slump range for concrete

The slump value of a freshly mixed concrete is an indirect measure of how fluid and workable the concrete mix is. It also gives an indication of consistency, both from a quality-control perspective and to determine how stiff or soft concrete is.

Slump tests involve filling a slump cone with fresh concrete and measuring how far it sinks or slumps down when removed. Typically, the value of a slump test ranges from nearly zero (which would indicate an extremely stiff and dry concrete) to a point where a freshly mixed concrete is so wet and flowable that it completely collapses when removed from the cone.

How to do a slump test

To perform a slump test, you will need a slump cone and a steel tamping rod. Place the slump cone on a flat, level surface and scoop in about one-third of your concrete mix into the cone. Once filled to the 2/3 mark, tamp it down 25 times using the steel rod.

Tamping the concrete with the rod ensures that the sample is compacted evenly throughout. Start at the edges and work your way toward the center of the sample.

Once you have uniformly tamped the concrete with the tamping rod, scrape away any excess concrete and level out the sample. Then, fill the sample with the remaining one-third of your concrete and tamp it down 25 times again. Once the sample is tamped down to the exact top of the slump cone, remove it from the base and clean it up.