Understanding Slump

Slump refers to the measure of concrete fluidity and consistency, and it shows the flow and workability of premixed concrete. When mixing concrete, figuring out slump quality should be a priority because it directly affects the ease or difficulty of working with the concrete. It is essential to clearly understand slump, including what it is, how to test it, how to interpret the results, and many other facts. This article will help you learn more about the slump of concrete.

Slump Test

The test is done using a slump cone, usually in the shape of a conical frustum. The cone is open-ended and has handles attached to both sides of it. The cone has a diameter of around 3.6 inches at the top and 7.8 inches at the bottom. The height is about 12.1 inches. At the start of the test, the cone is placed on a hard surface that is not absorbent. Fresh mini concrete is put into the cone in three stages.

When each layer is added, it is tamped about 25 times with a long bullet-nosed metal rod. In stage three, the concrete is levelled off at the top of the mould. Then the mould is carefully lifted vertically to avoid disturbance of the concrete cone, and the concrete subsides. The distance from the top of the slump cone to the top of the slumped concrete is measured.

Interpretation of Slump Test Results

The profile of the slumped concrete determines the shape it is considered in the results of the test. The categories of the results are a true slump, collapse slump, or shear slump. An excessively wet mix is called a collapsed slump. For the shear slump, the top portion of the concrete shears off and slips towards the sides.

A 0-25 mm slump is considered very dry and used in construction projects such as road construction. Concrete with a slump of around 10-39 mm has low workability and is used for light reinforced foundations. A 50-91 mm slump has medium workability and is used as typical reinforced concrete. High workability concrete has a slump of above 100. This type is used to fill tight spaces for reinforcements and concrete that needs to flow long distances.

What Happens If the Concrete Slump Is Too High or Too Low?

If the slump is too high or too low, it means that the concrete has low workability. The workability makes it hard to handle. When the specified range is exceeded, shrinkage may occur. The concrete slump should be maintained at a workable range depending on the type of project you are doing.


The slump of the concrete is significant when using concrete during construction. It is essential to understand concrete slump clearly so that no mistakes are made when completing a construction project. This information can also help you make your projects more durable.