UC Davis

Escalating demands for infrastructure materials and energy worldwide necessitate exploration of means to efficiently utilize resources to support growing consumption. This work evaluates the potential symbiotic relationship between cultivation of an agricultural product (namely, rice), energy conversion, and utilization of bioash in the production of cement-based materials to improve the sustainability across multiple industries. Primarily, leaching methods of biomass that benefit energy conversion are evaluated as a means to simultaneously improve ash properties for use in cement-based materials. Specifically, this study considers water leaching and H3PO4 leaching of rice hulls and rice straw, which were subsequently ashed at three different temperatures, 600, 850, and 1100 °C. The effects of leaching on the ash characteristics, on the performance of ash-cement mortars, and on the greenhouse gas (GHG) emissions from both the mortars and energy produced are quantified. Findings showed that while acid leaching led to higher GHG emissions for electricity generation, leaching decreased concentrations of undesirable alkali metals and chlorides in the ash. Regardless of treatment and ashing temperature, the inclusion of bioash delayed the early strength development of the cement-based mortars. Yet, several permutations of treatment, feedstock type, and ashing temperature were found to contribute to the later-age strength development of cement-based materials while reducing related GHG emissions. Specifically, after 28 days of curing, mortars containing 15% cement replacement with unleached ash prepared at 600 °C had 1-5% lower compressive strength, and after 56 days, mortars with leached rice hull ash prepared at 600 °C had 5-6% lower compressive strengths. Further, the use of unleached and water-leached ashes in mortar led to reductions in GHG emissions up to 15%. Hence, this work shows that pretreatment methods applied to rice biomass residues may contribute to desirable cobenefits for energy and materials production.