Study of depassivation of carbon steel in simulated concrete pore solution using different equivalent circuits

Depassivation and corrosion of reinforcing steels submitted to chloride in simulated concrete pore solution was studied with electrochemical methods. Measurements included half-cell potential (HCP), linear polarization resistance (LPR) and electrochemical impedance spectroscopy (EIS). Three different equivalent circuits, i.e., R(QR), R(QR)(QR) and R(Q(R(QR))), were proposed to fit and elucidate the EIS data, respectively. Results showed that large-scale depassivation and corrosion of steel occurred when chloride content exceeded 0.05 mol/L. All the three equivalent circuits revealed a good fitting degree of Nyquist plots at early stage, while only circuit R(Q(R(QR))) still retained a most appropriate fitting at severe corrosion stage, of which the chi-square ranged from 3.1E−4 to 8.5E−4 throughout the whole exposure test. Verification could be obtained that circuit R(Q(R(QR))) with two time constants was effective to fit and explain the depassivation process in regard to steel corrosion induced by chloride in simulated concrete pore solution.