What is a slump test?

A slump test is a method used to determine the consistency of concrete. The consistency, or stiffness, indicates how much water has been used in the mix. The stiffness of the concrete mix should be matched to the requirements for the finished product. All concrete is a combination of aggregate (gravel and/or sand), cement, and water, but the proportions of the mix can be varied. A larger proportion of water causes a softer, wet concrete mix, which is easier to handle during the pour and requires less care during curing. It also results in a slightly softer and less durable finished product. A smaller amount of water causes a stiffer, wet concrete mix, which is harder to manage but makes a stronger and more durable finished product, one with a higher concrete pounds per square inch (PSI). Contractors order wet concrete with a slump rating suitable for the job. A slump test is performed when the concrete is delivered to double-check the stiffness of the mix. A separate slump test is ...  more

A slump test is performed to determine the consistency of the concrete, which relates to the workability of the concrete. Most specifications limit the slump to 4 inches, which is the vertical distance that concrete subsides after being deposited into a 12" tall cone shaped mold, which is subsequently removed by pulling off the deposited concrete in an upward motion. In theory, and for lack of a more practical means of measuring, the more water that is in the concrete, the greater distance it will subside after the mold is removed, and the higher the measured slump. The slump test does not determine how much water is in the concrete, but it does give a very good indication of the water in the concrete when compared to the designed slump produced by the proportions of the known mix design.  more