Slump is the measure of the consistency in a specific batch of fresh concrete. A slump test accesses the consistency of the fresh concrete, and to ensure that the correct amount of water has been added to the mix.
To conduct the test, an Abrams slump cone is used, a bottomless, 12” high circular cone with an 8” in diameter base and a 4” in diameter top. The cone is placed on a level, impermeable surface and filled in three stages with equal amounts of concrete. Each layer is tamped down using a special rod to make sure the concrete is compacted and leveled off with the top of the cone. The cone is then carefully removed and the concrete is left to settle or “slump.”
The slump cone is placed alongside the pile of concrete in order to measure the height of the concrete in comparison to the top of the cone. Measurements are taken to the nearest 5mm. Wikipedia states, “The slumped concrete takes various shapes, and according to the profile of slumped concrete, the slump is termed as true slump, shear slump or collapse slump.”
If the concrete simply subsides but generally maintains its shape, it is considered to be a true slump. In the case of a shear slump, the top portion of the concrete shears off. If the test results in a “collapse slump”, it typically indicates the mix is too wet; or it may be a high workability mix that needs to have a flow test done rather than a slump test.
Up until just a few decades ago, concrete was made from portland cement, aggregate and water. In this type of concrete mix, the coarse aggregate dictated the water content, and concrete with a lower slump value contained less water and resulted in a better quality of concrete. Today much of the concrete we produce is a blend of not only cement and aggregate but admixtures, fibers and polymers. This means the aggregate is not the only thing that influences the amount of water added and other factors have to be considered to determine the proper consistency of the concrete.
At The Conco Companies, we are one of the leading concrete contractors in the Western U.S. and offer a wide range of quality services and products. Our experience includes providing services for commercial, educational, parking and other construction development as well as public works projects. We serve California, Washington State, Oregon, Colorado and Nevada.