A concrete slump test is simply a measurement of concrete workability (consistency), more specifically of how far a sample will 'slump' when measured against a 300mm high steel cone.

How to perform a Concrete Slump Test

To perform a concrete slump test, take a sample of freshly mixed concrete. This is then packed with a rounded steel rod into a 300 mm (12 in.) high cone, 200 mm (8 in.) wide at the bottom and 100 mm (4 in.) wide at the top, which is open. The concrete is smoothed off level with the top rim of the cone, and the cone is then carefully lifted, so that the concrete is left unsupported. The test rod is then placed on top of the cone. The slump is the distance from the underside of the steel compaction rod to the highest part of the 'slumped concrete'. The test measurement is reported to the nearest 10mm.

If the concrete slump test collapses or shears to one side the test result will be recorded as such. A collapse slump test is an indication that the concrete mix is too wet and a sheared slump test is an indication that the concrete does have enough fines or sand in the mix.

Although the concrete slump test does not directly measure the work needed to compact the concrete, it gives a reasonable indication of the how easily a mix can be placed into a structure. The concrete slump test is only suitable for reasonably workable, cohesive mixes.

Very stiff mixes do not slump enough for useful measurements to be made and un-cohesive mixes tend to shear or collapse. A slump of less than 25 mm (1 in.) indicates a stiff concrete and a slump of more than 125 mm (5 in.) indicates a wet mix.

A typical specified concrete slump value for a standard mix is around 70mm or S2 consistency class to the new concrete standards. When a concrete supplier is given a consistency value to comply with the onsite measured concrete slump test value can be acceptable within certian tolerances.

The new EN standards from Dec 2003 now refers to the concrete slump test or "workability" as consistency and the concrete slump test remains with us as a means of measuring the consistency. More information can be found on various locations around the internet. Alternatively use our own search facility here at dataseen to find more information.

There are other means available to measure consistency other than the concrete slump test.