What type of tests are performed on hardened concrete?

The selection of compressive strength tests and durability tests as the correct answer is appropriate because these tests directly assess the performance and quality of hardened concrete.

Compressive strength tests are fundamental in evaluating how well concrete can withstand loads without collapsing, which is critical for structural integrity. This measurement is typically performed using standardized methods such as the use of a hydraulic press to determine the maximum load the concrete can bear before failure.

Durability tests assess how concrete will perform over time when exposed to various environmental conditions, such as moisture, freeze-thaw cycles, and chemical attacks. These properties are essential in ensuring that concrete structures remain viable and functional for their intended lifespan.

Other options present tests that may not be commonly performed on hardened concrete. For example, tensile strength tests are more relevant during the fresh concrete state or for holistic material properties, while flexibility tests are generally not applicable to concrete due to its inherently brittle nature. Thermal conductivity and color tests are typically not standard practice for assessing hardened concrete performance. Impact tests mostly target impact resistance but aren't as widely standardized for hardened concrete as compressive strength and durability tests are. Finally, slump tests measure the consistency of fresh concrete rather than hardened material.