A multi-species reactive transport model based on gas-ion-solid phase interaction for the carbonation of cement-based materials

• Published in: Cement and concrete research 2024-01, Vol.175, p.107349, Article 107349
• Main Authors: Sharmilan, Suntharalingam, Stang, Henrik, Michel, Alexander
• Format: Article
• Language: English
• Subjects: Carbonation process; Chemical equilibrium; Gas dissolution; Multi-component gas transport; Reactive transport model
• ISSN: 0008-8846; 1873-3948
• DOI: 10.1016/j.cemconres.2023.107349

This study presents a reactive transport modelling framework for understanding carbonation processes through pore solution composition, phase assemblage changes in cement-based materials, and pore solution composition changes on steel corrosion. The study emphasizes the significance of considering pore structure changes on mass transport and utilizing a surface complexation model for predicting changes in pore solution composition and comprehending its influence on steel corrosion. A clear enrichment in sodium and potassium content in carbonated regions is observed upon carbonation, which leads to a decrease in alkali concentration in the pore solution, and alkali ions are transported toward the carbonated zone. Simultaneously, the opposite behaviour is observed for both the sulphur and chloride content. The increase in the concentration of sulphur and chloride in the pore solution was observed upon the decomposition of the solid phase. Calcium ions are transported to the carbonated zone, further increasing calcite formation near the exposed surface. •A comprehensive reactive transport modelling framework for the carbonation of cement-based materials is proposed, including multi-component gas, multi-ionic, moisture transport, and chemical equilibrium computation.•Using Henry's law, the multi-component gas transport model was developed, including gas dissolution into the pore solution.•A comprehensive description of the relationships between phase assemblage, pore structure, and mass transport is presented to account for pore structure changes on the mass transports.•An interfacial gas transfer coefficient is proposed to consider the effect of temperature on the dissolution of gas into the pore solution.•The proposed modelling framework agrees with several experimental observations provided in the literature and, moreover, provides a stringent and physical explanation for various hypotheses postulated to describe the observed carbonation process as well as the effect of the pore solution composition changes on steel corrosion.