Carbonation mechanism of unsaturated ettringite-rich cements: a diffusion-reaction model approach

A diffusion-reaction model is developed to accurately predict carbonation of unsaturated ettringite (AFt)-rich cements, where CO2 gas diffusion and dissolution in pore solution, moisture transport within the cement and convection at air-cement interface, and chemical reactions are comprehensively considered between CO2 in its liquid phase and the hydrated products such as Portlandite (CH), Calcium Silicate Hydrates (CSH) and AFt. Particularly, AFt carbonation is involved for generation of Calcium Carbonate (CaCO3) and water, which is neglected in previous studies. Furthermore, the theoretical model is validated with carbonation experiments, where good agreements are achieved. Afterwards, the carbonation process is numerically investigated under varying AFt amounts, CO2 volume fractions, and water-cement ratios. Results show that AFt carbonation is necessarily considered due to its significant impact on porosity, saturation, and solid substances such as CH, CSH, CaCO3. Hopefully, the developed model can provide theoretical guidance for durability design and optimization of cementitious materials.