Accelerated corrosion tests need to ensure compatibility between acceleration of corrosion and reproduction of atmospheric corrosion in actual coastal environments. However, gordaite, a highly protective zinc-corrosion product, is not produced in cyclic corrosion tests using general NaCl aqueous solutions. Moreover, the ratio of the corrosion rates of steel/zinc after those tests is too small compared to that after outdoor exposure. Conversely, when artificial seawater is used, the corrosion products contain too much gordaite, and the ratio of corrosion rate of steel/zinc is too large compared with that for outdoor exposure. With these solutions, the corrosion resistance of zinc is underestimated or overestimated. Therefore, we developed a new test solution for reproducing the atmospheric corrosion behavior of zinc in coastal area. The solution enables us to evaluate corrosion resistance of zinc-rich paint and galvanized steel in coastal areas more accurately than other solutions do.

In this study, the corrosion behavior of zinc in a simulated soil environment was investigated at various degrees of saturation, S_r by using surface observation, corrosion depth analysis, electrochemical impedance spectroscopy, and potentiodynamic polarization tests to evaluate the effect of soil moisture on corrosion morphology and corrosion rate and of zinc. At high soil moisture content （S_r＞80％）, the average corrosion rate of zinc remained low and did not change much with S_r. On the other hand, at low moisture content （S_r＜80％）, the average corrosion rate increased significantly and showed a peak at around S_r＝50％. In addition, the corrosion morphology of zinc became more heterogeneous with decreasing S_r, indicating that the corrosion depth became deeper. The effects of soil moisture on the corrosion morphology and corrosion rate of zinc were discussed based on the changes in cathodic reduction of oxygen and anodic reaction of zinc in a simulated soil environment.