What Does Realkalization Mean?
Realkalization is a concrete treatment process used to combat carbonation-induced corrosion of steel in concrete.
When CO2/CO from the atmosphere penetrates into concrete and reacts with calcium hydroxide to form calcium carbonates, it is known as carbonation. CO2/CO in the presence of moisture converts to carbonic acid and attacks concrete, which reduces the alkalinity of concrete. The process of realkalization reverses the carbonization process and returns the material to a stronger state.
Corrosionpedia Explains Realkalization
The pH of hardened concrete is generally in the range of 12.6 to 13.5. Carbonation will result in a reduction of concrete's pH, resulting in rupture of the passivating layer around the embedded reinforcement. Carbonation is one of the main reasons for the corrosion of reinforcement. Corrective action is initiated to restore the building by realkalization of the reinforcement members, which will improve the pH of concrete considerably.
Realkalization is carried out by temporarily applying an electric field between the reinforcement in the concrete and an externally mounted anode mesh. During the process an alkaline electrolyte, such as sodium or potassium carbonate solution, is transported into the concrete, increasing the alkalinity of the cover zone. At the same time, electrolysis at the reinforcement surface produces a high pH environment. This process returns the steel reinforcement to a passive condition. The treatment is monitored by determining the voltage-to-current ratio. Once this reaches an approximately constant value, the process is considered to be complete.
Realkalization is used in:
- Concrete buildings
- Parking structures
- Other carbonated structures
Features and benefits of realkalization include:
- Mitigates active corrosion - addresses the cause of corrosion by re-establishing a high pH environment and repassivating the reinforcing steel
- Long-term protection - structure will not re-carbonate in the treated areas
- Global protection - treats the entire structure, not just isolated patches
- Low maintenance - no permanent system to maintain or monitor
- Environmentally friendly - vastly reduced concrete breakout reduces noise, dust and environmental pollution