2018 Volume 67 Issue 2 Pages 83-87
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, charge transfer resistance of electrode/concrete interface, Rct, was about 1400 kΩ in the uncarbonated concrete, indicating that passive film was formed on probe electrode. The Rct in the carbonated concrete was about 80 kΩ 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 the probe electrodes was employed to evaluate the carbonation of a reinforced concrete structure on an expressway at 35 years after construction. The order of Rct was consistent with that in the uncarbonated concrete. In addition, the core was extracted from 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.