An innovative ternary carbon-fixing cementitious system of cement-fly ash-carbonated steel slag

The present work introduced an innovative cementitious system named CFCS, combining cement, fly ash (FA), and carbonated steel slag (CS), which exhibited both high early and later-age compressive strength along with significantly lower carbon emissions. This was achieved by producing highly reactive silica gels and carbon-fixing calcium carbonates (Cc) from steel slag (SS) via CO₂-assisted wet grinding. The results indicate that CFCS shows remarkable improvements in compressive strength, about 26 % and 34 % higher compared to the system of cement-FA-limestone (CFL) at 1 d and 28 d, respectively. The superior early performance of CFCS is attributed to the high pozzolanic reactivity of silica gels in CS, which facilitates the formation of additional calcium-silicate-hydrate (C-S-H) gels. Additionally, reactive Cc readily reacted with aluminates to form monocarbonate (Mc). These gels act as nucleation sites, promoting a higher cement hydration degree and contributing to early strength development. The accelerated cement hydration induced by CS creates a favorable environment for the higher reaction degree of fly ash (FA), resulting in sustained enhancement of compressive strength at later stages. Moreover, the carbon reduction of CFCS can reach about 64 % compared to ordinary Portland cement, representing an ultra-low carbon cementitous system.