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:
- Clean the internal surface of the mould and apply oil.
- Place the mould on a smooth horizontal non- porous base plate.
- Fill the mould with the prepared concrete mix in 4 approximately equal layers.
- 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.
- Remove the excess concrete and level the surface with a trowel.
- Clean away the mortar or water leaked out between the mould and the base plate.
- Raise the mould from the concrete immediately and slowly in vertical direction.
- 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
|
good info about slump test
ReplyDelete