Kathmandu University Civil Labs
WORKABILITY OF FRESHLY MIXED CONCRETE BY SLUMP TEST
OBJECTIVE:
To determine the workability of fresh concrete of given proportions by slump test where the nominal
maximum size of the aggregate does not exceed 38 mm.
APPARATUS REQUIRED:
b) Mould- the mould for the test specimen shall be in the form of the frustum of a cone having the
following internal dimensions
Bottom diameter = 200 mm
Top diameter = 100 mm
Height = 300 mm
c) Tamping rod – The temping rod shall be of steel or other suitable material 16 mm in diameter,
600 mm long and rounded at one end.
THEORY:
The goal of the test is to measure the consistency of concrete. Many factors are taken into account when
satisfying requirements of concrete strength, and to make sure that a consistent mixture of cement is being
used during the process of construction. The test also further determines the "workability" of concrete.
Engineers use the results to then alter the concrete mix by adjusting the water-cement ratio or adding
plasticizers to increase the slump of the concrete mix.
The strength of concrete of a given proportion is affected by the degree of compaction. The work done for
compaction of concrete is basically overturning friction between individual particle in the concrete.
The ease and homogeneity with which the fresh concrete can be mixed, compacted and finished is known
as its workability. A workable concrete should not show any segregation or bleeding.
In the slump test fresh concrete is filled in a mould of specified shape and dimensions. The supporting
mould is removed. Fresh unsupported concrete flows to the sides and sinking in the height takes place.
This vertical settlement is known as slump. The slump measured should be recorded in mm of subsidence
of the specimen during the test.
Slump = original height of concrete – the height of highest part of concrete in subsided position
When the supporting mould is removed, the slump may take one of three forms. In a true slump, the
concrete simply subsides, keeping more or less to shape. In a shear slump the top portion of the concrete
shears off and slips sideways. In a collapse slump, the concrete collapses completely. Only a true slump is
of any use in the test. If a shear or collapse slump is achieved, a fresh sample should be taken and the test
repeated. A collapse slump will generally mean that the mix is too wet or that it is a high workability mix,
for which the flow test is more appropriate.
Types of work Recommended slump (mm)
Road and mass concrete 25-50
Foundation without reinforcement 25-75
Foundation of RCC walls footing 50-100
RCC ordinary slab, beam etc. 50-125
Column, thin vertical section and retaining wall 75-125
PROCEDURE:
i) The internal surface of the mould is thoroughly cleaned and applied with a light coat of oil.
ii) The mould is placed on a smooth, horizontal, rigid and nonabsorbent surface.
iii) The mould is then filled in four layers with freshly mixed concrete, each approximately to one-fourth
of the height of the mould.
iv) Each layer is tamped 25 times by the rounded end of the tamping rod (strokes are distributed evenly
over the cross-section).
v) After the top layer is rodded, the concrete is struck off the level with a trowel.
vi) The mould is removed from the concrete immediately by raising it slowly in the vertical direction.
vii) The difference in level between the height of the mould and that of the highest point of the subsided
concrete is measured.
viii) This difference in height in mm is the slump of the concrete.
Note: the nominal maximum size of aggregate does not exceed 38mm.
Figure:
OBSERVATION AND CALCULATION:
Initial height of concrete =
Final height of concrete =
Slump =
CONCLUSION:
Go Through Above-Mentioned drive link for complete clarity.
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