Slump Test of Concrete

The concrete slump test is an empirical test that measures the workability of fresh concrete. The test is performed to check the consistency of freshly mixed concrete in a specific batch.

Consistency refers to the ease and homogeneity with which the concrete can be mixed, placed, compacted and finished. This test is most widely used due to the simplicity of apparatus and simple test procedure.

The slump test gives satisfactory results for the concrete mix of medium to high workability and unfortunately, it does not give the correct indication of low workability, which may give zero slumps. This test is also known as slump cone test.

APPARATUS:

1.   Mould or slump cone

·         height of 300 mm,

·         bottom diameter 200 mm, and

·         top diameter 100 mm.

2.   Standard tamping rod.

·         1.6 cm diameter,

·         61 cm long rounded at one end

3.   Non-porous base plate.

4.   Measuring scale.

FIGURE:

PROCEDURE OF TEST:

1.    Clean the internal surface of the mould and apply oil.
2.    Place the mould on a smooth horizontal non- porous base plate.
3.    Fill the mould with the prepared concrete mix in 4 approximately equal layers.
4.    Tamp each layer with 25 strokes of the rounded end of the tamping rod in a uniform manner over the cross section of the mould. For the subsequent layers, the tamping should penetrate into the underlying layer.
5.    Remove the excess concrete and level the surface with a trowel.
6.    Clean away the mortar or water leaked out between the mould and the base plate.
7.    Raise the mould from the concrete immediately and slowly in vertical direction.
8.  Measure the slump as the difference between the height of the mould and that of height point of the specimen being tested.

The subsidence of concrete is known as the slump and the value of slump is measured in mm.

Results of Slump Test on Concrete:

Slump for the given sample= _____mm

When the slump test is carried out, following are the shape of the concrete slump that can be observed:

·         True Slump – True slump is the only slump that can be measured in the test. The measurement is taken between the top of the cone and the top of the concrete after the cone has been removed as shown in figure-1.

·         Zero Slump – Zero slump is the indication of very low water-cement ratio, which results in dry mixes. These type of concrete is generally used for road construction.

·         Collapsed Slump – This is an indication that the water-cement ratio is too high, i.e. concrete mix is too wet or it is a high workability mix, for which a slump test is not appropriate.

·         Shear Slump – The shear slump indicates that the result is incomplete, and concrete to be retested.

Recommended Values of Slumps for Different Concrete Mixes:

Types Of Concrete	Slump Range In mm
1. Heavy mass construction	25-50
2. Pavements	20-30
3. Bridge deck	25-75
4. Beams and slabs	50-100
5. Columns, retaining walls and thin vertical members etc.	75-150
6. Vibrated concrete	12-25