D E Montgomery, (March 2001)
The monetary cost of low-cost walling in developing countries is greatly dependent on the expensive additives that are used to manufacture the building units and the cost of transportation of raw materials or finished products to the site of construction. Another cost associated with the production of anything is an energy cost and that can give an approximate overall measure of environmental impact. Within this paper several different types of existing walling materials are investigated for their overall cement and energy consumption. The purpose is to see how favourably they compare with high-density compressed and stabilised soil blocks using these suitable comparative measures. Assessment of suitability of local and on-site production will also be indicated for each of the materials in this study.
The study indicates that only three of the materials examined utilise less than 15kg/m²of cement, two of those are unsuitable for local production and the third uses about three times the energy in production. High-density compressed and stabilised soil blocks use slightly more than 15kg/m² of cement but have a low energy requirement for production. The other sections of this paper deal with the possible methods of
further reducing the cement requirement of high-density compressed and stabilised soil blocks to a value below 15kg/m².
Several different cement-reducing methods are outlined within this paper. These include: placing voids in the block, incorporation of a cement rich-skin (either within the block itself or applied as a render), interlocking blocks requiring very little or no mortar and taller blocks that reduce the number of block courses needed for mortaring. In isolation each method does not reduce the cement demand below 15kg/m². However, it is possible to apply several of these methods together that safely brings the cement requirements to well below the target of 15kg/m² with a low energy cost.