A study on chloride-induced depassivation of mild steel in simulated concrete pore solution

The effect of chloride ions on passivity breakdown of steel in simulated concrete pore (SCP) solution was studied using electrochemical techniques. In this regards, the sensitivity of cyclic potentiodynamic parameters such as ΔE (difference between Epit and Erep), ipeak and AC-impedance parameters like Rct, Rf, Ci, Rad and Cad to chloride ion concentration was investigated. Adsorption of OH− ions on the metal surface in free chloride SCP solution and also displacement of those ions by Cl− ions were demonstrated in high frequency part of Nyquist plots. In addition, a severe decrease in resistance of interfacial reaction (Rf+Rct) was observed through breakdown of passive film in the [Cl−]/[OH−] ratio of 0.6. The interfacial capacitance, Ci, was abruptly raised when localized corrosion changed to general one.