Polarization resistance measurements of bars embedded in concrete with different chloride concentrations: EIS and DC comparison

The experimental conditions for corrosion rate measurements of reinforcement by means of the polarization resistance technique, R-p, in order to obtain reliable values (in accordance with the gravimetric losses simultaneously measured) must consider some factors as are: the need to subtract ohmic drop generated by the high resistivity of the concrete, the need to wait a certain time after application of the current, the use of a certain sweep rate in order to obtain a quasi-steady-state value of the conjugated variable (potential/current), the need to avoid the overlapping with other processes, and the need to use a correct B value in Stern formula. These experimental requirements should be optimized for the individual kinetic of each system. From time to time several papers are published wondering whether R-p measurements in concrete are reliable. Present paper extends the study of the experimental conditions influence in the R-p determination in order to look more in detail to the accuracy of R-p technique. Several sweep rates in potentiodynamic tests, different waiting times with galvanostatic and potentiostatic pulses and different frequencies in electrochemical impedance spectroscopy, EIS, were tested in order to compare the most suitable parameters that provide correct values of the corrosion rate, I-corr.