Properties at Corrosion Sites Formed on Pure Iron during Wet-dry Cycling Test and on Steel during Exposure Test

Steels are widely used as a structural material for infrastructure, such as bridges. However, some of bridges built in Japan, have passed more than 50 years, since construction. Thus, these bridges will need to be reconstruction, because atmospheric corrosion of these materials will occur in this condition. However, there are numerous bridges in Japan, and reconstruction of these bridges would need much cost. Therefore, it is necessary to establish the technique for selection of the bridges with severe damage by atmospheric corrosion. To establish a new non-destructive and non-contact techniques for identifying the sites of atmospheric corrosion occurred in steel, used as structural materials for bridges, the relation between corrosion site and color of corrosion product, surface morphology or distribution of surface potential of the pure iron and steel after corrosion test were evaluated. Pure iron specimens after wet-dry cycling test with NaCl solution to simulate the atmospheric corrosion, and steel after exposure test, were observed, in this study. From these results, there is a good matching between the site of corrosion and color of corrosion product and distribution of surface potential for pure iron after wet-dry cycling test. On the other hand, there is a good relationship between the site of corrosion and distribution of surface potential for steel after exposure test.