Study on Corrosion Monitoring of Rebar in Concrete Structure under Service with Electrochemical Impedance Spectroscopy.

The purpose of this study is to establish an electrochemical technique to monitor corrosion of rebar in concrete. Electrochemical impedance spectra of probe electrodes installed in uncarbonated concrete specimens and carbonated concrete specimens were measured. As a result, the charge transfer resistance of electrode/concrete interface, Rct, was about 1400 kO in the uncarbonated concrete, indicating that a passive film was formed on the probe electrode. Rct in the carbonated concrete was about 80 kO, and this value was 20 times smaller than that measured in the uncarbonated concrete. From these results, it was found that carbonation of concrete can be judged by the impedance measurement with probe electrodes. Electrochemical impedance spectroscopy with probe electrodes was employed to evaluate the carbonation of a reinforced concrete structure on an expressway 35 years after construction. The order of Rct was consistent with that in the uncarbonated concrete. In addition, the core was extracted from the concrete near the probe electrodes and a carbonation test with a phenolphthalein solution was performed. As a result, the concrete at the same depth as the rebar was not carbonated. The results of electrochemical impedance spectra and phenolphthalein test were consistent. It was found that the corrosion environment of the rebar in the concrete can be evaluated by the impedance measurement with probe electrodes. [ABSTRACT FROM AUTHOR]