The Effects of Chloride, Nitrate, and Nitrite on the Localized Corrosion of Carbon Steel in Simulated Concrete Pore Solutions

Localized corrosion is a precursor to the deterioration of carbon steel reinforcing bars in concrete. The localized corrosion of carbon steel in simulated concrete pore solutions was investigated by cyclic potentiodynamic polarization (CPP) technique. A four-factor, two-level, full factorial design and a five-factor, two-level, Plackett-Burman design were used to study the effects of OH⁻, Cl⁻, ⁠, ⁠, with Na⁺ and Ca²⁺ cations on the localized corrosion of carbon steel. The results show that the occurrence of localized corrosion can be evaluated by the type of CPP curves (negative, mixed, or positive hysteresis) and the difference between the open-circuit and repassivation potentials (OCP-E_rp). The lowest (OCP-E_rp), indicating a low risk of pitting corrosion, could be obtained with high OH⁻, high ⁠, and low Cl⁻, whereas the effect of was not significant. The corrosion activities near the OCP were measured using linear polarization resistance and electrochemical impedance spectroscopy methods. They indicated that $NO2−$ and Cl⁻ were the main factors influencing the corrosion rate. The cationic species did not have a significant influence on the electrochemical parameters.