In recent years, the concrete industry has experienced growing criticism of the traditional concrete slump test. Many people say it is outdated and no longer provides useful information for the industry because of how modern concrete mixes are designed. Others claim that the information it provides can still be useful. Today, we’re going discuss some of the history of the test and how the use of slump change admixtures may mean we should reconsider how we understand the concrete slump test.

What Did the Slump Test Originally Measure?

The earliest concrete slump tests were performed in the United States in the 1920s. So this test is more than 100 years old. The test was designed to measure the workability of concrete mixes, and therefore the amount of water in the mix. Before the advent of admixture, a low slump meant the load had a lower water-cement ratio, and a higher slump indicated a higher water-cement ratio. By this, the slump was able to provide some estimation of the strength of the concrete.

Enter the Concrete Admixture

The advent of superplasticizers and viscosity-modifying agents makes it almost impossible to establish the strength of the concrete based on the slump. A flowing mix no longer means a higher water-cement ratio if the mix contains a superplasticizer. A loose mix can be transformed into a low-slump mix without the addition of cement just by adding a VMA to the mix. It is because of this conundrum that many in the industry are suggesting that the slump test is no longer serving its purpose.

Wait – the Original Purpose Was About Workability

While the slump test is no longer able to provide information about the strength or water-cement ratio in a batch of concrete, it actually still does provide important information about the consistency of a mix. The slump test provides information to ready-mix drivers regarding the amount of admixture required for a desired consistency. It provides information to quality control specialists who are responsible for ensuring the load meets the workability specifications of the job. It helps keep everyone on the same page regarding the consistency needed for each job. So while it may no longer provide any information about the strength of the concrete, it can still be a very useful tool for measuring the consistency and workability of a load of concrete.

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