Rice husk ash

This chapter reviews the performance of rice husk ash (RHA) as partial cement replace in ordinary Portland cement concrete. After pyroprocessing with controlled combustion, highly pozzolanic RHA can be produced. Due to the high specific surface area and pozzolanic properties, RHA shows very good performance as a supplementary cementitious material in concrete. For early age properties, concrete made of RHA needs more water and high dosages of superplasticizer compared to ordinary Portland cement concrete. The RHA concrete has slightly longer setting times than ordinary Portland cement concrete. When the replacement level of ordinary Portland cement by RHA is about 20% by weight of the total binder material, the compressive strength, tensile strength and flexural strength of concrete made of RHA are enhanced. Due to the special porous structures, RHA shows excellent capacity to keep high relative humidity in the concrete, thus RHA significantly mitigates the autogenous shrinkage of concrete, especially high performance or ultra-high performance concrete made with RHA as addition. From water permeability and chloride diffusivity tests the coefficient of water absorption of RHA concrete is lower and the chloride diffusion coefficient is reduced.