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

Abstract

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.