What is the main difference between slump and flow tests?

The main difference highlighted in the correct choice revolves around the specific applications and the types of concrete being tested. Slump tests are designed to assess the workability of fresh concrete, which means they provide insights into the ease with which the concrete can be mixed, placed, and finished. The slump test measures how much the concrete sample settles under its own weight when a cone-shaped mold is removed, giving a direct indication of its workability.

On the other hand, flow tests, particularly used for high-slump concrete, focus on measuring the consistency — that is, how the concrete spreads or flows. This is particularly important for mixtures that are highly fluid, where the traditional slump test may not provide enough information due to the nature of the mix. The flow test often involves a flow table and measures how far a concrete sample spreads when subjected to a specific influence, thus providing a clearer picture of its consistency compared to the slump test.

The other options present misunderstandings regarding the functions of these tests or mischaracterizations of the types of concrete they apply to. For instance, noting that slump tests assess hardened concrete or measure temperature and moisture content misrepresents their usage and purposes.