Chloride Adsorption Capacity of Monocarbonate: The Importance of Iron Doping

Resistance to chloride penetration is a concerned durability issue to ordinary Portland cement (OPC) based materials used in the marine environment. Monocarbonate has become an increasingly common hydration product observed in OPC-based materials and plays an important role in chloride adsorption. The Portland cement used in ocean engineering has a notably higher C₄AF content than C₃A, and C₄AF has become a particularly important aluminate phase in it. However, few studies have focused on the discrepancy in the chloride-binding capabilities of C₃A hydrates and C₄AF hydrates. The objective of this paper is to study the discrepancies in chloride adsorption between undoped and Fe-doped monocarbonates. The results suggest that the Fe-doped C₄(A,F)C¯ H₁₁exhibits superior chloride adsorption than undoped C₄AC¯ H₁₁because the doping of Fe weakens the restriction of the surrounding hydrogen bond connected to CO₃^2-in its interlayer. A pseudo-second-order kinetic model is more suitable for the characterization of the chloride adsorption process on monocarbonates. Freundlich isotherm is favorable to fit the experimental data of chloride adsorption by the monocarbonate. This study holds great promise for improving the chloride penetration resistance of Portland cement.