What is the primary purpose of a slump test?

The primary purpose of a slump test is to evaluate the consistency of concrete. This test measures the workability of fresh concrete by assessing how much the concrete will "slump" or yield when placed in a specific cone-shaped mold. A higher slump indicates a more workable concrete mix, while a lower slump suggests a stiffer mix that may be harder to work with.

Consistency is crucial in ensuring that the concrete can be effectively placed and finished without issues, which is vital for achieving the desired strength and durability in the final product. While other tests may measure aspects like temperature, moisture content of aggregates, or aggregate size distribution, the slump test specifically focuses on the fluidity and handling characteristics of the concrete mix itself. Thus, option C accurately reflects the main function of the slump test in concrete evaluation.