Slump Test For Workability of Concrete

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Apparatus: Mould shall consist of a metal frustum of cone having the following internal dimensions:
Bottom diameter-20 cm
Top diameter     -10 cm

Height                -30 cm

The mould shall be of a metal other than brass and aluminium of at least 1.6 mm (or 16 BG)
thickness. The top and bottom shall be open and at right angles to the axis of the cone. 
The mould shall have a smooth internal surface. It shall be provided with suitable foot pieces and handles to facilitatelifting it from the moulded concrete test specimen in a vertical direction as required by the test. 
A mould provided with a suitable guide attachment may be used.
Tamping rod shall be of steel or other suitable material 16 mm in diameter 60 mm long and rounded at one end.

Procedure: 

  • The internal surface of the mould shall be thoroughly cleaned and free form superfluous moisture and any set concrete before commencing the test. 
  • The mould shall be placed on a smooth horizontal, rigid and non-absorbent surface viz. levelled metal plate. 
  • The operator shall hold the mould firmly in place while it is being filled with test specimen of concrete. The mould shall be filled in four layers, each approximately one quarter of height of mould. 
  • Each layer shall be tamped with twenty five strikes of the rounded end of the tamping rod. The strokes shall be distributed in a uniform manner over the cross section of the mould and for the second and subsequent layers shall penetrate into the underlying layer. 
  • The bottom layer shall be tamped through out its depth. After the top layer has been rodded,the concrete shall be struck off level with trowel or the tamping rod, so that the mould is exactly filled.
  • Any mortar which shall leak out between the mould and the base plate shall be cleaned away. The mould shall be removed from the concrete immediately after filling by raising it slowly and carefully in a vertical direction. 
  • The moulded concrete shall then be allowed to subside and the slump shall be measured immediately by determining the difference between the height of the mould and that of the highest point of specimen.
  • The above operations shall be carried out at a place free from vibration or shock, and within a period of two minutes after sampling.

Result: 

  • The slump shall be recorded in terms of millimeters of subsidence of the specimen during the test. Any slump specimen which collapses or shears off laterally give incorrect result. If this occurs, the test shall be repeated with another sample.
  • The slump test shall not be used for very dry mixes as the results obtained are not accurate. 
As Per IS-456 Recommended Values of  Slump Test for Various Purposes of Concrete is as Below
Sl No Placing Conditions  Degree of  Workability  Slump Value
1 Mass concrete
Lightly reinforced sections in Slabs, Beams, Walls, Columns, Floors,  Hand placed Pavements, Canal lining, Strip Footings Low 25-75
2 Heavily Reinforced  Concrete
Sections in Slabs, Beams, Walls, Columns, Slipform Work, Pumped Concrete Medium 50-100
3 Trench fill- In-situ piling High  100-150



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