A compressed earth block (CEB), also known as a pressed earth block or a compressed soil block, is a
building material
Building material is material used for construction. Many naturally occurring substances, such as clay, rocks, sand, wood, and even twigs and leaves, have been used to construct buildings. Apart from naturally occurring materials, many man-ma ...
made primarily from an appropriate mix of fairly dry inorganic
subsoil, non-expansive
clay
Clay is a type of fine-grained natural soil material containing clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4).
Clays develop plasticity when wet, due to a molecular film of water surrounding the clay par ...
, sand, and
aggregate. Forming compressed earth blocks requires dampening, mechanically pressing at high pressure, and then drying the resulting material. If the blocks are stabilized with a chemical binder such as
Portland cement
Portland cement is the most common type of cement in general use around the world as a basic ingredient of concrete, mortar, stucco, and non-specialty grout. It was developed from other types of hydraulic lime in England in the early 19th ...
they are called ''compressed stabilized earth block'' (CSEB) or ''stabilized earth block'' (SEB). Typically, around of pressure is applied in compression, and the original material volume is reduced by about half.
Creating CEBs differs from
rammed earth
Rammed earth is a technique for constructing foundations, floors, and walls using compacted natural raw materials such as earth, chalk, lime, or gravel. It is an ancient method that has been revived recently as a sustainable building method.
...
in that the latter uses a larger formwork into which earth is poured and manually tamped down, creating larger forms such as a whole wall or more at one time, rather than building blocks. CEBs differ from
mud brick
A mudbrick or mud-brick is an air-dried brick, made of a mixture of loam, mud, sand and water mixed with a binding material such as rice husks or straw. Mudbricks are known from 9000 BCE, though since 4000 BCE, bricks have also been f ...
s in that the latter are not compressed, but solidify through chemical changes that take place as they air dry. The compression strength of properly made CEB usually exceeds that of typical mud brick. Building standards have been developed for CEB.
CEBs are assembled onto walls using standard
bricklaying
Brickwork is masonry produced by a bricklayer, using bricks and mortar. Typically, rows of bricks called ''courses'' are laid on top of one another to build up a structure such as a brick wall.
Bricks may be differentiated from blocks by siz ...
and
masonry
Masonry is the building of structures from individual units, which are often laid in and bound together by mortar; the term ''masonry'' can also refer to the units themselves. The common materials of masonry construction are bricks, building ...
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, or cement mortar may also be used for high strength, or when construction during freeze-thaw cycles causes stability issues.
Hydraform blocks are shaped to be interlocking.
Development
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
The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territori ...
, most general contractors building with CEB are in the Southwestern states:
New Mexico
)
, population_demonym = New Mexican ( es, Neomexicano, Neomejicano, Nuevo Mexicano)
, seat = Santa Fe
, LargestCity = Albuquerque
, LargestMetro = Tiguex
, OfficialLang = None
, Languages = English, Spanish ( New Mexican), Navajo, Ke ...
,
Colorado
Colorado (, other variants) is a state in the Mountain states, Mountain West subregion of the Western United States. It encompasses most of the Southern Rocky Mountains, as well as the northeastern portion of the Colorado Plateau and the wes ...
,
Arizona
Arizona ( ; nv, Hoozdo Hahoodzo ; ood, Alĭ ṣonak ) is a state in the Southwestern United States. It is the 6th largest and the 14th most populous of the 50 states. Its capital and largest city is Phoenix. Arizona is part of the Fou ...
,
California
California is a state in the Western United States, located along the Pacific Coast. With nearly 39.2million residents across a total area of approximately , it is the most populous U.S. state and the 3rd largest by area. It is also the m ...
, and to a lesser extent in
Texas
Texas (, ; Spanish: ''Texas'', ''Tejas'') is a state in the South Central region of the United States. At 268,596 square miles (695,662 km2), and with more than 29.1 million residents in 2020, it is the second-largest U.S. state by ...
. The methods and presses have been used for many years in
Mexico
Mexico (Spanish: México), officially the United Mexican States, is a country in the southern portion of North America. It is bordered to the north by the United States; to the south and west by the Pacific Ocean; to the southeast by Guatema ...
, and in
developing countries
A developing country is a sovereign state with a lesser developed industrial base and a lower Human Development Index (HDI) relative to other countries. However, this definition is not universally agreed upon. There is also no clear agreem ...
.
The
South Africa
South Africa, officially the Republic of South Africa (RSA), is the Southern Africa, southernmost country in Africa. It is bounded to the south by of coastline that stretch along the Atlantic Ocean, South Atlantic and Indian Oceans; to the ...
n Department of Water Affairs and Forestry considers that CEB, locally called "Dutch brick", is an appropriate technology for a developing country, as are
adobe,
rammed earth
Rammed earth is a technique for constructing foundations, floors, and walls using compacted natural raw materials such as earth, chalk, lime, or gravel. It is an ancient method that has been revived recently as a sustainable building method.
...
and
cob. All use natural building materials. In 2002 the
International Institute for Energy Conservation was one of the winners of a
World Bank Development Marketplace Award for a project to make an energy-efficient Dutch brick-making machine for home construction in South Africa. By making cheaper bricks that use earth, the project would reduce housing costs while stimulating the building industry.
The machine would be mobile, allowing bricks to be made locally from earth.
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.
An abnormal result of a compressive strength of 45 MPa (6,500 psi) was obtained in one sample. The authors of this paper intended to show, with the abnormal test result, that earth responds differently from brittle masonry, and perhaps should be tested using different methods than those used for traditional brittle masonry.
Advantages
* Minimal or no need for mortar, thus reducing both the labor and materials costs.
* Transport cost: Suitable soils are often available at or near the construction site.
* Strengths might exceed the ASTM standard for concrete blocks (1900 psi) in some instances. In India, the observed compressive strength and flexural strength of CSEB at 28 days of aging with 9% cement stabilization has been observed to be 3.2 MPa (464 psi) and 1 MPa (145 psi) respectively. With 7% cement and sandy soil 3-4 MPa (435 - 580 psi) compressive strength has resulted.
* Non-toxic: like bricks, materials are completely natural, non-toxic, and do not
out-gas (with the possible exception of chemically inert noble gases like helium or radon if
naturally occurring radioactive material
Naturally occurring radioactive materials (NORM) and technologically enhanced naturally occurring radioactive materials (TENORM) consist of materials, usually industrial wastes or by-products enriched with radioactive elements found in the envir ...
is present)
* Sound resistant: an important feature in high-density neighborhoods, residential areas adjacent to industrial zones
* Fire resistant: like bricks, earthen walls do not burn
* Insect resistant: like bricks, insects are discouraged because the walls are solid and very dense, and have no food value
* No need for
process heat Process heat refers to the application of heat during industrial processes. Some form of process heat is used during the manufacture of many common products, from concrete to glass to steel to paper. Where byproducts or wastes of the overall indus ...
in production or for
calcination
Calcination refers to thermal treatment of a solid chemical compound (e.g. mixed carbonate ores) whereby the compound is raised to high temperature without melting under restricted supply of ambient oxygen (i.e. gaseous O2 fraction of air), gener ...
of
calcium carbonate (unless cement is used) therefore the material is inherently low-carbon and can be made
carbon neutral
Carbon neutrality is a state of net-zero carbon dioxide emissions. This can be achieved by balancing emissions of carbon dioxide with its removal (often through carbon offsetting) or by eliminating emissions from society (the transition to the "p ...
quite easily (by employing carbon neutral power to the compression machines)
Disadvantages
*There is a wait-time required with this construction technique because after the blocks are pressed, materials must dry.
*The mixture of the interlocking blocks must be consistent and just moist enough. If the mixture is too dry, it will collapse after it has been hydraulically pressed; but if the mixture has too much water, it cannot be solidified.
*There is also the risk of erosion from weather conditions such as wind or rain that could threaten the stability of the blocks.
Reinforcement using plaster might be required to ensure that the wall is durable in weather conditions such as rain and wind.
*Power is needed on-site for the compressing machines.
In
off-grid
Off-the-grid or off-grid is a characteristic of buildings and a lifestyle designed in an independent manner without reliance on one or more public utilities. The term "off-the-grid" traditionally refers to not being connected to the electrical g ...
applications this is quite often supplied by a
diesel generator
A diesel generator (DG) (also known as a diesel Genset) is the combination of a diesel engine with an electric generator (often an alternator) to generate electrical energy. This is a specific case of engine generator. A diesel compression-ig ...
, thus worsening the carbon balance
*Workforce trained to produce and construct interlocking blocks is limited.
*Being understudied, the durability of these blocks has not been seen in environments other than rural developments.
*Like most unreinforced masonry, the
tensile strength
Ultimate tensile strength (UTS), often shortened to tensile strength (TS), ultimate strength, or F_\text within equations, is the maximum stress that a material can withstand while being stretched or pulled before breaking. In brittle materials t ...
is orders of magnitude lower than the
compression strength; this limits the architectural options.
*Earth blocks tend to lose strength and dimensional stability when coming in contact with water for a long period of time. In some cases, it may lead to the complete disintegration of the block.
Presses
CEB had very limited use prior to the 1980s. It was known in the 1950s in
South America
South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere at the northern tip of the continent. It can also be described as the sout ...
, where one of the 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 a single-block, manual-press that uses a long, hand-operated lever to drive a
cam
Calmodulin (CaM) (an abbreviation for calcium-modulated protein) is a multifunctional intermediate calcium-binding messenger protein expressed in all eukaryotic cells. It is an intracellular target of the secondary messenger Ca2+, and the bin ...
, generating high pressure.
Industrial 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
France (), officially the French Republic ( ), is a country primarily located in Western Europe. It also comprises of overseas regions and territories in the Americas and the Atlantic, Pacific and Indian Oceans. Its metropolitan area ...
,
England
England is a country that is part of the United Kingdom. It shares land borders with Wales to its west and Scotland to its north. The Irish Sea lies northwest and the Celtic Sea to the southwest. It is separated from continental Europe b ...
,
Germany
Germany,, officially the Federal Republic of Germany, is a country in Central Europe. It is the second most populous country in Europe after Russia, and the most populous member state of the European Union. Germany is situated betwe ...
,
South Africa
South Africa, officially the Republic of South Africa (RSA), is the Southern Africa, southernmost country in Africa. It is bounded to the south by of coastline that stretch along the Atlantic Ocean, South Atlantic and Indian Oceans; to the ...
and
Switzerland began to write standards. The
Peace Corps
The Peace Corps is an independent agency and program of the United States government that trains and deploys volunteers to provide international development assistance. It was established in March 1961 by an executive order of President John F ...
,
USAID
The United States Agency for International Development (USAID) is an independent agency of the U.S. federal government that is primarily responsible for administering civilian foreign aid and development assistance. With a budget of over $27 bi ...
,
Habitat for Humanity and other programs began to implement it into housing projects.
Finishing
Completed walls require either a reinforced bond beam or a ring beam on top or between floors and if the blocks are not stabilized, a plaster finish, usually stucco wire/stucco cement and/or lime plaster. Stabilized blocks can be left exposed with no outer plaster finish. In tropical environments, polycarbonate varnish is often used to provide an additional layer of wet-weather protection.
Foundations
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 should extend to an elevation not less than eight inches (200 mm) above the exterior finish grade. Rubble-filled foundation trench designs with a reinforced concrete grade beam above are allowed to support CEB construction.
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 square inch
The pound per square inch or, more accurately, pound-force per square inch (symbol: lbf/in2; abbreviation: psi) is a unit of pressure or of stress based on avoirdupois units. It is the pressure resulting from a force of one pound-force applied t ...
(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)
References
{{Commonscat
Soil-based building materials
Sustainable building
Appropriate technology
Masonry
Natural materials
Sustainable technologies