When compressive strength tests of laboratory-cured specimens fail to meet the specified acceptance criteria, core tests are commonly used to verify the strength and to obtain acceptance of the in-place concrete.
When the concrete is doubted or the structure is intended to be used for higher stress conditions, in-situ strength of concrete is determined to assess the current strength of a structure and to determine whether the strength and durability are adequate for its future use. From general perspective, the core test is required when the result of concrete cubes are not giving satisfactory result. In addition, concrete core test is also used for safety assessment of the existing concrete structure.
Concrete in the member represented by a core test is considered acceptable, if the average equivalent cube strength of the cores is equal to at least 85 percent of the cube strength of the grade of concrete specified for the corresponding age and no individual core has a strength less than 75 percent.