This paper aims to measure the change in corrosion rate over time of reinforcing steel inside concrete, including reinforced concrete (RC) after crack initiation. The corrosion rate is important information for residual life assessment of RC structures. In some previous studies, corrosion rate of RC specimens before crack initiation was evaluated using the polarization resistance method. However, few studies have considered application of the method for specimens after crack initiation, and evaluated the change of corrosion rate over time. In this study, we measured the corrosion rate of reinforcing steel inside concrete after crack initiation and after crack repair every 1-3 months for 2.5 years using the AC impedance method. As a precision test, we removed the steel bar out from specimens to measure the corroded area of the steel surface and corrosion mass loss. Our findings revealed that the corrosion rate could be calculated precisely by setting the measurement area of the steel surface to the corroded area when the steel was corroded locally. In addition, the measurement results showed that the corrosion rate of the steel inside the concrete under a salt environment increased with time after crack initiation, whereas the increase rate of corrosion rate became smaller over time. And an early crack repair can delay corrosion initiation and decrease corrosion rate of reinforced concrete. Based on these results, we proposed the prediction method of corrosion progress of reinforcing steel inside concrete over the entire service period.
