Compression tests, a fundamental assessment of concrete strength, reveal a notable discrepancy between results obtained using cubes and cylinders. While both methods subject the concrete to uniaxial compression, the failure mode in both cases is tensile splitting.
However, a key difference lies in the lateral expansion of concrete samples under compression. This expansion creates friction at the interface between the concrete and the testing machine. This friction introduces forces that artificially elevate the apparent compressive strength of the concrete. Notably, this effect is more pronounced in cubes due to their lower height-to-width ratio.
In contrast, cylinders, with their higher height-to-width ratio, experience less lateral restraint and, consequently, less friction-induced strength enhancement. This explains why compression test results using cylinders tend to be lower than those obtained with cubes.
As noted by Longman Scientific and Technical (1987), this phenomenon underscores the importance of considering sample geometry when interpreting compression test results. While cubes offer convenience and standardized dimensions, cylinders provide a more accurate representation of the concrete’s true compressive strength, as they minimize the influence of frictional forces.
Therefore, understanding the nuances of these testing methods is crucial for engineers and researchers. By recognizing the impact of sample geometry on test results, they can make informed decisions about material selection and structural design, ensuring the safety and reliability of concrete structures.