Compressive strength - hardened concrete

Concrete has a high compressive strength that can be increased by respective recipes (high performance concretes). For determining the compressive strength two test samples are made and tested after 28 days: one concrete cylinder with a length of 30 cm and a diameter of 15 cm as well as one concrete cube with an edge length of 15 cm. The results are the basis for the assignment of the concretes to the corresponding compressive strength classes with the respective terms. Example: C25/30: C = concrete, 25 = cylinder strength 25 N/mm², 30 = cube strength 30 N/m².