Effect of polycarboxylate on rice husk ash pozzolanic cement

In this study, OPC was partially substituted by RHA in the ratios of 4, 8, 12, and 16 mass\%. The results show that, the water of consistency increases with RHA content which adversely affects the mechanical properties, especially at a high content of RHA, (above 8 mass\%). The free lime content of pozzolanic cement pastes decreases with curing time and RHA contents. To improve the physico-mechanical properties of pozzolanic cement, different blends were made from OPC with 8 mass\% RHA and various dosages of superplasticizer (polycarboxylate admixture; 0.5, 1.0, 1.5, 2.0, 2.5 mass\%) and hydrated for 3, 7, 28 and 90 days. The cement paste with 8.0 mass\% RHA and 1.5-2.0 mass\% superplasticizer is the suitable mix, which gives good mechanical properties. The presence of polycarboxylate admixture decreases the pore volumes approaching the RHA from the lime liberated from the hydration of OPC, forming additional C-S-H hydration product as well as improving the microstructure of RHA-pozzolanic cement pastes and mortars.