For efficient and effective maintenance of reinforced-concrete structures, it is necessary to accurately diagnose and assess the state of corrosion of steel material in target structures. Nondestructive inspections are performed for this purpose, and a continuous monitoring technique using electrochemical measuring methods is drawing attention.

For measuring the half-cell potential and polarization resistance of steel material in concrete, noble-metal reference electrodes are generally used as sensors. However, the heterogeneity of concrete components and the environment inside an electrode make accurate measurement of half-cell potential and polarization resistance difficult. Therefore, in this research, we used internal-liquid reference electrodes to develop an embedded-type, 3-electrode sensor, which can accurately measure half-cell potential and polarization resistance.

To develop the sensor, we took the following two steps: In step 2, we used concrete specimens with different constituent ratios.

We measured impedance spectra using the electrochemical impedance spectroscopy to determine the effects of chloride-ion concentrations on the spectra. The following graph indicates the results. The figure's legend indicates cement type-water/cement ratio of concrete-concentration of chloride ions in concrete. The order of amplitude of each impedance spectrum was N-60-0>N-60-2>N-60-10. This result indicates the trend that the inclusion of chloride ions reduces the polarization resistance of steel material.

This research suggested that the 3-electrode sensor could be used for a practical continuous monitoring technique using electrochemical measurement methods.