The effect of repair work on durability enhancement of RC structures under marine environment was discussed in this study. The long-term performance of surface coating was evaluated by analyzing the chloride ion profile in concrete. The long-term performance of section repair was found to be decreased by the diffusion of chloride ion, which was already contained in the existing concrete. Moreover, it was verified that removal of chloride ion from concrete or electrochemical repair before surface coating is necessary to keep the long-term performance of surface coating. Furthermore, the total repair costs were calculated under several repair conditions with the use of different repairing materials and methods. Based on the calculated costs, the life-span simulation of the repaired RC structures considering re-deterioration of the repairing materials was conducted.
　To evaluate accurately the long-term performance of repaired RC members, methods for evaluating the performance of surface coating and the structural re-deterioration of the repaired RC beams were discussed.