New sights in early carbonation of calcium silicates: Performance, mechanism and nanostructure

Low calcium minerals were considered as a potential sustainable binder and reported to be reactive to CO₂. In this research, the carbonation characteristics of C₃S, β-C₂S and γ-C₂S at early age were investigated in some new sights. The results show that carbonation degree and compressive strength of C₃S increased most rapidly in the first 8 h carbonation, then slowed down. After 48 h carbonation, β-C₂S and γ-C₂S were close to C₃S in compressive strength, and apparently higher than C₃S in carbonation degree. The crystalline CaCO₃ generated by carbonation were mainly calcite and aragonite, while vaterite was observed in β-C₂S and γ-C₂S within 8 h carbonation. Carbonation curing increased MCL of C-S-H and silicate polymerization. Besides, based on the combination of TG-DTG, XRD and ²⁹Si NMR, the decalcify priority of Ca sites in C-S-H was analyzed. The results indicate that interlayer Ca atoms inside C-S-H participated carbonation first, then the calcium atoms within interlayer and silicate chains of C-S-H would be removed successively.