Influence of Binary Precursors on Wood Biomass Ash-Based Alkali-Activated Materials: A Comparative Study

The valorisation of significant quantities of wood biomass ash (WBA) in the production of building and construction materials is a sustainable approach to waste management. Due to their low chemical reactivity, the challenge for WBA-based alkali-activated materials (AAM) is improving their mechanical properties. To address this issue, WBA, containing wood biomass bottom ash and wood biomass fly ash, was used as the primary precursor. One aluminosilicate-rich material (coal fly ash (CFA), metakaolin (MK), or natural zeolite (NZ)) was added as a binary precursor at 10, 20, 30, and 40% of the total precursor mass (the mass of WBA plus the binary precursor) to compare its effectiveness. In the overall composition, the proportion of these aluminosilicate precursors was only 3.3–13.3%. Alkali activators consisted of 10% calcium hydroxide, 7 mol/L sodium hydroxide, and sodium silicate with the same solute mass as sodium hydroxide. Compressive strength and microstructural examinations (SEM-EDS, TG-DTA, XRD, XRF, and FTIR) were conducted on the produced AAM to analyse the mechanical performance and reaction mechanisms. A cradle-to-gate lifecycle assessment (LCA) was performed to evaluate the environmental impacts, including greenhouse gas emissions and energy consumption. The results show that NZ increased compressive strength by up to 57.62% when used at 6.6% in the composition. At the same time, MK and CFA increased strength by 33.05% and 47.15%, respectively. Binary precursors increased the greenhouse gas emissions and energy demands of AAM products, especially the MK, due to its energy-intensive calcination process. From a comprehensive view, NZ is the most efficient choice based on both mechanical and environmental insights.