Slump Cone Test and its Limitations
Slump Cone Test and its Limitations
The standard slump cone, as shown in the below figure, is placed on the ground. The operator holds the cone firmly by standing on the foot pieces.
The slump cone is filled with about one-fourth portion and then rammed with a rod which is provided with bullet nose at the lower end. The diameter of the rod 16 mm and its length is 60 mm. The strokes to be given for ramming vary from 20 to 30. The remaining portion of the slump cone is filled in with similar layers and then the top of concrete surface is struck off so that the cone is completely full of concrete. The slump cone is then gradually raised vertically and removed. The concrete is allowed to subside and then the height of concrete is measured. The slump of concrete is obtained by deducting height of concrete after subsidence from 30 cm.
Table below shows the recommended slumps of concrete for various types of concrete.
Advantages of slump cone test:
(i) It grants the facility to easily detect the difference in water content of successive batches of concrete of the same identical mix.
(ii) The apparatus is cheap, portable and convenient to be used at site.
Limitations of slump cone test:
(i) As such, there is no direct relationship between the workability and the value of slump.
(ii) It is not suitable for a concrete in which maximum size of the aggregate exceeds 40 mm.
(iii) There are chances of many shapes of slump to occur and it is difficult to decide which is the correct value.
(iv) The slump occurs only in case of plastic mixes. It does not occur in case of dry mixes.
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