The combined effects of carbonation and chloride attack can accelerate the degradation of reinforced concrete (RC) structures. In this study, the effect of natural carbonation on the chloride binding behaviours in Ordinary Portland cement (OPC) paste was investigated. The phase-equilibrium model for the dissolution/precipitation reactions and the surface complexation model for the ionic adsorption of C–S–H were adopted. An experiment from the literature was used as the benchmark. The results indicate that Kuzel's salt is produced when OPC paste is exposed to a mild chloride attack. During the natural carbonation process, Kuzel's salt is converted into Friedel's salt. As the carbonation continues, the Friedel's salt disappears. Complete natural carbonation results in a total loss of chemical binding capacity, and only a partial loss of the physical binding capacity in cement-based materials. This completely differs from the accelerated carbonation commonly used in the laboratory, which can cause complete loss of both chemical and physical binding capacity. Therefore, the durability design of RC structures vulnerable to the combined attack of chloride and carbonation based on the results of the accelerated carbonation is conservative.

Impressed current cathodic protection (ICCP) is an effective and direct method for controlling the corrosion of reinforced concrete (RC) structures. However, few investigations related to ICCP in cracked RC structures have been reported. In this study, the effect of cracks in concrete cover on ICCP of chloride-contaminated RC structures was investigated through a numerical model including steel polarisation, electrode reactions, and ionic migration. In the developed numerical model, cracked concrete cover is assumed to consist of sound concrete and cracks, and cracks have their own ionic diffusion coefficients. The results indicate that the ICCP can maintain its ability to remove Cl⁻ if concrete cover does not completely crack. Once the complete cracking in concrete cover occurs, the Cl⁻ removal ability of ICCP would decrease or even disappear. Cracking does not cause any adverse effect on the pH improvement of ICCP. In this case, a stronger cathodic polarisation is recommended.