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. Unfortunately, the simplicity of the test often allows a wide variability in the manner that the test is performed. The slump test is used to ensure uniformity for different batches of similar concrete under field conditions,[1]:127,128 and to ascertain the effects of plasticizers on their introduction.[1]:134
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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.
Slump cone (Abrams cone), scale for measurement.
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.[1]:128[2] 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.[3]:68
| Collapse | Shear | True |
|---|---|---|
| In a collapse slump the concrete collapses completely.[2] | In a shear slump the top portion of the concrete shears off and slips sideways.[2] | In a true slump the concrete simply subsides, keeping more or less to shape.[2] |
According to European Standard EN 206-1:2000 five classes of slump have been designated, as tabulated below.[3]:69
| Slump class | Slump in mm |
|---|---|
| S1 | 10 - 40 |
| S2 | 50 - 90 |
| S3 | 100-150 |
| S4 | 160-210 |
| S5 | ≥210 |
The slump test is suitable for slumps of medium to high workability, slump in the range of 25 - 125 mm, the test fails to determine the difference in workability in stiff mixes which have zero slump, or for wet mixes that give a collapse slump. It is limited to concrete formed of aggregates of less than 38 mm (1 inch).[1]:128
The slump test is referred to in several testing and building codes, with minor differences in the details of performing the test.
In the United States, engineers use the ASTM standards and AASHTO specifications when referring to the concrete slump test. The American standards explicitly state that the slump cone should have a height of 12-in, a bottom diameter of 8-in and an upper diameter of 4-in. The ASTM standards also state in the procedure that when the cone is removed, it should be lifted up vertically, without any rotational movement at all.[4] The concrete slump test is known as "Standard Test Method for Slump of Hydraulic-Cement Concrete" and carries the code (ASTM C 143) or (AASHTO T 119).
In the United Kingdom, the standards specify a slump cone height of 300 mm, a bottom diameter of 200 mm and a top diameter of 100 mm. The British Standards do not explicitly specify that the cone should only be lifted vertically. The slump test in the British standards was first (BS 1881–102) and is now replaced by the European Standard (BS EN 12350-2).[5] The test should be carried out by filling the slump cone in three equal layers with the mixture being tamped down 25 times for each each layer.
Numerous tests exist to evaluate concrete: a similar test is the K-Slump Test (ASTM C 1362). Other tests evaluating consistency are the British compacting factor test (BS EN 12350-4), the Vebe consistometer for roller-compacted concrete (ASTM C 1170), and the flow table test (DIN 1048-1).[6]