The slump test of concrete is a laboratory or field test that is used to determine the workability of concrete. The slump test is simply a measure of the wetness or consistency of the concrete mix.
Apparatus Used in Concrete Slump Test
slump test for concrete apparatus
slump test mould
The equipment or apparatus used to test the concrete slump is quite simple. It consist of 2 items – a tamping rod and a truncated cone that’s 300 mm tall, 100 mm in diameter at the top, and 200 mm in diameter at the bottom. You can use the image above to understand the structure of the mould.
You would also need some extra stuff such as a concrete mixing pan, measuring scale and weighing machine.
Procedure
First, fresh concrete is poured into the mould in four layers, each 1/4th of the height, and tamped with twenty-five strokes of the tamping rod’s rounded end.
The strokes should be evenly dispersed across the cross-section and should penetrate the underlying layer for the second and subsequent layers.
Throughout its depth, the bottom layer is tamped.
The concrete is struck off level with a trowel or the tamping rod after the top layer has been rodded, ensuring that the mould is completely filled.
The mould is removed as soon as possible by slowly and carefully elevating it vertically.
This allows the concrete to settle and the concrete slump is determined by calculating the difference between the mould’s height and the highest point of the specimen being evaluated.
The slump is measured in millimetres of specimen subsidence.
Observation
Measurement of Slump test
Measurement of Slump
Slumping that occurs equally all around is considered a true slump.
Shear slump occurs when one-half of a cone falls down along an inclined plane.
Shear slump is caused by a lack of cohesiveness in the concrete, and the proportions of the concrete should be changed.
Concrete mixes with a very stiff consistency have no slump, therefore no difference in workability may be seen in the very dry range.
A real slump in a lean mix with a tendency to harshness can readily be altered to a shear type, or even collapse, with a non-uniform distribution of aggregates, especially coarse aggregates, and widely varied values of slump can be obtained in separate samples from the same mix.
As a result, for lean blends, the concrete slump test is unreliable.
Below table shows the different workability values :
Degree of Workability Slump
Very Low 0 – 25 mm
Low 25 – 50 mm
Medium 25 – 100 mm
High 100 – 175 mm
workability values
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