In the present study, we developed a new method to determine the degradation of concrete using the cylindrical steel probes by EIS. Figure 1 shows the cylindrical steel probes developed in the present study. These probes have 10 mm diameter and 8 mm thick. These probes are embedded in concreate and the electrochemical impedance is monitored. We expect that the degradation of concreate can be determined by monitoring of the electrochemical impedance of the cylindrical steel probes. In order to establish the proposed monitoring method, the electrochemical impedance of the cylindrical steel probes embedded in concreate was measured. The size of concrete specimen was 100 mm × 100 mm × 200 mm. The two holes were drilled on the concrete surface of 100 mm × 200 mm. The diameter of each hole was 10 mm. The distance between both probes was 50 mm. The probes were embedded in these holes and fixed by the epoxy resin. The depth of the probes embedded in concrete specimen was 2.0 mm, 5.0 mm and 10 mm. The concrete specimen was immersed in 10 % sodium chloride aqueous solution. Figure 2 shows a schematic diagram of the measurement system. The air was continuously provided by pump during the immersion of the concrete. The electrochemical impedance was automatically monitored at 10 kHz and 10 mHz using a corrosion monitor (Corp. i-pec, CEM-100A) by two electrode system. The potential amplitude was 10 mV.
The charge transfer resistance Rct was estimated from the impedance of the cylindrical steel probes measured at 10 kHz and 10 mHz. The degradation of concreate was discussed based on the changes of values of Rct with time.
 J. L. Dawson, L. M. Callow, K. Hladky and J. A. Richardson, Corrosion/78, No-125 (1978).