Optimization of the Strength Activity of Rice Husk Ash in Cementitious Mixtures

Abstract

In this study, the effects of some of the important manufacturing parameters of rice husk ash (RHA) on its mechanical performance in mortar mixtures is investigated. All of the presented results belong to a comprehensive experimental program where samples of plain and acid-leached rice husks were slowly heated up to 700°C and combusted at such temperature for different lengths of time, from 0.25 to 16 h. The obtained ashes were ground for different lengths of time, ranging from 0.33 to 16 h, and the resulting pozzolans were replaced for cement at different levels (5%, 10%, and 15% by mass) in mortar mixtures with similar flowabilities. The 28-day compressive strengths of the mortars were measured, and the results were analyzed via regression analysis. The analysis outcome suggests that acid leaching does not necessarily lead to better mechanical performance, and precise optimization of other combustion parameters is needed to improve the performance of RHA. Under optimal conditions (acid leaching followed by combustion at 700°C for 16 h), replacement of 11% cement with such RHA was found to result in approximately 14% greater strength results compared to that of plain RHA-blended mixture and 78% greater strength compared to that of the 100% ordinary portland cement mixture. Despite the significant improvement in strength, it is concluded that acid leaching is not necessarily justifiable considering economic and environmental factors.