Compressed earth brick press
|Kiswahili - English|
- 1 Description
- 2 Opportunity
- 3 Literature Review
- 4 Criteria
- 5 Cost
- 6 Preparation
- 7 Project
- 8 Experimentation
- 9 Discussion
- 10 References
- 11 See Also
This project is an exploration of compressed earth bricks. Mostly because they're awesome.
CCAT, the campus center for appropriate technology, has recently relocated and their new grounds have many uncontrolled hillsides. With general erosion problems and hazards posed by downhill water flow over clay, the need for retaining walls is immediate.
Compressed Earth Brick (CEB) basics
Compressed earth bricks are building blocks formed from stabilized or un-stabilized compressed earth. The compression ranges from several hundred pounds total, to several tons. Because of the great gains in durability un-stabilized bricks are only used where nothing is available to stabilize the bricks. In addition to stabilization, the earth the bricks are to be made from is calibrated for durability, workability, and survivability.
When a brick is compressed it loses 30% of its volume. This is due to the mechanical compression of the press driving out air pockets and aligning wet clay particles and compacting the clay around the sand particles.
There are many stabilizers that can be used. They can be broadly classed into natural and manufactured. They include such wondrous things as plant juices, whey, resins, molasses, wood ashes, and lime just to name a very few. Here in the United States, the presence and low cost of cement makes it both physically and economically efficient. Some sources don't even recommend using stabilizers other than cement even when building in developing countries
Paper as a stabilizer
Papercrete, a cement and paper building material, has been fairly well researched and tested. The paper in papercrete is proported to have great effect as a stabilizer. Amongst the problems with papercrete are, mold, shrinkage, and slow drying time. 
In the end, process won out over product. Only about three dozen bricks have been made so far. That said, I am quite happy with the experience and the primary goals, education, experimentation, and repeatability, were satisfactorily met.
|Sand (sadly, after late game decision against on-site sand =(purchased)||30$|
|Boric Acid(as ortho boric acid from coachroach poison)||6$|
After testing your soil, preferably in multiple locations, you will have an earth mix that is about 75% sand and at least 10% clay and less than 35% clay, by volume. The amount of cement needed will be relational to how close you are to this ideal, ranging from 3-5% to 10%.. Now to think about making some compressed earth bricks...
After reading about all of the tests, about 6 are apparently widely in use, I settled on the two most simple. I chose, the 'block test' and 'salt water test'.
The block test:
|The block test is simply, to make a block out of your earth and measure the shrinkage. This requires a long ish box, think over a foot by 4 inches by four inches. The sides of the box must be slippery so use an oil if the sides are rough.|
The salt water test:
To perform this test: add salt and water to a least a cup of your soil in a clear container. Use a teaspoon ish of salt per cup of earth and cover the earth with water. Shake it up. Let it sit for about half an hour. Observe and measure earth separation.
Preface to Ram operation:
This is ideally a group activity. A minimum of two people are needed to operate a CINVA-ram. Four people is nice, six people is ideal in my experience. I will briefly describe a non-mechanical brick forming method that doesn't require any more than personal conviction, and minimal tools.
Materials needed(for non-mechanized mixing):
- metal rake
- several buckets(1-3)
- mixing surface(sheet of plywood, where available, to avoid mixing with cement on ground)
- measurer (ruler, tape measure, stick, etc.)
You will need to determine your mix as it relates to your buckets. If you are mixing down your earth with clay or sand you should be able to use the same method I've used to determine approximate cement quantities.
Figure out your Mix
First, fill a bucket full of earth mixture, deposit this bucket on mixing surface. Fill the bucket again, but only to half full, use marker to mark half way point with line all the way around, label line. For that mater, label everything. This is a group activity and as such labels will help to avoid confusion and error. Deposit the second bucket on the mixing surface, form one pile, divide this pile into 10 equal piles. This may take a little work, don't try for perfection, do a decent job of it and proceed. Carefully place one of the piles into the bucket, make tiny tick marks around the bucket at height of the soil. Repeat this process twice more. Approximate these ticks measure. Now draw a line, up this measured distance from your half way line. Label this new line, which should be some small distance above your half way line, 'cement'. This gives you approximately ten percent cement stabilization when measuring. If you are testing to determine best mix ratio, vary your cement input from 10% to 5% by halving the distance between the 'earth' and the cement lines. Then again halved between the 5% test line and the 10% line. Some documentation points to the possibility of getting the cement percentages as low as two percent. However, if you are using another stabilizer you will likely have to use twice as much.
Now to actually go about making some compressed earth bricks...
I attempted to employ the old "workshop = group labor camp" ploy, with limited success. The most successful work group ended up being my engineering 305 class. In general I have to say that I have grown to believe that most Americans are not particularly good at physical labor anymore. The literature proposes that the CINV-ram we have used, which by the way was made in Bogotá, Colombia, can produce between 40 and 60 blocks per hour. The best performance we could squeeze from it was about a quarter of that, with a 14 person team.
|Task||Number of People|
|Measuring and Testing||1||2||2||2||1|
|Filling and leveling||1||1||1|
|Removing and placing to dry||2||1|
|Total Human Power||15||10||8||6||3||2|
Teamwork means that there should be a smooth flow (See Table above) of:
|Digging||Harvesting the earth from the best site, doing a rough sort,
picking out big rocks and plant mater.
|Moving||Transporting the earth from the harvesting site to the
|Batching||Filling the buckets to the appropriate lines.|
|Mixing||Evenly distributing the cement, or other stabilizer, with the rest of the earth.|
|Testing||Drop testing the mix to ensure proper moisture level, adding water as necessary.|
|Filling||Filling the void in the press, keeping the press area tidy.|
|Compressing||Operating the press levers to compact brick.|
|Releasing||Operating the press levers to release the brick. Removing and Transporting – Pulling the brick from the press operation and moving it to the storage area.|
|Stacking||Stacking the bricks and setting aside any broken bricks for reprocessing.|
Smooth flow requires adaptation. Jobs overlap, bottlenecks naturally occur, people get tired, communication and fluidity of everyone's role are the tools that craft an efficient teamwork system, which is one of the funnest things ever.
Press operation is as follows
|mix well, but not too well...||Team work makes smiles||While working, it is best to practice your bigfoot pose as much as possible|
The compressed paper stabilized bricks that I formed are still curing, I will keep them wet(so the cement can cure) and test them in a month. That said, paper made the bricks much more durable out of the press. Processing the paper for mixing was exhaustive. I used a plastic trash can to store the paper in water.
I added an eighth cup of boric acid to the mixture of 50 gallons of paper and water to prevent molding. Molding is widely pointed to as a problem with paper-crete (the product closest to what I'm experimenting with). Yet, boric acid can be used as a human safe, anti mold agent.. My paper/water/boric acid mix has been easy to handle and mold free for six weeks so far.
I blended the paper in the water after a week with a drill mounted mixing blade. Then again after another week. I then laid it to dry on a screen atop a pallet.
After dry I crumbled it into a bucket and used the drill mixer again to reduce the particle size. I would rate this process as marginally successful. Far too much time invested, and the end product did not have small enough particle size for even distribution.
This is a cursory look at compressed earth brick technology. The technology has become dominated by industry and all of my references are a decade or more old.
While the process is resource conservative, it is labor and time intensive.
My interest in new materials that are 'hyper' efficient is ever persistent, feel free to contact me with questions and comments. eghant atgmail d0tc0m
- Stulz, Roland, and Kiran Mukerji. Appropriate Bulding Materials. 3rd ed. UK: Swiss Centre for Development Cooperation in TEchnology and Management, 1993.
- Spense, R.j.s., and D.j. Cook. Building Materials in Developing Countries. New York: John Wiley and Sons, 1983.
- Crystal.Netbook. Federal Ministry for Economic Cooperation and Development. http://www.crystal-netbook.info/