Principle 9 & 10 - Cathodic Control & Protection
Principle 9 concentrates on creating conditions in which potentially cathodic areas of reinforcement are unable to drive an anodic reaction. This relies upon restricting the access of oxygen to all potentially cathodic areas to the point when corrosion is prevented. An example of this is to limit the available oxygen content by the use of coatings on the steel surface Another is the application of an inhibitor in sufficient quantities, that can form a film on the steel surface which acts as a barrier to block access to oxygen.
Principle 10 refers to cathodic protection systems. An article that provides an in-depth overview of cathodic protection and sacrificial anodes can be found here. These are electrochemical systems which decrease the corrosion potential to a level where the rate of the reinforcing steel dissolution is significantly reduced. This can be achieved by creating a direct electric current flow from the surrounding concrete to the reinforcing steel, in order to eliminate the anodic parts of the corrosion reaction. This current is provided by an external source (Induced Current Cathodic Protection), or by creating a galvanic current through connecting the steel to a more reactive metal (galvanic anodes e.g. zinc).
In Induced Current Cathodic Protection, the current is supplied by an external electrical source and is distributed in the electrolyte via auxiliary anodes (e.g. mesh placed on top of and connected to the reinforcing steel). These auxiliary anodes are generally embedded in a mortar in order to protect them from degradation. To work efficiently the system requires the surrounding mortar to have a resistivity low enough to allow sufficient current transfer.
Komerco are suppliers of industry leading sacrificial (galvanic) anodes and accompanying embedding grouts: