The BDS ЕN 206:2013+А2:2021/NA:2021 standard describes the main criteria - specification, properties, production and conformity of concrete.

Inadequate classes are often used when concrete structures are built. They are selected by compressive strength only, without taking into account other criteria.

The compressive strength of concrete does not guarantee its durability!

The mix design of the concrete should reflect the situation and requirement of the structure and environment.

The mix design will also take into consideration the chemical aspects, physical aspects required by the concrete.

These are termed as Exposure Classes.

Exposure Classes are classified by the letter X, the type of chemical and physical aggression is defined by the next letter i.e., C, D, S, F, A. The numbers will indicate the intensity of the potential attack.