The term C20/25 in concrete refers to its characteristic strength concrete at 28 days but for two different specimens. It is used in a European standard for specifying concrete as in EN 206.
The word “C” stands for concrete and the number 20/25 represents the compressive strength of the concrete in megapascals (MPa).
- 20 MPa is a characteristic strength of a cylindrical sample of concrete tested at 28 days.
- 25 MPa: Characteristic strength of a cubic sample of concrete tested at 28 days.
Unlike other standards that use a single number to represent concrete grade, the European standard adopts a two-number system. This distinction accounts for the fact that cylindrical samples exhibit lower compressive strength compared to cubic samples. Thus, cylindrical specimens are slightly weaker due to their geometry and Cubic specimens provide a slightly higher compressive strength value.
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