Carbonation is a chemical process in which carbon dioxide from the air penetrates concrete and reacts with calcium hydroxide, reducing the concrete’s alkalinity and weakening its natural protection of embedded steel reinforcement.
Explanation
Concrete is naturally alkaline, which protects reinforcement from corrosion. When carbonation occurs, the pH level drops. Once the carbonation front reaches the depth of the reinforcement, the protective layer breaks down and corrosion can begin.
Carbonation progresses gradually from the surface inward and is influenced by:
- Concrete permeability
- Cover depth
- Environmental exposure
- Moisture levels
In the UK, carbonation is a common cause of reinforcement corrosion in ageing reinforced concrete structures.
Why It Matters
If left untreated, carbonation can lead to:
- Reinforcement corrosion
- Concrete cracking and spalling
- Reduced durability
- Costly structural repairs
Carbonation is typically assessed through carbonation testing. Prevention and remediation may include protective coatings, increased cover protection, and targeted concrete repair.