Slump test is very easy and simple. A non-technical person can perform it without any problem.
It is very useful to check batch to batch or hour to hour variation in the materials which will be fed into the mixer. Increase in slump means moisture content of aggregate has increased unexpectedly or deficiency of fine aggregate has changed. Too high or too low slump is an indicator of undesirable workability of concrete and mixer operator gets a warning to find a solution to remedy the problem.
This test does not require any special costly equipment. The sample is not required to be sent to a laboratory. It can be done in the construction area.
Slump test does not demand a long-time period to get the result. If we compare with compressive strength test, it requires almost a month to get the result but we can obtain slump value within some minutes.
Limitations/ Disadvantages of Concrete Slump Test
It is unreliable for lean mixes. In a lean mix, a true slump may convert into shear or collapse easily. Widely variation can be found from one sample of lean mix and it can be a great confusion to determine the exact result.
It is not exact measurement because slump bears no unique relation to workability. Even, for different types of aggregates, the same slump can be recorded for different workability. We should also keep in mind that slump does not measure the ease of compaction. The slump occurs under the self-weight of concrete only, it does not represent behavior under various conditions like vibration, finishing, pumping or moving through a tremie.
For a specimen, more than one shape can be resulted confusing the correct result. If shear slump occurs, it may attain true slump in next test.
It cannot differentiate in workability of stiff mixes as it shows zero slumps. In dry range, no difference can be detected between different mixes with different workability.
It is not suitable for concrete formed of aggregate higher than 40 mm.