Electrochemical and Gravimetric Assessment of Steel Rebar Corrosion in Chloride- and Carbonation-Induced Environments

This study investigates the corrosion performance of reinforced steel in concrete subjected to carbonation and chloride ingress. Four systems were examined: normal concrete (NC15), chloride-exposed (ClC15), carbonated (COC15), and chloride-exposed carbonated concrete (COClC15). A comprehensive assessment was carried out using electrochemical testing, gravimetric weight loss, chloride profiling, Temkin adsorption isotherm modeling, and SEM analysis. Electrochemical results showed a marked increase in corrosion activity under combined chloride–carbonation exposure. The highest corrosion current density (icorr) was obtained in COClC15 (0.4779 µA/cm2), compared with only 0.0106 µA/cm2 for NC15. Gravimetric analysis confirmed these findings, with COClC15 exhibiting a corrosion rate nearly 1.5 times greater than ClC15 and 52 times higher than NC15 after 120 days. Chloride profiling revealed reduced binding efficiency in carbonated concrete; at 5 mm depth, COClC15 bound only 0.06% chloride, while ClC15 retained 0.43%. The Temkin adsorption isotherm further quantified the weakened binding capacity. The binding coefficient (β) of COClC15 was considerably lower than ClC15 and NC15, reflecting the impact of C–S–H decalcification and aluminate phase transformation into carboaluminates, which restrict Friedel’s salt formation. SEM micrographs corroborated these observations, showing extensive microstructural degradation in COClC15. This study revealed that the synergy of carbonation and chloride ingress reduces chloride-binding capacity, accelerates depassivation, and severely compromises the durability of reinforced concrete in aggressive environments.