Tailoring high-magnesium cements for enhanced carbonation hardening and CO₂ sequestration

The reduction of CO₂ emissions from the cement industry remains a major challenge worldwide. This study investigates the feasibility of using high-magnesium limestone to prepare high-magnesium and low-calcium cementitious materials (HM-LCCs) with improved carbonation reactivity and CO₂ sequestration capacity. The carbonation reactivity, hardening properties, phase assemblage, microstructure, and pore distribution of HM-LCCs synthesized with varying proportions of high-magnesium limestone were characterized by XRD, TGA, FT-IR, SEM, and LF NMR. It is found that with increasing substitution of high-magnesium limestone, the main mineral phases in clinker transformed from C₂MS₂ to C₃MS₂ and eventually to β-C₂S and MgO, along with markedly enhanced grindability. The carbonation reactivity and degree increased progressively with increasing substitution of high-magnesium limestone. Properly tailored HM-LCCs exhibited excellent strength development up to 94.56 MPa after carbonation, dense microstructure, and significantly higher CO₂ uptake. This study provides new insights into developing low-carbon cement by utilizing high-magnesian raw materials. The carbonation hardening and CO₂ sequestration capacity of cement can be optimized by tailoring the Mg/Ca ratio and calcium silicate phase assemblage.