Non-Stabilised Rammed Earth Constructions

Department of architectural and civil engineering UniversitĂŠ libre de Bruxelles Vrije Universiteit Brussel

Alexandre Robert McCormack Supervisor :

Bertrand François

Brussels May 2013

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Abstract Earth constructions are gaining in popularity yet are still rarely subject to thorough academic research and are almost unknown to the general public. However, they present considerable environmental advantages in a time when the concerns of energy and lifecycle assessment are at their highest. The main concern with non-stabilised earth is the strength of the material compared to default construction materials such as steel or concrete. In this master thesis, the aim is to present the characteristics of non-stabilised rammed earth constructions and implement them into a project design adapted to a temperate climate.

would be to prevent shrinkage. On the other hand, the shrinkage limit was well over the water content used for the finer grain soil.

Without further analysis on a full scale rammed earth wall of the possible influence of shrinkage and cracking, 2.4 MPa was used for the project design. It was demonstrated that non-stabilised rammed earth could be adapted to a 4 storey building using a minimum of 70cm thick walls and a security factor superior to that of uncontrolled masonry. All the characteristics and implications of a non-stabilised rammed earth construction were fulfilled in the design of the Co-operative housing project and even instilled further ideas such as participatory building.

Geotechnical testing had to be modified to identify the parameters which contribute to the compressive strength of rammed earth constructions. Once non-stabilised rammed earth had been established as a feasible construction material, the characteristics were applied to an urban Co-Housing project in Brussels.

Water content and compaction energy were found to be the largest contributor to the strength of the material. A compressive strength of 3.8 MPa was achieved with a fine grain soil classified as clayey silt.

Furthermore, under ambient interior humidity it was demonstrated that at least part of a wall could attain an increase in strength through the natural drying process leading to a compressive strength of 7MPa. However, contrary to what was predicted, grain-size distribution did not play a further role in optimising compressive strength as a lesser value of 2.4MPa was reached. A possible advantage for a well graded soil

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Acknowledgements It could not have been done without the people who were behind me. I’d like to thank the following: My supervisor, Bertrand François gave me the opportunity to carry out this master thesis. It has been the most passionate part of my five years of studying architectural engineering.

Paul Jacquin took his time to read and answer all my questions during the year. He and his work have been brilliant guidance.

Nicolas Canu has been of great help in the laboratory. He showed me all the technical material and was always there whenever I had a problem.

The whole team I worked with on the rammed earth construction workshop in April 2012 in Flanders. They have certainly helped in my personal attraction for rammed earth. Thank you to Quentin Chansavang and Hugo Gasnier from CRATerre for their contribution.

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Table of Contents

2.1

Thermal inertia .............................................................................4

2.2

Hygrometry ..................................................................................4

2.3

Fire safety ..................................................................................... 4

2.4

Thermal transmittance .................................................................4

Abstract ....................................................................................................... 1 Acknowledgements ..................................................................................... 2 List of Figures............................................................................................... 5 3

Soil Characterisation (Franรงois, 2011; Verbrugge, 2010) .....................5

List of Tables ................................................................................................ 6 3.1

Porosity ........................................................................................ 5

3.2

Water content ..............................................................................5

3.3

Bulk density ..................................................................................5

3.4

Dry bulk density............................................................................5

3.5

Soil structure and fabric ...............................................................6

3.6

Soil-water interaction...................................................................6

3.7

Grain-size distribution ..................................................................6

Photos.......................................................................................................... 6 List of Drawings ........................................................................................... 6 Introduction ................................................................................................. 7 Rammed Earth Constructions ..................................................................... 7 Part One : Material Characteristics ............................................................. 1 1 Environmental advantages and lifecycle assessment of Rammed Earth ............................................................................................................ 2 1.1

2

Embodied Energy......................................................................... 2

3.7.1

Dry sieving analysis ..............................................................6

3.7.2

Sedimentation analysis ........................................................6

1.1.1

Concrete and Steel .............................................................. 2

1.1.2

Rammed Earth ..................................................................... 2

3.8

Shrinkage limit..............................................................................6

1.1.3

Embodied energy compared to the total building .............. 3

3.9

Compaction ..................................................................................6

3.10

Proctor compaction test...............................................................7

1.2

Recyclability ................................................................................. 3

1.3

Natural Resource Abundance ...................................................... 4

1.4

Water consumption ..................................................................... 4

4.1

Grain size classification ................................................................7

Building properties .............................................................................. 4

4.2

Consistency limits .........................................................................8

4

5

Soil classification ..................................................................................7

Compressive Strength Characteristics of RE ........................................8 3

1.1

Insulation ....................................................................................23

5.1

Laboratory Testing ....................................................................... 8

5.2

Soil preparation ........................................................................... 8

5.3

Soil identification ......................................................................... 8

2.1

Multigenerational bartering .......................................................24

5.4

Standard geotechnical testing ..................................................... 8

2.2

Multiple sociological backgrounds .............................................24

2.3

Participatory building .................................................................24

5.4.1

Normal proctor test ............................................................. 8

5.4.2

Unconfined Compression .................................................... 9

5.5

Optimising soil structure with grain-size distribution ............... 10

5.5.1 5.6

Optimum normal proctor .................................................. 11

2

Co-Operative housing.........................................................................23

3

Tour et Taxi.........................................................................................25

3.1 4

Adapting the testing procedure ................................................ 11

Local soil .........................................................................................26 Concept and Development ................................................................26

4.1

Context .......................................................................................26

5.6.1

Compaction energy ........................................................... 11

4.2

Preliminary approach .................................................................27

5.6.2

Compressive strength of optimally mixed soil .................. 11

4.3

Orientation and Sunlight ............................................................27

5.7

Cohesion .................................................................................... 12

4.4

Internal Walls .............................................................................29

5.8

Suction ....................................................................................... 12

5.9

Hygrometry................................................................................ 13

5.10

Size of samples .......................................................................... 15

5

Predimensioning ................................................................................31 5.1

Load calculations ........................................................................31

5.1.1

Floor loads ..........................................................................31

5.10.1

Increased size of cylindrical sample .................................. 16

5.1.2

Self-weight .........................................................................31

5.10.2

Imperfections .................................................................... 16

5.1.3

Combination of permanent and variable actions ..............31

5.11

Type of ramming ....................................................................... 16

5.12

Shrinkage ................................................................................... 16

5.2

5.2.1

Part Two : Application to Urban Co-Housing in Brussels .......................... 18

5.2.2

1

5.3

Identified technical characteristics ................................................... 22

Resistance to vertical loads ........................................................31 Security factor ....................................................................31 Vertical lifting loads ................................................................32 Resistance to horizontal loads (Wind) .......................................32 4

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Sustainability ..................................................................................... 33 6.1

Construction materials .............................................................. 33

6.2

Net zero energy building ........................................................... 33

6.3

Green roofs ................................................................................ 33

6.4

Solar panels ............................................................................... 33

6.5

Aquaponic systems .................................................................... 33

6.6

Water harvesting system........................................................... 33

ANNEX ....................................................................................................... 43 1.

Identification paper for MLD soil used in tests ................................. 43

2. Rammed Earth Workshop April 2012 : Construction of 50m² hunting house (photos by Nicolas Coeckelberghs)................................................. 50

List of Figures Figure 1 : Embodied energy comparison of different construction materials (Prof.Geoff Hammond, 2008) ...................................................... 2 Figure 2 : Energy for concrete structure compared to total initial embodied energy ........................................................................................ 3 Figure 3 : Energy for concrete structure compared to total amount of energy necessary over 100 years including replacement of materials ....... 3 Figure 4 : Normal proctor compaction test for MLD soil ............................ 8

Figure 5 : Compressive strength of equivalent dry density samples at different water contents ..............................................................................9 Figure 6 : Grain-size optimisation of MLD soil with sand and gravel .........10 Figure 7 : Compressive strength of compacted mixed soil at different water contents ...........................................................................................11 Figure 8 : Compressive strength of compacted non-mixed MLD soil at different water contents ............................................................................ 12 Figure 9 : Variation of mass of water in soil samples over 28 days at ambient interior relative humidity (+/- 40% RH, +/- 22°C) ........................13 Figure 10 : Variation of mass of water in soil samples over 28 days at controlled relative humidity simulating rainy conditions (94% RH, 22°C) .13 Figure 11 : Compressive strength of compacted non-mixed MLD soil specimens after 28 days at given relative humidity ..................................14 Figure 12 : High compaction energy non-mixed MLD soil at 8% water content at 50% relative humidity during 28 days ......................................14 Figure 13 : Compressive strength comparison of maximum dry density sample at 28 days under ambient interior conditions ...............................14 Figure 14 : Scheme of characteristic implementation of rammed earth to architecture ................................................................................................22 Figure 15 : Google Earth view on Tour et Taxi, Brussels Local soil ............25 Figure 16 : Penetration test point N°794 Tour et Taxi, Brussels, ULB soil mechanics laboratory ................................................................................. 26 Figure 19 : Diagram summarising stages of research ................................44

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List of Tables Table 1 : Estimated U-value for rammed earth and with added 10cm cork insulation ..................................................................................................... 5 Table 2 : Grain-size classification of the ABEM/BVSM (François, 2011) ..... 7 Table 3 : Laboratory standards of compaction test .................................... 7 Table 4 : Dimensions of samples used for testing ..................................... 16 Table 5 : Permanent loads used for pre-dimensioning wall thickness...... 31 Table 6 : Variable loads used for pre-dimensioning wall thickness .......... 31 Table 7: Characteristics and identification table of MLD soil used for testing ........................................................................................................ 43 Table 8 : Grain-size distribution curve of MLD soil.................................... 43 Table 9 : ABEM/BVSM soil classification (François, 2011) ........................ 43

Photos Photo 1 : Context scale model of Tour et Taxi, Brussels ........................... 28 Photo 2: Unconfined compression and comparison of size 1 and size 2 samples ...................................................................................................... 45 Photo 3 : Unconfined compression for small size samples ....................... 45 Photo 4: Some sheared samples ............................................................... 45 Photo 5 : Rammed Earth Block 15cm well graded soil .............................. 46 Photo 6 : Ramming 15cm block with 6kg hammer via a wooden piece ... 46 Photo 7: Laminated sample due to high compaction energy and low water content ...................................................................................................... 47 Photo 8 : Diagonal and cone shearing ....................................................... 47

Photo 9 : Preparation of soil dried at approximately 35°C ........................48 Photo 10 : Bell for controlled relative humidity.........................................48 Photo 11: Sheared sample with non-parallel surfaces ..............................49

List of Drawings Drawing 1 : Site implantation 1/ 500 .........................................................30 Drawing 2 : Sustainability scheme .............................................................31 Drawing 3 : Ground floor 1/200 .................................................................32 Drawing 4 : Second floor 1/200.................................................................33 Drawing 5 : Third floor 1/200 .....................................................................34 Drawing 6 : Fourth floor 1/200 ..................................................................35 Drawing 7: Section AA' ............................................................................... 36 Drawing 8 : Section BB' .............................................................................. 37 Drawing 9 : Section CC' .............................................................................. 38 Drawing 10 : Second floor plan insulation .................................................39 Drawing 11 : Render 1 ................................................................................ 40 Drawing 12 : Render 2 ................................................................................ 41 Drawing 13 : Render concept colour..........................................................42 Drawing 14 : Render 4 passageway ...........................................................43

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Introduction

Rammed Earth Constructions

The aim of this master thesis is to demonstrate the feasibility of earth as a construction material and more specifically within the rammed earth technique. It is developed to draw more attention towards this building material from the scientific academia as well as the general public.

The use of earth in buildings stretches back well over a millennia (A.Jacquin, 2008). Different techniques have been developed to achieve sufficient strength to be used as a construction material. One among these techniques is rammed earth or so called pise.

The thematic was essentially oriented towards non-stabilised rammed earth where adding concrete or lime diminishes some beneficial characteristics of the material. Besides the positive aspects of using earth as constructions, the main concern and disadvantage of non-stabilised rammed earth compared to modern construction materials is fundamentally its strength. On this behalf, the study takes place in two parts. First earth is defined as a construction material by identifying its characteristics. Secondly, the application of these characteristics and the achieved strength was implemented into a design case in order to illustrate its possibilities but also to understand its limits in modern architecture.

The technique of rammed earth is usually found in arid climates where the soil is drier. It consists of compacting successive layers of approximately 12 to 15cm of soil inside a formwork. The strength developed by this technique relies essentially in the compactness achieved. Historically, this was done by hand generally using a wooden rammer. In modern rammed earth buildings, pneumatic rammers are used to make it slightly less labour intensive and can help achieve a much higher compacting rate. However, even with this modernised technology this type of construction still remains very labour intensive. Although the construction material is cheap, the amount of labour needed renders these projects today rather expensive. If a market was developed for rammed earth buildings, the technique could be adapted and industrialised thus reducing labour cost. It would most certainly also favour control over the material.

Identifying the material characteristics was done mainly in three parts.

First it was pointed out the environmental advantages that make earth buildings so appealing and secondly the material was viewed from geotechnical standards. The third part takes part in identifying the main parameters contributes to the optimisation and development of the strength of the material. This was achieved by laboratory testing.

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Part One : Material Characteristics

1

Environmental advantages and lifecycle assessment ent of Rammed Earth

1.1 Embodied Energy The lifecycle assessment of a building is of the utmost concern when designing sustainable architecture. Embodied mbodied energy in construction materials is still rarely taken into account yet remains an important aspect to con consider. sider. The energy used to process the material impacts on the environment and directly or indirectly causes CO2 emissions. This needs to be factored in if high energy material is necessary for all structural cases of a building. We need to compare the embo embodied died energy of rammed earth with that of concrete and steel, generally the default building materials in modern architecture.

1.1.1 Concrete and Steel According to the so called ““process process analysis” analysis” for defining embodied energy in materials, it can be demonstrated that concrete requires 1GJ/m3. The same procedure for steel gives 23GJ/m3. However, considering the Crawford (2011) procedure, concrete requires 5.01GJ/m3 GJ/m3 and steel 85.46 GJ/m3. The Crawford (2011) is a much more precise technique for calculating embodied energy as it takes into account all of the elements required for the processing of the material itself. Obviously, to properly compare the materials, we must take into account the ratio of the embodied energy over the EE-modulus modulus of the material. If a mater material ial has enormous strength, less is required when it comes to designing the structure.

1.1.2 Rammed Earth It is still very difficult to determine the embodied energy of a material. In the case of the construction of a rammed earth project of 50m2, it was possible to quantify the amount of fuel required for the implementation of 1 cubic metre of rammed earth. Fuel was needed for ramming and in some cases for drying the soil with a heater. The fossil fuel consumption was then converted to the amount of energy required. required. However, this is not sufficient to calculate the total embodied energy used. The excavation of the soil was carried out by an excavator, the soil was mixed with an earth mixer and sand and gravel had to be transported to the site, but manpower was used for mixing and carrying. Nevertheless, even if we slightly over-estimate over estimate each of these components, the total energy used is in the order of MJ’s MJ’s per cubic metre. metre. With more precise calculations, it is estimated that non-stabilised non stabilised rammed earth has has an embodied embodied energy of 0.5GJ/m3 (Clare Lax, 2010) and therefore is low compared to the embodied energy of other materials (see see Figure 1).

15

Embodied Energy GJ/m3

1

10 5 0

Construction materials Figure 1 : Embodied energy comparison of different construction materials (Prof.Geoff Hammond, 2008)

2

It should be pointed out that the embodied energy for steel or other metals is disproportional when compared to other materials. H However, owever, the EE-Module of steel is consider considerably ably high, thus reducing the sections and quantity of steel used. It is for this reason that in order to compare realistically the embodied energy of materials, the sections generally used should be taken into consideration consideration. For example, It could be argued that rammed earth walls are twice or three times (sometimes more) thicker than concrete walls.

1.1.3 Embodied energy compared to the total building According to ULB PhD student AndrĂŠ Stephan, tephan, a concrete structure of a passive house represents 18.2% of the in initial itial embodied energy of all materials (see see figure 2 2) and 7.2% over 100 years if one considers the eventual replacement of some of these. However, taking into account the consumption of the building over 100 years, the energy used in the creation of a conc concrete rete structure represents only 3.7% of the total energy (see see figure 3 3).. This clearly demonstrates the importance of insulating a building above all other aspects. However, if we look at the accumulation of this percentage over a large number of dwellings, the energy then becomes considerable. For rammed earth buildings, this percentage would be insignificant and so continue to contribute to a decrease in the environmental footprint of the building. This is just one aspect of the lifecycle assessment, yet th there ere are other variables that establish the environmental footprint of a material.

1.2 Recyclability Some movements are taking into account the lifecycle of materials such as the cradle to cradle concept. There is a tendency now to exploit recyclable materials as much as possible.

It is essential that buildings buildings last in time, but it may be a bias to believe they will last forever. Perhaps this is not the way to view things, for although some buildings last for a century or more there is always the possibility that that they will be replaced as technologies emerge or as an urban area evolves; dwellings built in the 70’s were destroyed 20 or 30 years later. We have seen also, particularly in the recent economic boom and the following recession, how construction truction demand increased considerably and how we inherited vistas of urban scarification when the demand ceased. ceased If we take the examples of Ireland and Spain, we will see that construction was suspended and structural skeletons skeleton left visible for years to come.

18,2

81,8

Embodied energy of concrete structure

Figure 2 : Energy for concrete structure compared to total initial embodied energy

Rest of embodied energy 3,7

Figure 3 : Energy for concrete structure compared to total amount of energy necessary over 100 years including replacement of materials materi

Embodied energy of concrete structure Energy Consumption and rest of embodied energy including material replacement

96,3

3

1.3 Natural Resource Abundance Soil is one of the most predominant materials on earth. It is abundant and can be considered universal to some extent. A US geological survey shows that over half of the world’s production of cement comes from China (Oss, 2011). Using soil as a building material would avoid dependency on importation and could also prevent some change in landscapes due to excessive excavation. Moreover, organic soil is incompatible with earth construction and would not encroach on agricultural activity.

1.4 Water consumption There is a growing concern on freshwater scarcity in the world (Arjen Y. Hoekstra, 2012). Concrete requires a large fraction of drinking water for hydration reaction. The soil used in rammed earth building needs to be at the drier state which often leads to actually drying the soil rather than adding water to it.

2 Building properties 2.1 Thermal inertia It has been established in the case of low energy buildings that internal gains can become overwhelming requiring cooling systems to compensate. Thick walls that serve as thermal inertia can compensate the increase of heat. Furthermore, there is natural thermal regulation during summer as walls cool during the night and absorb the heat during the day.

As materials are improving and the amount we use in construction has financial consequences, we tend to minimise as much as possible materials used thus dealing with sometimes thin structures.

2.2 Hygrometry It has also been demonstrated that earth walls quickly absorb or emit water in the air in accordance with the ambient relative humidity. Dr Paul Jacquin shows that the pores in the earth walls become natural regulators. Relative humidity is an important factor in the interior quality of a building. This is one of the reasons that living in an earth home is qualified as being very comfortable.

2.3 Fire safety Rammed Earth is an inert material and is classified as non-combustible.

The Commonwealth Scientific and Industrial Research Organisation (CSIRO) gives a fire resistance rating of 4 hours (Earth Structures (Europe), 2013).

2.4 Thermal transmittance Rammed earth has a low insulating performance that can go up to a Uvalue of 2.0 W/m²K for a 300mm thick rammed earth wall (Vasilios Maniatidis, 2003). Passive houses in Belgium deal with values in the order of 0.15W/m2K (Descamps, 2012). The presented values in Table 1 can are estimated for different wall thicknesses assuming the thermal conductivity is λ = 0.6 W/m.K. It was also calculated with 10cm of added corkboard (EnviroNomix, 2009).

4

3.2 Water content Wall thickness

0,30

0,40

0,50

0,60

0,70

0,80

0,90

U-value RE + 10 cm cork

1,51 0,32

1,21 0,30

1,01 0,29

0,86 0,27

0,75 0,26

0,67 0,25

0,60 0,24

Table 1 : Estimated U-value for rammed earth and with added 10cm cork insulation

3 Soil Characterisation (François, 2011; Verbrugge, 2010) Soil is composed of solid particles that vary in size and nature. Voids between particles are filled with air or water. This leads to a three phase material and it is important to be able to define these phases in order to identify the structure of the soil. The deformation properties and resistance created by the soil depend essentially on how each phase is dealt with.

3.1 Porosity ܸ‫ݏ݀݅݋ݒ‬ ݊= ܸ‫݈ܽݐ݋ݐ‬ The porosity is defined by the ratio of the volume of voids in the material that are either a liquid or gas phase to the total volume of soil.

When all the pores of the soil are filled with water, it is called a saturated soil, when they are only partially filled it is an unsaturated soil.

‫=ݓ‬

‫ݓܯ‬ ‫ݏܯ‬

This is the mass of water over the mass of solid particles. It is an important factor in rammed earth constructions.

In order to determine the water content, a mass of soil is measured in its specific state. It is then dried in an oven at 105°C for 24 hours and reweighted in order to determine the loss of water. ‫ ݏܯ = ݈ܽݐ݋ݐܯ‬+ ‫ݓܯ‬

3.3 Bulk density ߩ=

‫݈ܽݐ݋ݐܯ‬ ܸ‫݈ܽݐ݋ݐ‬

This unit is kg/m3 and is defined by the mass of soil over the total volume.

Again an important factor when it comes to the material characteristics of rammed earth.

There are various ways in which the bulk density is determined experimentally. In this study, it was achieved quite simply, since the volume of the samples was known and the mass of soil was determined just by weighing the samples.

3.4 Dry bulk density ߩ݀ =

‫ݏܯ‬ ܸ‫݈ܽݐ݋ݐ‬

Usually, we take into account the dry bulk density which is the dry mass of soil over the total volume.

5

3.5 Soil structure and fabric We generally distinguish granular soils and fine-grained soils for which the mechanical behaviour differs. In granular soils, resistance is mainly by friction between coarse particles, finer soils generate their resistance essentially via physico-chemical forces between thin particles.

For rammed earth constructions, we deal with dense soil where particles are tightly agglomerated.

3.6 Soil-water interaction Three types of water are constituted in the structure of soil: free water which fills the large voids; absorbed water which is strongly linked to clay platelets and form water bridges between particles and finally constitutive water which enters the composition of clay platelets and is thus considered part of the solid phase.

3.7 Grain-size distribution 3.7.1 Dry sieving analysis Sieves of decreasing mesh size are stacked one on top of the other. A mass of dry soil is placed on top and the stack of sieves is then shaken for a given amount of time. Each sieve recuperates a fraction of the soil corresponding to a specific size of particles.

3.7.2 Sedimentation analysis For particles finer than 0.74 Âľm, a different procedure is needed to establish the grain size. The sedimentation analysis is based on Stockes law which leads to a relation between falling velocity of a spherical particles to their diameter. The standard procedure is made by dispersing

soil particles in a column of water and estimating their rate fall. In order to establish this, the density is measured over time with a hydrometer.

Coarser particles will sink faster, thus reducing the density at the top of the column.

3.8 Shrinkage limit As it dries, soil will continue to shrink until it reaches the shrinkage limit.

This is established by measuring the volume at different times during the drying process. The volume is measured through submersion in mercury and the water content given by weighing the specimen.

It is crucial for soil used in rammed earth constructions to be under the shrinkage limit or cracks or even stability problems will occur during the drying process of the walls.

3.9 Compaction In geotechnical engineering it is known that compaction has a key role in the mechanical properties of soil. The efficiency of compaction depends on the soil, the water content, the compaction energy, the type of compaction (dynamic or static) and the timing of compaction. Rammed earth constructions are generally formed by using dynamic compaction in the framework. It should be added, particularly in this type of construction, that the thickness of the layers successively compacted will affect the dry density achieved and therefore optimise the mechanical properties.

6

3.10 Proctor compaction test This test has been standardised in soil mechanics for field compaction. It determines the relation between water content and dry bulk density in order to establish the optimum water content. There are various standards that differ in compaction energy such as the number of compacted layers or the dimension of the mould as addressed here in this table (Table 3).

Normal Proctor

Modified Proctor

Mould Diameter [mm]

152,4

152,4

127

127

2,316

2,316

Diameter [mm]

50,8

50,8

Mass [kg]

2,49

4,54

Drop height [mm]

305

457

Number of drops per layer

55

55

Number of layers

3

5

Energy [Nm or J]

1229

5593

Volumetric energy [MJ/m3]

0,531

2,415

Height [mm] Volume [dm3] Rammer

Table 3 : Laboratory standards of compaction test

Usually, at least five points are addressed on the curve. The water content is verified precisely by extruding a soil specimen from the top, middle and bottom of the mould.

In this master thesis, we will see that the standard geotechnical proctor test is unsuitable for the study of rammed earth and that we are generally dealing with far greater compaction energy.

4 Soil classification 4.1 Grain size classification Particles are categorised by their grain size into different groups: gravel, sand, silt and clay (Table 2). Sand can be subdivided into coarse, medium and fine yet the classifications depend on what terminology is used.

Identifying particles only by their grain size can lead to false indications as some clay platelets may have the same dimensions as silt or vice versa yet they differ from a mineralogical point of view.

Fraction number I II III IV V VI

Name of group Clay Silt Fine Sand Coarse Sand Gravel Stone

Range of diameter (mm) <0,002 0,002-0,06 0,06-0,2 0,2-2 2-20 >20

Table 2 : Grain-size classification of the ABEM/BVSM (Franรงois, 2011)

7

4.2 Consistency limits

5.3 Soil identification

In order to better qualify the soil and at the same time consider some of its mechanical properties, classifications such as ABEM/BVSM have taken into account the plasticity index in the criteria.

Sieving and sedimentation analysis tests were carried out to specify the grain-size distribution. Liquid and plastic states were delimited with their respective experimental determinations. The soil identification is given in anew.

5 Compressive Strength Characteristics of RE

5.4 Standard geotechnical testing

5.1 Laboratory Testing

5.4.1 Normal proctor test The density and water content were defined with a standard proctor test.

The normal proctor test was performed 3 times for each of 5 different water contents. The optimal water content was 14.79% and dry density was 1840kg/m3 (See figure 4).

The aim of the laboratory testing was to understand the characteristics leading to maximum compressive strength in rammed earth. The identification of the parameters was performed by questioning former publications on the subject of non-stabilised rammed earth. The starting point was from standard geotechnical testing.

5.2 Soil preparation

18,40

Soil used throughout the whole study originated from Marche-les-Dames, Belgium. Once it had arrived at the laboratory, it was first dried in small layers on plates in a hot room at approximately 40°C, over several days.

The soil was then collected and separated in a grinder without altering the particles. A water content of approximately 0-0.3% was obtained yet throughout testing this was considered null. Anytime a specific water content was needed, the corresponding amount of distilled water was added and thoroughly mixed. To ensure the soil had uniformly distributed the water between particles, it was kept in a cool room for over 24 hours in a sealed bag.

18,20 18,00 17,80

gd (KN/mÂł )

18,60

Saturation Line

17,60 17,40 17,20 10

11

12

13

14

15

16

17

18

19

20

w (%) 21

Figure 4 : Normal proctor compaction test for MLD soil

8

5.4.2.1 Specimen at optimum proctor water content The first samples sheared at 0.23 MPa into a barrel shape. The soil clearly demonstrated high plasticity and was not suitable for rammed earth. The resulting compressive strength was demonstrated to be much too low to be exploitable as a construction material.

5.4.2.2 Dried specimen The water content appeared to be too high thus contributing to the plasticity of the soil. To complement this observation, the same samples were put into a confined chamber set at 30째C for 14 days. Under the same conditions they sheared abruptly with a quick cracking sound at 5 MPa. The water content was found to be 1.8%. It is unclear whether any chemical reaction occurred within the clay platelets or if the soil structure had been altered at this temperature. It seemed that the conditions set by standard geotechnical procedures were unsuitable for testing the strength characteristics of rammed earth. However, the first parameter to be identified that could play key role was the water content of the

material. It was assumed that by initially lowering the water content, it may increase the compressive strength.

5.4.2.3 Equivalent dry density The same soil samples at different water contents (2%, 4%, 6%, 8%, 10%), were taken while decreasing the dry density to 1732kg/m3. This dry density was meant to reflect the dry density achieved during the standard proctor test. However, the optimum proctor dry density could not be achieved with 2% water content so a slightly lower overall dry density was taken. High compaction energy and high density leaded to lamination of samples (See Photo 7 in Annex). In this case, the compaction energy was ignored only to achieve the wanted density. The samples at 2% turned out to be brittle and difficult for testing. Their shearing results were inconsistent. All the samples with over 4 % water content were demonstrated to have consistent shearing values. The unconfined compression test at 6% showed the highest compressive strength of 1.4 MPa. This value is what the NZ requires for non-stabilised rammed earth constructions and can be used safely for a one-storey building.

Compressive strength [MPa]

5.4.2 Unconfined Compression Cylindrical samples of 72mm in height and 36mm in diameter were made at first using a static compaction method. The cylindrical mould was lubricated before the soil was put in order to reduce friction at release.

The mass of soil and its water content used for the testing was determined with the optimum proctor. For each compression, 3 to 4 samples were tested for statistical consistency. All samples were put under unconfined compression. The displacement of the press was at 0.0667mm/min and the stress and strain was taken every 2 seconds.

1,5 1 Water content

0,5 0%

2%

4%

6%

8%

10%

12%

Figure 5 : Compressive strength of equivalent dry density samples at different water contents

9

5.5 Optimising soil structure with grain-size distribution Soil used for rammed earth is most commonly a mixture of clayey silt, sand and gravel. The evenly graded grain size creates more density in the soil, filling in the gaps between the coarse particles with finer particles.

The assumption would be to approach the theory as one would with concrete where a structural skeleton is achieved using gravel and sand.

Cementation then holds the grains in place.

The sand used for optimising the grain-size distribution of the soil is a graded calibre used for concrete. Small sized gravel used for concrete was also added to the mix. Taking into account the diameter of the samples generally used, it was decided to avoid using a calibre greater than 5mm.

The optimal grain size distribution was achieved using the suggested interval by CRATerre (CRATerre, Hubert, & Houben, 2006).

The soil soon appeared to lack a percentage of medium and large size sand. This part of the curve was optimised accordingly by comparing 4 different mixes of soil and sand that were respectively: 40/60, 50/50, 60/40, 70/30. The amount of clay was thought to play an important part in the cohesion of the soil, thus 50% of soil and 50% of sand was considered the best compromise. The grain-size distribution was extended by mixing small gravel with 50% of the original soil. 2 different mixtures of soil/sand/gravel were made: respectively 50/25/25 and

50/37.5/12.5. Mixing the gravel did not seem to affect much the previous shape of the curve after adding the sand and simply further extended the grain size with the mixture of 50% soil, 25% sand and 25% gravel.

I

0 10 20 30 40 50 60 70

II

III

IV

V

Retained particle fraction (%)

The possible contributing factors as to why there is optimal water content with the same porosity could be explained by unsaturated soil theory briefly mentioned in 5.8.

80 90 100 0,001

0,01 100% MLD soil 40/60 60/40 50/37.5/12.5

0,1

1

10 Grain size (mm) 100 30/70 50/50 50/25/25 Craterre optimal interval

Figure 6 : Grain-size optimisation of MLD soil with sand and gravel

10

At first the geotechnical tests were in fact not questioned and it was thought to be grain structure the main problem. It was later understood that the water content and compaction energy were other factors to be considered. The way the laboratory testing and how the hypotheses were raised are resumed in diagram in the annex.

5.6.1 Compaction energy The compaction energy was increased by sequentially ramming the soil mixture in layers with a 2.5kg proctor hammer directly inside the mould.

The compaction was achieved until the hammer bounced and no longer seemed to affect the thickness of the layer. The dynamic compaction in multiple layers was to mimic the same ramming process in-situ. The proctor hammer would however impact the soil via a metal rod closely fitting the mould, so the compaction process would be considered confined as the soil did not have room for displacement.

5.6.2 Compressive strength of optimally mixed soil The sample at a water content of 4% sheared at the highest stress value of 2.4 MPa. However, its achieved dry density was 2198 kg/m3 yet lower than the sample at 6% which was 2212 kg/m3 with a shear value of 1.4 MPa. This reinforces the assumption that water content is a greater factor in the resistance of the material than soil density.

4

2250

3,5

2200

3 2150

2,5 2

2100

1,5

2050

1 2000

0,5 0 0

A sample was taken at each water content in order to establish the maximum density achieved with the proctor hammer in the mould, after which the soil did not appear to compact further. The process was again

Dry density [kg/m3]

5.6 Adapting the testing procedure

repeated at the given density for the final samples in 5 successive layers at 6 different water contents (dried soil, 2%, 4%, 6%, 8%, 10%). The samples at a theoretical 0% water content were unusable as the samples became laminated and quickly dismantled at the limits of their compacted layers.

Comprssive strength [MPa]

5.5.1 Optimum normal proctor The optimum normal proctor was established for the well graded mixed soil. At optimum proctor water content and dry density, the compressive strength did not pass 0.27 MPa. Once again, the achieved dry density did not reflect that of what is achieved on site. The standard geotechnical testing procedures being put to question, a new testing setup was undertaken.

2 4 6 Mixed max compaction

1950 8 10 12 14 Water content % Dry density mixed maximum compaction

Figure 7 : Compressive strength of compacted mixed soil at different water contents

11

Another possible factor contributing to the strength of the material was cohesion. It seemed from the previous results that high water content could cause the material to be too plastic or low water content would render the material brittle and less cohesive. The hypothesis that the main contributor to cohesion was clay content had been raised. It was assumed that the water content may be ideal for the clay platelets to be partially submerged in water thus contributing to electro-statical forces in the material.

It appeared inconvenient to add clay to the mixture (different clay type, difficulty in mixingâ&#x20AC;Ś), therefore samples using only the original soil were made whilst taking into account the adjusted testing procedure. 5 different water content samples were set at 10%, 8%, 6%, 4% and 2%. At maximum compaction energy and an ideal water content of 8%, the sample sheared at a surprising 3.8 MPa. This study questions the necessity of having a well graded soil as suggested by CRATerre or by any scientific publication. The optimal mixture and high density may not necessarily contribute to the strength of the material but this may be for other reasons. Another important

5

2050

4

1950

3 1850 2 1750

1 0

Dry density [kg/m3]

5.7 Cohesion

factor to consider in earth construction is shrinkage. ThIS is discussed further in the master thesis at 5.12.

Compressive strength [MPa]

The shear value of 2.4 MPa represents a very satisfying result for rammed earth construction. The water content and the mixture are feasible and fewer risks are taken when using well graded soil as theoretically it is less prone to shrinkage. This will be the value used for the architectural application in Part II of the Master Thesis.

1650 0

2

4

6

Non mixed maximum compaction

8

10

12

14

Water content % Dry density non-mixed maximum compaction

Figure 8 : Compressive strength of compacted non-mixed MLD soil at different water contents

5.8 Suction In reality, cohesion is not only made by clay particles. Doctorate Paul Jacquin points out in his thesis (A.Jacquin, 2008) that the tensile strength formed by liquid bridges contributes to strength developed in nonstabilised rammed earth constructions. It was demonstrated by the relation between suction and strength (Paul Jacquin, 2009). Geotechnical testing does not take these phenomena into account.

12

A certain amount of water content at a certain density is important for the strength of the material. Also, it was shown that if the sample dries further, its strength also increases in time. However, the water content dealt with is rather low, thus raising the question that perhaps under a given hygrometric state the rammed earth wall may on the contrary absorb water, thus perhaps decreasing its strength.

11 Water content variation (g) ΔWC = WC1-WCn

5.9 Hygrometry

2% sample 1 2% sample 2

9

4% sample 1

7

4% sample 2

5

6% sample 1 6% sample 2

3

8% sample 1

1

10% sample 1

0

5

6

21

28 Days

10% sample 2

Figure 9 : Variation of mass of water in soil samples over 28 days at ambient interior relative humidity (+/- 40% RH, +/- 22°C) 10% sample 1

3

10% sample 2

2

8% sample 1

1

8% sample 2

0

-1

The goal was not to study the kinetics of absorption, but to test the strength of the samples once they reached final equilibrium. The mass of each sample was taken every few days in order to follow the fluctuations and determine when they reached their final state. It was observed rather quickly, all the samples converged to equilibrium. The specimens were put through the standard pure compression test after 28 days to be sure they met an equilibrium state.

8% sample 2

-1

Water content variation (g) ΔWC = WC1-WCn

In order to underlay this question, samples of same dry density with the original soil (1740 kg/m3), at different water contents were put under a specific hygrometric state. 2 samples of each water content (2%, 4%, 6%, 8%, 10%) were set at a controlled relative humidity of 94% (temperature 22°C) and at ambient relative humidity (+/- 43%, 22°C) in a non-occupied room. These various levels of humidity were to reflect normal interior conditions and outside rainy conditions. In order to achieve 94% relative humidity, a saturated solution of potassium nitrate (KN03) filled the bottom of a bell. The samples were all placed within the same bell on a porous plate over the solution.

0

3

21

28

6% sample 1 6% sample 2

-2

4% sample 1

-3

4% sample 2

-4

2% sample 1 2% sample 2

-5 Days

Figure 10 : Variation of mass of water in soil samples over 28 days at controlled relative humidity simulating rainy conditions (94% RH, 22°C)

13

2,2 2,15 2,1 01-mai

29-avr.

27-avr.

25-avr.

23-avr.

21-avr.

19-avr.

17-avr.

15-avr.

13-avr.

11-avr.

09-avr.

2,05 05-avr.

Bulk density

On the other hand, under relative humidity of 94% samples at 2% and 4% had absorbed water (Figure 10). Under compression, they sheared at a lesser value than Day 0. However, the sample at 6% which had seemed to have a rather stable water content over time had gained in resistance.

Samples at 8% and 10% had lost water content and therefore gained in strength.

07-avr.

It was revealed that at interior ambient relative humidity all samples except those at 2% have dried out (Figure 9). As it had thought to be, the compressive strength had increased. However, the samples at 8 and 10% that were much less resistant at day 0 became the most resistant.

In order to illustrate that the same process also occurs even for greater dry density. The specimen of 8% water content of dry density 2180 kg/m3 was put under the same interior conditions (50% relative humidity) for 28 days. In fact, it also quickly reached equilibrium under a few days (Figure 13). The compressive strength had gone from 3.8MPa to 7 MPa (Figure 12). This is a great achievement for non-stabilised rammed earth.

Compressive strength after 28 days [MPa]

3,5 Figure 12 : High compaction energy non-mixed MLD soil at 8% water content at 50% relative humidity during 28 days

3

2,5 Day 0 50% 94%

1,5 1

0,5 0

Stress [MPa]

8

2

6

Max compact 8% Day 0

4

Max compact 8% Day 28 ambient RH

2

Figure 11 : Compressive strength of compacted non-mixed MLD soil specimens after 28 days at given relative humidity

3,40

3,17

2,95

2,72

2,50

2,27

2,04

1,82

1,59

1,36

1,14

0,91

0,68

10%

0,46

6% 8% Water content %

0,23

4%

0,00

0 2%

Strain [mm]

Figure 13 : Compressive strength comparison of maximum dry density sample at 28 days under ambient interior conditions

14

5.10 Size of samples It was clear that the size of the samples were rather small compared to standard compression concrete blocks. Australian codes have suggested the size of the samples for rammed earth strength testing need to be cylinders of 200mm in height and 110mm in diameter.

In this case, blocks of 150x150x150mm (see Photo 5) were made with the ideal soil mixture, a dry density of 1996kg/m3 and optimal water content.

While using a 6kg hammer rather than a 2.5kg (see Photo 6), it was quickly revealed with the first try that it became much easier to achieve the dry density when ramming. Not only did the weight of the hammer obviously play a role but also the soil had more room to move as only a partial area was rammed. In this case, the aim was to be able to compare only the size of the samples, thus the same dry density needed to be carefully achieved.

In order to achieve the wanted dry density, the mass of soil was calculated for the given volume. The formwork blocks where marked in height every 3cm to control the compaction ratio of each layer. The necessary amount of soil for each layer was then carefully compacted until the given height was reached.

Qualitatively, the blocks seemed robust but slightly more fragile than the smaller cylindrical samples. The sides were brittle and the corners were more likely to break. It was difficult to achieve a planar surface but it was presumed that the ductility of the material would contribute to making the surface planar during the compression.

The compression test was performed on a press designed for concrete thus dealing with at least a compressive strength of 10MPa. The first trial was using a displacement far more superior than the displacement used in the previous trials. The material quickly failed at 17 kN, which translated to 0.76 MPa for the block. This is over 3 times less strong than that achieved with smaller samples. It was predictable that the block would shear at a lesser value due to imperfections but the difference was far too significant. Some assumptions were raised: it could be that the scale of the sample plays an essential factor, indeed the surface was far too non-planar, the corners of the blocks did not contribute to the strength of the material and/or the loading rate was too high. Generally, for non-stabilised earth constructions, the corners of the walls are bevelled. According to concrete experimentalists1, the change of geometry between a cube and a cylinder changes empirically by a factor of 1.26. A non-planar surface can also alter the results by an even greater factor that makes them too erroneous to even take into consideration.

The loading rate in the previous tests took over 35 minutes before shearing as to this test it took less than a minute.

It is impossible to demonstrate here if the scale of the sample does indeed change significantly the compressive strength of the material. Of course, the factor of slenderness of the sample surely contributes to a change.

15

5.10.1

Increased size of cylindrical sample

5.10.2

Imperfections

In order to be able to compare the previous results on the smaller samples, all other factors had to remain constant. A larger cylindrical sample was put to test. The geometry and height to diameter ratio of 2 were kept, thus not influencing the slenderness or form (see Table 4 and Photo 2). The same loading rate was kept by using the same press in the soil mechanics laboratory. The test was made with the mixed soil. The samples were 51mm in diameter and 102mm in height. They were compacted with a 6kg hammer via a round stem.

In order to illustrate the effect of imperfections on a rammed earth sample under compression, a cylindrical specimen of size 2 (Table 4) was made with non-parallel top and bottom surfaces. It could be seen slightly by eye but was more distinguishable when put on the press. The results to the stress developed had deviated by 68%. The resulting fractured sample showed that less than half of the specimen had clearly fractured and was submitted to most of the stresses in the material (see Photo 11 in Annex)..

The suspected load to be achieved was slightly less by 6.7 %. This difference could be accountable for more imperfections on the larger contact surface and a slightly less dry density on average. In this case, the maximum stress value reached was 2.23MPa for the mixed soil.

During the whole testing procedure, a dynamic compaction with distinguishable blows was used. Another mechanical procedure was tested whilst using an electrical vibrating hammer used for concrete. In order to test the efficiency of the ramming, a block of a well graded soil of 15x15x15cm was produced. While ramming manually with a hammer of 6kg via wooden piece in the mould, a dry density of 2150kg/m3 was achieved. On the other hand, with the electric vibrating hammer, the soil would not compact further to achieve more than 2080 kg/m3 in dry density. CRATerre states that this type of ramming is not well adapted for rammed earth (CRATerre, Hubert, & Houben, 2006).It is perhaps preferred that ramming should be done by fewer concentred energy blows rather than many lower energy blows.

Size 1

Size 2

Height [mm]

72

103

Diameter [mm]

36

51

2

2,01960784

Area [mm²]

1017,87602

2042,82062

Volume [cm3]

73,2870734

210,410524

Ratio h/d

5.11 Type of ramming

5.12 Shrinkage Table 4 : Dimensions of samples used for testing

This is an important aspect to earth constructions in general. Rammed earth is slightly less subject to shrinkage than other techniques yet it is crucial to the stability of a wall. CRATerre suggests that if there is 16

shrinkage of 1mm over 1m of rammed earth then some problems will naturally occur (CRATerre, Hubert, & Houben, 2006).

The shrinkage of the material is known to be caused mostly by clay platelets. The soil mix at 4% water content is not expected to be subject to much shrinkage. It can be pointed out for the non-mixed soil, the shrinkage limit had been determined with the geotechnical procedure.

Knowing that its optimal water content for greatest resistance is at 8%, the shrinkage limit occurs in fact at 15% water content. This suggests that the soil no longer varies in volume under this value. Itâ&#x20AC;&#x2122;s not yet clear whether it is the case when the soil density is high but it does suggest that perhaps the original soil could be used for a rammed earth project.

However, a test at the scale of construction should be considered before validating this data and this type of testing for rammed earth constructions.

17

Part Two : Application to Urban Co-Housing in Brussels

18

The aim is to drive the attention of the public to earth buildings and demonstrate usage of earth as a potential construction material even in temperate climates such as in Belgium.

It is essential to understand the characteristics of the material and keep them in mind throughout the whole design process of a rammed earth building. In this case, we are essentially dealing with all the characteristics of non-stabilised rammed earth and implementing them into a feasible urban co-housing project.

These were the characteristics that were primarily considered : − −

−

−

1 Identified technical characteristics The project’s technical constraints are more of a necessity in order to take advantage of the characteristics of the material rather than some fixed limits. Surely the compressive strength will be a factor to the limitation in height of the project or the loadings that it can withstand but the technicality of the material will determine the expression of the building.

In this case, the material becomes the essence of the project and therefore an elaborate understanding and control of rammed earth constructions needs to be the tool to any architectural application. There is no linear process to architecture, so these characteristic determinations are a small mindset to the context and program of the project (see Figure 14). It is crucial for any architect to consider these aspects if they are willing to exploit all the advantages of non-stabilised rammed earth constructions as well as creating a durable and long lasting project.

−

−

Structure o Rammed earth is the structure and skeleton of the building Expression and identification o Users and public should perceive the material outside and inside the building Need of insulation o An added insulating envelope is needed to answer passive house standards Hygrometry o The internal surface of a rammed earth wall should be in contact with the air inside the building.

Protection o In temperate climates, it is preferred to have protection against direct contact to rain Thermal mass o Rammed earth walls should be inside the building

Exterior expression Insulating envelope Interior expression Protection Figure 14 : Scheme of characteristic implementation of rammed earth to architecture

22

1.1 Insulation

two separate parts. Sirewall stabilises their walls with up to 20% of cement thus increasing the resistance and dealing with thinner walls. As for the non-stabilised non stabilised rammed earth project in this master thesis, this solution will be abandoned.

It can be iimplemented mplemented in 3 differents ways to a façade.

Interior Thermal mass and hygrometric properties are lost but the structure appears on the outside.

Inside

Outside

2 Co-Operative Operative housing

Exterior Thermal mass and hygrometric properties are kept yet the structure does not appear.

Inside

Outside

Middle This te technique chnique is used by Sirewall. The material is expressed on both sides, part Outside of the thermal mass and hygrometric Inside regulation is exploited. It may seem to be the best solution, however, the technique implies that the insulation can never be changed without the destruction of the walls. Another characterisation of a rammed earth can be that dismantling or changing part of the building is easily implemented without a destructive procedure or environmental impacts. Also, the insulation is directly in contact with the soil. Most insulating materials lose their quality and performance when in contact with a moist environment. Furthermore, the wall is no longer acting as a whole but as

The co-operative co operative housing program is essentially interesting in the case of o RE constructions as it is already dealing with a community that is generally concerned with their way of living and their environment. The scale of the project also stays residential. It is less common for an urban project to be developed with this type of program and therefore the strategy of the program should lay within the concept concept of densifying the urban area.

This way of living is becoming a new wave in modern society. A group of individuals and families who live in their respective homes are brought brough together by sharing spaces and tasks. The group of residents develop a sense of community by co-operating co operating as a whole. The motives for this choice of living are various seen as multiple aspects convey advantages that may not be found in traditional private private housing. In some cases, inhabitants are motivated by seeking a greater social experience. Some of the operatives in a dwelling are shared thus creating a sense of community and mutual support. Financial advantages can be found where sharing part of the site site contribute to a greater sentiment of ownership.

Furthermore, Furthermore, smaller financial benefits can also be developed by carpooling, reducing costs in maintenance tools (lawnmower, working tools, etcâ&#x20AC;Ś), etcâ&#x20AC;Ś), sharing meals. meals. Others may see the benefits of exchanging services between each other. In some co-housing co housing communities, people 23

are grouped together because they already share a common way of life (retirement, spiritual thinkers, environmentalists, etcâ&#x20AC;Ś).

2.1 Multigenerational bartering A unique feature that can be found while deliberately mixing age groups in a co-housing community is the exchange of services. For example, an old age group whom are retired can use their spare time to look after children of working parents. In exchange, a younger generation may help and perform chores that an elder may no longer be able to achieve so easily such as grocery shopping, driving or home maintenance. This may reduce costs for social helpers and provide a sense of belonging for the elder who tend to be dissociated from the rest of society.

2.2 Multiple sociological backgrounds All the operatives are distributed according to what one another can provide. Some may indeed be retired or temporarily unemployed and could spare time and notion for the maintenance and development of the building. Working class people may have technical qualifications that could contribute in that sense or others may indeed have a greater income yet less spare time to spare and could therefore perhaps contribute with an extra income for maintenance, tools or enhancement.

It may be utopic at a greater scale of sociability. However this can be easily implemented within a small community of co-housers.

2.3 Participatory building A very unique feature of earth constructions is the simplicity of how itâ&#x20AC;&#x2122;s achieved. During the participation on site of a rammed earth project in Flanders, Belgium, the whole construction was made by mostly non-

qualified people, as for this reason it is often considered as DIY construction. The only technical part played essentially in the formwork, thus needing a supervisor to ensure its quality and reliability.

Due to the laborious aspect, yet very simplistic and comfortable way of building with earth, it can be considered the possibility for future inhabitants to participate themselves in the construction process. This could not only accelerate and reduce the costs of labour but it also constitutes a preliminary relationship with their new home. Another value is accorded to the building where the inhabitants can relate to it as part of their own work.

In the case of co-operative housing or so called co-housing, the future inhabitants can also create a sense of community before actually living in their homes. This is completely unique to earth constructions, at the opposite to timber frames where connections and placements are crucial or to concrete constructions which demands great care, detail and qualifications.

Furthermore, the material is pleasant to work with. During the two week participation on the rammed earth construction site, hands were constantly plunged into the slightly moist and fresh soil. On the other hand, the few days concrete had to be used on site (footings and lintels), it became lot less enjoyable due to the unpleasant smell, the sensation of dry skin, inhalation of cement dust, the use of unpleasant machines such as a concrete vibrator ( and finally the maintenance of machinery.

24

3 Tour et Taxi The masterplan is not the main concern in this study, however the feasibility of the project must be made by considering context and should take into account the potential evolution of this site. This is why different existing masterplans (Modus Expert, Citec, Bas Smets, 2008) made by architects and students were taken into account rather than starting over on the research which could be a whole master thesis to itself due to its complexity.

There are two main reasons for choosing Tour et Taxi as the site for a rammed earth project. Firstly, it is a growing part of Brussels that is gaining more and more attention by the younger public. This is an advantage for displaying a rammed earth construction and getting people to know more about it in the future. It also corresponds well with the idealistic way of living such as co-housing seen as the site itself is surrounded by residents yet is also becoming quite culturally oriented.

Secondly, it is a vast terrain that covers a large surface in the middle of an urban setting. If the project was to be developed with local soil, it would be a great achievement to have the whole process done in-situ. This requires a large area and space that is offered in Tour et Taxi. It was made sure that the sites soil was viable for earth construction. Its layers were studied via soil coring that had been effectuated by the soil mechanic laboratory in the past. Under a 2 metre layer of embankment, there is clayey silt which was the type of soil studied in the first part of the master thesis.

Figure 15 : Google Earth view on Tour et Taxi, Brussels Local soil

25

3.1 Local soil Geotechnical map 31.3.5 dating 1977 from the soil mechanics laboratory of ULB shows many penetration tests on the site of Tour et Taxi. There are two zones to which the side is divided that define two different lay layer er types. Overall, eembankments mbankments vary in depth from 2 to 4m, alluvial clay between 0 and 4m, silt between 0 and 10m and finally alluvial sand and gravel between 2 and 6m. It was not feasible to test the soil on the site but it was considered that the clayey silt used for testin testing is rather common in Belgium and an analogical type could be easily found in the alluvial clays or silt of Tour et Taxi (see Figure 16).

Figure 16 : Penetration test point N°794 Tour et Taxi, Brussels, ULB soil mechanics laboratory

4 Concept and Development Development 4.1 Context Most masterplans suggested residences in the south-west south west corner of the site. After comparing and understanding how these masterplans were developed, it was finally taken into consideration only the t south-west west parcel. It was viewed as a part that would shape the rest of the site into something perhaps clearer. The issue was to relate the existing hanger with the residential urban tissue on the north side. side. Some masterplans proposed rows of residential residential and office buildings that redraw a circulation through the site and transits into the urban tissue. These rows of separate blocks communicate with the long existing building to the south yet create transparencies through the site and relate to some extent extent with the “îlots” or “island” Brussel typology on the North side. It was wanted that the rammed earth buildings would be seen via the big agora, that its function is fully residential and so it was decided that the north row would be the place of implantation implantation for a co-housing co housing community. Furthermore, there was an urge for the project to extend on the whole row, yet a coco housing community can become difficult when exceeding 30 or 40 dwellings. It was decided that multiple co-housing co housing communities would be implemented lemented in the same row.

A co-housing co housing community is beneficial for each inhabitant. inhabitan A group of coco housing communities can be beneficial for every individual group as it extends the possibilities and relationships. relationships. Furthermore, this group of communities can can be beneficial for the rest of the neighbourhood via services that they can provide.

26

The blocks are all interconnected via a more intimate green promenade on the north side and via the strong public circulation axis on the south side. Also, the communities have the possibility to organise meeting altogether or proceed in an exchange monthly or yearly.

4.2 Preliminary approach

4.3 Orientation and Sunlight The orientation of the row of buildings does not allow the sun to penetrate directly into a whole façade. It was necessary for preliminary analysis on how the sunlight could be optimised in a single building block.

The boxed structure was still kept in mind and could be optimised in order to maximise sunlight.

There was a first intention for people to be able to common exterior and interior spaces. However, it is important for individuals to sometimes evade and have their own intimacy. A private home and private terrace or garden was the first wish to be implemented whilst having a common circulation and space. This led to the idea of a stacked boxed shaped structure that could be moved and shaped according to sunlight and context.

Once building volume and itâ&#x20AC;&#x2122;s structure was more or less defined, the walls had to be pre-dimensioned as they would clearly have consequences on the spatial organisation of the project. The total surface needed was calculated for approximately 25 units. Apartments were given different areas accordingly to whether it was for a large family (4-3 bedroom), a small family (2 bedroom), for a couple or for a single person (1 room).

27

Photo 1 : Context scale model of Tour et Taxi, Brussels

28

4.4 Internal Walls The structure was preferred to have the least contact with any other construction layer as possible in order to conserve all the hygrometric properties as possible. Also, due to passive house standards, even a 90cm earth wall could not provide the sufficient thermal resistance (Part one, 2.4), therefore it was clear that insulation was going to be needed. Other aspects such as protection from erosion and taking the advantage of thermal inertia had to be considered. This is where it was considered is greater advantage to keeping the walls internal.

A skeleton was defined with straight lines. The idea of having linear walls was to simplify the construction process and the formwork needed.

Nearly all the walls were decided to be transversal to the faรงade, thus keeping them inside in order to maximise all the benefits of this type of construction material. However, they were ever so inslightly inclided in order to take into account the direction of the sun, the shadow upon the other buildings and the intimacy in the apartments.

An extra thermal insulation could come around and protect the walls. On the other hand, the structure could let the walls show the material on the outside in order to attract attention to the material by passer byers. All of the walls were simply further extended thus giving an interesting perspective and showing the material.

To improve the privacy of the inhabitants, all floors are set higher than the circulation spaces including bottom ground. Ground floor apartments have higher ceilings for more light penetration

Distribution to the apartments is done via an internal footbridge. In front of all vertical circulation, a large free space is given to encourage social interaction.

29

30

Drawing 1 : Site implantation 1/ 500

5 Predimensioning 5.1 Load calculations

A 4 storey building was presumed to be 14 metres high. The rammed earth wall would be 13 metres high if we subtract 1m of footing. A 70cm wall thickness was considered and thus its self-weight was 275 kN/m.

All calculations were based on the Eurocode. However, the approach was clearly simplified as it was only to give estimation to what the wall dimensions would be for the design case if we wanted to achieve a 4 storey building.

5.1.3 Combination of permanent and variable actions Permanent and variable loads were multiplied by their respective partial coefficients. NEd = 1.35g + 1.5q

5.1.1 Floor loads A maximum span of 5m was considered between each wall. The flooring was to be of wooden beams and finishing.

The total load NEd was equal to 400 kN/m. It is interesting to point out that nearly 93% of the achieved loading is the self-weight of the wall.

The considered loads for the building are showed in table 4.

The compressive resistance of 2.4 MPa that was achieved with the mixed soil during laboratory testing defined in Part One was chosen as the design value. The calculated resistance for a 70cm thick wall turned out to be :

Permanent Loads Wood flooring Partitions Roof

Span [m] 5 5 5

Load [kN/m²] 2,5 0,5 1,5

Repetition 3 3 1

5.2 Resistance to vertical loads

NRd = 1680/ ϒM = 420 MPa

thus NRd > NEd

Table 5 : Permanent loads used for pre-dimensioning wall thickness

Variable Loads Dwelling Maintenance/Snow

Span [m] 5 5

Load [kN/m²] 2 0,5

Repetition 3 1

Table 6 : Variable loads used for pre-dimensioning wall thickness

5.1.2 Self-weight The self-weight of a rammed earth wall was taken as 2290kg/m3 considering a 2200kg/m3 dry density and 4% water content of the soil used.

A 70cm wall thickness is a satisfying design value, however there are some other factors to be considered when realistically dimensioning the walls such as the height and slenderness of the wall.

5.2.1 Security factor The security factor on the material was taken as ϒM = 4. The highest security factor given for fired earth bricks is 3.0 to 3.5. The arbitrary value of 4 seems to be a reasonable coefficient and can be accountable for the fact that there is still, as of today, very little control over the material and many factors could contribute to decreasing the resistance. On the other 31

hand, unlike fired earth bricks, in the case of rammed earth constructions, its resistance will incre increase in time.

If the rammed earth project was designed with the original soil that developed a compressive strength of 3.8 MPa demonstrated in Part One One, the security factor could go up to 6.

There are some negative effects with in in-situ situ ramming such as: control ntrol of quality over the soil, the possible change of water content in function of outside relative humidity (especially in rainy conditions), the quality of compaction and some possible eccentricities or loss of uniform repartition of stresses in the mat material. erial. Nevertheless, it has been demonstrated in Part 1, 2.2 that rammed earth is most likely to dry to a certain extent and thus increasing its performance. Even if this should not necessarily be taken into acc account ount in the design, it does prove a positive effect on the durability.

5.3 Resistance to horizontal loads (Wind) During the building process, the walls will be subject to wind. This should be taken into account especially in this this case where the walls are individual and stand alone. It is only when they receive a concrete/bentonite chaining on each level and that they are secured altogether with the wooden flooring could we consider the wind will no longer be a factor of stability. stability The resistance resistance to wind was calculated in analogy to a retaining wall. The resultant was calculated

5.2.2 Vertical lifting loads Due to overhangs and depression on slanted roof roofs,, there is the possibility for uplifting to occur. Tension is unfavourable for a rammed earth wall and in fact its tensile strength could be considered null. It is possible to resume tension through the second faรงades or it is possible to post tension a rammed earth wall (Ward, 2006).

2006)

Where e is the equivalent eccentricity of the applied load and is given by :

It is very unlikely that the project needs this kind o off technology. The roof structure and the exterior passage way work together as a whole via metal rods.

A wind load of 0.4kN/m2 was taken. Itt was multiplied by the coefficient of variable actions 1.5 and a reduction factor of 80% was applied applied due to an urban situation. situation The results were the following :

e = M / V = H.L / V < l/6 where I is the wall thickness, V is this case case the selfweight and L the height of the wall. l/6 is the value taken for retaining structures. This is discussed further.

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H 6,72 [kN] V 275 [kN] L 13 [m] e 0,31767273 [m] l/6 0,11666667 [m] It has been demonstrated that e > l/6. This suggests the wall would be rather unstable to wind. However, the resultant still remains within the wall. l/6 is for long term retaining structures and in fact may not be necessary for a short term construction process. Also, the period that the construction would take place is most likely to be during summer when there is less wind (NASA, 2001). However, to reduce the risks of the wall collapsing, struts would have to be placed on the wall during the construction process. In the case, we took e < l/6, they would have to be placed up to 8 metres high for a 13 metre wall.

6.2 Net zero energy building

6 Sustainability

6.5 Aquaponic systems

6.1 Construction materials

The energy produced could contribute to aquaponic systems in the basement. The systems can provide food all year round.

As it was discussed in part 1, the environmental advantages and the material properties of rammed earth contribute to the sustainable aspects of the building. Also, very little concrete is used and is only exploited to achieve lintels and support the terraces and circulation area.

Furthermore, the second material most used is wood which was taken for the floors. The type of insulation included is cork. All these materials are of low embodied energy and have a low environmental footprint.

Even if the thermal transmittance is high for rammed earth, a 70cm still insulates quite significantly. By adding 10cm of with all the detailing of insulation taken into account, the energy performance of the building is high. The large area of solar panels contributes to easily achieving NZEB standards.

6.3 Green roofs A large area of green roofs is provided thus contributing to improving the quality of the urban atmosphere

6.4 Solar panels The slanted roofs were designed to be oriented towards the south. A considerable amount of energy can be provided by the large surface of solar panels that are in optimal position.

6.6 Water harvesting system The slanted roofs were also designed to control the rainflow and be able to harvest water that will be stored in the basement. The stored rainwater can be reused in many ways including watering green roofs and plants, washing clothes and flushing toilets.

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Water harvesting roof design

Southern oriented solar panels

Underground aquaponic systems Green roofs

Drawing 2 : Sustainability scheme

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32 Drawing 3 : Ground floor 1/200

33 Drawing 4 : Second floor 1/200

34 Drawing 5 : Third floor 1/200

35 Drawing 6 : Fourth floor 1/200

Section AA’ (Night and Day) 1/200

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Drawing 7: Section AA'

Section BB’ 1/200

Drawing 8 : Section BB'

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Section CC’ 1/200

Drawing 9 : Section CC'

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Insulation detailing 15mm for 1m

39 Drawing 10 : Second floor plan insulation

Drawing 11 : Render 1

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Drawing 12 : Render 2

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Drawing 13 : Render concept colour

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ANNEX 1. Identification paper for MLD soil used in tests Soil Origin

Grain-size distribution criteria

Clay

Plasticity index Ip > 25

Sandy clay

15 < Ip < 25

III+IV+V > 50%

Silty clay

15 < Ip < 25

III+IV+V < 50% and II < 50%

Silt

15 < Ip < 25

III+IV+V < 50% and II > 50%

5 < Ip < 15

III+IV+V < 50%

Clayey sand

5 < Ip < 15

III+IV+V > 50% and I > IIa*

Silty sand

5 < Ip < 15

III+IV+V > 50% and I < IIa*

Sand with a few clay

5 < Ip < 15

I > IIa*

Sand with a few silt

Ip < 5

I > IIa*

Fine sand

Ip < 5

III > 50%

10

Medium sand

III+IV > 50% and IV < 50%

20

Coarse sand

IV > 50%

30

Fine gravel

V > 50%

40

Medium and coarse gravel

VI > 50%

Shrinkage limit Plastic limit Liquid limit Plasticity Index (Ip) Clay proportion I Silt proportion II ABEM classification

No criterion

Table 8: Characteristics and identification table of MLD soil used for testing

50 60

*IIa corresponds to the fine silt fraction (from 0.002mm to 0.02mm)

70 80

Table 9 : ABEM/BVSM soil classification (Franรงois, 2011)

I

0

II

III

IV

V

Retained particle fraction (%)

Soil classification

MLD Marche-Les-Dames, Belgium 17.4% 22% 33.44% 13.24 13% 58% Silt / Silty Clay

90

Grain size (mm)

100 0,001

0,01

0,1

Drawing 14 : Render 4 passageway Table 7 : Grain-size distribution curve of MLD soil

1

10

100

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Figure 17 : Diagram summarising stages of research

44

.

Photo 2: Unconfined compression and comparison of size 1 and size 2 samples

Photo 3 : Unconfined compression for small size samples

Photo 4: Some sheared samples

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Photo 6 : Ramming 15cm block with 6kg hammer via a wooden piece

Photo 5 : Rammed Earth Block 15cm well graded soil

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Photo 8 : Diagonal and cone shearing

Photo 7: Laminated sample due to high compaction energy and low water content

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Photo 10 : Bell for controlled relative humidity

Photo 9 : Preparation of soil dried at approximately 35째C

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Photo 11: Sheared sample with non-parallel surfaces

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2. Rammed Earth Workshop April 2012 : Construction of 50m² hunting house (by BC-as)

50

Bibliographie

Jacquin, P. (2007). Study of historic rammed earth structures. Durham: Durham University.

A.Jacquin, P. (2008). Analysis of Historic Rammed. Durham: Durham University.

Arjen Y. Hoekstra, M. M. (2012). Global Monthly Water Scarcity: Blue Water Footprints versus Blue Water Availability.

Burroughs, S. (2008). Soil Property Criteria for Rammed Earth Stabilization. ASCE. C. M. Gerrard, P. A. (2006). Analysis of Historic Rammed Earth construction. New Delhi.

Clare Lax, P. W. (2010). Life cycle assessment of rammed earth. Bath: Bath University.

CRATerre, Hubert, G., & Houben, H. (2006). Traité de construction en terre.

Grenoble: Parenthéses.

Debra F. Pflughoeft-Hassett, B. A. (2000). Use of bottom ash and fly ash in Rammed-Earth Construction. Grand Forks,: University of North Dakota.

Descamps, F. (2012). Advanced Building Physics Course Notes. Brussels: VUB. Earth Structures (Europe). (2013). Retrieved from http://www.earthstructures.co.uk/: http://www.earthstructures.co.uk/SREregcompliance.pdf EnviroNomix. (2009). Cork insulation. Retrieved from http://www.corkinsulation.com/.

Modus Expert, Citec, Bas Smets. (2008). Hefboomgebied n°5 «Thurn en Taxis» Richtschema. Brussels.

NASA. (2001, October). Global Wind Speed. Retrieved from www.earthobservatory.nasa.gov: http://earthobservatory.nasa.gov/IOTD/view.php?id=1824 Oss, H. G. (2011, January). Retrieved from http://minerals.usgs.gov/: http://minerals.usgs.gov/minerals/pubs/commodity/cement/mcs-2011cemen.pdf Paul Jacquin, C. E. (2009). The strength of unstabilised rammed earth materials.

Scientific publication.

Prof.Geoff Hammond, C. J. (2008). Inventory of carbon and energy (ICE). Bath: University of Bath.

Rauch, M. (n.d.). Retrieved from lehmtonerde: http://www.lehmtonerde.at/en/ Stuart Fix, R. R. (n.d.). Viability of Rammed Earth Building in Cold Climates.

Vasilios Maniatidis, P. W. (2003). A Review of Rammed Earth Construction. Bath: University of Bath.

Verbrugge, J. C. (2010). Mécanique des sols. Brussels: P.U.B. Ward, T. (2006). Patent No. US 7, 033, 166 B1. United States.

François, B. (2011). Soil Mechanics Course Notes. Brussels.

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