Synergistic effects and mechanisms of composite supplementary cementitious materials with carbon-fixing steel slag powder and aluminum-containing mineral admixtures

This paper explores the optimal utilization of carbon-fixing steel slag powder to elevate its reactivity. When combining carbon-fixing steel slag powder with aluminum-containing mineral materials, fly ash (FA) emerges as the most suitable complement. Hydration heat data indicate that, compared to cement-based materials doped with FA alone, when the ratio of bacterial mineralized steel slag powder to FA is 1:1 by mass, the Qmax is augmented by 19.71 %. The aluminum phase accelerates the transformation of biological calcium carbonate, leading to the formation of more monocarboaluminate beneficial to strength enhancement. When the mass ratio of alumina to calcium carbonate falls within the range of 1.5–4.5, a significant synergistic effect is achieved, resulting in an optimal activity index of approximately 97 %. Notably, at the same carbon sequestration levels, microbial-assisted mineralized of steel slag powder yields superior results compared to direct carbonization, due to its finer calcium carbonate grain size. •The hydration activity of the composite SCM can reach the effect of '1+1>2′.•The ratio of carbon-fixing steel slag powder to fly ash of 1/1 is the best.•When the Al2O3/CaCO3 mass ratio is 1.5–4.5, a strong synergistic effect ensues.•Microbial-assisted mineralized of steel slag powder yields superior results.