Compressive strength and durability properties of pozzolan obtained from co-fired clay and rice husk

This study investigated pozzolan from the co-firing of clay and rice husk. Rice husk was used to replace clay at 1.0%, 1.5% and 2.0% and calcined at 800°C. Pozzolanic strength activity index (PSAI) was performed on the calcined powder materials in accordance with the ASTM C311 standard. The calcined material that obtained the highest PSAI was selected and used to optimize the calcined pozzolan added to Portland cement. The optimum mixture proportions were used for ²⁹Si and ²⁷Al MAS NMR as well as water sorptivity and shrinkage studies which involved autogeneous and drying shrinkages. The results of the study showed that calcined clay that contained 2.0% rice husk had the optimum PSAI whereas 30 wt.% replacement content was the optimum cement replacement. The ²⁹Si and ²⁷Al MAS NMR showed that the superior strength of the optimum mortar mix to the control was due to a stable monosulphate phase formed at the octahedral environment and the formation of extra calcium aluminosilicate phases in the mortar mix. The initial and secondary sorptivity values of the pozzolan were 0.0055 and 0.0022 mm/sec^1/2 respectively, lower than the values of the control , which were 0.0299 and 0.0083 mm/sec^1/2 respectively. The shrinkage performances of the Portland cement-pozzolan mix were much enhanced than the unblended mortar mix. The inclusion of the co-fired materials reduced the embodied carbon by approximately 29%. The use of the co-fired material could be a sustainable means to dispose of waste rice husk and also reduce embodied carbon.