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）,β-dicalcium silicate （β-C2S）,tricalcium aluminate （C3A）,and tetracalcium ferroaluminate （C4AF）,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,β-C2S,C3A and C4AF 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 β-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 C3A>C4AF>β-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.