Basic principles of electrochemical techniques

All of these treatments are suitable for reinforcing steel in concrete. However, the passing of electric current and of the voltages used can have adverse effects on concrete and on steel. They can only be applied with great 

Impressed current cathodic protection works passing a small direct current (DC) from a permanent anode on top of or fixed into the concrete through the concrete to the reinforcement. The power supply passes sufficient current from the anode to the reinforcing steel to force the anode reaction (7.1) to stop  

The reinforcement network then becomes cathodic and corrosion is suppressed. However, another cathodic reaction can occur if the potential gets too negative  

The problems of hydrogen embrittlement and of gas evolution are usually controlled by limiting the potential of the steel to below the hydrogen evolution potential. However, in acidic pits or crevices it may be possible for the potential to exceed the hydrogen evolution potential without being sensed by measuring electrodes. The cathodic protection of prestressed structures should only be undertaken with great care and input from experienced corrosion experts. An excellent state-of-the-art report on the cathodic protection of prestressed has been published (NACE, 2001). 

The generation of hydroxyl ions in equations (7.2) and (7.3) will increase the alkalinity and help to rebuild the passive layer where it has been broken down by the chloride attack. 

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