Evaluation of electrochemical impedance with constant phase angle component from the galvanostatic step response of steel in concrete

A current step excitation method for obtaining the parameters of a system characterized by a solution resistance R(s) in series with the parallel combination of a polarization resistance Rp with a constant phase angle element (cpe) is described. The cpe has a base admittance Y-0 and a frequency exponent n. A numerical procedure is developed to obtain the value of the system parameters (Rp, Y-0, n and R(s)) by analysis of the potential response of the system to the current excitation step. Experiments with specimens of galvanized steel in concrete are reported in which the galvanostatic step technique is applied and the analysis procedure is performed. Good agreement with the results of independent electrochemical impedance spectroscopy (EIS) of the same specimens is demonstrated.