Structural classification and minimum cover due to environmental conditions cmin,dur
Eurocode 2 part 1-1: Design of concrete structures 188.8.131.52 (5)
The minimum cover for reinforcement and prestressing tendons in normal weight concrete taking account of the exposure classes and the structural classes is given by cmin,dur.
The recommended Structural Class (design working life of 50 years) is S4 for the indicative concrete strengths given in Annex E (see § E.1 (2)) and the recommended modifications to the structural class is given in Table 4.3N. The recommended minimum Structural Class is S1.
The recommended values for cmin,dur are given in Table 4.4N (reinforcing steel) and Table 4.5N (prestressing steel).