Investigation of the local response of the steel-concrete interface for corrosion measurement

An equivalent circuit representation for the steel-concrete interface is determined from direct potential measurements at the steel surface. The local response of steel-concrete interface to a given polarization applied at the concrete surface is investigated using an Ag/AgCl embedded reference electrode and a test system which allows simultaneous measurements at the steel-concrete interface and on the concrete surface. It is shown that the impedance spectrum on Nyquist plot for the steel-concrete interface comprises of a single arc. The equivalent circuit representation of the steel-concrete interface comprising of a parallel combination of a constant phase element (CPE) and a resistance was found to be suitable for representing the observed frequency response above 10 mHz. The parameters for the equivalent circuit obtained from the frequency-domain impedance measurements are shown to provide close prediction of the transient time-domain response from a linear polarization resistance measurement. The equivalent circuit was found to be suitable for interpreting the transient response of the steel-concrete interface during the linear polarization measurements. Available results indicate that while the response of steel undergoing active corrosion exhibits a distinctive CPE behavior, the passive steel approaches a pure capacitor. The value of resistance when the measured current increases linearly with time during a linear polarization measurement from the concrete surface provide acceptable measurements of the charge transfer resistance, and the Ohmic resistance of the concrete. (C) 2009 Elsevier Ltd. All rights reserved.