Vector Corrosion Blog
How Does Impressed Current Cathodic Protection Work in Concrete RepairNovember 6th, 2019 in Cathodic Protection
A major contributor to concrete deterioration is corrosion of embedded metals. In particular, corrosion of reinforcing steel, corrosion of epoxy coated steel, and corrosion of prestressed concrete when unchecked can eventually lead to major rehabilitation costs or structure replacement.
Cathodic protection is a proven solution to make new and existing structures last longer. Concrete repair alone is not a long–term solution when corrosion is the source of the deterioration. After repairing corrosion–induced spalls and delaminations, there will likely still be chloride–contaminated concrete surrounding the rebar in areas adjacent to the chloride–free patch repair. Unfortunately, this situation can lead to the initiation of secondary corrosion sites in areas around the repair.
To provide a longer–term solution, there are various cathodic protection methods available. All of the systems are similar in that they deliver a protective current to the reinforcing steel but have different advantages and uses.
Impressed Current Cathodic Protection (ICCP) systems consist of anodes that are connected to a power source to provide a perpetual source of electrical flow. This process prevents corrosion by converting all of the anodic (active) sites on the metal surface to cathodic (passive) sites by supplying electrical current (or free electrons) from an alternate source. ICCP systems are designed by qualified and experienced National Association of Corrosion Engineers (NACE) CP4 Cathodic Protection Specialists or The Institute of Corrosion (ICorr) CP Level 3 Senior Cathodic Protection Engineer.
ICCP systems consist of permanent inert galvanic anodes, such as MMO titanium mesh and ribbon, conductive ceramics or conductive coatings and an external DC power source to supply sufficient current is delivered to the steel to overcome the natural concrete corrosion activity.
A galvanic anode is the main component of a galvanic cathodic protection (CP) system used to protect buried or submerged metal structures from corrosion. They are made from a metal alloy with a more "active" voltage (more negative reduction potential / more positive electrochemical potential) than the metal of the structure. The difference in potential between the two metals means that the galvanic anode corrodes, so that the anode material is consumed in preference to the structure.
The loss (or sacrifice) of the anode material gives rise to the alternative name of sacrificial anode.
Corrosion is a chemical reaction occurring by an electrochemical process. During corrosion there are two 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.
In most environments, the hydroxide ions and ferrous ions combine to form ferrous hydroxide, which eventually becomes the familiar brown rust.
As corrosion takes place, oxidation and reduction reactions occur and electrochemical cells are formed on the surface of the metal. These surface deposits start to take up more space than it did before the corrosion, expanding inside the concrete and causing the concrete to crack or crumble or flake. When this happens, the integrity of the structure is compromised and is no longer as strong as it was before corrosion set in.
Impressed Current Cathodic Protection stops the corrosion of the metal inside the concrete. A current is connected to the concrete structure and electrons flow from outside the concrete to inside the concrete. This constant current stops the destructive chemical reactivity of the corroding reinforcing rebar. Impressed Current Cathodic Protection requires some monitoring and maintenance, but it’s an efficient system that extends the service life of concrete structures for 25+ years or more.
Vector Corrosion Technologies is the leading supplier of corrosion mitigation products and services for reinforced concrete and masonry structures like buildings and bridges. We have offices in Canada, the UK, and USA. If you have any questions about this article or would like to talk to us about corrosion protection for your structure, please email us at firstname.lastname@example.org or use the form on our Contact page.