Rammed Earth: Reusable Site Model Methodology Report

Compressed Earth Reusable cast site models

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Objective: To achieve a cast block from low-impact and reusable materials.

This research facilitated a semester-long project on compressed earth blocks culminating in a full architectural site model .

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Researchers: Georges Fares, Jiahui Huo, Yasser Masri, Aaron mcmurry, Mila Santana.

Course: Materials Lab Research Instructor: Jen Wong Materials

Tools

Local soil from a construction site at the Pickle Research Center Clay soil from Local soil from J-V Dirt + Loam Three sizes of cork granules 10/20, 20/40, 40/80 Expanded shale

Five gallon bucket Five quarts buckets Scoops Measuring cups Spray bottle Mallet Adhesive tape Different sizes of tampers HDO plywood Clamps Sharp edged tool for scratching the soil surface Scale Classifiers 1/2”, 1/4”, 1/8”

Material determinant: Early test blocks were done using basic rammed earth materials, soil and water. Different aggregates were added based on their weights and resolution: large aggregates were used for volume (shale) while smaller ones were used for texture and resolution (cork).

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Soil mixes: The model contained three layers of mix, the bottom layer is a mix of soil and water so we can achieve a nice clear imprint, middle layer contained cork so we can reduce the weight, while the top layer (bottom of the model) contained expanded shale to save on soil and have less compression.

First layer : basic soil : Ingredients : Soil + water Info: The best choice for a smooth, high quality finish. There is several types of soils that can be used, best ones are the clay soil that once wet, turns into a clay that is highly compressible (loses around 1/3 of it’s volume) and can be easily shaped.

Second layer : small lightweight aggregates: Ingredients : 1/3 Cork + 2/3 soil + water Info: Mix proportion can be 1/2 aggregates sometimes, depending on the binding force of the soil used. We used 10/20 cork because it’s large particles and absorbs less water than the 20/40 or 40/80 ones. But note that the less soil you use, the more you are risking failure. The advantage of using light weight aggregates is that they highly reduce the final weight of the block. But note that the cork has a compression rate almost similar to soil, at 1/3 of its volume.

Third layer : large lightweight aggregates: Ingredients : 1/3 Expanded shale + 2/3 soil + water Info: It’s recommended to have only 1/3 of large aggregates in the mix because the more aggregates you have, the less binding force there is, which might cause the mix to fail. Advantages of a such a mix is that it’s space filling due to it’s low compression rate which allows the use of less soil, but results in a heavier model.

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Local soil

10/20 Cork

Expanded Shale 4

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Formwork: We used High Density Overlay plywood due to it’s smooth surface and high tolerance to pressure from ramming, but any other wood would work okay as long as it has a smooth surface and is strong, reusable and easy to dissemble.

The formwork is divided into four parts : Sides: cut to shape based on the desired depth and size Base: which will become the model’s TOP when the whole thing is flipped and is the LAST thing you remove. So make sure it’s not attached to anything.

Top: which will become the base when the model is flipped and is typically left under the model to avoid damage or breakage when moving around.

Topography: several layers of topography were laser cut from masonite, and laminated to produce an inverted model insert. This insert is placed at the bottom of the formwork which is flipped after tamping is complete. Any final protruding clay elements, such as buildings, should be represented as negative cutouts in the topography layers. NOTE: The insert can be CNC cut in foam, which may be cheaper and faster, but may suffer from lack of resolution or deformation through compaction.

After the formwork pieces are ready, use clamps to hold the whole thing together. Although you can screw it all in place, clamps allows the formwork to be easily dismantled and put together.

NOTE: take into consideration the compression rate when planning the formwork depth, along with the thickness of the top and bottom piece of wood. also keep an eye on the base part when ramming, as it may slide out.

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Topography insert - note how the buildings are holes and the river is protruded.

Other tools: After the formwork is built and ready to go, you need to have prepared: Water: some water in a small bucket or in a spray bottle.

Tampers: couple hammers if there is more than one person working, set of large manual tampers too (you can find instructions on how to make a manual tamper on page 10) Sharp tool: you basically need to do scratches of about quarter inch deep, in any direction, on the surface of each rammed layer, which would help binding the layers together, and avoid splitting. You can use a large screw, a pen or your fingers, as long as you don’t ruin the rammed layer.

Buckets: for mixing and pouring, you can use a small five quart bucket for small batches (especially when layering the formwork with different mixes) or use a large five gallon bucket for a larger mix.

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Setting up the formwork: Step 1: start by laying down the wood base (which will be the top piece after flipping the mold), then clamp all four sides with four clamps, but don’t tighten them hard just yet, leave them little bit loose.

Step 2: place the model insert you prepared on top of the wood base.

Step 3: tighten the clamps hard to avoid any problems from the pressure that comes from compressing the layers.

Formwork pieces

B

B

B

E

A: Top piece, which will become the base of the model

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B: Side pieces

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C: Chamfered piece, due to the model having an angled side D: Base piece, where the topography goes

B

B

B

C

D

A B

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E: Clamps

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Soil preparation: Sifting: To get the best result with the soil, it’s better to use finely sifted, particlefree soil. Use a fine sifter, strainer or classifier, to remove any large granules, small rocks, pebbles or any other particles. For best results use a series of classifiers that fits on a 5 Gallon bucket.

Mixing: It’s preferable to mix the dry ingredients first. For large mixes use a 5 gallon bucket, or a 5 quarts for small batches. Make sure that everything is well mixed and scrape off the sides. TIP: transferring soil between buckets helps mixing it too.

Wetting the mix: Carefully and slowly add bits of water to the mix. If you’re doing a small batch, then use a spray bottle, or else just slowly pour water in and keep mixing by hand. We are looking for a firm, MOIST, not WET or watery mix.

While mixing, the ingredients should start forming together.

How to know when to stop adding water: It all depends on the ingredients. As stated before, some ingredients, like the cork, use more water than others. As a way to know when to stop adding water, grab some of the mix in your hand and squeeze it HARD in your palm, water should not be coming out from between your fingers (unless you’re using cork or paper as an aggregate), and when you open your palm, the mix should stand firm and stay in shape and not fall apart when grabbed with two fingers (see following images).

Troubleshooting: Mix is not holding: It’s either you use a lot of water or you might have used too much aggregates and you need more soil to work as a binder.

Mix is too watery: Add more soil or more of the dry mix to stabilize it.

NOTE: Mix small batches in small buckets for better controlled results.

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Dry soil - notice how loose and grainy

Moist soil - NOT WET, it looks dry but it holds up together

Testing the mix by squeezing in palm

Releasing fist - mix should hold the shape of your fingers

Test Mix is strong enough to be held with two fingers without falling apart

Other tests: There are several other tests that can be applied to the soil mix, like the Ball dropping test, Ribbon test, Acid test, Cutting test and several others. But each can have a different outcome that differs from one mix to another, so it’s preferable to stick with the squeezing test in this project due to it working on all the mixes we are using.

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Tampers: Tampers can be purchased or fabricated. What you require is a heavy compression tool with a base that won’t get soil stuck on it.

You need: Stainless Steel Pipe. We used FOUR 3/4 thick x 6 in pipes.

Stainless Steel Coupling. Same size as the pipes.

You need THREE 3/4 thick ones.

Stainless Steel Cap. Just one to close the end of the handle.

Base Flange.

Structural Pipe Fitting. Also 3/4 so you can attach the handle to piece of wood.

Rectangular 4x4 wood tamper using a large piece of wood block.

Custom angel tamper made out of plywood.

One side of the rectangle has a sharp angle.

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Final tamper

Same as the 4x4 tamper except that it’s made of pieces of plywood.

Compression: You will need to ram your mixes in layers to achieve a good, firm block that won’t break apart and have a good, compressed and smooth finish.

Tampers: For our project, we used two tamper types. One with a simple rectangular base, and another with an angled edge (if case your cast has a 30 degree angel not a 45 degree one for example, it might be better to have a tamper that can go inside that corner) First layer: First prepare a wet well mixed batch of your first layer mix.

The first base layer will be the smooth, sifted clay mix (or basic soil mix to achieve a good imprint and cast), pour it evenly at the base, using hand to smooth it out flat. It’s better to have a 2 inch layer at least.

Ramming the first layer: To avoid loose mix and future problems, use fingers to firmly ram the soil inside every small cavity of your imprint (tampers are wide and flat and cannot ram small areas, so it’s better to use fingers first).

Once that is taken care of, use a flat tamper to evenly flatten and ram the whole first layer. FIRST go in a random manner all around the layer, then start from a corner and go from side to side and keep repeating until you feel it’s not compressing anymore. (Use the edged tamper for hard corners) Second layer: Before pouring in the second mix, scrape and scratch the surface of the base layer. Use a pen, finger, a screw or anything hard enough to do a at least 1/4 inch deep scratch to the surface. That will help bind the layers together.

Once the scratching is done, pour in the second layer of the cork mix and repeat the previous steps without the need to use fingers here, you can go straight to using tampers.

Third layer: Repeat previous steps by scraping the cork layer then pouring in the final top layer of the expanded shale mix, leveling it then ramming it flat.

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Releasing the formwork: Make sure you leave a space at the top of the mix to fit the final piece of wood.

Once all the layers are done and you’re ready to close up, place the top layer of wood on the top and add couple more clamps vertically to hold it tight in place (screwing it in place would work too).

Place a piece of wood on the table to help keep the mix off the table and avoid injuring any fingers when flipping it.

Use more than one person to flip the mold, slowly and at the same time.

Then carefully remove the vertical clamps, then the side ones.

Remove the side pieces first, then the top and then carefully remove your imprint.

Leave the block to dry up to 3 days, depending on the materials used and the size.

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Releasing Clamps

Removing the sides

Taking off the top piece of wood ( which was the base before flipping )

Carefully removing the topography cutout

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Tips • Regularly clean the tampers between each use by damping it in water and wiping it to avoid any sticking with the soil.

• If you’re building a large block, it might be better to fabricate more than one formwork.

• Assign roles: consider having a tamper, a dry mixer and a wet mixer for fast work and cleaner results.

• Do not leave wet materials out for long. Make sure you do all the work at the same time. If by any case you left out wet materials for the next day, you might need to sift it again and break all large dry pieces.

• Do not make more wet mix than you need. Work in small batches to avoid throwing out materials. Mixes with no aggregates might loose up to 1/3 of their volume, while mixes containing rocks, shales or any large un-compressable aggregate might not lose volume. So take that into consideration.

• Always wipe down and clean your cast after you’re done. the mix is always easier to clean when wet. it might dry and ruin your wood work if left out uncleaned.

• The top layer of wood becomes the base of the model when flipped, so It might be a good idea to create several top layers if you are creating more than one model from your formwork.

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