This test is performed to measure consistency or workability of fresh concrete, where the nominal maximum size of aggregate does not exceed 38 mm using slump test apparatus.
IS : 1199 – 1959 – Method of sampling and analysis of concrete.
Equipment & Apparatus
Slump cone (Height = 30 cm, Base dia = 20 cm, Top dia = 10 cm)
Tamping rod (Length = 60 cm, Dia = 16 mm)
The internal surface of the mould is thoroughly cleaned and freed from superfluous moisture before commencing the test. And if the cone is in completely dry condition then dampen it using a damp cloth.
The mould is then placed on a smooth, horizontally leveled rigid and non-absorbent surface such as a rigid plate. It is held firmly in place during filling by the operator by standing on the two foot pieces provided in the slump cone.
The mould is filled by concrete in four layers, each approximately one-quarter of height of the mould, and each layer is tamped down with 25 strokes of tamping rod with pointed end in a uniform manner.
After tamping the top layer, the concrete is struck off level with a trowel and any mortar leaked out between the mould and base plate is cleaned away.
The mould is then removed from the concrete immediately by raising it slowly and carefully in a vertical direction.
The slump is measured immediately by determining the difference between the height of the mould and that of the highest point of specimen.
Report the slump in terms of millimeters to the nearest 5 mm of subsidence of the specimen during the test.
Notes to Remember
If concrete consists of aggregates of size larger than 38 mm, then that concrete should be first sieved on a 38 mm sieve. Concrete passing the 38 mm sieve is then tested for workability using the slump cone apparatus of above mentioned dimension.
If the slump test shows shearing of the concrete mass or become completely collapsed, then the test results are invalid and the slump test is repeated.(see the figure below)
After completion of the slump test, to get an idea on cohesiveness of concrete, tap slightly the outer perimeter of the slumped concrete. If it subsides further, then it is an indication of good quality concrete having required cohesiveness. But if it gets collapsed or shears away then the concrete lacks cohesiveness and this is an indication of poor quality concrete.
Safety & Precautions
Use hand gloves & shoes while testing.
Equipment should be cleaned thoroughly before testing & after testing.
The apparatus should remain free from vibrations during the test.