Strength properties of rice husk ash-lime mortars

Abstract eng:
Rice is a major staple food produced in developing countries. The rice husk which forms about 200 kg for every tone of rice that is processed is either disposed of by burning or is abandoned in the fields and this causes environmental pollution. If this husk is burnt under controlled combustion it produces about 20% Rice Husk Ash (RHA) which is pozzolanic and when mixed with either lime or Portland cement it produces a binder with good mechanical properties and durability. Studies carried out on concrete where RHA was incorporated in the mix indicated that the ash filled the micro-pores in the concrete, reduced the permeability and increased the durability of the concrete. It is also reported in studies that up to 30% replacement level of cement with RHA in concrete led to reduced chloride penetration due to decreased permeability, and improved the strength and corrosion resistance properties of the concrete. In this study the influence of RHA/lime ratio on the strength properties of sand mortars was investigated. The ratios investigated were 40/60, 50/50, 60/40, 70/30 and 80/20 RHA/Lime ratios as binder. The binder/water ratio was kept at 0.88 in all the cases. Results indicated that the optimum mix proportion for maximum strength was 60/40 which gave strengths of 5.28 N/mm2 at 28 days. The strengths of the mortars obtained for all the above investigated ratios were, however, greater than that specified in BS 5628-3:2001 for mortar designation type (iii) which is 3.6 N/mm2 in the laboratory and 2.5 N/mm2 at site for masonry construction. The results obtained from this study shows that RHA and lime can be used for mortars in masonry constructions and also for making bricks and blocks for low cost housing. The pollution problems arising from lack of viable methods of disposal of the millions of tons of rice husks produced in developing countries could be solved by the construction of kilns which would convert the rice husks into this useful ash.

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