Exposure classes¶
Serviceability checks are mainly aimed at protecting the durability of the structure. Every check must therefore be referred to the environmental conditions to which the member is exposed. EN 1992-1-1 §4.2 (together with EN 206) classifies the environment into the following exposure classes:
| Class | Environment |
|---|---|
| X0 | No risk of corrosion or attack |
| XC1–XC4 | Corrosion induced by carbonation |
| XD1–XD3 | Corrosion induced by chlorides other than from sea water |
| XS1–XS3 | Corrosion induced by chlorides from sea water |
| XF1–XF4 | Freeze/thaw attack, with or without de-icing agents |
| XA1–XA3 | Chemical attack |
Broadly, three levels of aggressiveness can be distinguished:
- Ordinary — low relative humidity, or high relative humidity only for short periods (e.g. X0, XC1, XC2, XC3, XF1);
- Moderately aggressive — high relative humidity without corrosive agents (e.g. XC4, XD1, XS1, XF2, XF3, XA1, XA2);
- Very aggressive — presence of particularly corrosive liquids or gases (e.g. XD2, XD3, XS2, XS3, XF4, XA3).
The exposure class governs the minimum concrete cover (EC2 §4.4.1) and the limiting crack width \(w_{max}\) (EC2 §7.3.1, Table 7.1N) adopted in the crack-width check.