The exposure class describes the impact of environmental conditions on a concrete structure. A correctly designed and constructed element, taking into account the exposure classes, should remain durable in a specific environment that can affect the structure physically or chemically. Concrete can be exposed to several harmful factors, which must be taken into account when determining exposure classes.
The PN-EN 206+A2:2021 standard specifies the requirements for the composition and properties of concrete for a given exposure class:
Minimum cement content,
- Maximum w/c ratio,
- Minimum class of concrete for compressive strength,
- Additional requirements for certain environmental classes (minimum air content, aggregate with adequate frost resistance, sulphate-resistant cement SR or HSR).
The national supplement PN-B-06265:2022 also takes into account exposure classes XM due to the threat of abrasion:
For exposure class XM, the concrete surface treatment or aggregate with high abrasion resistance should be taken into account in the requirements.
Concrete structures made with exposure classes in mind should remain durable in the specific environment for which they were designed, provided that they are manufactured in accordance with standards and technical documentation and that appropriate care and maintenance are carried out.
In prefabrication, different exposure classes can be found depending on the intended use of the product. Examples of exposure classes in prefabricated elements:
- Pillars and walls inside industrial halls with normal air humidity – XC1
- Exterior walls exposed to contact with water – XC4, XF1
- Retaining walls of road structures exposed to frost and de-icing agents – XC4, XF2
- External walls exposed to water and chemical attack – XC4, XF1, XA1
- Pre-tensioned prestressed concrete beams exposed to water, chlorides not from seawater, de-icing agents – XC4, XD1, XF2.
