Question

5. In concrete compression test, normally 150mmx150mmx150mm concrete cube samples is used for testing. Why isn’t 100mmx100mmx100mm concrete cube samples used in the test instead of 150mmx150mmx150mm concrete cube samples?

Answer 1

The purpose of a concrete cube test is to ensure that the concrete meets its expected compressive strength. 

The force supplied by a concrete compression machine is a definite value.

For normal concrete strength application, say below $50\ MPa,$ the stress produced by a $150\ mm\times150\ mm\times150\ mm$ cube is sufficient for the machine to crush the concrete sample.

However, if the designed concrete strength is $100\ MPa,$ under the same force (about $2000\ kN$) supplied by the machine, the stress under a $150\ mm\times150\ mm\times150\ mm$ cube is not sufficient to crush the concrete cube. Therefore, $100\ mm\times100\ mm\times100\ mm$ concrete cubes are used instead to increase the applied stress to crush the concrete cubes.

For normal concrete strength, the cube size of $150\ mm\times150\ mm\times150\ mm$ is already sufficient for the crushing strength of the machine.