Concrete strength evaluation through the use of small diameter cores

Synopsis When cores are tested to establish the in situ strength of hardened concrete, it is current practice to use 100 or 150 mm diameter cores. For various reasons. such as the small size of a member or congestion of reinforcement, drilling of smaller cores is preferred, but these are not yet fully recognized in standards and guidance documents. The compressive strengths of 50mm diameter cores are compared with the strengths of 100mm diameter cores and control cubes. Other effects on the measured strengths of 50 and 100mm diameter cores are studied, including diameter, length/diameter ratio, direction of drilling, curing conditions, age of concrete and location of cored specimen. The results are compared with available published data. Results obtained. involving over 1000 samples, support the viability of using 50mm diameter cores to estimate the in situ strength of hardened concrete.