Taku J. K^1,, Amartey Y. D², Kassar T¹

In this study, the effect of the calcination temperature of rice husk on the pozzolanic properties of the resulting rice husk ash (RHA) especially its silica content was investigated. Rice husk was collected from a rice milling plant and washed to remove sand and other impurities, beneficiated using the water beneficiation method and calcined at temperatures of 400, 500, 600, 700and 800°C, respectively for three hours. Samples were taken for XRF analysis, setting time determination and specific gravity test. The result of XRF analysis revealed that RHA calcined at temperatures between 400°C and 800°C contains more than 70% silica as stipulated by ASTM C618 for pozzolanas. The silica content though varies slightly with different calcination temperature of the rice husk ash. Also, calcination removed impurities present in the rice husk. Besides that, the specific gravity of RHA decreases with increasing calcination temperature from 2.00 at 400°C to 1.05 at 800°C. Setting times of RHA mortars at 15% replacement of OPC with RHA shows no definite pattern with increasing temperature. However, the initial and final setting times of OPC-RHA mortars at all calcination temperatures were higher than that of OPC mortar. As a whole, calcination improves the silica content of rice husk ash for use as a pozzolana as well as removes mineral impurities that may affect the pozzolanic properties of the rice husk ash.

rice husk ash, calcination temperature, oxide composition, setting time, specific gravity