Performance of Carbon-Neutral Rice Hull Ash as a Supplementary Cementitious Material In Portland Cement Mortars

This presentation is the second of the two presentations that focus on rice hull ash (RHA). In this presentation, the performance of a carbon-neutral RHA as a supplementary cementitious material for use in portland cement composites will be discussed.  The RHA used in this study was developed through an improved combustion technique that resulted in very low unburnt carbon content in the RHA.  Also, with its very high levels of amorphous biogenic silica, the RHA has a significant potential for use as a supplementary cementitious material in portland cement composites.  Various tests conducted in this study focused on investigating the influence of RHA on selected properties of portland cement pastes and mortars.  In specific, effort was focused on studying its microstructure, pozzolanic reactivity and the effect of grinding RHA on its pozzolanic reactivity.  In addition, the effect of RHA dosage on the workability (flow) and mechanical properties of cementitious mortars was studied.   Based on the results from these studies, it was found that RHA was highly pozzolanic in nature.  Also, the use of RHA as a cement replacement level at dosage levels up to 20% by mass of cement yielded significant improvement in compressive strength of mortars. Grinding RHA to a finer size further improved the performance of RHA as supplementary cementitious material.  However, the use of RHA as a supplementary cementing material resulted in substantially increased water demand of the mortars, regardless of the dosage level.  The increased water demand was easily alleviated by the use of adequate amounts of high-range water reducing agent in the mortars.  Further investigations on the impact of RHA on durability of portland cement composites are being investigated.  It is anticipated that with further evaluation and refinement, the biogenic silica from rice hull can be a valuable resource in developing environmentally sustainable construction materials.