Concrete slump test
The
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. It is used to inclined degree of wetness.
vPrinciple :-
The slump test measures the
resulting behaviour of a compacted inverted cone of concrete under the action
of gravity. It indicates consistency or wetness of concrete.
v
Apparatus :-
Metal mould, in the shape of the
frustum of a cone, open at both ends, and provided with the handle, top
internal diameter 4 in (100mm), and bottom internal diameter 8 in (200mm) with
a height of 1 ft. (300mm). A 2 ft. (600mm) long bullet nosed metal rod, 5/8 in
(16mm) in diameter.
v
Procedure :-
The test is carried out using a
mould known as a slump cone or Abram cone.The cone is placed on a hard non-absorbent surface. This cone is
filled with fresh concrete in three stages. Each time, each layer is tamped 25
times with a rod of standard dimensions. At the end of the third stage, concrete
is struck off flush to the top of the mould. The mould is carefully lifted
vertically upwards with twisting otion, so as not disturb the concrete cone.
The subsidence is termed as
slump, and is measured to the nearest 5mm if the slump is <100mm and
measured to the nearest 10mm if the slump is>100mm.
vInterpretation of results :-
The slumped concrete takes
various shapes, and according to the profile of slumped concrete, the slump
concrete, the slump is turned as true slump. If a shear or collapse slump is
achieved, a fresh sample should be taken and the test repeated. A collapse
slump is an indication of too wet a mix.
Only a true slump is of any use
in the test. A collapse slump will generally mean that the mix is too wet or
that it is a high workability mix, for which the slump test is not appropriate.
Very dry mixes; having slump 0-25mm are used in road making, low workability
mixes; having slump 10-40mm are used for foundations with light reinforcement,
medium workability mixes; 50-90mm for normal reinforced concrete placed with
vibration, high workability concrete; 100mm.
Collapse
|
Shear
|
True
|
In a collapse slump the
concrete collapses completely.
|
In a shear slump the top
portion of the concrete Shear off and slips Sideways.
|
In a true slumps the concrete
simply subsides; keeping more or less to shape.
|
v
European classes of slump :-
According to European Standard EN
206-1:2000 five classes of slump have been designated, as tabulated below.
Slump
|
Slump in mm
|
S1
|
10-40
|
S2
|
50-90
|
S3
|
100-150
|
S4
|
160-210
|
S5
|
>220
|
v
Limitation of the slump test :-
The slump test is suitable for
slumps of medium to high workability, slump in the range of 5-260mm, the test
fail to determine the difference in workability in stiff mixes which have zero
slump, or for wet mixes that give a collapse slump. It is limited to concrete
formed of aggregates of less than 38mm(1.5 inch).
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