Estimation of steel corrosion rate in reinforced concrete by means of equivalent circuit fittings of impedance spectra

Abstract

Three equivalent circuit models were utilized to fit the alternating current (AC) impedance spectra obtained from the 5-year-old, ‘lollipop-like’ reinforced concrete samples. The RC parameters obtained from two of the equivalent circuit fittings were compared. Specifically. the differences in polarization resistance, Rp, and double layer capacitance, Cdl, were evaluated and the variation in the values ol these elements found to be up to 70%. These two parameters were also determined from the fitting of the low-frequency portion of the corresponding impedance spectrum for the third equivalent circuit, and the differences were within 40%. The other RC parameters and their relationship with Rp, were also discussed. Finally, the corrosion rates ol the ‘lollipop-like’ samples. determined from both the AC impedance and linear polarization methods. were compared and the differences in this study found to be about 100%.