Analysis of the electrochemical phenomenon at the rebar–concrete interface using the electrochemical impedance spectroscopic technique

The corrosion rate of rebar during the various stages where it occurs, such as passivation, initiation of corrosion and severe corrosion, needs to be determined non-destructively for the maintenance, restoration and replacement of concrete structures. The double layer capacitance (Cdl) and the charge transfer resistance or polarisation resistance (Rp) of the corrosion processes have been associated with the slope of the low-frequency arc in the Nyquist plot, and this can be related to the electrochemical phenomenon that occurs at the steel–concrete interface. The present studies, based on electrochemical impedance spectroscopy (EIS) conducted on three different densities of concrete with addition of 0·5 and 1% chloride over a period of 1765 days, reveal that the capacitive behaviour of a low-frequency arc with a slope more than −1 indicates the passive condition of rebar. Warburg diffusion behaviour with a slope exactly equal to −1 denotes the initiation of corrosion on the rebar. A slope of less than −1 ...