The strength relationship between the cube and cylinder

Concrete laboratory tests compressive strengths differ in a laboratory depending on whether the shape of the concrete specimen is either a cube or a cylinder. General assumption has defined the cylinder to possesses, approximately 80% of the cube strength. The validity of this approximation needs to be assessed; as several studies have shown that this approximation to be invalid. This investigation assessed the effect of compressive strength and curing age of concrete on the Cylinder–Cube Strength Relationship (CCSR) of South African Concretes. Cubes and cylinders were cast for 7, 28 and 56 day curing ages from 36 concrete mixes varying in strength, aggregate type and cement type. Concrete strength did not influence the CCSR, but rather, the CCSR was influenced by the curing age (r = 0.998). The general CCSR values were 83.66%, 84.88% and 86.96% (on average) for 7, 28 and 56 day concrete, respectively. The overall average CCSR, calculated considering results across all curing ages, was 85.17%. This research shows that 80% is not an accurate representative value of the average CCSR for typical concretes varying in composition. In addition, this study also acknowledged that the CCSR cannot simply be represented by a single value. This research does however propose that if there should be a value that provides a better guideline to what can generally be expected, should accuracy not be a requirement, an average CCSR of 85% should be adopted, as opposed to 80%.