The time-domain response of a corroding system with constant phase angle interfacial component: Application to steel in concrete

Abstract

The time-domain response of reinforcing steel in concrete during a polarization resistance test was examined based on the electrochemical impedance spectroscopy behavior of the system. The analysis considered the effect of apparent interfacial capacitances that approached the behavior of a constant phase angle element (CPE). The response of an interface behaving as the parallel combination of a polarization resistance and a CPE was examined analytically. The calculations showed that significant error could develop in the estimation of corrosion rates from the apparent polarization resistance obtained during a potential scan experiment. The predicted error was largest when corrosion rates were small. The error could be significant at commonly used potential scan rates (0.1 mV s −1) and constant phase element exponents (0.7 < n < 0.9) typical of steel in concrete. A numerical model was developed to predict the time domain behavior for the combined case of solution resistance, polarization resistance, and CPE. The model predictions were confirmed using actual specimens of passive plain and galvanized steel in concrete.