Principle 11 - Control of Anodic Areas
Principle 11, The Control of Anodic Areas focuses on preventing corrosion of the steel reinforcement by creating conditions in which potentially anodic reactions of reinforcement are unable to take part in the corrosion reaction.
In considering the control of anodic areas to prevent corrosion with Principle 11, it is important to understand that particularly in heavily chloride contaminated structures, spalling due to reinforcement corrosion happens first in areas of low concrete cover. Additionally it is also important to protect repaired areas from the future ingress of aggressive agents (carbonation, chlorides). A protective cement slurry can be applied directly on the reinforcement after appropriate cleaning, to prevent further steel dissolution at the anodic areas. Additionally, to protect against the formation of incipient anodes in the areas surrounding the patch repairs, a corrosion inhibitor can be applied to migrate through the concrete and reach the reinforcement, where it forms a barrier, also protecting the anodic zones.
The control of anodic areas is undertaken by three methods:
Method 11.1 - Active coating of the reinforcement
Active coatings, which contain Portland cement or electrochemically active ingredients, which may function as inhibitors or which may provide localised cathodic protection. Komerco's active coatings include MasterEmaco P5000AP and Sika MonoTop 910.
Method 11. 2 - Barrier Coating of the reinforcement
These barrier coatings work by completely isolating the reinforcement from oxygen or water. Therefore they require higher levels of surface preparation and application control. This is because they can only be effective if the steel is completely free from corrosion and fully coated without any defects – this can be very difficult to achieve in site conditions. Any effective reduction in the bonding of the repair material to the treated reinforcement should also be considered. Komerco's barrier coatings include Sikadur 32 and MasterEmaco 2525.
Method 11.3 - Applying corrosion inhibitors in or to the concrete
Applying corrosion inhibitors to the concrete surface, they diffuse to the reinforcement and form a protective layer on the surface of the bars. These corrosion inhibitors can also be added as admixtures to the repair mortar or concrete that is used for the concrete reinstatement works. For repair mortars or materials that contain corrosion inhibitors then generally speaking look for 'FG' in the Sika range of products and 'CI' for MBS range of products. Importantly refer to the TDS and/or a Komerco representative.
Corrosion inhibitors that can be applied to the surface of concrete include: