The corrosion potential measurement and Electrochemical Impedance Spectroscopy （EIS） are explained for the observation of the corrosion of reinforced steels in concrete. In the case of environment factors in concrete, the measurements for the concentration of chloride ions and pH are applied. Besides, by using the actual concrete block, the corrosion of the steel and environmental factors are measured by these methods, and the meaning of the results are explained. Finally, the electrochemical methods are shown in the application for the actual concrete bridge.

Electrochemical measurement methods for studying metallic corrosion in a simulated soil are described. First of all, the characteristics of soil corrosion are briefly explained, and then the electrochemical cells for studying the soil corrosion in laboratory is illustrated. Finally, some examples of the electrochemical measurements results are shown.

This research aimed to confirm the formation of Fe₃O₄ film on Fe immersed in aqueous 45 mass％ NaOH solution containing some oxidants at the boiling temperature, to recognize the optimum immersion time for the formation of thick and protective film, and to reveal the absorption behavior of D₂O in the Fe₃O₄ film at room temperature. The results were obtained as follows. It was confirmed that Fe₃O₄ film was formed on Fe immersed in the NaOH solution for a time more than 0.6 ks, and the film thickness increased parabolically with an increase in the immersion time. D₂O absorption test was carried out to the films formed in the NaOH solution for immersion times of 1.2 and 3.6 ks. An amount of D₂O absorbed into the film increased with an increase in an absorption time up to 1000 ks, and an absorption time more than 1000 ks made an amount of D₂O constant. The constant amount of D₂O was larger for the film formed on Fe immersed in the NaOH solution for 3.6 ks than that for 1.2 ks. The transient of the amount of D₂O absorbed into the film was analyzed on the basis of Fick’s law for diffusion, and diffusion coefficients of D₂O were obtained to be 5.1×10^－15 and 9.9×10^－15 cm²･s^－1 for the films formed for 1.2 and 3.6 ks, respectively. Therefore it was estimated that the diffusion coefficient of the Fe₃O₄ film was in the region from 5.1×10^－15 to 9.9×10^－15 cm²･s^－1.

In-situ measurement of electrical conductivity of solution within crevice of SUS316L stainless steel in 288℃ water has been conducted with newly developed electrochemical sensor system. The sensor consists of electrode （φ≈ 250μm stainless steel） and insulator （high purity alumina） directory imbedded into crevice former plate. The sensor measures local electrical conductivity of crevice solution beneath the electrode （κ_crev） with electrochemical impedance method. The sensors were installed at different positions within tapered crevice of SUS316L stainless steel. The crevice specimen with the sensors were immerged into 288℃, 8 MPa, pure oxygen saturated high purity water for 100 h. κ_crev at a position with crevice gap（g） of ≈ 59.3μm was 8～11μS･cm^－1, least deviate from conductivity of 288℃ pure water （3.7μS･cm^－1） and no localized corrosion occurred. On the contrary, κ_crev at a position with g ≈4.4μm increased with time and showed maximum value of ≈1600μS･cm^－1 at 70 h. Localized corrosion occurred in the vicinity of this position. Thermodynamic equilibrium calculation based on oxide in the crevice and the maximum κ_crev（1600μS･cm^－1） showed that pH of crevice solution can be reached to 3.53. It can be concluded that acidification occurred in tight crevice even under high purity bulk water and resulted in localized corrosion.