A chloride class is a classification that indicates to what extent concrete is exposed to chlorides (salts), so that the correct concrete mix can be specified to prevent corrosion of the reinforcement. The classes are defined in the European standard EN 206.
Why chloride classes?
Chlorides (from de-icing salt and seawater) are the greatest threat to reinforced concrete:
- Corrosion — chlorides penetrate the concrete and attack the steel reinforcement
- Spalling — corroding reinforcement expands and pushes off the concrete cover
- Structural failure — severe corrosion reduces the load-bearing capacity
The classes
| Class | Description | Example |
|---|---|---|
| XD1 | Moderate humidity | Multi-storey car park (splash from vehicles) |
| XD2 | Wet, rarely dry | Swimming pools with chlorinated water |
| XD3 | Cyclic wet and dry | Bridge decks, roads treated with de-icing salt |
In addition, XS classes cover exposure to seawater chlorides.
Application
The chloride class determines:
- Minimum concrete cover — greater cover protects the reinforcement better
- Concrete strength class — a higher class gives a denser structure
- Maximum water-cement ratio — a lower w/c ratio gives less porous concrete
- Minimum cement content — more cement makes the concrete less permeable
Related terms
- Concrete
- Reinforcement
- Corrosion
- Exposure class
- Concrete cover
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