Concrete Slump Test

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Concrete Slump Test

The concrete slump test is an empirical test that measures workability of fresh concrete.

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 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 in which the test is performed. The slump test is used to ensure uniformity for different batches of 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 measures the resulting behavior of a compacted inverted cone of concrete under the action of gravity. It indicates consistency or wetness of concrete.

Concrete Slump Test 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 (100 mm), and bottom internal diameter 8 in (200 mm) with a height of 1 ft (300 mm). A 2 ft (600 mm) long bullet nosed metal rod, 5/8 in (16 mm) in diameter.

concrete slump test apparatus

Concrete Slump Test 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, 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 motion, so as not to disturb the concrete cone.

Concrete subsides. This subsidence is termed as slump, and is measured 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.

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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 – 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.

concrete slump test results

Collapse
In a collapse slump the concrete collapses completely.

Shear
In a shear slump the top portion of the concrete shears off and slips sideways.

True
In a true slump the concrete simply subsides, keeping more or less to shape.

Limitations of the Concrete 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 (1.5 inch).

Concrete Slump Test Standards

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 (ASTM C 143) or (AASHTO T 119).

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 (BS 1881–102) and is now replaced by the European Standard (BS EN 12350-2). 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. source: https: //en. wikipedia.org/ wiki/ Concrete_slump_test.

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