Use of biomass wood ash to produce sustainable geopolymeric pastes

Abstract

Biomass stands out as a more sustainable energy source, and forecasts indicate an increase in its use mainly due to environmental aspects. The resulting ash has potential application to produce geopolymers, alternative materials to Portland cement. Thus, this study aimed to produce geopolymer systems with metakaolin (MK) replacement by 10 and 20 wt% of three different sources of biomass wood ash, namely WA-A, WA-B, and WA-C. Rotational rheometry, isothermal calorimetry, 7-d and 28-d compressive strength, Fourier-transform infrared spectroscopy (FTIR) and an environmental analysis were conducted. The specific surface area (SSA) of the WA has a great influence on the rheological parameters and the hydration kinetics of the geopolymers. Overall, the higher the SSA (SSA WA-A > SSA WA-C > SSA WA-B), the higher the yield stress, viscosity, and reactivity of WA-geopolymers. Thus, geopolymers produced with WA-A and WA-C exhibited a comparable 7-d and 28-d compressive strength to the control samples for MK to WA replacement percentages of up to 20 and 10 wt%, respectively. FTIR results support the occurrence of geopolymerization in pastes with MK and WA and the continuous formation of geopolymer products from 7 to 28 days. The WA has CO2 emissions ∼ 65 % lower than MK. Thus, reductions up to 10.32 kg of CO2-eq/m3 of WA-based geopolymer were observed compared to the control sample.