Workability test- Slump test

AIM

To determine the workability or consistency of concrete mix of given proportion by slump test.

APPARATUS 

Iron pan to mix concrete, weighing machine, trowel slump, cone, scale and tamping rod.

THEORY

The slump cone is a hollow frustum made of thin steel sheet with internal dimensions, as the top diameter 10 cms. The bottom diameter 20 cms, and height 30cms. It stands on a plane nonporous tamping rod.

The slump cone is a hollow frustum made of thin steel sheet with internal dimensions, as the top diameter 10 cms. The bottom diameter 20 cms, and height 30cms. It stands on a plane nonporous surface. To facilitate vertical lifting from moulded concrete it is provided with a suitable guide attachment and suitable foot pieces and handles. The tamping rod is 16mm dia. 60cm.long and is bullet pointed at the lower end.

PROCEDURE

1) Mix the dry constituents thoroughly to get a uniform colour and then add water.

2) The internal surface of the mould is to be thoroughly cleaned and placed on a smooth, horizontal, rigid and non absorbent surface.
3) Place the mixed concrete in the cleaned slump cone in 4 layers each approximately 1/4 in height of the mould. Tamp each layer 25 times with tamping rod.
4) Remove the cone immediately, rising it slowly and carefully in the vertical direction.
5) As soon as the concrete settlement comes to a stop, measure the subsistence of the concrete in cms, which gives the slump.

Note: Slump test is adopted in the Laboratory or during the progress of the work in the field for determining consistency of concrete where nominal max., size of aggregates does not exceed 40mm. Any slump specimen which collapses or shears off laterally gives incorrect results and at this juncture the test is repeated only true slump should be measured.

OBSERVATIONS:

S.No	W/c Ratio	Slump in mm
1	0.5
2	0.6
3	0.7
4	|0.8

PRECAUTIONS:
1) The strokes are to be uniformly applied through the entire area of the concrete section.
2) The cone should be removed very slowly by lifting it upwards without disturbing the concrete.
3) During filling the mould must be firmly pressed against the base.
4) Vibrations from nearly machinery might also increase subsidence; hence test should be made beyond the range of ground vibrations.

Discussion

This test is not a true guide to workability. For example, a harsh coarse mix cannot be said to have same workability as one with a large portion of sand even though they have the same slump.

Recommended slumps of concrete mix of various works

S.No	Description of work	Recommended slump in cms
1	Road work	2.5 to 5.0
2	Ordinary beams to slabs|	5 to 10
3	Columns thin vertical section & retaining Walls etc	7.5 to 12.5
4	Mass concrete(Runway, |Pavements)	2.5 to 5

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