sealant & backing rod

Timber window frame

PVC flashing

HEAD DETAIL

Timber window frame Sealant & backing rod Sealant Modified acrylic plaster finish

Corner strip

ICF block system

Corner protection Intermittent timber blocks. Fix galv. nails skew nailed to timber & cast in concrete infill. Internal finish. Return to reveal

JAMB DETAIL Timber sill Fit timber sill over flashing & timber packing Sill flashing External finish. Carry under flashing.

Timber plate

Continuous H3 timber, shaped to fall

ICF block system

SILL DETAIL 46

Internal finish

These details, like those on the facing page, rely on the fixing capacity of cast in timber blocks. The interior finishes here are shown to return in to the window frame as a reveal. This is effective in creating a â&#x20AC;&#x153;massiveâ&#x20AC;? look to the walls. External corners of ICF are vulnerable and must be protected with PVC corners integrated with the plaster system.


I n s u l a t i n g C o n c re t e Fo r mwo r k D e t a i l s

Aluminium door details It is good practice to step back the concrete slab edge at door openings to avoid an awkward and vulnerable sill outside the door. This requires particular coordination between the concrete placer, ICF contractor and metal door and window supplier. It is also advisable to allow for a threshold that is robust and easy to pass over, this may require the aluminium frame profiles to be modified.

ICF block system

Lining

Corner strip

Intermittent H3 timber blocks. Fix galv. nails skew nailed to timber & cast in concrete infill.

Form drip edge Front sealant after planter Back sealant before planter

Aluminium door frame with timber reveals

HEAD DETAIL

Aluminium subframe

Front sealant after planter Back sealant before planter

Corner strip ICF block system External plaster finish

Intermittent H3 timber blocks. Fix galv. nails skew nailed to timber & cast in concrete.

JAMB DETAIL

Aluminium door frame with timber reveals

Aluminium door frame over sill flashing

Shaped Timber on DPC Reinforced conc. slab

Step back concrete slab edge to suit reveal Paving level

SILL DETAIL 47


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Timber door details Exterior plaster finished

Corner strip

Slope to form drip edge Sealant & backing rod PVC flashing. Plug & screw into conc.

ICF block system Interior finish. Return to reveal

Intermittent timber blocking. Fix galv. nails skew nailed to timber and cast in concrete infill. Sealant Timber door & frame

HEAD DETAIL

Sealant & backing rod Aluminium flashing

Timber door & frame Sealant Interior finish. Return to reveal

Corner strip

Exterior finished plaster ICF block system

Intermittent timber blocking. Fix galv. nails skew nailed to timber and cast in concrete infill.

JAMB DETAIL

Timber door & sill. Recess sill into slab. Butyl rubber sill flashing

ICF block system. EPS stripped. Plaster smooth

Paving level

SILL DETAIL 48

Flooring Reinforced conc. slab

The timber frame is set in the centre of the massive ICF wall. This massiveness is accentuated by returning the interior and exterior wall finishes into the reveal. Careful coordination of the rebate for the door sill will allow a near seamless transition from inside to out. All timber must be separated from concrete by DPC.


I n s u l a t i n g C o n c re t e Fo r mwo r k D e t a i l s

Hybrid construction detail Interior lining Timber framing

It may be desirable to combine structural systems as this detail indicates. The important coordination exercise here is to ensure that the timber framing is set out to allow the exterior finishes to continue flush from the ICF to the Exterior Insulation Finishing System. Note that the acoustic separation provided by this timber framed floor is minimal. Refer to the manufacturerâ&#x20AC;&#x2122;s literature for guidance on details that can improve acoustic performance.

Exterior insulation system

Continuous top plate fixed @ 750max ctrs with cast in bolts

Exterior finish system ICF block system

DPC Internal plaster finish

HYBRID CONSTRUCTION DETAIL

High thermal mass detail Exterior finish system

Internal plaster finish Reinforced conc. slab

100

Extend plaster finish to footing

150

To overcome the thermal mass being separated from the internal space, it is possible to remove the inner skin of ICF to reveal the concrete cores which can then be plastered smooth to a finish that is tough and durable.

ICF block system. Interior EPS removed

Paved G.L.

Unpaved G.L.

DPC Reinforced concrete footing

Sand blinding Granular hardfill

HIGH THERMAL MASS DETAIL

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Concrete masonry veneer

Cavity Concrete masonry veneer

ICF block system

Waterproofing membrane

Internal finish

Veneer ties extending to vertical reinforcing

Skirting & lining on intermittent fixing blocks

Weep holes @ 800 crs

Reinforced conc. slab

Unpaved G.L. DPC Sand blinding Granular hardfill

FOUNDATION

Cavity Concrete masonry veneer Veneer ties 2 coats waterproofing membrane

ICF Block system Lining Timber blocks. Fix galv. nails skew nailed to timber & cast in concrete infill.

MS angle Fibre cement sheet Aluminium flashing

Aluminium Window section with Timber Reveals

HEAD

Aluminium window joinery Timber reveals Tile sloping sill on 9mm fibre cement board on shaped timber

Timber plate Timber block

2 coats waterproofing membrane ICF block system Concrete masonry veneer Veneer ties extending to vertical reinforcing

SILL 50

Waterproofing of the ICF outer face (in the cavity) is usually by a painted on system such as bituminous paint. The veneer (10 series) must be secured to the structure by way of ties that are embedded in the concrete cores. This will require special attention to coordination of ties with anticipated joints.

Paved G.L.

Strip outer face of ICF

It is possible to combine the excellent durability and appearance of concrete masonry with the insulating qualities of ICF.

Internal fininsh


I n s u l a t i n g C o n c re t e Fo r mwo r k D e t a i l s

Roof details Flashing

Roofing Building paper Timber rafter

Providing adequate and appropriate fixings for additional structural or architectural elements is critical. All three of these details show typical fixings that must be allowed for.

Fascia Insulation Soffit DPC

Ceiling batten Top plate embedded in ICF block. 12mm Galv. bolt cast in Conc.

ICF block system Internal finish

OVERHANGING VERGE Slope top of blocks in towards gutter.

External finish

Apply sealant in chase then insert flashing. Flashing

Roofing on purlins ICF block system

Steel reinforcing Ceiling batten Rafter fixed to block with galv. bolt.

PARAPET

DPC Slope top of blocks in towards gutter.

Ensure adequate provision is made for overflow should the primary system block up. Internal gutters should be wide to allow ease of service and deep enough to accommodate the expected runoff.

External finish

Fix Butynol into chase in block, fix 90째 PVC angle cap to Butynol edge and seal in place. Finish Plaster down onto PVC angle Fix Butynol on Plywood base to form gutter as shown

Purlins on edge

Joist hanger ICF block system Reinforcing Plywood base fixed to timber framing Stringer fixed to block with galv. bolt.

PARAPET

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Terrace details

FALL

Raised terraces over living space are now very popular. Detailing of terraces presents a number of challenges in Fix waterproofing membrane into chase cut into wall. Fix 90° PVC angle cap to Membrane edge and seal in place. Plaster down onto PVC angle External finish

Timber decking

• allowing ease of transition – inside vs. outside • preventing water ingress at door openings • preventing water ingress at walls, especially at construction joint between slab and upstand

Waterproofing membrane on Conc. roof

Construction joint

Construction joint ICF block system Reinforcing

Precast concrete slab Insulating plasterboard lining Linings

Timber Decking

Waterproofing Membrane carried up under door joinery.

Aluminium Door section

Reinforced Conc. topping

Precast concrete slab Insulation ICF block system Reinforcing

52

Linings

A step in raised concrete floor levels requires a special coordination effort to ensure continuity of structure and support of the concrete flooring systems.


I n s u l a t i n g C o n c re t e Fo r mwo r k D e t a i l s

Services ICF present the easiest way of reticulating services of any concrete structural system. Services up to 40 mm, depending on the thickness of the polystyrene face, can be accommodated by cutting away a chase. Generally these services must be securely fixed to the concrete core by way of lamps and tappets. The chases must then be covered over by the finishing process. Plasterboard is generally able to span across the gaps but care must be taken to not place a sheet joint on the chase. Plaster systems will require a bandage. The supplier should be contacted for details. Services can also pass through the walls but positions and sizes must be approved by the manufacturer.

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P re c a s t C o n c re t e

Precast Concrete

General . . . . . . . . . . . . . . . . . . .57 Design . . . . . . . . . . . . . . . . . . .58 Specification . . . . . . . . . . . . . .60 Construction

. . . . . . . . . . . . . .62

Details . . . . . . . . . . . . . . . . . . .65

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P re c a s t C o n c re t e

he development of concrete precasting techniques in this country has allowed reinforced concrete to compete favourably with other forms of construction. Curiously it has not made a serious entry into the residential construction market until the past 10 years. This later period has coincided with the development of proprietary self insulating precast systems. Details of such systems are presented in this section but there is also plenty of scope for applied insulation systems.

T

Concrete precast methods were pioneered in the US early in the 20th century. The New Zealand industry is well developed and generally acknowledged as a world leader. There are good supplies of the raw materials and technology in most parts of the country. Precasting, whether done in factory conditions or on site, offers the opportunity to control the quality to a high standard. Advantages of precast concrete construction systems include the following: •

quality control – the quality is better able to be controlled by casting multiple units in the same mould, by casting walls flat rather than standing upright and through the ability to better control environmental conditions.

lower costs for the reasons noted above.

finishing options inherent in solid concrete construction

interesting shape and texture possibilities

speed of construction – with off site production the panels and other precast elements can be made while the site is being prepared. It is possible to set up a house in two days with an experienced crew.

The Pascal House in Auckland by Cook, Hitchcock & Sargisson. 57


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Precast flooring systems are ideal for use in a concrete home. A number of different flooring systems are currently available in New Zealand. These proprietary systems have been developed for commercial buildings, but are also suitable for the span and loading demands that can be anticipated in residential construction. Suppliers generally offer design services which can be incorporated into the overall structural design philosophy. These flooring systems can be categorised as follows: •

flat slab

hollow core slab

rib and infill

steel tray permanent formwork

The systems all offer excellent stiffness, durability, acoustic and thermal performance, they can be planned to include penetrations and openings and are cost competitive with timber flooring systems. They are also not prone to annoying squeaks that can occur with timber floor systems.

Precast concrete systems include floor units in addition to walls.

design As with in-situ concrete (refer to In-situ section), there are choices to be made with respect to the following: Surface Texture

There are many opportunities with precast concrete to create interesting surface textures. Finishing techniques for the formed (underside) face are described in the surface finishes section. The screeded face (topface) generally becomes the ‘second side’ or back. Texture options include: •

exposed aggregate

acid etched

ground and polished

board formed

Colour

Concrete used in precast work can be coloured. This can be achieved with colour throughout the mix, or alternatively, it is possible to place coloured concrete on the exposed face with standard concrete behind. Panel or unit format Combining surface finishes can help break down the scale of a building.

58

The size and layout of individual panels is essentially limitless. However, there are some practical limitations. Typical parameters that may dictate panel size are: •

the area available for casting (when casting on site). This may be an area of a floor slab or a separate temporary casting slab.

efficient repetitive use of special moulds

site access

capacity of lifting equipment or transport

the positioning of panel joints relative to openings.


P re c a s t C o n c re t e

â&#x20AC;˘ there are also aesthetic considerations to be made. Panel size will dictate joint set out and affect scale, texture and surface articulation of the house design.

Sandwich construction allows concrete panel to be left exposed inside and out.

The designer must also take into account panel thickness. There are structural aspects to consider for both transport and permanent positions. The designer may be particularly interested in panel thickness when considering opening reveal depths and thermal mass benefits. Commonly panel thickness varies between 100 mm and 150 mm. Jointing Details

The width and depth of joints between panels, as well as the profile of the panel edges, must be considered by the designer. Examples of weatherproofing details are shown to the left, the most commonly used detail in the face-sealed joint. Other considerations include how connections are made between panels, to the floor, and to any other structural or non-structural elements. These deliberations will most certainly include the structural designer for the project. Options include expressing plates and bolts, countersinking and plastering over welded plates or to conceal entirely by using pressure grouted tubes. Edge details Typical panel jointing details.

Individual panel edges, especially when exposed to view, are a design opportunity. These considerations are best made in the context of the joint design but should also look at corners, openings, top edges and junctions to other materials. Panel edges are vulnerable, especially during placement of panels. It is very difficult to successfully cast a crisp 90° corner on any concrete panel, it is therefore advisable to chamfer the corners. 59


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Insulation and weatherproofing

Although more waterproof than other forms of concrete, such as masonry, precast concrete is still permeable to water and requires waterproofing. Waterproofing can be achieved by application of acrylic paint systems, which can be applied direct or as part of a plaster finish system. Veneer cladding systems can also provide the required waterproofing. Insulation can be placed on the exterior, interior or between skins of concrete. This latter strategy has given rise to a number of specialist panel systems which allow all the positive aspects of concrete to be realised without compromise. These systems make use of a polystyrene sheet, between an outer skin or veneer of concrete, and an inner skin which typically acts as the structure. The two faces are held together by thermally non-conductive ties which are cast into each wythe.

specification Sandwich construction detail.

Designers have a choice to make between proprietary ‘sandwich’ construction and the traditional forms of precast. If the choice is to use a proprietary system, the specification should be generic to allow a range of proprietory systems to be evaluated. A proprietary system supplier may be required to provide Producer Statements, guarantees and construction recommendations. It may be prudent to require the contractor or precaster to produce sample panels for evaluation of such aspects as surface finishes. Work should not be allowed to proceed without the designer’s approval of these samples. The Standards which apply to precast concrete construction are as follows: NZS 3101:1995 Concrete Structures Standard The design of concrete structures NZS 3104:1991 Specification for concrete production – High grade and special grade NZS 3109:1997 Concrete construction NZS 3112 Methods of test for concrete NZS 3113:1979 Specification for chemical admixtures for concrete NZS 3114:1987 Specification for concrete surface finishes NZS 3402:1989 Steel bars for the reinforcement of concrete NZS 3121:1986 Specifications for water and aggregate for concrete NZS 3421:1975 Specification for hard drawn mild steel wire for concrete reinforcement Joining plate can be left exposed as a design feature. 60


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NZS 3422:1975 Specification for welded fabric of drawn steel wire for concrete reinforcement

Comprehensive lifting systems are available.

Materials

All materials should be procured from a dependable source. Where appropriate, the builder must ensure that quality records are kept for all precast concrete work. These records must be easily retrievable should they be required. Formwork Formwork requirements are detailed in NZS 3109. Reinforcing steel To comply with NZS 3402, NZS 3422. Concrete Readymix concrete to the specified compressive strength and to the requirements of NZS 3104. Special aggregates For special finishes specify the aggregate type, colour, size, range and depth of exposure. All aggregate to comply with NZS 3121. Lifting inserts Proprietary lifting devices are preferable. It is important to match the lifting inserts with the apparatus that will be used for lifting and the processes that will be adopted for casting and lifting.

Tolerances for precast panels (measured as defined in NZS 3109) shall be: Panel dimension (metres) Up to 3

3–6

Over 6

Steel connection plates It is recommended to galvanise any mild steel fixings that will be exposed to weather.

Width (mm)

+0, -5

+0, -10

+0, -12

Height (mm)

±5

±10

±10

Planeness (mm)

±5

±5

±5

Workmanship

Squareness (mm)

±5

±15

±15

Construct formwork in the configuration necessary to produce the required set out and detail of panels. Pay particular care to edge details.

Edge straightness (mm)

±5

±7

±10

Thickness (mm)

±10

±10

±10

The construction and casting of panels should be carried out by tradesmen experienced in precast concrete construction.

Ensure existing surfaces all comply with the tolerance requirements.

Place and cure concrete to produce the specified finishes and tolerances. Curing should be carried out for at least 7 days. Surface finishes shall be as specified by the designer and as defined in NZS 3114. Allow to cast in all items required for fixings or services. This requires coordination between the trades before the panels are designed and cast. The installation should be carried out by contractors experienced in precast construction. All necessary components such as gaskets, sealants and flashings should be supplied and fitted. Rigging and lifting must be done using the lifting points specified. Take care not to knock or drag panels along the ground. Panels must be secured in place before any temporary supports are removed. At all times during the construction process, but especially the lifting of panels, the health and safety of all workers and the public must be ensured.

Panel erection underway.

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Concrete panel will be set over the reinforcing steel.

construction Planning the sequence of activities, especially if the panels are to be cast on site, can save substantial time and frustration. Good planning will allow the panels to be cast earlier and will allow work to carry on around the panels once they are cast. With on-site casting planning the site is critical. The location to be used for casting must be of appropriate size and in a location that can continue to be accessed as the panels are erected. Access must be available for materials and for the crane. The sequence of casting panels must be logical if they are to be cast one on top of the other, last on is first off. Normally panels are erected sequentially from one corner. Setting out

If the panels are to sit on the ground floor slab, it is critical to confirm constructed dimensions of the slab, prior to constructing the panels. It is also critical to coordinate and check positions of starter bars and grout tubes. Weather conditions

The wall panels must not be cast in rain or cold conditions below 4°C. Particularly in hot, windy weather it is important to prevent excessive surface evaporation which can lead to plastic cracking. A common method of providing protection is to use anti-evaporative spray. Precast panels are particularly prone to this potential problem, due to their large surface area. Once the panels are cast and ready for erection, the construction process need not be affected by the weather. Panel erection & finishing Preparation for the second concrete skin in sandwich type wall panel.

After factory produced panels are cast and adequately cured, they must be transported to site. Suppliers of these panels have delivery and erection systems in place which should be of benefit to the builder. The tilt-up panel erection process begins with the separation of panels. The performance of the bond breaker during this operation is critical. The bond breaker must: •

permit clean complete separation of panels

not discolour the panel surface

minimise suction at time of separation

be compatible with the curing components that may be used.

Note that release agents used to facilitate the stripping of formwork in in-situ construction are not suitable as bond breakers. The crane is critical to the erection process. It must be rated to achieve the panel lift at the maximum anticipated working radius. The lifting capacity of a crane reduces considerably with larger working radii. The crane must be able to access the site 62


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and be adequately supported in each position it will be set. The rigging, lifting point and support design for movement of panels is critical. The strategies must be discussed and agreed between the appropriate parties. The builders concern will be access for fixing operations and ease of panel handling, the engineer will be concerned that the support points are structurally appropriate and the designer will want to make sure the lifting inserts can be hidden from view after the panels are in place. One of three strategies can be adopted:

Planning for crane access is important.

â&#x20AC;˘ Top edge lifted panels will hang vertical but this is not economical for units over 3-4 metres in height. â&#x20AC;˘ Face supported panels will hang slightly off vertical, however, they can easily be plumbed with adjustable props once in position. Face lift points may require plastering or alternatively they can be deliberately featured. â&#x20AC;˘ The use of lifting points on the face and top edge is sometimes used but requires a crane with two separate ropes. The crane must move the panels smoothly into position, avoiding shock loading which can induce cracking in the unit. Panels must be supported entirely by the crane until they have been secured into final position and propped. It is important to select propping positions that will not interfere with other construction activities. Surface finishes

While the design and specification of surface finishes falls within the scope of the designer, it is the builder or precaster who must ensure the specified finish is achieved. The surface finish treatment must be coordinated with the lifting and casting strategy. The most common face to treat with an integral finish is the face cast down. As lifting points will be on the back face, this allows the bottom face to be completely monolithic. The table indicates common methods for achieving surface textures.

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The exposed aggregate finish warrants special consideration. Chemical retarders are often used to allow the surface to be etched. The cement matrix can then be removed with a water blaster once the panel has been lifted. The use of chemically impregnated paper can simplify this process but also gives the designer additional scope for achieving patterns in the surface. Architects Herzog and de Muron have experimented with retarder impregnated paper to achieve stunning concrete effects. Sandblasting is also an option but has largely fallen out of favour with the introduction of the processes described earlier. Types of Finish

Face-up (single casting)

Face-down (single or stack casting)

Rebates, grooves and patterns

Hammer form into top surface (Position and depth difficult to control) Finish panel with bull float and trowel (Common paving technique)

Fix form to base slab (Position and depth easy to maintain)

Plain, smooth surfaces

Exposed Aggregate

Water washed (Special aggregates and patterns difficult to control)

Fine Textures

Broomed, Combed, Imprinted, Rolled

Coarse Textures Cutaway of door opening in a precast sandwich type wall.

Finish off floor or casting pad (Reproduces all imperfections of that surface) Sand embedment (Special aggregates and patterns easy to achieve, independent of concrete mix) Timberforms, Formliners Timber forms, Profiled steel sheeting, Polythene over stones, Formliners

A three level project planned using off site precast concrete panels.

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External insulation on tilt panel

Roofing on building paper on wire netting

100mm insulation

The details illustrated here are of the exterior envelope consisting of a concrete slab on grade, site precast wall panels and timber framed intermediate floor and roof. External weatherproofing and insulation is provided by one of many rigid polystyrene systems with acrylic plaster/paint. In this case the panels, designed to be seen from the inside should be cast with this face down. Lifting inserts will be covered by rigid insulation.

Plywood ceiling panels Rigid insulation panels

Roof beams @ 1200 cts

External waterproofing system

Timber plate on DPC with cast-in anchor

Structural conc. panel

WALL TO ROOF

If skirting is required, allowance should be made to cast-in fixing blocks. Vertical panel joints will be seen internally and should be detailed accordingly.

Flooring External waterproofing system

Bolt connection

Rigid insulation panels Joist hanger Continuous stringer on DPC Seal concrete. Exposed finish

INTERMEDIATE FLOOR

Reinforced conc. slab

Rigid insulation panels

Insitu concrete between slab & wall panels 50 MIN

100 MIN

Waterproofing system extend min. 50mm below floor level

150 MIN

The panel to slab connection is made after the panels are erected. This is very efficient structurally and economically but requires special consideration if the floor slab is to be exposed.

Skirting on cast-in fixings

PAVED

UNPAVED

Site precast panel. (Tilt slab) Sand blinding on compacted hardfill Reinforced concrete footing

WALL TO FLOOR

Extend DPC under footing

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18mm construction ply screw & adhesive fixed on DPC

Continuous aluminium angle screw fixed over butyl & sealant

Butyl roofing membrane extend up & over parapet

Timber plate on DPC secured by bolt

Non structural conc. veneer

18mm Plywood

Insulation Insulation between framing Joist hanger Ceiling lining Structural conc. panel

WALL TO ROOF Structural conc. panel Preformed duct structural joint

Non structural conc. veneer

Skirting fixed to cast-in timber fixing blocks Sealant joint with weep holes @ 900 ctrs 50 MIN

Insitu conc. topping

Insulation

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Concrete flooring units Structural conc. panel

INTERMEDIATE FLOOR

Structural conc. panel

Insulation

Preformed duct filled with expansive grout

100 MIN

150 MIN

Sealant joint with weep holes @ 900 ctrs

Skirting fixed to cast-in timber fixing blocks

Paved G.L.

Unpaved G.L. Sand blinding Compacted hardfill Reinforced conc. slab on grade

WALL TO FLOOR 66

Sandwich panel construction These details indicate the use of polystyrene insulation between concrete panels in wall section. Also shown is a horizontal joint detail, which must be carefully considered in the elevation design. Concrete flooring system can be designed to lock into supporting walls, as shown, or supported on a surface mounted steel angle, as shown on the following page. Grouted duct connections allow shorter panels than the detail shown previously, and for the floor slab to be cast in one operation. This makes it easier to achieve a uniform finish, which can be an advantage if it is intended to leave the slab exposed.


P re c a s t C o n c re t e D e t a i l s

Sandwich panel construction

Veneer panel is shown to thicken near the top, at the expense of the structural panel thickness. This allows veneer to cantilever as parapet. Insulation thickness is maintained.

Butyl membrane on 18mm construction ply Concrete parapet Vapour barrier

Rigid insulation

External waterproofing system

Rigid insulation Non structural conc. veneer Structural concrete panel

WALL TO ROOF

Concrete flooring units

Suspended plasterboard ceiling system

Internal finishes options 째 plasterboard 째 paint system only 째 acrylic plaster system 째 unfinished Structural concrete panel

Non structural conc. veneer

Skirting fixed to spaced timber blocks

Steel reinforcing connector cast-in

Rigid insulation

Concrete flooring units

INTERMEDIATE FLOOR Structural conc. panel Non structural conc. veneer

Skirting adhesive fixed

Rigid insulation

Mortar

Panels set on packing. Apply sealant with weepholes @ 900 crs

Reinforced concrete slab Floor covering

150 MIN

This wall section indicates precast panels (site or factory) which extend from floor slab to parapet in one section. This eliminates the need for a horizontal joint between panels which is often not architecturally desirable.

Continuous aluminium flat screw fixed over butyl

UNPAVED LEVEL

DPC

WALL TO FLOOR

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Jointing details Fibre composite/ non metalic connector

Hole to expel grout (when cavity full)

Rigid insulation

Grouted duct Hole to feed grout Backing rod & sealant 10mm - 20mm joint 6mm arris all edges Backing rod & sealant Weep holes @ 900 crs

Donut seal Structural panel Threaded connector Steel reinforcing

HORIZONTAL JOINT Non structural conc. veneer Rigid insulation 10mm - 20mm joint 6mm arris all edges Backing rod & sealant Weep holes @ 900 crs Non structural conc. veneer Rigid insulation

CORNER JOINT

Structural conc. panel Bolted plate connection countersunk to maintain flush surface. Oversize hole in plate to allow for potential movement.

Structural conc. panel Structural conc. panel

10mm - 20mm joint 6mm arris all edges Backing rod & sealant Weep holes @ 900 crs

Bolted plate connection countersunk to maintain flush surface. Oversize hole in plate to allow for potential movement.

Non structural conc. veneer Structural conc. panel

VERTICAL JOINT 68

The architectural expression of joints between panels requires consideration. Design decisions include; how the edges are shaped, the width of joints, integration with other details, and proportions that result from their set out. The structural fixings can be expressed as steel plates or hidden from view. Flexible silicon based sealants are typically used to weatherproof the joints. It is important that these sealants are checked and maintained periodically.


P re c a s t C o n c re t e D e t a i l s

Miscellaneous details It is important to limit heat conduction through cold bridges by insulating adequately. This detail shows rigid insulation fixed to the back face of the concrete parapet to limit this transfer. Plywood is fixed over this as a substrate for the butyl rubber roofing membrane.

Continuous aluminium angle screw fix over butyl membrane

18mm construction ply capping to falls screw fix to parapet Butyl roofing membrane on 18mm construction ply on rigid insulation

Conc. topping to falls

An aluminium extrusion is used to secure the end of the butyl and provide a crisp edge to the parapet. Precast conc. flooring units Continuous steel angle support bracket

WALL TO ROOF

The open web steel framing members allow a spacious ceiling, reminiscent of warehouse structures. This can add architectural interest and allow long spans, but sound transmission can be a problem.

Structural conc. panel

Timber flooring Rigid insulation

Open web floor framing members

Structural conc. panel

Continuous steel angle support bracket

INTERMEDIATE FLOOR

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Steel joinery details Rigid insulation fixed on site over conc. panel

Acrylic plaster system

Mild steel fixing plate cast into concrete reveal

Mild steel fixing blocks welded to plates PVC head flashing screw fixed to concrete panel

Mild steel window frame

Mild steel window frame Mild steel fixing blocks welded to plates

Rigid insulation fixed on site over conc. panel

Mild steel fixing plate cast into concrete reveal

Acrylic plaster system

JAMB DETAIL

Folded GMS flashing painted to match frame

Sloping sill tile adhesive fixed. Cut around frame fixings

Rigid insulation fixed on site over conc. panel Acrylic plaster & waterproofing system

SILL DETAIL

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These details indicate the window frame screw fixed to steel fixing blocks which have been welded to steel plates cast into the opening reveal. Inside, the window reveal is left as natural concrete, placing high requirements on the standard of finish in this area.

HEAD DETAIL

PVC angle flashing screw fixed to concrete panel

Steel door and window sections are regaining popularity with designers in many circumstances. Steel frames are narrower than aluminium or timber therefore presenting a finer line in the elevation design.

Mild steel window frame Mild steel fixing blocks welded to plates Mild steel fixing plate cast into concrete reveal


P re c a s t C o n c re t e D e t a i l s

Timber window details Timber joinery can be an attractive design option in an exposed concrete wall. The colour, texture and substance of exposed timber is a positive choice in this detail. It is critical to plan for adequate fixings for the frame, and to separate the timber frame from the concrete by DPC.

Rigid insulation fixed on site over conc. panel Acrylic plaster system

Precast conc. panel

Backing rod & sealant 10mm arris

PVC head flashing

Timber sash & sill

Timber architrave. Scribe cut.

Counter sunk & plugged fixing

HEAD DETAIL

Counter sunk & plugged fixing

Sealant

Timber frame on packing

Flashing Rigid insulation fixed on site over conc. panel

Precast conc. panel

Acrylic plaster system

JAMB DETAIL

Counter sunk & plugged fixing Timber sash & sill Sealant

Timber architrave

Sloping sill

Flashing under sill

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Aluminium window details External waterproofing system

Insulation Interior lining Building paper

Reinforced concrete wall

Timber strapping

Form drip PVC angle cast-in as flashing raglet. Fill with sealant over flashing

Timber reveal

Timber reveal

Timber strapping Interior lining

Building paper External waterproofing

Insulation

JAMB DETAIL

Position framing to allow drainage from within Flashing Tiled sill Timber strapping

External waterproofing system

Interior lining Insulation Building paper

SILL DETAIL 72

The exterior face of the concrete is shown to be sealed. The sealer should be applied to the concrete around the window opening before installation of the frames. A second line of defence is the building paper. Timber reveals give a more traditional appearance inside. The insulation in this example separates the thermal mass from the internal space.

HEAD DETAIL

PVC angle cast-in as flashing raglet. Fill with sealant over flashing

A step in the concrete reveal is formed and maintained by the casting in of a PVC angle. The window frame is fitted against the angle with a space allowed for sealant.


P re c a s t C o n c re t e D e t a i l s

Aluminium door details These details demonstrate the use of intermittent cast-in fixing blocks around the entire opening, a practice quite common in ICF detailing. Blocks are about 150 mm long and placed at approximately 450 mm centres. The step for the door frame, allows a more positive weathering detail. It is achieved by stopping the external installation short of the concrete edge. Internally the concrete can be left exposed and the edges are shown to be arrised. Sealant here is used architecturally to conceal the packing space between the concrete and the timber reveal.

Rigid insulation fixed on site over conc. panel

Structural conc. panel

Acrylic plaster & waterproofing system PVC head flashing

Sealant over packing space

HEAD DETAIL

This detail requires close tolerances which can be achieved with precast concrete. Timber reveal

PVC flashing

Sealant over packing space

Rigid insulation fixed on site over conc. panel

Intermittent timber blocks. Fix galv. nails skew nailed to timber & cast in concrete infill.

Acrylic plaster & waterproofing system

Structural conc. panel

JAMB DETAIL

Aluminium door frame over sill flashing

Aluminium door frame with timber reveals Shaped timber on DPC Reinforced conc. slab

Reinforced Acrylic plaster system over slab edge

Paving level

SILL DETAIL 73


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Timber door details Non structural conc. veneer Insulation

Intermittent timber fixing block

Head flashing 6mm arris to all exposed edges

HEAD DETAIL

Timber frame

Sealant

Counter sunk & plugged fixing

Timber architrave

Flashing

Non structural conc. veneer

Structural conc. panel

Insulation

JAMB DETAIL

Recessed timber door & sill Butyl rubber sill flashing

Non structural conc. veneer Insulation

Paving level Structural conc. panel

SILL DETAIL 74

Intermittent timber fixing block

Floor coverings Reinforced conc. slab

These timber door frames are shown to mask the exposed edge of polystyrene sheeting. Fixing for the frame is by plug and screw into the concrete. Architrave profile has been scribe cut to follow concrete.


P re c a s t C o n c re t e D e t a i l s

Services installation Internal gutter

Electrical and other cable services can be easily accommodated by all precast concrete systems with adequate planning. Services flush box cast into wall

These details indicated conduits cast into the concrete panels from ceiling to skirting level. In this example, the actual service point is located in a deep skirting.

WALL TO ROOF PVC or metal conduit cast into wall Window section

Services flush box cast into wall

Skirting Externally insulated concrete wall

Services face plate mounted to skirting

Reinforced concrete slab

WALL TO FLOOR

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Concrete Cast In-Situ

General . . . . . . . . . . . . . . . . . . .79 Design Issues

. . . . . . . . . . . . .80

Specification . . . . . . . . . . . . . .81 Construction

. . . . . . . . . . . . . .83

Details . . . . . . . . . . . . . . . . . . .85

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n-situ concrete is the traditional form of concrete construction. Until the early part of the 20th century it was the main method used. While in-situ concrete above ground level is used less in New Zealand with the advent of precast systems, it still widely used in many other countries.

I

Systems are being developed and used in both Europe and the U.S. to allow cast in place concrete to be cost and time efficient. In developing parts of the world, in-situ concrete, which relies on higher labour input than other forms of concrete construction, is still dominant. In New Zealand it is often not cost effective to design traditional load bearing cast-in-situ concrete structures in the face of competition from precast and modular systems. There are however some situations where in-situ is the ideal structural material, such as building sites that have difficult access. Cast in-situ concrete has become a material that designers exploit for its structural qualities above all else. The chance to cast monolithic building elements – walls, columns, beams, suspended floors and roofs which are beautifully detailed – appeals to many designers both in New Zealand and offshore. The work of Le Corbusier, Louis Kahn, Carlo Scarpa and more recently Tadao Ando in Japan is familiar to many. The perception of their work is very closely linked to their ability to exploit the qualities of in-situ concrete. Briefly, they are: • limitless flexibility of size and shape with no modular restrictions. Current developments in the U.S. are toward entire buildings being poured monolithically. • a wide variety of surface textures and colours can be achieved. • it can be cast as a “sandwich” incorporating an integral polystyrene sheet insulation. • a robust material which does not require much maintenance • it is a universally available material.

A house designed by the renowed architect Enrique Norten in Mexico City. 79


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design issues Most of the design issues begin and end with the formwork possibilities. The major cost of any cast concrete is that of the formwork. The relative cost of this element is reduced significantly when the formwork is able to be re-used. However repetitive uses on the same project suggests the need for construction joints. Construction joints occur between different placements of concrete. The detail and set out of these joints should be practical and coordinated with the overall design of the project. These joints can be unsightly if not properly planned and constructed. The colour of the concrete can vary slightly from one batch to the next. In large wall or soffit areas it may be desirable to introduce many joints in a pattern, some as construction, others as ‘dummy’ joints to mask the impact. In addition to construction joints, it may be necessary to provide control joints to allow for shrinkage and thermal movements in walls. These joints should be shown on the drawings. As a general rule, for domestic construction, control joints should be placed at 6 metre centres. Work closely with the builder to understand his strategies for use of formwork on the particular job; and with the structural engineer, who can advise specific requirements for shrinkage control joints. The desire for a particular surface finish or “look” may have drawn the designer to cast in-situ concrete. There are many textures and combinations thereof that have been explored to date. No doubt there are an equal number that have not. Some possibilities are: • board formed surfaces, achieved by constructing the formwork of roughsawn timber planks. The boards can be arranged in a pattern which will be mirrored in the final product.

The effective construction of formwork is the key to in-situ concrete walls

• exposed aggregate – this is more difficult with in-situ concrete than with precast, but it can be done by washing the surface with acid. The use of a retarding agent combined with waterblasting is an effective method of achieving an exposed aggregate finish. • fairface surface finish with a pattern of holes created by the removal of formwork ties. This finish has been made popular recently by Japanese architects and is achieved through careful consideration of the formwork and casting processes. • coloured concrete. Oxides and pigments can be used to tint the concrete to a wide variety of colours. In-situ concrete is only as good as the formwork, which must cope with dynamic loading during the placement and consolidation phases of work. Shuttering can bulge, settle and lean, all of which have the potential to induce small variations in the structure. In addition, the concrete will shrink as it dries. Detailing must therefore consider these and allow adequate tolerances.

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Edge details should take into account the difficulty of filling all corners of the formwork with concrete. Concrete may not find its way into corners, leaving them vulnerable to being damaged during removal of the formwork. It is recommended practice to soften these edges with a chamfer or bullnose or, at minimum, a bead of sealant in the corner of the form smoothed out with a finger. As discussed earlier, load bearing walls are not the only form insitu concrete may take. The designer can consider a column and beam structure with infill or hung curtain wall or claddings. Such systems can also be used in combination with walls. Such a concrete structure would have the advantages of allowing large internal and perimeter spans which will give opportunities for expansive open walls spaces and access to sun and views. The use of cast in-situ floor and roof planes can give the benefits of concrete systems such as acoustic and thermal performance. The concrete can be left exposed from below due to its monolithic form.

Formwork for a suspended concrete floor.

specification The written specification for in-situ can follow the form of specifications for commercial work with a greater emphasis placed on workmanship issues. Standards

NZS 3104 Concrete production â&#x20AC;&#x201C; high grade and special grade NZS 3109 Concrete construction NZS 3114 Concrete surface finishes NZS 3402 Steel bars for the reinforcement of concrete NZS 3422 Welded fabric of drawn steel wire for concrete reinforcement NZS 3604 Light timber frame buildings not requiring specific design NZS 3101 Concrete structures standard NZS 3610 Formwork for concrete

Board formed concrete texture.

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Formwork construction to achieve a board formed texture.

Insulation and waterproofing

As with all concrete wall systems, in-situ concrete must be waterproofed and insulated to meet NZBC requirements. Most often waterproofing is achieved by the use of acrylic paint and/or plaster systems. Insulation may be placed on either interior or exterior faces or may be cast within the wall. Materials

Reinforcing Bars Bars are to be to the requirements of NZS 3402 Spacers and Chairs One strategy for the formation of a construction joint.

Precast concrete or purpose made moulded PVC to approval. Concrete spacer blocks to only be used where the concrete surface is not exposed in the finished work. Ready Mixed Concrete High or Special grade to NZS3104. Maximum aggregate size 19 mm. Concrete strength as specified by the engineer.

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Construction joint and rebates set out to a pattern. Note the use of plastic waterstop.

Concrete shall not be allowed to free fall more than 2 metres in any oneplacement operation. This is an important consideration where the construction details call for the height of the wall to be cast in one operation. Curing of concrete to occur for the first seven days after placement. This is generally done by keeping exposed surfaces moist during that time. If any curing compounds are to be used they must first be approved by the designer and checked that they will not adversely affect the application of finishes.

construction Formwork

Workmanship

Require that all formwork and reinforcing be inspected and approved prior to the concrete being placed. Allow to build in all bolts and fixings as required by other trades and as shown in the drawings. This is an important consideration particularly for the main contractor who is responsible for facilitating the coordination between trades.

The exposed soffit of an in-situ concrete floor above.

Minimum concrete cover shall comply with table 5.5 of NZS3101 but shall in no circumstances be less than 40 mm. Where concrete is cast against ground the minimum cover shall be 75 mm, or 50 mm if using a damp proof membrane between the ground and the concrete. Pumping and placement of concrete is to be in accordance with NZS 3109. Coordinate with the supplier of the concrete to ensure appropriate specification of the concrete mix.

Planning the efficient and effective use of formwork is critical to the success of in-situ concrete. The nature of the formwork will depend on the designerâ&#x20AC;&#x2122;s objectives. It is important to consult with the designer regularly throughout the process to ensure the formwork is appropriate. Equally, the designer must consider, at an early stage, the way in which the formwork will be made. Poor communication between the designer and builder can result in diminished quality or cost escalation. The formwork must be constructed to accommodate the plastic of concrete which has a mass of approximately 2400 kg/m3. The general requirements are set out in NZS 3109. Setting out

While it is critical to get things right with in-situ concrete, it is not a construction method of high technology. It is important to coordinate all services, rebates, penetrations and surface finish requirements before concrete is placed in the forms. 83


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Weather conditions

Concrete should not be cast in wet or cold conditions. NZS 3109 provides guidance on precautions that should be taken for hot or cold weather concreting. Interestingly, in places like Canada and Scandinavia, concrete is placed in cold conditions throughout the winter. This often requires extensive heating of formwork which is not justifiable in our relatively mild climate. Moisture

Only a small proportion of the water in concrete is required for adequate hydration of the cement to occur. The excess water must not be allowed to escape too quickly as it is required for the curing process. This is especially important in the first 7 days.

An early house built in Wellington combining in-situ walls with precast concrete roof elements.

84

Conversely, after casting is completed it is desirable for water to escape quickly to allow timely application of finishes. Concrete dries at a rate of about 25 mm per exposed surface per month, depending on the time of year. This implies that a 100 mm concrete wall will take around 2 months before moisture sensitive finishes can be applied. Construction programmes must allow for adequate natural drying to occur. Forced drying, through heating, is not recommended due to the unevenness in drying. Often it is just the surface which is dry. Contractors are advised to check moisture levels with appropriate measuring equipment and to coordinate with the manufacturers of applied finishes.


C o n c re t e C a s t I n - S i t u D e t a i l s

Sandwich construction details

Butyl into chase cast in concrete wall

Butyl on plywood Insulation laid to a fall

These details of the external envelope indicate how proprietary polymer ties and polystyrene insulation board can be used in an in-situ application. This form of construction is best known in its precast context. The formwork must be set up to allow the insulation to remain in place while the concrete is placed in both faces. This is best done by balancing the pour to both faces up the height of the wall.

Reinforced outer wythe

Proprietry Insulation system cast into concrete

Hollow precast unit landed on structural wall

Composite Connector Reinforced Concrete wall

At suspended floor level the wall is cast full height eliminating the need for a construction joint. In this case the chosen concrete floor system is supported on a steel angle bolted to the finished wall.

WALL TO ROOF

At ground floor level the in-situ wall is connected to the slab and foundation by starter bars.

Proprietry Insulation system cast into concrete

The outside veneer face has weep holes formed to allow any water that enters above to trickle down the face of the insulation and escape without affecting the internal space.

Composite Connector

Hollow core flooring units & conc. topping

Reinforced Concrete wall Proprietry suspended ceiling

INTERMEDIATE FLOOR Proprietry Insulation system cast into concrete Composite Connector

100 MIN

150 MIN

Weep hole formed at base of wall

Wall keyed into slab Reinforced Concrete slab

Paved G.L.

Unpaved G.L. Sand blinding on compacted hardfill Concrete footing starter bars at required spacing

DPC

WALL TO FLOOR 85


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Dress butyl roofing into groove & seal

Upstand beam

In-situ floor and roof plane detail

Butyl on plywood on insulation laid to falls

One of the great advantages of in-situ concrete is the ability to create soffits that can be left exposed for reasons of aesthetics, cost and thermal mass.

Form drip Concrete column Commercial glazing section 80mm. Bed on sealant

At the lower level the in-situ wall is left exposed externally and insulated inside. Corbels and wall thickenings transfer the structural loads from above.

WALL TO ROOF

Frame on sill section. Bed on sealant

Cast in-situ floor. Exposed soffit

Construction joint

Clear sealer on in-situ formed wall Corbel @ columns

Plasterboard lining on strapping & building paper & insulation between.

INTERMEDIATE FLOOR Plasterboard lining on strapping & building paper with insulation between. Clear sealer on in-situ formed wall

Starter bars at required spacing

Ground & polished concrete floor slab on DPC

Sand blinding on compacted hardfill Reinforced concrete footing

WALL TO FLOOR 86

These details indicate at upper level how such a roof can be supported on cast in-situ or precast concrete columns. This will allow expansive areas of glass to be used.

The external walls are cast before the ground floor slab, enabling a controlled environment which may suit some finishes.


C o n c re t e C a s t I n - S i t u D e t a i l s

External wall details In-situ comcrete allows the designer to incorporate profiles and features which may not be possible with other forms of constrcution.

Flashing Waterproofing membrane on cast in-situ gutter

Insulation above suspended ceiling

An integral gutter, or any other profile, is able to provide architectural relief while serving a practical purpose. At suspended floor level there may be a need to incorporate construction joints as part of the overall wall pattern. It is important to specify the appropriate joint profile and make allowances for barriers to water ingress. At foundation level, openings may be necessary for a variety of reasons, in this case to ventilate the crawl space.

Timber rafters

Cast Insitu Concrete Wall. Exposed.

Stringer bolted to conc. wall. Countersink bolt head Internal Linings.

Waterproofing

WALL TO ROOF Cast Insitu Concrete Wall. Exposed.

Insulation. Internal Linings.

Joint detailed to express rather than hide the joint

Construction joint

Building Paper. Continuous. Timber strapping on DPC. Reinforced concrete slab

Construction joint Precast flooring unit PVC waterstop cast into lower part

INTERMEDIATE FLOOR Insulation. Reinforcing as required

Stringer bolted to wall

Internal Linings. Building Paper. Continuous. Timber floor on floor joists

Vent openings Conc. dish channel

Insulation foil faced

Cast in-situ concrete wall

Starter bars at required spacing.

Reinforced concrete footing

WALL TO FLOOR 87


r e s i d e nt i a l co n c r e te d e ta i l i n g a n d s p e c i f i c at i o n g u i d e

FALL

Spaced timber decking Butyl rubber membrane on plywood on furring to falls

Cast in-situ reinforced concrete upstand wall

Rigid insulation between furring strips Overflow pipe

Roof parapet details This roof is used as a trafficable deck with top laid insulation. The concrete soffit is left exposed internally, supported on columns rather than walls. The veneer wall in this example is internal, stopping short of the roof structure to avoid being loaded structurally.

Drip edge

Cast in-situ conc. slab

Commercial glazing section 75mm

Conc. column

GLASS WALL TO ROOF FALL

Butyl rubber membrane on 18mm ply on furring to falls Rigid insulation

Dress butyl into raglet and seal

Conc. topping Hollow core conc. slab

Structural concrete wall

MS angle to support roof slab Detail joint edges in sympathy with other edge details Composite connector

Suspended ceiling and insulation Cast in-situ wall sandwich construction

WALL TO ROOF Detail joint edges in sympathy with other edge details

EXTERIOR

Construction joint Conc. veneer panel

INTERIOR

10mm gap. Backing rod & sealant Composite connector

CONSTRUCTION JOINT

88

Concrete structural panel

This plan view of the vertical joint in a sandwich type wall suggests the edges are formed in sympathy with other joint details. Weathersealing is by sealant over backing rod, a minimum 10 mm gap is necessary.


C o n c re t e C a s t I n - S i t u D e t a i l s

Aluminium door details These walls are insulated and lined internally, giving a more traditional appearance. At the head, a rebate is cast in by a removable insert in the formwork. This delicate operation allows the head flashing to be seated securely.

Reinforced conc. cast in-situ

Head flashing

At sill level, the concrete slab edge should be set back to allow the threshold to overhang.

Internal lining

Intermittent H3 timber blocks. Fix galv. nails skew nailed to timber & cast-in concrete infill.

Timber reveal

Aluminium door frame with timber reveals

HEAD DETAIL

Timber reveal Aluminium subframe 2 beads of sealant

Continuous timber packer Timber strapping

JAMB DETAIL

Aluminium door frame with timber reveals

Aluminium door frame over sill flashing

Shaped timber sill on DPC Reinforced conc. slab

Step back concrete slab edge to suit reveal

SILL DETAIL 89


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Timber door details External insulation fixed to concrete External waterproofing system

Flashing

Reinforced concrete cast in-situ exposed finish Timber H3 fixing block cast-in

Timber architrave

HEAD DETAIL

Timber architrave

Corner protection Timber H3 fixing block cast-in External insulation fixed to concrete External waterproofing system

JAMB DETAIL

Timber door & sill. Recess sill into slab.

Flooring Reinforced conc. slab

Butyl rubber sill flashing

External insulation fixed to concrete Paving level

SILL DETAIL 90

Note the architrave, which is scribe cut to the reveal. Weatherseal at the jambs is sealant, which will require periodic maintenance.

Timber window frame and sash

Sealant & backing rod

These externally insulated walls have a pronounced chamfer on the internal reveal edge. The frame, positioned in the centre of the finished wall, is fixed to cast in fixing blocks at head and jambs.


C o n c re t e C a s t I n - S i t u D e t a i l s

Aluminium window details This set of details indicate the use of domestic joinery profiles in a concrete wall which is strapped and lined internally. The insulation is placed between the strapping. The window frame is shown fitting flush to the outside. While sealants provide adequate weathering at the jambs, at the head a flashing is shown fitted into a formed rebate. Note that it is advisable to have the window supplier measure the opening after the formwork has been stripped. This detail has not incorporated timber fixing blocks for the frame. Therefore, it will be necessary to install the frame by screw fixing into plastic plugs fitted into drilled holes in the concrete. It is important to wait until the concrete has gained adequate strength before drilling.

External waterproofing Reinforced concrete wall cast in-situ

Insulation Interior lining Building paper

Form drip Timber strapping PVC angle cast-in as flashing raglet. Fill with sealant over flashing

Timber reveal

Glazing in aluminium window frame

HEAD DETAIL

Glazing in aluminium window frame

Timber reveal

PVC angle cast-in as flashing raglet. Fill with sealant over flashing Timber strapping Interior lining

External waterproofing

Building paper Insulation

JAMB DETAIL

Position framing to allow drainage from within

Timber reveal

Flashing External waterproofing/ plaster/tiled

Timber strapping

Interior lining Reinforced concrete cast in-situ

Insulation Building paper

SILL DETAIL 91


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Timber window details External insulation fixed to concrete External waterproofing system Cast-in H3 timber fixing block Flashing

Reinforced concrete cast in-situ exposed finish

Sealant & backing rod

Note the use of fixing blocks cast into the opening allows the frame to be installed in a manner using standard nail fixings.

Timber window frame and sash

The frame is set to the depth of the wall and is held away from the concrete visually by a 5 â&#x20AC;&#x201C; 10 mm negative joint. The joint lacks the crispness that may be possible with lightweight linings, but it is important to respect the nature of the concrete materials and allow the chamfer as shown here.

HEAD DETAIL

Sealant & backing rod Corner protection Cast-in H3 timber fixing block

Sealant & backing rod

Reinforced concrete cast in-situ exposed finish

JAMB DETAIL

Timber internal sill

Timber sill and sash Timber packer Galvanized metal sill flashing External insulation fixed to concrete External waterproofing system

SILL DETAIL 92

The timber window frame is fitted into a wall with external rigid insulation and applied acrylic plaster as the weatherproofing. Flashing details are incorporated using the proprietary flashings that can be ordered with most External Insulating Finishing Systems.

Reinforced concrete cast in-situ exposed finish


C o n c re t e C a s t I n - S i t u D e t a i l s

Steel door and window details Steel windows are regaining popularity in the residential construction market. Fixing of the window frames to the structure is by way of lugs welded onto the frame before delivery to the site. These lugs are screw fixed to intermittent timber fixing blocks, the positions of which must be coordinated with lug positions. Frames are fitted against a PVC angle held in the formwork by the fixing blocks. The angle will stabilise the concrete edge and provide suitable backing for sealant.

External waterproofing Reinforced concrete wall cast in-situ

Rigid insulation

Cast-in H3 timber fixing blocks

Form drip

Continuous sealant bead in PVC angle Glazed hinged door in steel frame

Continuous timber fixing block

Timber reveal

HEAD DETAIL Glazed hinged door in steel frame

Timber reveal

Sealant in cast-in PVC angle

Continuous timber fixing block Cast-in H3 timber fixing blocks Rigid insulation

JAMB DETAIL Steel door sill & frame Timber threshold Flooring

Silicon sealant

Sloped paving

Reinforced concrete slab

SILL DETAIL 93


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Services Internal gutter

Services flush box cast into wall

WALL TO ROOF PVC or metal conduit cast into wall

Services flush box cast into wall

Skirting

Reinforced concrete slab

WALL TO FLOOR

94

Electrical services generally drop from the ceiling in the space to be served which demands a long conduit drop. An alternative would be to extend the service from the level below. Be sure to allow sweeps in the conduit both at the top and bottom to allow the cables to be drawn easier.

Window section

Externally insulated cast in-situ concrete wall

It is possible to cast-in allowance for services in concrete walls. It is important to coordinate this provision with the structural engineer and the relevant subtrades.

Services face plate mounted to skirting

It may be prudent to allow spare capacity or spare dropper points for future alterations.


G e n e ra l I n f o r m a t i o n

References Websites

ConcreteNetwork.com (1999). ConcreteNetwork.com [Online]. Available: http://www.concretenetwork.com [2000, June 30] Gates & Sons, Inc. (1997). Concrete gates forming systems: concrete forms [Online].Available: http://www.gatesconcreteforms.com [2000, July 7] Insulating Concrete Form Association. Insulating Concrete Form Association [Online]. Available: http://www.forms.org [2000, July 7] Portland Cement Association. Insulating concrete forms: a better way to build a better home [Online]. Available: http://www.concretehomes.com/sys-icf.htm [2000, July 7] Precise Forms, Inc. Precise forms [Online]. Available: http://www.preciseforms.com [2000, July 7] Formasera AB. Formasera AB [Online]. Available: http://www.formasera.se [2000, July 7]. Books

Ambrose, J. (1997). Simplified design of concrete structures ( 7th ed.). New York: John Wiley & Sons Inc. Brand, R. (1990). Architectural details for insulated buildings. USA: Van Nostrad Reinhold. BRANZ house insulation guide. (1995). Wellington, [N.Z.]: BRANZ Publications. Bulleyment, A. (1998). Good concrete floors and basements practice. Wellington: BRANZ Publications. Burry, M., & Preston, J. (Eds.). (1999). Construction primer: student edition 1999. Wellington: Victoria University of Wellington. Cement mason’s guide. (1987). (PA122.04H). Skokie, [Ill]: Portland Cement Association. Childe, H. L. (1969). Everyman’s guide to concrete work. London: George Godwin Ltd. Chisholm, D. (1996). Tilt-up technical manual. Wellington: Cement and Concrete Association of New Zealand. Concrete ’93 : New Zealand Concrete Society, technical conference and AGM, Waipuna Lodge, Mt Wellington, Auckland, Friday 8 to Sunday 10, October 1993. (1993). Wellington: The Concrete Society. Concrete detail design. (1986). London: The Architectural Press. Concrete in housing. (1983). Wexam Springs, [U.K.]: Cement and Concrete Association.

Concrete: the natural alternative for home building. (1993). Skokie, [Ill]: Portland Cement Association. Dore E. (1983). Suspended concrete ground floors for houses. Wexam Springs, [U.K.]: Cement and Concrete Association. Full brick/block house construction. (1980). Australia: Cement and Concrete Association of Australia. Futagawa, Y. (Ed.). (1991). Tadao Ando: details. Tokyo: A.D.A Edita Tokyo Co. Ltd. Gage, M. (1970). Guide to exposed concrete finishes. London: The Architectural Press. Gjerde, M., & Ingham, J. (1999). Masonry buildings not requiring specific engineering design: part 4.2. Wellington: Cement and Concrete Association of New Zealand. Guide to suspended concrete floors for houses. (1991, May). (T40). North Sydney: Cement and Concrete Association Australia. Kosmatka, S.H. (1991). Finishing concrete slabs with color and texture. Skokie, [Ill]: Portland Cement Association. Masonry villas: detail guide. (3rd ed.). Newmarket: Firth Industries. Panarese, W.C., Kosmatka, S.H., & Randall Jr, F.A. (1991). Concrete masonry handbook: for Architects, Engineers, Builders. Skokie, [Ill]: Portland Cement Association. Prescriptive method for insulating concrete forms in residential construction. (1998). Skokie, [Ill]: Portland Cement Association. Pringle, T. (1998). Good exterior coating practice. Wellington: BRANZ Publications. Reinforced concrete slab floors for houses – a selection guide. (1990). Australia: Cement and Concrete Association of Australia; Steel Reinforcement Institute of Australia. Residential concrete. (2nd ed.). (1994). Washington: Home Builders Press. Roller, J.J. (1996). Design criteria for insulating concrete form wall systems. Skokie, [Ill]: Portland Cement Association. Roper, P. (1987). A practical guide to: blockwork. London: International Thompson Publishing. Thermal insulation – roofs. (1983, April). (IB023). Porirua: New Zealand Concrete Research Association. Thermal insulation for: insitu/precast concrete walls. (1983, April). (IB022). Porirua: New Zealand Concrete Research Association. Thermal insulation: avoiding risks – a guide to good building construction. (1989). Watford, [U.K.]: Building Research Establishment.

Concrete masonry in housing seminar. (1974). Wellington: Concrete Publications Ltd. 95


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Thornton, G. (1996). Cast in concrete: concrete construction in New Zealand 1850 – 1939. Hong Kong: South China Printing Company Ltd. Tilt-up housing construction in Victoria. (1990). Melbourne: Cement and Concrete Association of Australia ; Steel Reinforcement Institute of Australia. Tovey, A.K., & Roberts, J.J. (1990). Efficient masonry housebuilding: detailing approach. Wexham Springs: British Cement Association. Tovey, A.K., & Roberts, J.J. (1990). Efficient masonry housebuilding: detailing approach. (48.054). Wexham Springs, Slough: B.C.A. Unifloor: composite steel/concrete floors for dwellings on sloping sites. (1995). Australia: Cement and Concrete Association of Australia. Vanderwerf, P. (et al.). (1997). Insulating concrete forms for residential design and construction. New York: McGraw-Hill. Vanderwerf, P.A., & Munsell, W.K. (1996). Insulating concrete forms: construction manual: successful methods and techniques. U.S.A.: Portland Cement Association. Waddell, J. (1974). Precast concrete: handling and erection. Detroit [U.S.A.]: American Concrete Institute. Waddell, J., & Dobrowolski, J. (3rd ed.) (1993). Concrete construction handbook. . U.S.A.: McGraw-Hill Inc. Wynn, A.E., & Manning, G.P. (1974). Design and construction of formwork for concrete structures. London: Cement and Concrete Association. Articles

A concrete opportunity. (1992, June/July). New Zealand Concrete Construction, pp.26-28. Adrienne R. (1996, December/January). Solid solutions. New Zealand Home and Building, 1: 104-107. Ardres, R.P., & Fisher, T. (1995, August). How to build concrete homes using foam forms. Aberdeen’s Concrete Construction, 40 (8): 659-667. Barnard, D., & Chisholm, D. (1992, July/August). Swing to concrete housing, cladding. Architecture New Zealand, pp. 70 – 72,74. Burry, M. (1995, September). New technologies. Architecture New Zealand, pp.98-104. Chisholm, D. (1993, August/September). Residential concrete gets competitive. New Zealand Concrete Construction, pp.5-6, 8-10. Concrete blocks – making them work. (1991, December). Build, pp.7-8. Examples of the use of concrete in residential design. (1991, May). New Zealand Concrete Construction, 35: 8-13.

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Insulated precast housing. (1998, August/September). New Zealand Concrete Construction, 42 (4): 10-11. Lewis, W.R. (1998, August/September). Concrete for New Zealand housing. New Zealand Concrete Construction, 42 (4): 6-9. Mills, M. (1991, March/April). External wall insulation: cladding for refurbishment. The International Journal of Construction Maintenance and Repair, 5 (2): 11-15. Munsell, W.K. (1995, January). Stay-in-place wall forms revolutionize home construction. Aberdeen’s Concrete Construction, 40 (1): 12-19. Pratley, J. (1993, May). Tilt-up techniques: tilt-up takes on the housing market. Australian Concrete Construction, 6 (2): 8 – 10. Priest, J. (1998, August/September). Masonry homes. New Zealand Concrete Construction, 42 (4): 21-22. Real houses for real people. (1999, December). New Zealand Concrete Construction, 43 (4): 10-16. Residence in the desert. (1994, February/March). New Zealand Concrete Construction, 38 (1): 31-32. Sharman, W. (1993, October/November). Good practice the key to durability. Build, pp.33, 34. The Congreve house. (1995, August/September). New Zealand Concrete Construction, 39 (4): 30-31. Tovey, A. (1998, Spring). Visionary aims and traditional construction. Concrete Quarterly, pp.12-13. Vanderwerf, P.A. (1996, December). Tips for placing concrete into insulating wall forms. Aberdeen’s Concrete Construction, 41 (12): 925-930. Vanderwerf, P.A., & White, J.G.A. (1998, October). Choosing an insulating concrete form system. Aberdeen’s Concrete Construction, 43 (10): 845-851.


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