The concrete slump test is an empirical test that measures the workability of fresh concrete.
More specifically, it measures the consistency of the concrete in that specific batch. This
test is performed to check the consistency of freshly made concrete. Consistency is a
term very closely related to workability. It is a term which describes the state of
fresh concrete. It refers to the ease with which the concrete flows. It is used to indicate
the degree of wetness. Workability of concrete is mainly affected by consistency i.e. wetter
mixes will be more workable than drier mixes, but concrete of the same consistency may vary
in workability. It is also used to determine consistency between individual batches.
The test is popular due to the simplicity of apparatus used and simple procedure. Unfortunately,
the simplicity of the test often allows a wide variability in the manner that the test
is performed. The slump test is used to ensure uniformity for different batches of similar
concrete under field conditions, and to ascertain the effects of plasticizers on their introduction.
In India this test is conducted as per IS specification.
Principle The slump test result is a slump of the behaviour
of a compacted inverted cone of concrete under the action of gravity. It measures the consistency
or the wetness of concrete. 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, and bottom internal diameter 8 in with a height
of 1 ft. A 2 ft long bullet nosed metal rod, 5/8 in in diameter.
Procedure
The test is carried out using a mould known as a slump cone or Abrams cone. The cone is
placed on a hard non-absorbent surface. This cone is filled with fresh concrete in three
stages, each time it is tamped using 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, so as not to disturb the concrete cone. Concrete subsides. This
subsidence is termed as slump, and is measured in to the nearest 5 mm if the slump is <100 mm
and measured to the nearest 10 mm if the slump is >100 mm.
Interpretation of results The slumped concrete takes various shapes,
and according to the profile of slumped concrete, the slump is termed as true slump, shear slump
or collapse 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 slump test is not appropriate. Very
dry mixes; having slump 0 – 25 mm are used in road making, low workability mixes; having
slump 10 – 40 mm are used for foundations with light reinforcement, medium workability
mixes; 50 - 90 for normal reinforced concrete placed with vibration, high workability concrete;
> 100 mm.
European classes of slump According to European Standard EN 206-1:2000
five classes of slump have been designated, as tabulated below.
Limitations of the slump test The slump test is suitable for slumps of medium
to high workability, slump in the range of 5 – 260 mm, the test fails 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 38 mm.
Differences in standards The slump test is referred to in several testing
and building codes, with minor differences in the details of performing the test.
United States In the United States, engineers use the ASTM
standards and AASHTO specifications when referring to the concrete slump test. The American standards
explicitly state that the slump cone should have a height of 12-in, a bottom diameter
of 8-in and an upper diameter of 4-in. The ASTM standards also state in the procedure
that when the cone is removed, it should be lifted up vertically, without any rotational
movement at all. The concrete slump test is known as "Standard Test Method for Slump of
Hydraulic-Cement Concrete" and carries the code or.
United Kingdom and mainland Europe In the United Kingdom, the standards specify
a slump cone height of 300 mm, a bottom diameter of 200 mm and a top diameter of 100 mm.
The British Standards do not explicitly specify that the cone should only be lifted vertically.
The slump test in the British standards was first and is now replaced by the European
Standard. The test should be carried out by filling the slump cone in three equal layers
with the mixture being tamped down 25 times for each layer.
Other tests There are many tests for evaluating slump
in concrete: one example is the K-Slump Test. Other tests evaluating consistency are the
British compacting factor test, the Vebe consistometer for roller-compacted concrete, and the flow
table test. Another way of determining slump is to use
an automated slump meter. Sensors and controls enable the meters to measure and display slump.
Their reliability has by now earned them acceptance in various standard codes such as ASTM International.
Some automated slump meters, such as the one by Verifi also can add water to the concrete
mix in the delivery truck while in transit. In 2013 ASTM C94/C94M was revised to allow
water additions during transit for trucks equipped with automated slump monitoring and
measurement systems. See also
Plasticity Flow table test
References ^ a b c d e f Gambhir, M. L.. Concrete technology.
Tata McGraw-Hill. Retrieved 2010-12-11. ^ W.B. Mckay; J.M. Mckay. Building Construction
Vol. Ii. Orient Longman Private Limited. p. 32. ISBN 978-81-250-0941-2. Retrieved 9 June
2012. ^ a b c d e "Slump test". The Concrete Society.
Retrieved 2010-12-11. ^ a b Lyons, Arthur. Materials for architects
and builders. Butterworth-Heinemann. Retrieved 2010-12-11.
^ Tattersall, G.H.. Workability and quality control of concrete. London: E & FN Spon.
ISBN 0-419-14860-4. ^ qpa.org; QPA BRMCA Committee Bulletin 3
^ ASTM Complete Set. 2013 ISBN:9781622042715 ^ CSN EN 12350-4 - Testing fresh concrete
- Part 4: Degree of Compactability ^ ASTM C1170/C1170M-08 October 2008 Standard
Test Method for Determining Consistency and Density of Roller-Compacted Concrete Using
a Vibrating Table ^ Panarese, William C.; Kosmatka, Steven H.;
Kerkhoff, Beatrix. Design and control of concrete mixtures. [Skokie, Ill.]: Portland Cement
Association. ISBN 0-89312-217-3.