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

Abstract

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.

Keywords

accelerated carbonation / portland cement / calcium carbonate / water-to-solid ratio

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