Reinforcement is vulnerable to corrosion when the concrete cover above it is missing, contaminated with chlorides, carbonated, has insufficient thickness, or has been damaged by impact or erosion. Corrosion of reinforcement can cause damage to the concrete, so it is common practice to address the repair and protection of reinforcement simultaneously. This involves repairing damaged concrete and applying protective layers, among other techniques.
The EN 1504-9 standard lists principles and methods of repair and protection related to reinforcement pathologies, including protecting or restoring passivation (Principle 7, Method 7.1-7.5 of the EN 1504-9 standard), increasing the electrical resistance (Principle 8 of EN 1504-9), modifying the cathodic region (Principle 9 of the EN 1504-9 standard), cathodic protection (Principle 10 according to the EN 1504-9 standard), and anodic area treatment (Principle 11 of the EN 1504-9 standard).
The following are some of the principles for ensuring the protection and repair of the reinforcement. See more on the Technology Guide from ACRP:
1. Increase the thickness of the covering layer of reinforcement
The thickness of the reinforcement cover layer can be increased by adding cement mortar or concrete to create an alkaline environment around the reinforcement and prevent corrosion. This method requires the use of mortars or concretes with Portland cement, or a similar binder providing sufficient alkalinity and cannot be used with other binders such as magnesium phosphate cements, aluminate cements, or polymeric binders.
2. Replacement of contaminated or carbonated concrete
A contaminated or carbonated concrete that is no longer protecting the reinforcement from corrosion can be replaced by removing the carbonated concrete near it. Corroded materials must be removed from the reinforcement, and heavily affected reinforcement must be replaced with new reinforcement. Then, high alkalinity repair materials can then be used to passivate the reinforcement against corrosion. As with the previous method, this procedure requires the use of mortars or concretes with Portland cement or a similar binder providing sufficient alkalinity.
3. Electrochemical re-alkalization of carbonated concrete
The electrochemical re-alkalization of carbonated concrete involves attaching a conductive fibre mat to the surface of the concrete and saturating it with a suitable alkaline solution. A direct current source is attached to the mat on one side and the weakened reinforcement on the other, causing ions to migrate under the action of the electric field contained in the alkaline solution into the carbonated concrete, increasing its alkalinity.
4. Re-alkalization of carbonated concrete by diffusion
The re-alkalization of carbonated concrete by diffusion involves applying a suitable alkaline solution to the surface of the carbonated concrete, which penetrates the concrete structure by diffusion induced by the concentration gradient of the solution.
This method depends on the existence of conditions that allow sufficient diffusion and on the ability of the repaired layer to prevent corrosion of the reinforcement by its alkalinity during the required design life of the element.
If you want to know more about this list, visit the Guide about Technologies of repair and reinforcement of concrete structures.