Modeling and experimental validation of carbonation mechanism of ye’elimite-gypsum-water system

Calcium sulfoaluminate cement is a promising low-carbon alternative to Portland cement, and the carbonation of its hydration products influences its mechanical performance. However, a comprehensive theoretical model describing its carbonation mechanism remains elusive. This paper established a theoretical reaction range, including different zones and boundaries for ye’elimite (C₄A₃S̅)-gypsum (CS̅H₂)-water (H₂O)-carbon dioxide (CO₂) system via priority-based theoretical calculations of chemical reactions. The reactions and product evolution within each boundary and zone were summarized. A theoretical database was obtained, including the change of Gibbs energy and enthalpy, solid volume and chemical volume, and the theoretical carbon absorption. Calculation results reveal that the reactions of each zone and boundary occur spontaneously and exothermically. The solid volume increases, while the chemical volume decreases conversely. The maximum carbon absorption of 1 mol C₄A₃S̅ is 3 mol theoretically regardless of the amount of gypsum. The modeling obtained by Gibbs Energy Minimization software (GEMS-PSI) and experimental verification were carried out to validate the fidelity of the established theoretical reaction range, which demonstrate that the evolution of carbonation products in each zone and boundary was in line with the theoretical calculations. Compared with GEMS modeling, the theoretical reaction range can distinguish the source of ettringite in detail, and provide a more direct and insightful representation of carbonation process.