The quality of fresh concrete has a direct effect on the quality of hardened concrete in terms of strength, durability, and performance. One of the important properties is the workability, which defines the ease with which concrete can be managed and placed at the site. Workability is typically determined by the slump test, which is standardized in ASTM C143 and other standards in other countries and involves measuring the vertical settlement of a concrete cone when the mould is removed. This is a test that engineers use to maintain consistency across batches and to meet design specifications.
Principle of the Slump Test
The slump test is also based on the measurements of the vertical deformation, which takes place when a fresh concrete specimen is left to settle under the influence of its own weight. The slump cone is then raised, and the concrete sinks under the force of gravity; the amount of subsidence will depend on the consistency of the material used. An increase in slump values implies high workability, whereas low values imply that the mixes are stiffer and less flowing.
Test Apparatus and Materials
A typical slump test device will include a frustum-shaped metallic mould, a tamping rod, a hard base plate, and a measuring scale. The mould is also standardized in dimensions so that there is uniformity in the results. New concrete samples are supposed to be representative of a batch under test, and they should be taken in accordance with good practice to prevent the effects of segregation or drying up.
