The slump test is the most common way to check the workability of fresh concrete. It needs very little equipment: a slump cone, a tamping rod and a base plate. Because it is quick, it is used on site to check that each batch is consistent with the mix design.
How the test is done
The cone is placed on a flat, non-absorbent base and filled in layers, each layer tamped a set number of times with the rod. The top is struck off level and the cone is lifted straight up. The concrete settles, and the drop in height from the top of the cone to the top of the concrete is the slump.
Reading the result
A true slump keeps its shape and drops evenly. A shear slump, where one side slides away, usually points to a harsh or lean mix and the test should be repeated. A collapse slump means the mix is very wet or is a high-workability mix that needs a flow test instead.
For mixes that are too stiff or too fluid for a meaningful slump, a compaction factor apparatus or a flow table gives a better picture of workability.
