Study on the superiority of biomass ash composite activation in blast furnace slag-coal gangue-fly ash system: A novel high-strength alkali-activated cementitious material

Alkali-activated materials are excellent alternatives to ordinary Portland cement, and their comprehensive performance and environmental impact are closely related to the type of alkali activator. In this study, blast furnace slag (BFS), coal gangue (CG), and fly ash (FA) were used as precursors for alkali-activated materials. Based on macroscopic performance tests and microscopic characterization methods, a comprehensive evaluation was conducted on the activation efficiency and performance advantages/disadvantages of four alkali activators (sodium hydroxide solution, modified sodium silicate solution, biomass ash (BA) solution, and composite alkali activator) in the BFS-CG-FA ternary solid waste system. This study introduced a novel BA composite activation method, which combines modified sodium silicate solution with potassium-rich and calcium-rich BA. The resulting alkali-activated cementitious material exhibited high strength, with a 28d compressive strength of 48.75 MPa. The results showed that, for the BFS-CG-FA system, BA composite activation exhibited excellent activation efficiency both in the early and late stages of the reaction. Moreover, BA more significantly enhanced the activation efficiency of low-concentration sodium silicate solution. The addition of BA not only enabled the material to achieve higher 28d compressive strength but also significantly increased the 1d compressive strength by 66 times (32.21 MPa vs. 0.48 MPa), greatly improving the early strength of the cementitious material. The findings of this study are conducive to promoting the research and development of environmentally friendly alkali activators as well as the popularization and engineering application of high-performance alkali-activated materials.