Effect of mix retention and curing on low-cement walling blocks

Compressed and cement-stabilized soil blocks (CSBs) are building components of growing importance in tropical countries. Their performance (e.g. durability) has sometimes been lacking, so that its improvement is critical to their obtaining a larger market share. CSB durability is influenced by the interplay of three main factors: the process by which the CSB was produced, the choice of the constituent materials and the nature of the exposure conditions in service. This paper addresses a critical aspect of the first factor, examining the effects of retention delay before compaction moulding and curing conditions after demoulding. In the past, undue emphasis has been placed on the quantity of cement used rather than on the more critical quality of the production process employed to facilitate its proper hydration. From the experiments performed, it is concluded that moulding should occur within 30 minutes of the damp mixing of soil, cement and water, and that poor curing regimes, commonly observed in the field, waste over 85% of the wet compressive strength obtainable with ideal curing. The higher degree of hydration achieved via better curing ensures the realization of the full binding capacity of OPC. In this way, higher strength blocks, which are therefore dimensionally stable and durable, can be produced at tolerable cement cost.