Concrete strength classes: the values of Cmin and Cmax
Eurocode 2 part 2: Design of concrete bridge structures 3.1.2 (102)P
The strength classes in this code are based on the characteristic cylinder strength fck determined at 28 days with a minimum value of Cmin and a maximum value of Cmax.
Recommendation
The recommended values for the strength classes Cmin and Cmax are C30/37 and C70/85 respectively.