What is Carbonation?
Concrete is a highly alkaline material. If uncarbonated concrete has a pH in the region of 12.6. Carbonation starts on the surface of the concrete and can ultimately reach the depth of the steel reinforcement. Reinforcement bars are required in most concrete structures as concrete is strong in compression but weak in tension, therefore reinforcement is added to provide tensile strength. The alkaline state of the concrete provides a passive resistive layer to the surface of the steel reinforcement that prevents corrosion.
Once concrete comes into contact with carbon dioxide and other pollutants within the air, then a reaction may occur. Carbon dioxide can form carbonic acid with the water in the cement that then neutralizes the alkaline state of the concrete. If this happens, then carbonation moves through the concrete as a front that gradually reduces the pH value to 8pH; neutral is 7pH. However, corrosion to the reinforcement can occur if the pH value falls below 11pH.
Different factors determine the time frame of carbonation, such as the quality of the concrete. For example, if the cement is very porous or has low cement content then the time frame will be significantly quicker than if the concrete is not very porous and has high cement content.
Carbonation Prevention Using Anti-Carbonation Coatings
Preventing and slowing down carbonation in concrete is quite simple. You can apply Anti-carbonation coatings to the cleaned surface of the concrete. This will prevent the ingress of carbon dioxide and other pollutants. This method should prevent carbonation for approximately 10 years.