Carbonation of Pure Minerals in Portland Cement: Evolution in Products as a Function of Water-to-solid Ratio

Minerals in Portland cement including tricalcium silicate (C3S), beta-dicalcium silicate (beta-C2S), tricalcium aluminate (C(3)A), and tetracalcium ferroaluminate (C(4)AF), show a significantly different activity and product evolution for CO2 curing at various water-to-solid ratios. These pure minerals were synthesized and subject to CO2 curing in this study to make an in-depth understanding for the carbonation properties of cement-based materials. Results showed that the optimum water-to-solid ratios of C3S, beta-C2S, C(3)A and C(4)AF were 0.25, 0.15, 0.30 and 0.40 for carbonation, corresponding to 2 h carbonation degree of 38.5%. 38.5%, 24.2%, and 21.9%, respectively. The produced calcite during beta-C2S carbonation decreased as the water-to-solid ratio increased, with an increase in content of metastable CaCO3 of vaterite and aragonite. The thermodynamic stability of CaCO3 produced during carbonation was C(3)A>C(4)AF>beta-C2S>C3S. The carbonation degree of Portland cement was predicted based on the results of pure minerals and the composition of cement, and the error of predicted production of CaCO3 was only 1.1%, which provides a potential method to predict carbonation properties of systems with a complex mineral composition.