The compressive test of concrete samples is aimed at determining the compressive strength of concrete. If the samples are drawn from a structure, the test has high reliability, since it is a direct measure of the concrete under investigation. However, the conditions under which the test is performed are not the same as those that had the concrete before extraction. The resistance value obtained in the compression test, whatever the quality of concrete to be tested, depends on several factors including: the diameter of the specimen, its slenderness, its moisture content and direction of reinforcement extraction with respect to that of concrete. The minimum diameter of the probe recommended by the Spanish legislation is 100 mm. The diameter, in any case must be between 3 and 4 times the maximum aggregate size of concrete study. The slender ideal test of the specimen (length / diameter) is 2, although values are accepted between 1 and 2 but I know of any correction factor in the EHE.

The direction of extraction of the specimen in relation to the direction of concrete can affect the resistance value between 5 and 10%. Ideally, both directions were parallel, which is not always possible depending on the operator's capacity carrier extraction. The concrete compressive strength test result is greater the lower the degree of saturation. The difference in strength between dry and wet concrete can be between 10 and 20%. However, the modulus of elasticity of concrete (Ec) is lower in dry concrete in saturated concrete. Finally, it should be noted that the values of concrete strength we get from testing of a control probe containing armor may be different from those obtained in specimens without armor.