How do cathodic protection systems work in concrete?
Cathodic protection (CP) is the oldest and most proven electrochemical technology applied to reinforced concrete structures. Cathodic protection promotes the development of steel passivity as a result of the production of hydroxyl ions at the steel-concrete interface to stabilise the protective passive film. In addition, the direct effect of CP includes shifting the steel potential to more negative values, which inhibits the corrosion of iron, and removes the chloride ions away from the steel toward the anode.
There are various types of impressed current anodes applied to atmospherically exposed reinforced concrete. In Australia, the most commonly used types of anodes are Mixed Metal Oxide (MMO) mesh or ribbon anodes in a cementitious overlay or in grout filled chases and MMO discrete anodes embedded in drilled holes in the concrete.
For submerged reinforced concrete structures, impressed current anodes are normally located in the surrounding water or soil.
For impressed current CP systems, it is essential that the system is regularly monitored as a part of the maintenance program of the asset.
Impressed current cathodic protection technology has gained very rapid acceptance in Australia over the past 25 years. As a result, many structures suffering from chloride induced corrosion are protected by cathodic protection systems.
Key features of this technology are:
Environmentally friendly: Major reduction of concrete breakout.
Maintenance: Regular monitoring is essential to ensure the optimum operation of the system.
Long term global/local protection: Provides effective treatment for the entire area of application. Areas of high level of corrosion can be targeted with localised CP application.
Proven technology: Long history and an excellent track record.
Our recommended application:
Chloride contaminated structures in marine environments and in particular tidal, splash and atmospheric zones (wharves, dolphins, bridges.. etc).
Structures with high corrosion activities or/and constant exposure to chloride ingress.
Structures where long term reliable and effective corrosion protection is required.
Standard: Australian Standard AS 2832.5-2008 – Cathodic protection of metals Part 5: Steel in concrete structures.