Rammed Eartha comprehensive Construction study
Contents 03 What is Rammed Earth ? 04 Advantages 07 Dis-advantages 08 Stabilized Rammed Earth (SRE) Comparison between Stabilized rammed earth & Rammed earth
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Stabilized Rammed Earth (SRE) construction Composition SRE Foundation SRE Foundation process
SRE Wall Design guidelines Formwork Preparing formwork Construction Process
23 Post-Construction Maintenance
What is Rammed Earth ? Rammed earth is a structural wall system built of natural mineral soils compacted in thin layers within sturdy formwork. The strength and durability of the wall results from the densification of a clay, sand, and gravel matrix. It is an ancient building method that has seen a revival in recent years as people seek more sustainable building materials and natural building methods. Rammed-earth walls are simple to construct, non-combustible, thermally massive, strong, and durable. They can be labour-intensive to construct without machinery (powered tampers), however, and they are susceptible to water damage if inadequately protected or maintained. Historically, such additives as lime or animal blood were used to stabilize the material, whilst modern construction uses lime, cement or asphalt emulsions. The availability of useful soil and a building design appropriate for local climatic conditions are the factors that favour its use.
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Advantages Thermal mass Thermal mass keeps the internal room temperature stable due to the length of time required for heat to transfer through the walls. For eg., a 300mm thick rammed earth wall will take 8-9 hours for heat to transfer through the wall to the other side. The solar passive building designer needs to ensure that summer sun does not shine directly on any walls but at the same time allow the direct sun on the walls in winter for as long as possible. This will allow the warmth from the sun to be absorbed by the walls in winter when it is needed the most. So, more the thickness of the walls, the higher is the thermal mass and higher the time for transfer of heat from one side to the other. Insulated rammed earth contains insulation which is placed in such a way to slow the heat transfer even further. This is great in sub-zero temperatures however in warmer temperatures the insulation will have a detrimental effect as it will prevent the warmth of the sun from being stored in the wall. It also shields from electromagnetic fields & radiations.
Aesthetics Natural beauty of the rammed earth material. Variations in texture, colour and finish are possible, and elements such as artwork, patterns, circular windows, alcoves and feature stones can be incorporated that makes it versatile in nature. It is a natural product which blends beautifully with the environment and other natural building materials, as well as with light weight man-made materials.
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Structural Aspects Rammed earth is very strong in compression which results in large load bearing capacity and thus can be used for multistorey load-bearing construction. These walls can withstand earthquakes to a greater extent comparative to the masonry walls.
Sustainability Sustainable for 1000+ years, uses local materials for walls. Uses subsoil, not the topsoil. Its thermal properties lowers the cost for heating and cooling. And the construction cost is comparable to the conventional construction cost. Rammed earth is non-toxic, non-polluting and ‘breathes’. This creates safer, more people-friendly buildings. It is very low in embodied energy, and extremely comfortable to live in.
Minimal Maintenance Rammed earth walls are extremely low maintenance. Once they are built and sealed, they shouldn't need any further attention for 10-20 years. At that point they may perhaps need a second coat of sealer, which is an easy process. They are features that stand alone and don’t need finishing with plasterboard or render. There is no need to ever again spend time and money painting. But should you want a different finish, rammed earth walls can be treated in the same way as other masonry walls.
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Fire Resistant Earth doesn’t burn. This is an ideal material for bush settings and leafy suburbs. CSIRO tests showed that a 250mm earth block wall achieved a 4 hour fire resistance rating. A 150mm earth block wall achieved a rating of 3 hrs 41 minutes. The walls are stronger, being 300mm thick and of monolithic rather than block construction (so have no vulnerable mortar joints).
Insect, termites, rodent proof Termites and other pests simply aren’t interested in rammed earth, and as the walls are load bearing it reduces the amount of termite-tempting structural timber. There are no cavities in rammed earth walls for pests to live in, or to use as a route to the roof or other timbers. Free of fungicides and pesticides.
Noise Reduction The thickness and density of the walls mean that unpleasant noises, such as traffic or wild weather, are very much reduced. Rammed earth walls are also extremely useful in providing sound insulation between areas with different needs — for instance between living and sleeping areas, between a public or family room and a study area, etc. CSIRO tests indicate a sound transmission rating of over 50 decibels for a rammed earth wall of 250mm.
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Dis-advantages Thermal Resistance/ insulation
Insulated Rammed Earth
Poor thermal resistance – external walls require additional insulation despite of its high thermal mass because in some regions where the temperature is extremely low, the thermal mass doesn’t work effectively. Therefore, it requires an extra insulation. Insulation can be external in which outer surface is plastered with lime and lightweight aggregate and can be internal in which a minimum space is left as cavaity and then timber studwork infilled with insulation with an insulationbacked plasterboard., but that would be a big compromisation for the appearance of the wall. It can also be within the wall and its thickness can vary from 1” to 8” depending on the requirement.
rammed earth
insulation
footing
unfinished or limewashed external face rammed earth
minimum 25mm ventilated cavity timber studwork infilled with insulation insulation-backed plasterboard Vapour permeable insulating render ( eg, lime render with lightweight aggregate ) Rammed earth Protective coating (to reduce dust) OR plaster (clay/lime) to internal surface
Labor intensive Mixing soils, building wall forms, ramming the walls,etc., all these processes are very labor intensive which makes it costly in the regions where the labor cost is quite high.
Construction time Longer than average construction period. So, as the time increases, the construction cost will also increase.
Composition and soil type Not all the soil types are appropriate. And the composition should be very effective and meets the requirements in terms of properties. High clay content can cause moisture movement which can affect the structure. Addition of too much cement can compromise the environmental credentials. An un-stabilised rammed earth building will require more ongoing maintenance than a standard home. z High levels of construction quality control are required. z
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Stabilized Rammed Earth (SRE)
The main problem associated with the durability of the rammed earth primarily external surface protection, water resistance, shrinkage and strength which can be averted by adding a stabilizer ( cement, lime or pozzolan ). Stabilizer speeds the construction process, improves durability, allows thinner walls and requires less of a surface treatment. Stabilised rammed earth walls need little added protection but are usually coated with an air-permeable sealer to increase the life of the material. They require no extended eaves, no regular coats of lime wash and they don’t fall down when they get wet. Consequently, when considered in the longer term, i.e. the life of the building, cement stabilised earth walls are far better, safer and require less energy than unstabilised earth walls or walls built using other stabilisers. "Stabilised Rammed Earth is not perfect but it is the best environmental solution for building walls that is available at the moment."
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Comparison between Stabilized rammed earth & Rammed earth Stabilized Rammed Earth (SRE)
Rammed Earth (RE)
Requires normally 4 or 12% cement as stabiliser when built.
Does not use any stabiliser.
Can be made from soil, quarry waste or recycled building rubble.
Must be made from soil with a high clay content.
Insoluble, unaffected by immersion.
Remains water soluble, hence will collapse if moisture rises above 13%. This could be from a blocked gutter, flooding, sprinklers, burst pipe or similar.
Unaffected by rain.
Needs wide eaves and surface protection.
Needs no exterior protection.
Needs protection by cladding systems or regular coats of lime wash or render.
Can incorporate insulation.
Needs to have additional exterior or interior layer of insulation and cladding.
Benefit of high thermal mass is maintained.
If interior insulation is used thermal mass effect is lost.
Normally build walls 300mm thick.
Normally 500-700mm thick.
Does not need larger foundations.
Needs larger foundations to support thicker walls.
High strength achieved quickly, 70% of full strength within 7 days.
Slow drying means it can take up to 2 months to get near full strength.
Very small amounts of shrinkage experienced as wall sets.
As wall dries, significant and unpredictable shrinkage occurs due to high proportion of clay as binder.
Can incorporate steel reinforcing, lintels, etc. so windows, doorways and large openings can be formed in walls.
Poor results with reinforcement. Only small openings possible.
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Stabilized Rammed Earth (SRE) construction Composition Rammed earth construction begins with site selection and the acquisition of very specific materials: soil mix, water, and an optional stabilizer. z Since topsoil is organic and biodegrades, a mix of subsoil is used. The approximate proportion of subsoil is 30 % clay/silt to 70 % sand/gravel. z Water has a direct impact on the strength of finished walls, and depending on the soil mix, is 8 to 16 % of the mix. z An optional stabilizer may be added – 4 to 12 % depending on conditions such as bonding strength of the clay, seismic activity, desired construction process, or desired wall proportions. Stabilizers include cement, lime, or pozzolan added to the mix. z
Effective composition : 23 % course sand 30 % fine sand 32 % silt 15 % clay 10 % water by mass
SRE foundation The soil is excavated from the trench foundation. It is sieved and then measured at the same time on the side of the trench. Sand always needs to be added. Usually the top level of the foundation is at the level of the original ground. The section of the foundation should normally be square. It is essential that it is not wider than deeper, as the load of the wall will create a pointed load and the foundation could not bear it.
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SRE Foundation Process
Digging the trench and sieving the soil in the frame
Lifting the frame
1
3 5
Marking the top level of the foundation with a water level
Adding 200 litres of sand on the pile of soil
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Levelling the soil in the frame to get 500 litres
500 litres of soil sieved from the trench
Mark for the top level of the foundation
Adding 1 bag of cement (50 Kg)
2
4 6
8 11
Mark for the top level of the foundation
Sprinkling water on the previous course
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Pouring the stabilised earth mix in the trench
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11
14
Checking the thickness of the course (12 cm)
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Adding water and mixing 2 or 3 times wet
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Pouring the stabilised earth mix in the trench
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Adjusting the thickness of the course (12 cm)
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Ramming first with a large rammer (200 cm2)
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Ramming with a smaller rammer (100 cm2)
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Sprinkling water on the previous course
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Ramming the foundation
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Ramming to get a step (to finish a course)
25
Checking the thickness of the course (12 cm)
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Checking the quality with the pocket penetrometer
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Ramming to get a step (to finish a course)
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Penetrometer should not go in more than 6 mm
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Steps as wide as long for overlapping the courses
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Adjusting the thickness of the course (12 cm)
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Ramming to get a step (to finish a course)
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Laying some blocks as formwork when the top level of the foundation is higher than the ground (site with a slight slope)
29 Ramming the last course
30 Filling the last course
31 Levelling the last course
Checking the level of the last course
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Ramming the last course
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35
Checking the top level of the foundation from the reference level
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Scraping the top of the last course after checking with the string line
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Slight ramming of the top layer after having it scraped
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SRE Wall Design guidelines Stabilization of walls Stabilization through shapes To stabilize rammed earth walls of less thickness, use elements in the shape of L, T , U, X, Y & Z. Due to their angles they show better stability against lateral forces. z If the wall is 300 mm thick, the free ends of the elements should not be longer than ¾ and not shorter than 1/3 of their height. This minimal length is necessary to transfer the load diagonally to the plinth or foundation. z Nevertheless, the height should be not more than 8 times the width. z
l≤0.75h, ≥0.33h
h
30 cm h
d ≥ h/8
h
l≤0.75h, ≥0.33h
Stabilization for corners ( angles in the walls ) •For corners i.e., 90 degree angles in the walls, we have to make a separate formwork to make the angles which means that angle should be build as a single element. And to provide stability to these corners to make the structure earthquake resistant, we have to leave some space for a vertical rod which is fixed to the foundation and to the beam above and use as a part of reinforcement.
Formwork Vertical rod as reinforcement Rammed earth wall
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Joints and internal reinforcement Joints Walls are built in panels of approximately 3.5m in length with flexible joints to comply with building rules requirements for masonry structures. When a wall consists of more than one panel a recess is built into the end of the first wall. The second wall then moulds into this to lock the walls together for lateral stability. And this joint is called as tongue and groove joint. However, if the elements are well linked to a ring beam above and to a plinth below, there is no need of the tongue and groove joint.
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Internal Reinforcement Internal reinforcement is the method of stabilizing the rammed earth walls against horizontal forces by using vertical rods of bamboo, wood or steel in the wall. These elements should be fixed to the foundation below and to the ring beam above. The joints between the rammed earth elements, are pre-designed rupture joints which can crack in an earthquake and allow independent movement of each element. So, the kinetic energy of the seismic shock will be absorbed by deformation, but the element being fixed at the top and the bottom will not fall. After the earthquake, the open joints can easily be closed again with earth.
Beam
Vertical rod as reinforcement
Rammed earth wall
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Formwork Basic elements for any formwork system z z z z z
z
Shutters- the two sides of the form; End stops- the boards which close-off the open ends of the formwork; Ties and Bolts- these can be either direct through-bolts, cantilever bolts, threaded ties or ties with wedges; Props or Stays- the (fixed or movable) vertical posts used to brace the form; Spacers- bolting often requires spacers in order to set the width of the wall. Spacers should be softer than the formwork in order to prevent damage to the form faces; Wedges- for adjustment of the formwork.
1-1/8� plywood bulkhead
2*4-beveled for keyway
2*10 trusses
Wedges hold bulkheads away from
Bulkhead Form Truss Wedge Clamp Masonite
Traditional : timber
Modern : mild steel
Pony pipe clamps fit through holes in forms
Foundation detail
1-1/8� plywood forms faced with 1/4� tempered Cast concrete foundation with ledge for forms
Formwork is similar to that for concrete, and should be in place before water is added to the soil mix. However, different from concrete, the formwork cannot have ties running through it. This is because all areas of the form must be accessible to tamping. And this renders the minimum thickness for the walls. Concentration for formwork is on strength and stiffness, lightness, and ease of alignment. Possible materials include plywood, wood planks and framing, mild steel, or a combination for a desired finished appearance. Like concrete, sheet materials give good offform finished surfaces. Dependant on the quality of soil and presence of stabilizer is the height of the formwork. Unstabilized soil is concentrated horizontally, and alignment is from layer to layer of wall. Stabilized soil is concentrated vertically, and alignment is between forms. Openings for doors and windows within the wall are created with blockouts.
Tampers used for ramming the walls
Pneumatic backfill tamper Some typical manual rammers
Pneumatic rammer Vibrating plate
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Prepairing formwork Particle wood board
If we’re using any textured or rough wood for formwork, then we have to apply oil on the inner surface so that the mixture won’t stuck to the surface. z Instead of using steel, we can also use wood to make this formwork. z
Two Particle wood board are joined by washer-nut bolt
Steel C-Section Conduits are provided, so after removing the formwork, wall doesn’t get damage because of bolts. Even because of these conduits, we can also and maintain the distance between the boards and that won’t become bulgy.
300 mm
300 mm
600 mm
300 mm
300 mm
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Construction Process
1
2
Ramming the second form
First panels and adjusting the end shutters
4
3
Lifting panels of the first form to the third one
6
Ramming the fourth form
5
Ramming the third form
Lifting panels of the second form to the fourth one
7
Ramming a corner wall in the first form
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9
8
Adjusting panels of the second form of a corner wall
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Adjust panels of the third form of a corner wall Moist earth : mixture of sand, gravel, clay and concrete
Step 1 : framework is built and a layer of
Lifting panels of the second form to the fourth one of a corner wall
Step 2 : the layer of moist earth is
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12
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Reinforced plywood frame
Lifting panels of the first form to the third one of a corner wall
Ramming the fourth form of a corner wall
Pneumatic backfill tamper
Step 3 : next layer of moist earth is added
Ramming a long wall in the second form
Visible layers of compacted earth
Step 4 : successive layers of moist earth are added and compressed
Step 5 : framework is removed leaving the rammed earth wall
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Post-Construction Maintenance
Rammed earth walls needs extremely low maintenance. Once the formwork is removed after construction, the natural earth tones are visible and compaction layers produce the unique character of the wall surface. Then, we can use polymer sealer to seal the walls to prevent it from water penetration and dust, eliminating the need for rendering or painting the wall surface. As the walls are not rendered, maintenance is minimal. Depending on the climatic conditions, the sealer applied on the external wall surfaces should not need re-application before 10 to 15 years. At that point they may perhaps need a second coat of sealer, which is an easy process. They are features that stand alone and don’t need finishing with plasterboard or render. There is no need to ever again spend time and money painting.
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Bibliography i i i i
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Aerecura Rammed Earth Builders - FAQs Benefits of Rammed Earth Construction by Clifton Schooley and Associates. http://www.rammedearthconstructions.com.au/ http://www.noyes.com.au/planning/design-considerations-for-rammed-earth-construction/item/designconsiderations-for-rammed-earth-construction http://www.earthstructures.co.uk/whystab.htm http://www.rammedearthliving.com.au/ http://www.fab-form.com/fastfoot/fastfootProjectMuskokaSustainableBuilders.php http://rammedearthenterprises.com.au/ ‘Rammed Earth: Design and construction guidelines’, Peter Walker et al, BRE 2005. Handbook for Building Homes of Earth_ Chapter 11_ Making rammed earth walls Historic Rammed Earth HowStuffWorks _Benefits of Rammed Earth Construction_ HowStuffWorks _Challenges of Rammed Earth Construction_ http://earthdwellings.com/rammed-earth/ http://rammedearth.davis.net.au/refaq.php staff.bath.ac.uk/abspw/rammedearth/ A Review of Rammed Earth Construction for DTi Partners in Innovation Project Developing Rammed Earth for UK Housing’ Earth Building Association of Australia. 2012. Australian Institute of Architects (AIA). 2010. Environment design guide. Melbourne. http://www.the-self-build-guide.co.uk/rammed-earth.html Olnee Constructions 2014 http://www.earth-auroville.com/sre_walls_en.php Rammed earth walls - CIDBIMENA RAMMED EARTH - Build It International www.mdpi.com/2071-1050/5/2/400/pdf http://naldc.nal.usda.gov/download/ORC00000481/PDF THE USE OF CEMENT STABILIZED RAMMED EARTH FOR BUILDING A VERNACULAR MODERN HOUSE BY GABRIELATEODORA CIURILEANU (CIOCA)* and ILDIKO BUCUR HORVATH