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Is the slump test really measures the workability?

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The slump test used widely in construction to test the concrete. The popularity of the slump test can be attributed to the small size of the apparatus and the simple procedure of conducting the test. Figure no:1 showing the slump test apparatus. The slump cone will be filled with concrete on layers. The slump cone will be filled with three layers of concrete. Each layer will receive 25 blows by the tamping rod. Then the cone will be lifted vertically, and the slump will be measured, as shown in figure no:2.
Figure 1
Actually, the slump test used to evaluate the consistency of concrete, not the workability. Consistency can be defined as the ability of concrete to hold all the ingredients without segregation. There is no connection between the results of the slump test and the workability of concrete. Moreover, the test procedure doesn't resemble the site conditions. The ease of placing and compacting of concrete will determine the degree of concrete workability. The slump test results can be the same for different concrete samples with different workability. 
Figure 2

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