What does the term "slump" refer to in concrete work?

The term "slump" in concrete work specifically refers to the vertical drop measured during a slump test, which is a method used to determine the workability and consistency of fresh concrete. In this test, a conical mold is filled with concrete, and then the mold is removed, allowing the concrete to settle. The distance that the concrete slumps or drops from the original height of the mold is measured, and this measurement indicates the fluidity or viscosity of the mix. A high slump value signifies a more fluid mix, which is often desirable in certain applications, while a low slump indicates a stiffer concrete that may require more effort to work with. This characteristic is crucial for ensuring the concrete can be placed properly and will achieve the desired strength and durability when it cures.

The other options relate to aspects of concrete work but do not define the term "slump." The horizontal spread relates to the consistency of the mix but is not what "slump" measures. Drying time pertains to the curing process and does not reflect the workability of the fresh mix. The strength of the concrete mix is an entirely separate characteristic that assesses the durability and load-bearing capacity of the concrete after it has cured, not its workability prior to setting.