Computer Modeling of Effect of Corrosion Macrocells on Measurement of Corrosion Rate of Reinforcing Steel in Concrete Available to Purchase

The corrosion rate of steel in concrete can be significantly underestimated if corrosion is non-uniform, because of short-range uneven distribution of the excitation current during polarization measurements. This effect occurs in addition to large scale current distribution problems originating from the use of small counter electrodes or similar causes. Short range macrocells create zones that at low frequencies have much smaller interfacial impedance than the remainder of the steel. However, the impedance is small and uniform at high frequencies due to the presence of interfacial capacitance. The resulting variation of current distribution pattern with frequency prevents correct application of solution resistance compensation techniques. Finite difference computation of current distribution are combined with matrix analysisof the a.c. current distribution to illustrate this behavior. Calculations of the degree to which corrosion is underestimated as a function of system parameters are presented.