The concrete slump test is an emprical test that measures the workability of fresh concrete. More specifically, it measures the consistency of the concrete in that specific batch. It is also used to determine consistency between individual batches. The test is popular due to the simplicity of apparatus used and simple procedure.
The slump test result is a measure of the behaviour of a self-compacted inverted cone of concrete under the action of gravity. It is a measure of the concrete's workability or the dampness of concrete.
The slumped concrete takes various shapes, and according to the profile of slumped concrete, the slump is termed as true slump, shear slump or collapse slump. If a shear or collapse slump is achieved, a fresh sample should be taken and the test repeated. A collapse slump is an indication of too wet a mix. Only a true slump is of any use in the test. A collapse slump will generally mean that the mix is too wet or that it is a high workability mix, for which slump test is not appropriate. Very dry mixes; having slump 0 - 25 mm are used in road making, low workability mixes; having slump 10 - 40 mm are used for foundations with light reinforcement, medium workability mixes; 50 - 90 for normal reinforced concrete placed with vibration, high workability concrete; > 100 mm.
| Collapse | Shear | True |
|---|---|---|
| In a collapse slump the concrete collapses completely. | In a shear slump the top portion of the concrete shears off and slips sideways. | In a true slump the concrete simply subsides, keeping more or less to shape. |