The Compressed Earth Block process:
The first step in the earth block process is sourcing the soils and homogenizing the material in a blender where the stabilizer is also added. If the option is to use available crushed rubble into the mix, then this is added after the stabilizing agent and mixed well before feeding into the hydraulic compactor. Equipment manufactured by Advanced Earthen Construction Technologies (AECT) is to compress the soil, mixed waste and cement stabilizer mixture into compressed earth blocks. Each block machine is able to make 350 compressed earth blocks per hour. Once produced the blocks are stacked on a pallet, wrapped with a plastic sheeting and left to cure for a period of seven days.
Sourcing the components:
The soil component required to make the blocks is sourced either from the site where the blocks are to be made; one can make use of spoil material in larger development from cut-and-fill operations, or the material can be sourced from unusable overburden from quarries and borrow-pits. Since a 10% to 50% clay content in the soil is required to make compressed earth blocks, the higher the clay content the more ideal for USE-IT’s requirements in blending additional inert waste.
The waste component required to make the blocks is normally sourced from building rubble, however, other types of inert waste can also be used such as crushed ceramics, glass and certain mine tailings. Most recently, USE-IT has used recalled ceramic mugs from Unilever as the mixed waste component of the earth blocks. Instead of the mugs being crushed at a cost of R3.50 per kilogram and sent to landfill, the ceramic waste was crushed by USE-IT for R2.00 per Kilogram and then used to produce compressed earth blocks. For this project, a total of 760,000 mugs (230 tons) was used in the production of 118,000 compressed earth blocks.
The benefits of compressed earth blocks:
The following are benefits of using compressed earth blocks over conventional cement blocks:
The cost of the blocks: The compressed earth blocks are 20% cheaper than conventional cement blocks.
The building process is faster and simpler because of the bonding process. Soil slurry, composed of the same material used in the earth blocks, is used instead of traditional cement mortar and therefore, there is no need to wait for long periods for the cement to dry.
The compression strength of the blocks: The compression strength of the earth blocks is three to five times stronger than concrete blocks, depending on the quality of soil used.
Thermal efficiency: The thermal insulative capacity of the earth blocks is ten times better than concrete blocks, which can result in energy savings as the structures built will be cooler in summer and warmer in winter.
Carbon savings: United Nations Centre for Human Settlements estimates that eight tonnes of carbon (8tCO2e) can be saved for every 50m2 building that is built from compressed earth blocks rather than concrete blocks.