Electrochemical behavior of steel in concrete and evaluation of the corrosion rate

Various electrochemical methods for evaluation of corrosion. of steel reinforcement in concrete were studied regarding their applicability in the field. Laboratory experiments were carried out with steel in synthetic pore water and in concrete blocks with chloride (Cl-) additions. Field measurements were performed at a large, coastal concrete bridge. Methods examined included manual potential mapping, automatic measurements of corrosion potential (E-corr) with embedded reference electrodes (RE), potentiokinetic linear polarization resistance (LPR) measurements with cut reinforcement bars, analysis of the shape of galvanostatic charging curves, and LPR measurements of the reinforcement with a commercial instrument containing a guard ring. Corrosion rates determined with the guard electrode (GE) instrument were not in good agreement with estimates based upon potential mapping or visual inspection. Because of the high interfacial capacitance (C) of the steel in concrete, potentiokinetic LPR measurements were ill-suited for determination of corrosion rates. Good experience was obtained by computer modeling of the galvanostatic charging curve with calculation of the polarization resistance (R-p) from this type of data. Advantages of this method were that it was influenced little by electrical resistance in the concrete and that unreliable measurements could be sorted out when curves did not follow the theoretical pattern.