Earth Architecture: Sustainable Design for Rural Mali
“Through Compressed Stabilized Earth Block (CSEB), earth architecture has evolved from a traditional craft to a modern technology. This achievement has been (made) possible by taking advantage of the research in laboratories and in the field of many organizations, working all over the world.
Compressed Stabilized Earth Blocks are undoubtedly part of the renaissance of earth architecture which started 50 years ago with Hassan Fathy, the famous Egyptian architect, who promoted adobe (sun dried bricks) and Nubian vaults and domes.” -S. Maini, Auroville Earth Institute, 1996
Test blocks with various soils laying our to dry. The richer orange colors come from the humidity of the soil when pressed.
-“Sophisticated Buildings Will Be Made Out Of Mud”, #1 on Smithsonian’s “40 Things You Need to Know About the Next 40 Years”*
-According to a study by the UNCHS (now UN-Habitat), 40 % of the world population lives in earthen buildings
-One of the oldest know earthen buildings, the Vaults of Ramesseum, near Luxor, Eygpt, dates back to 1300 B.C. The ancient granaries and storehouses adjacent to the temple of Ramesses II have mud-brick vaults that have been standing for over 3,700 years.
The Vaults of Ramesseum
Compressed Stabilized Earth Blocks
By using compressed stabilized earth blocks, we can build schools that are stronger, cheaper, and easier to construct. Most importantly, earth is an abundant resource which can be quarried, pressed, and constructed on-site in Mali. In both Ghana and Mali I have observed many decrepit structures that were recently built by foreigners using foreign materials. Without the means to repair inevitable damages to relatively sophisticated materials, many structures (particularly in urban areas) quickly spiral into disrepair. However, rural areas have fewer abandoned structures because of the vernacular building style, which relies on traditional earth construction techniques and locally available materials.
Our all-Malian construction crew has nearly wrapped up the block making process for our first school in Soumabougou. In January of this year, I got to see them at work as they demonstrated their skills with the new technology (the block press) that African Sky has provided.
In addition to mastering the block press, our friends in Mali now have a great deal of experience composing ideal mixtures of soil, cement, and water in order to make the strongest block possible.
“Green” building is an increasingly relevant and popular topic in the world of architecture. Despite newfound popularity, “green” buildings are rarely as environmentally friendly as we are led to believe. This is because most modern buildings have a great deal of embodied energy, which is the sum of all the energy required to produce goods and/or services. Steel, glass, and concrete require a staggering amount of embodied energy to take shape. This energy accounts for a formidable portion of the world’s carbon dioxide emissions (which is noted as the primary cause of global warming).
Thanks to CSEB technology, we are able to minimize the quantity of cement required to make a formidable block. Cement production alone accounts for 5% of the world’s carbon dioxide emissions, making it a major player in global warming**. Each one of our CSEBs uses approximately 5% cement as a stabilizer. This ratio is two to three times lower than the cement content in most concrete mixtures.
Lime is often used in earth construction as an alternative to a cement stabilizer. However, the manufacturing of lime in a rural context can be difficult and dangerous. Limestone requires a minimum temperature of 898˚ C (1,648˚ F) to oxidize and create calcium oxide (also known as “quicklime”). This temperature far exceeds the capacity of kilns found in the rural villages that we serve.
Instead of mortar, we will use an extremely thin layer of slurry which is similar in composition to the mixture that we use to make the CSEBs. The thinness of this layer consequently reduces the amount of labor and cement required to complete the building.
Our Auram press squeezes the soil, cement, sand, and water with a great deal of pressure to create solid blocks that we use for our buildings. The CSEBs look similar to much more labor-intensive fired clay bricks. Their uniformly sharp edges and interior perforations are a far cry from the crumbly , shovel pressed earth blocks of the past. However, the manufacturing of fired bricks emits 2.4 times more pollution and consumes 4.9 times more energy than CSEBs. The two holes in the middle of our blocks make them substantially lighter than their precedents. It also reduces the amount of material required for each block, which saves time, sweat,and cement. Perhaps most importantly, our block walls can keep the classrooms up to 20 degrees Fahrenheit cooler than one made with concrete walls.
Earth Blocks vs. Compressed Stabilized Earth Blocks
Regular earth blocks are made by casting the soil mixture into molds, packing them by shovel, and then upturning and placing them into rows for sun-baking. The fragile mixtures often crumble as the form is removed from the upturned block. It is highly likely that water will be responsible for returning nearly every earth block back into soil. Small pieces of straw and other organic materials are traditionally incorporated into the mixture to help strengthen the blocks. Ancient vault builders (as well as modern masters of Nubian dome building) used straw to create lighter bricks for their spans. Unfortunately, this weakens the blocks over time as the organic material decomposes. This is a bigger issue in Mali, where termites can expedite the erosion process by feeding off the organic material in the blocks.
When quarrying soil for compressed stabilized earth blocks, we minimize organic material by first removing the topsoil. Our soil tests in Mali proved that the earth in Soumabougou and Dissan was excellent for block-making. By eliminating organic material, we can better ensure the integrity of each CSEB. Proof of the block’s water resistance is in the following video of tests and demonstrations conducted at the Auroville Earth Institute.
**Rosenthal, Elisabeth. “Cement Industry Is at Center of Climate Change Debate.” New York Times 26 October 2007. http://www.nytimes.com/2007/10/26/business/worldbusiness/26cement.html