DEVELOPMENT OF BLENDED CEMENT AND SAND-LATERITE BLOCKS FOR LOW-COST HOUSING

Abstract

The utilization of agricultural wastes and other locally available materials in the construction industry would foster environmental sustainability and even lead to overall reduction in construction cost. This research investigates the optimum use of rice husk ash (RHA), coconut husk ash (CHA) and laterite for the production of low-cost blocks. RHA and CHA were used to replace Ordinary Portland cement (OPC) by volume, at various levels (0%, 5%, 10%, 15%, 20% and 25%) and different combinations while laterite was used to replace sand as fine aggregate at similar levels using two different blends (binary and ternary). The mix ratio adopted was 1:6 (one part of cement to six parts of fine aggregates) by volume, to mould a total of one hundred and seventy four (174) 150mm by 150mm by 150mm blended cement sand-laterite blocks. Physico-chemical properties and strength tests were conducted on the ashes/fine aggregates and moulded blocks to ascertain their suitability for use and conformity with relevant standards.The chemical compositions of the ashes indicated that they are good pozzolans. The setting time of the mix was found to be decreasing as the quantity of the ashes increases.The soundness and fineness of all the blends were very small and within the stipulated limits. The densities of the blended cement-sand-laterite blocks were lower than those of OPC/Sand mix. Although the compressive strength of the blocks increased with age for all the combinations used, the values obtained were lower than those of the control experiment (OPC/Sand mix only).The values were also found to be decreasing with the quantity of the ashes and laterite in the mix. According to the Standard Organization of Nigeria and the Nigerian Industrial Standard, the minimum allowable strength of blocks at 28 days curing age for load bearing walls should be 2.0N/mm². This minimum value was obtained from a block of 80% and 20% binder compositions of OPC and RHA respectively in addition to 80% and 20% fine aggregate compositions of sand and laterite respectively for RHA binary blend (OPC/RHA/Sand/Laterite block). Similarly, for the CHA binary blend (OPC/CHA/Sand/ Laterite block), the minimum allowable strength was obtained at 85% and 15% binder compositions of OPC and CHA respectively in addition to 85% and 15% fine aggregate compositions of sand and laterite respectively. However, for the ternary blend (OPC/RHA/CHA/Sand/Laterite block), the standard strength was obtained at 80%, 15% and 5% binder compositions of OPC, RHA and CHA respectively in addition to 70% and 30% fine aggregate compositions for sand and laterite respectively. These replacement levels were the maximum possible levels beyond which any further increment will give a reduction in the standard strength. For the cost comparison with OPC/Sand block, there was reduction by 10.5%, 8.3% and 11.1% for OPC/RHA/Sand/Laterite (RHA binary blend), OPC/CHA/Sand/Laterite (CHA binary blend) and OPC/RHA/CHA/Sand/Laterite (RHA/CHA ternary blend) blocks respectively. This indicates that RHA and CHA are good supplementary cementitious materials and laterite is a good supplementary fine aggregate which can all be utilized for the production of low-cost blocks.