Compressed Stabilized Earth Block and Rammed Earth for Construction; Hilary D Smith

Compressed Stabilized Earth Block and Rammed Earth for Construction; Hilary D Smith

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Earth Institute, Auroville
photographs: Hilary D Smith, Auroville Earth Institute

‘In Auroville, examples of the Earth Institute’s work range from the Visitors’ Center, with its elegant use of arcades and domes, to small dismountable houses, or to multistory apartment complexes such as Vikas and Realization. The high compression achieved with the Auram 3000 press, which can reach to 7.5 MPa, permits them to be used in multistory construction as well as for wide-span arches, vaults, and domes. The variability of size and shape gives them versatility in appearance and applicability’, says Hilary D Smith, Auroville Earth Institute

Earth architecture, long relegated to the realm of cultural heritage in the mindset of modern architects, has enjoyed a place of honor in the architecturally innovative international township of Auroville in Tamil Nadu. Two earth building techniques that have come to the forefront for their versatility, cost-effectiveness, and low ecological impact are compressed stabilized earth blocks and rammed earth.   These two methods have been successfully employed by the Auroville Earth Institute in Auroville and beyond.

Compressed Stabilized Earth Blocks, known as CSEB, are unfired blocks produced by mixing soil, sand, stabilizer (cement or lime), and water and compressing the mixture into block form with either a manual or a motorized press. These blocks can then be used in masonry construction in buildings up to four stories tall without concrete column reinforcement. They also lend themselves well to arches, vaults, and domes, which can supplement the need for concrete slab roofing. They present interesting attributes in their cost-effectiveness stems from small production costs and no transportation costs, as soil can be excavated from the site of construction making it less expensive than country-fired brick and reinforced concrete. The monetary investment goes primarily toward labor rather than into the construction materials industry. Their ecological attributes are evident in their production from a renewable source, soil, without polluting manufacture processes. Country-fired brick has approximately 9.6 times higher carbon emissions and reinforced concrete has 48 times higher carbon emissions. The production of the blocks is highly scalable to the size of the building project and can accommodate small relief shelters as well as expansive public buildings. And at the end of the building’s lifespan, the blocks are bio-degradable, taking only ten to twenty years to decompose once the structure has been demolished.

The locally selected soil must undergo testing to ascertain its suitability, as not all soils are ideal for use in block production. Based on these tests, the amount of stabilizer and/or additional soil components can be ascertained. Cement is generally used to stabilize sandy soils whereas lime is used more to stabilize clayey soils. Following the analysis of the soil samples, soil is excavated from the site and collected in piles where it can be measured out and used for block production. The resulting excavation pits can be used for basement floors, landscaping purposes or rainwater harvesting and wastewater treatment facilities.

Then block production can begin. Soil must be dug, sieved, and measured. The additives—sand and appropriate stabilizer—are added to the soil, dry mixed, and then combined with water.  When thoroughly combined, the mixture can be pressed into blocks using a manual or a motorized press. In India, where labor is relatively inexpensive and manual labor is an aspect of the local economy, the manual press is an optimal choice. The Earth Institute uses a manual press that it has developed which is adapted to these conditions, called the Auram 3000. With ten workers, an output of 850 to 1000 blocks can be produced daily. With the interchangeable molds, it can make round, rectangular, hollow, and interlocking blocks of varying dimensions. Prior to their use, blocks cure for 28 days, during which they must be kept moist. They are then dried and readied for construction.

CSEB are suited to a wide range of construction types. In Auroville, examples of the Earth Institute’s work range from the Visitors’ Center, with its elegant use of arcades and domes, to small dismountable houses, or to multistory apartment complexes such as Vikas and Realization. The high compression achieved with the Auram 3000 press, which can reach to 7.5 MPa, permits them to be used in multistory construction as well as for wide-span arches, vaults, and domes. The variability of size and shape gives them versatility in appearance and applicability.

  • Earth Institute, Auroville <br> photographs: Hilary D Smith, Auroville Earth Institute
    Earth Institute, Auroville
    photographs: Hilary D Smith, Auroville Earth Institute
  • Visitors Centre, <br> photographs: Hilary D Smith, Auroville Earth Institute
    Visitors Centre,
    photographs: Hilary D Smith, Auroville Earth Institute
  • Deepanam school, <br> photographs: Hilary D Smith, Auroville Earth Institute
    Deepanam school,
    photographs: Hilary D Smith, Auroville Earth Institute
  • Realization, <br> photographs: Hilary D Smith, Auroville Earth Institute
    Realization,
    photographs: Hilary D Smith, Auroville Earth Institute
  • Dismountable houses, <br> photographs: Hilary D Smith, Auroville Earth Institute
    Dismountable houses,
    photographs: Hilary D Smith, Auroville Earth Institute
  • Rammed earth, <br> photographs: Hilary D Smith, Auroville Earth Institute
    Rammed earth,
    photographs: Hilary D Smith, Auroville Earth Institute
  • AURAM press; photographs: Hilary D Smith, Auroville Earth Institute
    AURAM press; photographs: Hilary D Smith, Auroville Earth Institute

Plastering is not required with CSEB construction, although it can be employed for added benefits. The Earth Institute has conducted extensive research into the use of earth plasters with the special additives of lime, marble powder, alum, and cactus juice to provide added waterproofing properties to structures.

CSEB is also adaptable to regions contending with seismic activity and has governmental approval for utilization both in India and Iran. Hollow interlocking CSEB are very resistant to earthquakes when combined with earthquake-conscious design principles such as regular, symmetrical shapes, careful placement and sizing of windows and doors openings, and reinforcement with secondary materials like concrete, bamboo, or timber.

Rammed Earth has also been used in Auroville, though less extensively than CSEB. A notable example constructed by the Earth Institute is the Deepanam School. Rammed earth can boast a faster construction speed than CSEB, but does not have the same adaptability architecturally. Rammed earth walls are constructed through the assembly of a formwork into which soil is compacted with a manual or pneumatic tamper. This soil does not have to be stabilized; however, stabilization allows for thinner walls, increased strength, and reduced maintenance. In addition to soil, selected from the construction site, the Earth Institute generally adds 25 to 30% sand and 5% cement to the quantity of soil for both CSEB and rammed earth.

Additionally, rammed earth can be used for foundations as an alternative to the conventional reinforced concrete. The soil is excavated from a trench foundation, mixed with sand and cement, and compressed into the trenches using tampers. These foundations are excellent to distribute the loads of rammed earth or CSEB walls.

To build rammed earth walls, the soil is mixed with the appropriate proportions of sand and cement and pressed into a formwork, which is coated with diesel to prevent sticking. The soil mixture is then compressed using a tamper. While pneumatic tampers can produce superior results, the Earth Institute uses manual tampers as they are more adapted to the labor environment and largely sufficient. The lower formwork is removed and repositioned in order to continue the height of the wall.

With their sustainable attributes, low cost for implementation, and esthetic appeal, these two earth building techniques have had great success in the construction of private homes, public buildings, and housing developments in Auroville. And through its training programs and consultation throughout India and abroad, the Auroville Earth Institute strives to innovate practices and widen the familiarity with and proper usage of these techniques.

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