Compressed earth block, often referred to as CEB, is a type of manufactured construction material made in a mechanical press, which forms a mix of dirt, nonexpansive clay, and an aggregate into a compressed block. Creating CEBs differs from using rammed earth in that the latter technique employs 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 installed onto the wall by hand, and then a slurry made of a soupy version of the same dirt and clay mix, sans aggregate, is spread or brushed very thinly between the blocks for bonding. There is no use of mortar in the traditional sense.
The advance of CEB into the construction industry has been driven by manufacturers of the mechanical presses, by a small group of eco-friendly contractors, and by the cultural acceptance of the medium in areas where it is seen as superior to adobe. In the US, most general contractors building with CEB are in the Southwestern states: New Mexico, Colorado, Arizona, California, and to a lesser extent Texas. However, manufacturers of the mechanical presses enjoy their heaviest sales overseas. Mexico and third world countries have been attractive markets for the presses for years.
The advantages of CEB are in the minimal wait time for material, the elimination of shipping cost, the low moisture content, and the uniformity of the block, which minimizes the need for mortar and decreases both the labor and materials costs.
- Low wait time: CEB can be pressed from humid 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 sq f (110 m2) house in one day.
- Low 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 nonexistent.
- Uniformity: CEB can be manufactured to a predictable size and has true flat sides and 90-degree-angle edges. This uniformity makes design and costing easier. It also provides the contractor the option of making the exteriors look like conventional stucco houses.
CEB had very limited use prior to the 1980s. It was known in the 1950s in South America, where the Cinva Ram was developed by a Colombian engineer. The Cinva Ram is a lever-action, manual press that makes one block at a time.
US manufacturers produce much larger machines that run with diesel or gasoline engines and hydraulic presses that receive the soil/aggregate mixture through a hopper. The mixture 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, and Switzerland began to write standards. The Peace Corps, United States Agency for International Development (USAID), Habitat for Humanity, and other programs began to implement it in their housing projects.
The construction method is simple. Less skilled labor is required; wall construction can be done with unskilled labor, so self-sufficiency and community involvement are encouraged. If the blocks are stabilized with cement or fly ash, they can be used as bricks and assembled using standard masonry techniques of brick-laying.
Soil mix conditions: The soil mix is 15–40% nonexpansive clay, 25–40% silt powder, and a sharp sand to small gravel content of 40–70%. 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% 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 Atterburg Limits, as determined by laboratory testing.
Other advantages:
- Non-toxic nature: Materials are completely natural and do not outgas toxic chemicals.
- Sound resistance: This is an important feature in high-density neighborhoods and in residential areas adjacent to industrial zones.
- Fire resistance: Earthen walls do not burn.
- Insect resistance: The walls are solid and very dense, discouraging insects.
- Mold resistance: There is no cellulose material—such as in wood, oriented strand board or drywall–that can host mold.
Completed walls require either a reinforced bond beam or a ring beam on top or between floors and, if the blocks are unstabilized, 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.
Foundations: Standards for foundations are similar to those for brick walls. A CEB wall is heavy. Footings must be at least 10 in. thick, with a minimum width that is 33% greater than the wall width. If a stem wall is used, it should extend to an elevation not less than eight in. above the exterior finish grade. Rubble-filled foundation trench designs with a reinforced concrete grade beam above are allowed to support CEB construction.
CEB's strongest market in the US is probably New Mexico, which has incorporated the method into its Earthbuilding Code family. The first CEB Code Development meeting in New Mexico took place December 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., Pagosa Springs, Colorado
- 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, Colorado
- 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.
CEB Strength: 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 sq in. (p.s.i) (2 x 106 Pa) minimum. This is a higher standard than for adobe, which must score an average minimum of 300 p.s.i. (2 x 106 Pa)
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.
The blocks are strong. CEB can have a compressive strength as high as 2,000 p.s.i. (13.7 x 106 Pa). Blocks with compressive strengths of 1,200 (8.27 x 106 Pa) to 1,400 p.s.i. (9.65 x 106 Pa) are common.
Thermal advantages: Also, due to the enormous mass (these are monolithic walls), CEB has excellent thermal performance, which reduces heating and cooling costs.
Thermal testing: From May 31 to June 3, 2004, the Biology Department 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. The following chart shows interior temperatures. The maximum ambient temperature during the testing was 107 °F (42 °C).
| Concrete Module: |
111 °F (44 °C) (42 ° F 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.
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Compressed earth block."
