Cathodic Protection

The Gunite Group prides itself on being one of the founder members of the Concrete Repair Association and as a market-leading innovative specialist contractor Gunite can assist you with your corrosion prevention and cathodic protection requirements.

In brief, corrosion of embedded steel reinforcement is a chemical reaction occurring by an electrochemical mechanism (a redox reaction) During corrosion there are two main reactions, oxidation, where electrons leave the metal (and results in the actual loss of metal) and reduction, where the electrons are used to convert water or oxygen to hydroxides).

As corrosion takes place, oxidation and reduction reactions occur and electrochemical cells are formed on the surface of the metal so that some areas will become anodic (oxidation) and some cathodic (reduction).

Electrons flow from the anodic areas into the electrolyte as the metal corrodes. Conversely, as electrons flow from the electrolyte to the cathodic areas the rate of corrosion is reduced. The flow of electrons is in the opposite direction of the flow of electric current.

Cathodic protection is used to prevent and reduce corrosion rates within reinforced concrete structures. Corrosion of embedded steel reinforcement is an electrochemical process resulting from the formation of cathodes and anodes at different positions on the surface of the reinforcement.

Cathodic protection works by connecting the reinforcement to another material that is anodic in relation to it. The reinforcement becomes a cathode, and its corrosion rate is greatly reduced.

The Gunite Group, design and install two main systems: sacrificial anodes and impressed current systems.

In sacrificial anode systems, the material of the anode is more reactive than the metal in the structure, for example zinc or magnesium; the anode is consumed and slowly deteriorates in preference to the embedded steel reinforcement.

In impressed current systems, the anode material itself may be inert but is maintained in an anodic state relative to the structure by being connected to the correct pole of a constant direct current power supply. The anode is distributed over the surface (either an inert metal mesh or a conductive coating) or many discrete anodes are fixed in drilled holes within the concrete.

It is usual to carry out a commissioning survey once the impressed current system has been activated to check that the reinforcement is achieving the required degree of polarisation. Often a permanent monitoring system is installed to check that the system is continuing to operate successfully over time.