SLUMP TEST
Slump
test measures consistency of concrete in that specific batch. It is performed
to check consistency of freshly made concrete. Consistency refers to the ease
with which concrete flows.
OBJECT: To determine the workability of concrete using slump test.
EQUIPMENTS REQUIRED FOR CONCRETE SLUMP TEST: Mould for slump test, non porous base plate, measuring scale, temping rod. The mould for the test is in the form of the frustum of a cone having height 30 cm, bottom diameter 20 cm and top diameter 10 cm. The tamping rod is of steel 16 mm diameter and 60cm long and rounded at one end.
SAMPLING OF MATERIALS FOR SLUMP TEST: A concrete mix (M15 or other) by weight with suitable water/ cement ratio is prepaid in the laboratory and required for casting 6 cubes after conducting Slump test.
PROCEDURE
FOR CONCRETE SLUMP 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 3 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.
NOTE: The above operation should be carried out at a place free from Vibrations or shock and within a period of 2 minutes after sampling.
SLUMP
VALUE OBSERVATION:
The slump (Vertical settlement) measured shall be recorded in terms of millimeters of subsidence of the specimen during the test.
RESULT
OF CONCRETE SLUMP TEST:
Slump for the given sample = (i) …………mm (ii) ………….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 slumps is the
indication of very low water-cement ratio, which results in dry mixes. This
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.
