Effect of carbonization on chloride penetration in rapid repair mortar derived from solid waste-based CSA cement

The development of highly corrosion-resistant rapid repair mortar (RRM) for marine concrete is of great importance, particularly given the significant role that Cl^- corrosion plays in the deterioration of marine construction materials. In this work, the penetration effects of Cl^- in RRM derived from solid waste-based CSA cement was experimentally characterized. The impact of carbonization and the incorporation of hydrothermal carbon on the anti-Cl-permeation characteristics was investigated. The evolution of the mineral phase composition and microstructure of the RRM in response to Cl^- corrosion was analyzed. The results showed that ettringite in RRM was transformed into an unstable Cl-ettringite with elevated Cl^- concentrations, which subsequently decomposed into minerals such as zunyite. Nevertheless, ettringite adsorbs chloride onto its surface at low Cl^- concentrations, thereby impeding the diffusion of Cl^-. Carbonization reduced the resistance of RRM to the penetration of Cl^- in two ways: firstly, ettringite is carbonized to produce minerals such as CaCO₃ and CaSO₄∙2 H₂O, which reduces the binding capacity of RRM for Cl^-; secondly, carbonization results in smaller pore spaces and higher connectivity, which enhances capillarity and facilitates the penetration of the solution to the interior. The addition of hydrothermal carbon can improve the binding capacity of RRM for Cl^-, but does not prevent the carbonization process.