To determine the workability of fresh concrete by slump test as per IS: 1199 – 1959.
- Slump cone
- Tamping rod
- The internal surface of the mould is thoroughly cleaned and applied with a light coat of oil.
- The mould is placed on a smooth, horizontal, rigid and nonabsorbent surface.
- The mould is then filled in four layers with freshly mixed concrete, each approximately to one-fourth of the height of the mould.
- Each layer is tamped 25 times by the rounded end of the tamping rod (strokes are distributed evenly over the crosssection).
- After the top layer is rodded, the concrete is struck off the level with a trowel.
- The mould is removed from the concrete immediately by raising it slowly in the vertical direction.
- The difference in level between the height of the mould and that of the highest point of the subsided concrete is
- This difference in height in mm is the slump of the concrete.
The slump measured should be recorded in mm of subsidence of the specimen during the test. Any slump specimen, which collapses or shears off laterally gives incorrect result and if this occurs, the test should be repeated with another sample. If, in the repeat test also, the specimen shears, the slump should be measured and the fact that the specimen sheared, should be recorded.
- When is a slump test carried out on site?
A slump test is carried out on site before the concrete is poured in place . A sample is taken from the lorry when it arrives on site.
- What does a slump test measure?
Workability of fresh concrete
- What affects slump?
Amount of water in mix (Water cement ratio)
- How many times do you tamp a 75 mm layer of concrete?
TYPES OF SLUMPS
- Collapse slump : Mix is too wet or high workability mix , slump test isn’t appropriate for such mix.
- Shear Slump: Again perform the experiment to avoid shear slump . It is an indication of lack of cohesion of the mix .
- True Slump: Mix has high stiff consistency. In a true slump concrete just subsides shortly and more or less maintain the mould shape. This type of slump is most desirable.
- Zero Slump: If concrete maintains the actual shape of the mould, it is called zero slump which represents stiff, consistent and almost no workability.
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