Interlocking Stabilized Soil Blocks (ISSB)
Interlocking Stabilized Soil Blocks (ISSB) are bricks that are made from compressed mixed soil using an ISSB machine.
Interlocking Stabilized Soil Blocks, also called Interlocking Compressed Earth Blocks (ICEBs), are bricks that are made from mixed soil that can be found on or off the construction site. The soil is usually mixed with cement, water, and other additives to improve its characteristics. The soil is compressed using an ISSB machine and the blocks are laid with mortar in a staggered pattern similar to other types of masonry.
Africa, Asia, Australia, North America, Latin America & the Caribbean, East Africa, Uganda, Kenya, Tanzania, South Africa, India
A report from UN Habitat estimates that in 2009 the cost of ISSB in Uganda was approximately 10 USD per square meter (35,000 Ugandan Shillings).
ISSBs compete with CEBs that do not have the interlocking component, concrete block, clay fired brick, and mud thatch. ISSB requires less mortar and is faster to lay because the ridges guide the mason.
Goal 11: Sustainable cities and communities
Public sector, private sector, households, businesses
Either can be mass produced, made to order, or made directly on the site with soil found on the site
Users can obtain the blocks from an implementing organization, manufacturer, or distributer, or with the correct training and equipment can produce the blocks themselves.
Size of the component
List of primary materials in the component
List of secondary materials in the component
Measurement, calculated in hours, of the component’s resistance to fire
R value associated with material/product
The compressive strength of the component, measured in megapascals
List of suitable climates for use of this components
Arup produced a report for compressed earth blocks in general that includes information for soil preparation, stabilizers, block dimensions, compression or extrusion, curing, block property testing, construction, finishing, and design parameters such as wall thickness, percentage of windows in a wall, and considerations when building in non-seismic and seismic areas.
UN Habitat in collaboration with Good Earth Trust (GET) has a report specifically for ISSBs and presents similar information in a series of simple diagrams.
Most ISSBs in East Africa are made with an ISSB machine that compresses the soil into the interlocking form. Depending on the machine, the following blocks can be produced: Straight Double Interlocking Block, Curved Double Interlocking Block, Wide Format Interlocking Block, Straight Single Interlocking Block, or Grooved Double Interlocking Block.
Planning the production of ISSBs starts with the site and properties of the soil there. A sedimentation test can be performed to determine the percentages of clay, silt, sand, and gravel in the soil. Other tests include shrinkage tests, sending the soil to the laboratory, or using a portable soil-testing kit.
Stabilizers include cement lime or bitumen, fibrous natural materials, chemicals and resins, or sands and gravels. It is important to refer to more detailed material to determine what stabilizer is most appropriate for the type of earth mix that is being used.
The process of producing the blocks includes steps of training the labour force (quality assurance is extremely important for ISSB production), excavation, sieving, mix preparation, mixing, measuring the mix, compressing the mix, removing the block, dry and stack, and quality check.
Technical support can be found from the manufacturer or distributer, or from the reports listed in the Design specifications section. Another resource is the Auroville Earth Institute, and on their links page they list their full network of earth-building specialists including CRAterre, Cartoterra, Dachverband Lehmbau (the German association for building with earth), Earth Block International, and Rural Housing Knowledge Network, among others.
It is unlikely that repairs are needed (see Lifecycle section), however new blocks can be produced should sections of a structure need to be rebuilt.
Though the full lifespan is unknown, historical precedent and testing signify that if built to a high level of quality and with the most appropriate soil mix and detailing, ISSBs and ICEBs can last decades similar to the lifespan of fired earth bricks.
Performance targets include affordability, sustainability, ease of use, good performance, and versatility. A key factor for ISSB is that care must be taken to ensure quality.
Many universities including the University of Bath, Makerere University, and the University of Colorado; ARUP; and the Uganda National Bureau of Standards.
Workers are subject to the general dangers of a construction site including working from heights and with sharp tools. ISSBs do not require operation of any large machinery.
Allen GTR. 2012. Strength Properties of Stabilized Compressed Earth Blocks with Varying Soil Compositions. University of Colorado at Boulder, ProQuest Dissertations Publishing.
Leitão D. 2017. Thermal performance assessment of masonry made of ICEB’s stabilised with alkali-activated fly ash. Energy and buildings. 139: 44-52.
Irwan JM, Zamer MM, and Othman N. 2016. A Review on Interlocking Compressed Earth Blocks (ICEB) with Addition of Bacteria. MATEC Web of Conferences. 47.
Villamizar MC, Araque VS, Ríos Reyes CA, Silva RS. 2012. Effect of the addition of coal-ash and cassava peels on the engineering properties of compressed earth blocks. Construction and Building Materials. 36: 276-286.
Heath, A et al. 2009. Compressive strength of extruded unfired clay masonry units. Proceedings of the ICE — Construction Materials, 162(3): 105-112.
Heath A, Maskell D, Walker P, Lawrence M, and Fourie C. 2012. Modern earth masonry, structural properties and structural design. The Structural Engineer, 90(4): 38-44.
Huber H and Guillaud H. 1994. Earth construction: a comprehensive guide. ITDG.
Minke, G. 2002. Construction manual for earthquake-resistant houses built of earth. Eschborn.
Morton, T. 2008. Earth masonry, design and construction guidelines. BRE Press.
Oti J, Kinuthia, JM, and Bai J. 2009. Unfired clay bricks: from laboratory to industrial production. Proceedings of the ICE — Engineering Sustainability 162(4): 229-237.
Smith, E. 2010. Interlocking stabilised soil blocks: appropriate technology that doesn’t cost the earth. The Structural Engineer, 88(15/16): 25-29.
Walker P. 2002. HB195-2002. The Australian earth building handbook. Standards Australia.
Specifications for unfired earth blocks exist in Australia, El Salvador, France, Belgium, Germany, India, Kenya, New Zealand, Uganda, and USA. Broader earth specifications are also available in Peru and the Ivory Coast. A table with the specific names and page counts of these design codes are included in the Arup report.
The soil mix is evaluated by performing several tests such as sedimentation tests, shrinkage tests, and laboratory tests, and the blocks are evaluated visually and by testing for water absorption and compressive strength.
Makiga has a project gallery of structures made with ISSB.
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