CHARACTERIZATION OF SURFACE CORROSION OF REINFORCING STEEL IN CEMENT PASTE BY LOW-FREQUENCY IMPEDANCE SPECTROSCOPY

Surface corrosion of reinforcing steel embedded in cementitious materi als containing chloride ion is described by characteristic change of i mpedance spectra. Phase angle shift, surface impedance and capacitive responses, recorded at very low frequency (100Hz-10mHz), are demonstra ted to be very sensitive to surface corrosion processes. Information t hat is difficult to obtain by traditional dc techniques is provided. I t was found that longer immersion of specimens in chloride ion solutio n results in a more significant decrease of the phase angle. A modifie d equivalent circuit model considering surface corrosion of the steel- cement interface was constructed to simulate the steel surface oxidati on behavior. Circuit parameters can be used to explain the experimenta l results in a qualitative way. The low frequency impedance technique appears to be a very useful non-destructive method for assessing reinf orcing steel corrosion.