Cathode protection is one of the effective, well known, and extensively used methods for prevention of corrosion in concrete structures in more advanced countries. Due to high cost and long term monitoring required for this method, it is not very much used in India.
The cathode protection comprises of application of impressed current, to an electrode laid on the concrete, above steel reinforcement. This electrode serves as anode and the steel reinforcement, which is connected to the negative terminal of a DC source acts as a cathode.
In this process, the external anode is subjected to corrode and the cathode reinforcement is protected against corrosion and hence the name 'Cathode Protection'.
In this process, the -ve chloride ions, which are responsible for the damage of the passivating film, are drawn away from the vicinity of steel towards the anode, where they are oxidized to form chlorine gas.
The other recent development in corrosion control methods are Re-alkalization and De-salnation. The re-alkalisation process allows to make the concrete alskline again and passivate the reinforcement steel, by electro-chemical method. This brings back the lost alkalinity of concrete of sufficiently high level to reform and maintain the passive layer on the steel.
In the desalination process, the chloride ions are removed form the concrete, particularly from the vicinity of the steel reinforcement by certain electrical method to re-establish the passive layer of the steel.
It appears that the application of cathodic systems for protection of concrete structures, offers some real hope to the concrete technologist, but the field remains open for the introduction of innovative methods to overcome problems of both technique and cost.