Compressed earth block
|This article does not cite any references or sources. (September 2009)|
Compressed Earth Block often referred to simply as CEB, is a type of manufactured construction material formed in a mechanical press that forms a compressed block out of an appropriate mix of fairly dry inorganic soil, non-expansive clay, aggregate, and sometimes a small amount of cement. Typically, around 3000 psi is applied in compression, and the original soil volume is reduced by about half. The compression strength of properly made CEB can meet or exceed that of typical cement or adobe brick. Building standards have been developed for CEB.
Creating CEBs differs from rammed earth in that the latter uses a larger formwork into which earth is poured and tamped down, creating larger forms such as a whole wall or more at one time.
CEB blocks are assembled onto walls using standard bricklaying and masonry techniques. The "mortar" may be a simple slurry made of the same soil/clay mix without aggregate, spread or brushed very thinly between the blocks for bonding. Cement mortar may also be used for high strength, or when construction during freeze-thaw cycles causes stability issues.
CEB technology has been developed for low-cost construction, as an alternative to adobe, and with some advantages. A commercial industry has been advanced by eco-friendly contractors, manufacturers of the mechanical presses, and by cultural acceptance of the method. In the United States, most general contractors building with CEB are in the Southwestern states: New Mexico, Colorado, Arizona, California, and to a lesser extent in Texas. The methods and presses have been used for many years in Mexico, and in developing countries.
Various types of CEB production machines exist, from manual to semi-automated and fully automated, with increasing capital-investment and production rates, and decreased labor. Automated machines are more common in the developed world, and manual machines in the developing world.
There are many advantages of the CEB system. On-site materials can be used, which reduces cost, minimizes shipping costs for materials, and increases efficiency and sustainability. The wait-time required to obtain materials is minimal, because after the blocks are pressed, materials are available very soon after a short drying period. The uniformity of the blocks simplifies construction, and minimizes or eliminates the need for mortar, thus reducing both the labor and materials costs. The blocks are strong, stable, water-resistant and long-lasting.
- CEB can be pressed from damp earth. Because it is not wet, the drying time is much shorter. Some soil conditions permit the blocks to go straight from the press onto the wall. A single mechanical press can produce from 800 to over 5,000 blocks per day, enough to build a 1,200 square feet (110 m2) house in one day. A high performance CEB press, of open source design, named "The Liberator", can produce from 8,000 to 17,000 or more blocks per day. The production rate is limited more by the ability to get material into the machine, than the machine itself.
- Shipping cost: Suitable soils are often available at or near the construction site. Adobe and CEB are of similar weight, but distance from a source supply gives CEB an advantage. Also, CEB can be made available in places where adobe manufacturing operations are non-existent.
- Uniformity: CEB can be manufactured to a predictable size and has true flat sides and 90-degree angle edges. This makes design and costing easier. This also provides the contractor the option of making the exteriors look like conventional stucco houses.
- Presses allow blocks to be consistently made of uniform size, while also obtaining strengths that exceed the ASTM standard for concrete blocks (1900 psi).
- Non-toxic: materials are completely natural, non-toxic, chemical-free, and do not out-gas
- Sound resistant: an important feature in high-density neighborhoods, residential areas adjacent to industrial zones
- Fire resistant: earthen walls do not burn
- Insect resistant: Insects are discouraged because the walls are solid and very dense, and have no food value
- Mold resistant: there is no cellulose material - such as in wood, Oriented Strand Board or drywall - that can host mold or rot
CEB had very limited use prior to the 1980s. It was known in the 1950s in South America, where one of the most most well-known presses, the Cinva Ram, was developed by Raul Ramirez in the Inter-American Housing Center (CINVA) in Bogota, Colombia. The Cinva Ram is single-block, manual-press that uses a long, hand-operated lever to drive a cam, generating high pressure.
U.S. manufacturers produce much larger machines that run with diesel or gasoline engines and hydraulic presses that receive the soil/aggregate mixture through a hopper. This is fed into a chamber to create a block that is then ejected onto a conveyor.
During the 1980s, soil-pressing technology became widespread. France, England, Germany, South Africa and Switzerland began to write standards. The Peace Corps, USAID, Habitat for Humanity and other programs began to implement it into housing projects.
Construction method is simple. Less skilled labor is required; wall construction can be done with unskilled labor encouraging self-sufficiency and community involvement. If the blocks are stabilized with cement, fly ash, lime, or rice husks they can be used as bricks and assembled using standard masonry techniques of brick-laying or even in some cases dry stacked further reducing total construction costs.
Soil mix conditions
The soil mix is 15-40 percent non-expansive clay, 25-40 percent silt powder, and sharp sand to small gravel content of 40-70 percent. The more modern machines do not require aggregate (rock) to make a strong soil block for most applications. Soil moisture content ranges from 4 to 12 percent by weight. Clay with a plasticity index (PI) of up to 25 or 30 would be acceptable for most applications. The PI of the mixed soil (clay, silt and sand/gravel combined) should not exceed 12 to 15; that is the difference between the Upper and Lower Atterberg limits, as determined by laboratory testing.
Completed walls require either a reinforced bond beam or a ring beam on top or between floors (8')and if the blocks are stabilized, a plaster finish, usually stucco wire/stucco cement and or lime plaster. Stabilized blocks create a brick wall that if properly stabilized can be left exposed with no outer plaster finish.
There are also countless local materials that can be used for natural plasters and tuck pointing techniques that help to reduce the total cost of construction.
Standards for foundations are similar to those for brick walls. A CEB wall is heavy. Footings must be at least 10 inches thick, with a minimum width that is 33 percent greater than the wall width. If a stem wall is used, it shall extend to an elevation not less than eight inches (203 mm) above the exterior finish grade. Rubble-filled foundation trench designs with a reinforced concrete grade beam above are allowed to support CEB construction.
In the USA, the largest market for CEB is probably New Mexico. Regulators added the method to Earthbuilding Code family. The first CEB Code Development meeting in New Mexico took place Dec. 12, 2001. The persons present at that meeting are considered today the leading experts in the field. They include:
- Fermin Aragon, general bureau chief of the Construction Industries Division for Santa Fe, New Mexico
- Joe M. Tibbets, publisher of Adobe Builder Trade Publications, Bosque, New Mexico
- Larry Elkins, Adobe International Inc., Milan, New Mexico
- Jim Hallock, Earth Block Inc., San Antonio, Texas
- Lawrence Jetter, A.E.C.T., San Antonio, Texas
- Jim Hands, P.E., Red Mountain Engineering, Santa Fe, New Mexico
- Todd Swanson, Bio-Hab Inc., Hesperus, Colo.
- Joaquim Karcher, architect, Taos, New Mexico
Code work was completed June 10, 2002 and melded into New Mexico's new section, R1100 Earthen Building Materials.
The CEB code is different from the adobe code in numerous respects. For instance, the CEB code allows slip mortars and permits blocks ejected from a press to go directly to the wall.
Using the ASTM D1633-00 stabilization standard, a pressed and cured block must be submerged in water for four hours. It is then pulled from the water and immediately subjected to a compression test. The blocks must score at least a 300 pound-force per square inch (p.s.i) (2 MPa) minimum. This is a higher standard than for adobe, which must score an average of at least 300 p.s.i. (2 MPa)
It must be emphasized that the compressive strength minimums for code compliance are nothing like the true strength of CEB blocks. New Mexico only sought to assure that CEB would be at least as strong as adobe.
CEB can have a compressive strength as high as 2,000 pounds per square inch (13.7×106 Pa). Blocks with compressive strengths of 1,200 (8.27×106 Pa) to 1,400 p.s.i. (9.65×106 Pa) are common.
Also, due to the enormous mass — these are monolithic walls — CEB has excellent thermal performance, reducing heating and cooling costs.
Thermal testing: From May 31 to June 3, 2004, the Biology Dept. of Southwest Texas Junior College, Del Rio, Texas, conducted tests for thermal change on three structures: concrete block, adobe and compressed earth block.
Results indicate the interior temperature of the adobe and CEB modules were significantly lower than for concrete blocks.
With a maximum ambient temperature of 107 °F (42 °C), the interior temperatures were:
|Concrete Module:||111 °F (44 °C) (four degrees Fahrenheit above ambient)|
|Adobe Module:||95 °F (35 °C)|
|CEB Module:||91 °F (33 °C)|
The CEB module was consistently cooler inside than the adobe by approximately 3 degrees.