Cathodic Protection for Rebars in Concerete

There has been a growing demand of cathodic protection (CP) for the rehabilitation of salt damaged concrete structures. A brief introduction is given for the major CP systems used for concrete structure and the criteria of protection. In the present paper discussion is also given on the mechanism of protection, materials flow and electrical conduction within concrete, a solid system with low mobility and high electrical resistivity placed in atmosphere. Cathodic polarization protects steel reinforcement not only by shifting the metal potential in cathodic direction but also by modifying the environment factors favorable for steel protection such as an increase in pH and a decrease in chloride ion in the vicinity of metal surface resulting in protection conditions that satisfy the criteria. The environmental modification is thought to be the principal effect of CP. It is not seldom in concrete CP that a system that has been in operation below the criteria in the early stage would be changed to be satisfactory after long run owing to the modified environments. It is thus required to establish design and maintenance criteria in consideration of chronic changes.