What is a Concrete Slump Test?

We’ve talked often on this blog about the importance of getting the right concrete mix for the job in hand – but how do you know for sure whether you’ve achieved it or not?

Partly, that’s down to experience, but if you want to be absolutely certain, there are tests you can carry out to verify that your concrete is performing as you want and expect it to.

We recently explored the benefits of cube testing as one means of checking a concrete mix. In this article, we’ll be looking at another: the concrete slump test.

What is the concrete slump test?

At its simplest, the concrete slump test measures how far a fresh concrete mix ‘slumps’ when released from a container. Unlike cube testing, which needs the full 28-day curing period to produce useful results, it’s a quick and simple means of checking on the quality of the mix that can be carried out immediately before the pour.

But the concrete slump test has another significant benefit, which is that you can also ensure multiple batches are of a consistent standard by testing each batch and checking that the results match.

How is a concrete slump test carried out?

A concrete slump test is a relatively simple procedure that can be carried out with a special cone, sometimes referred to as an Abrams cone. There are specific actions you need to take when carrying out the test to ensure your results are in accordance with BS EN 12350-2.

The cone needs to be placed on level ground and secured in place by having the person doing the test stand on footholds. You fill the cone in three equal layers with your concrete mix and compact each layer 25 times with a tamping rod.

The cone then needs to be raised vertically and placed next to the concrete. The gap between the height of the cone and the height of the concrete is then taken to provide your results. 

To meet required standards, the cone should be lifted clear of the concrete in no less than three and no more than seven seconds. Measurement of the different heights should be taken immediately after lifting, and the whole procedure should take no more than 150 seconds from fill to final measurement.

If the slump is still changing a minute after raising the cone, the test should be considered invalid.

What do concrete slump test results mean?

• Zero slump: If the concrete doesn’t move at all, or no more than 25mm, then the mix will be too dry for any worthwhile purpose.
• True slump: When the mix sinks but also retains its shape. This is the ideal result, and how far it slumps will indicate its workability and potential uses. 
• Shear slump: With greater slump than a true slump, but importantly, the slump is not even. This indicates that the mix lacks cohesion, and will need to be adapted and retested.
• Collapse: A complete collapse of the concrete indicates that it is too wet to be of any practical use.

Reliable consistent quality concrete from Stewart Brothers Concrete

At Stewart Brothers Concrete, we mix and supply BSI Kitemark and ISO 9001 quality accredited concrete, so you know that you’re getting the right mix for your construction or landscaping project.

For more information on What is a Concrete Slump Test? talk to Stewart Brothers Concrete