What component of concrete is typically tested for compressive strength?

Concrete cylinders are typically tested for compressive strength because they provide a standard and consistent method of evaluating the performance of concrete under load. During the testing process, concrete is cast into cylindrical molds that are usually 6 inches in diameter and 12 inches in height. Once cured for the specified period, typically 28 days, these cylinders are subjected to axial loading in a compression testing machine.

The use of cylinders allows for controlled testing conditions and more predictable results, as the geometry of the cylinder reduces variables that could affect the compressive strength outcome. Additionally, testing cylinders aligns with industry standards such as ASTM C39, which outlines methods for measuring the compressive strength of concrete. This is crucial for quality control and assurance in construction, enabling engineers and builders to confirm that the concrete used meets required specifications for strength, which directly impacts safety and structural integrity.

Concrete beams, slabs, and blocks may also possess compressive strength, but they are not standardized in the same way for routine testing purposes to assess the strength of concrete. Beams and slabs can introduce complexities due to their different geometries and stress distributions, while blocks may not be used for testing in situations where the compressive strength of the mix itself is the focus.