Effect of lime on characteristics of Rice Husk Ash (RHA) based masonry blocks

Abstract

Rice husk, which is one of the major agro-waste material in Sri Lanka, is produced Rice Husk Ash (RHA) by burning as fuel in brick kiln. Mixture of sand, cement and water are extensively used to manufacture masonry blocks in Sri Lanka, although the cost of cement is high. Because of having highly pozzolanic constituents of RHA, it can be used as a material instead of cement to produce cement sand masonry blocks. It was frequently reported that compressive strength of RHA based blocks increase at 5% RHA usage and further addition of RHA caused decrease in compressive strength. This decrease may be caused by lack of Ca2+ in cement to react with SiO2 available in RHA to produce insoluble compounds. In this study, an attempt was made to increase utilization of RHA amount by adding Ca2+. Solid masonry blocks having the size of 360mm x100mm x 170mm were cast with the mix proportion of 1:6 Cement-Sand. Blocks were cast in two series. In the first series, RHA was used as addition with respect to cement weight. In this series of study, four different RHA contents (0%, 5%, 10%, and 15%) were used with constant lime content (10%). In the second series, with the well proved data for the addition of Ca2+ increases the utilization of RHA amount and compressive strength of blocks, RHA was used as partial replacement. In this series of study, RHA based cement sand blocks were produced with four different RHA contents (5%, 10%, 15% and 20%) and with constant lime content (10%).The blocks were tested for 7, 14 and 28 Day compressive strength. When RHA used as addition, the optimum 28 Day compressive strength of blocks was found as 4.937 N/mm2 for 10% RHA. It was 76% strength development comparing with the minimum standard value of 2.8 N/mm2. These blocks can be used well in load bearing walls. When RHA used as partial replacement, 28 Day compressive strength of blocks was found as3.467N/mm2 for 10% RHA. The RHA replacement for cement will help to reduce the unit cost of the sand cement block while improving sustainability.