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CATHODIC PROTECTION

Background
Cathodic protection is a widely accepted repair technique for concrete structures. Its development has largely been empirical with the success of early trials on experimental systems resulting in its widespread acceptance. Thus the design of such a system tends to be based on previous experience. This work was undertaken to improve aspects of the theoretical basis for the design of a reinforced concrete cathodic protection system. It follows the work of an earlier project aimed at assessing the feasibility of intermittent cathodic protection.
Basis for Protection

Basis for Protection
The conventional basis for cathodic protection relies on shifting the potential of the steel to more negative values. This is achieved by polarising the cathodic reaction and will reduce the tendency for iron to dissolve as positive ions. However, it was also noted that the conventional understanding of cathodic protection needs to be extended to include the significant polarisation of the anodic reaction kinetics at the cathode induced by the applied current. A current results in a less aggressive environment at the cathode that promotes steel passivity. A significant reduction in the open circuit corrosion rate of the steel occurs. This is particularly important when the cathodic reaction kinetics are weakly polarised as is often the case for steel in concrete.