Slump test is used to measure the workability of fresh concrete. It’s a simple and most popular test.
Apparatus used in test:
- Cone (300mm x 200mm x 100mm)
- Measuring scale
- Tamping rod
Procedure of slump test:-
- Internal surface of the cone should be cleaned properly and a light coat of oil should be applied.
- Cone should be placed on a horizontal place
- The cone is then filled with freshly mixed concrete in 3 layers.
- Each layer is tamped 25 times by the tamping rod.
- After filling the cone properly, the cone is removed from the concrete immediately by raising it slowly in the vertical direction.
- After removing the cone subsided concrete is measured
- The slump of the concrete = height of the cone – height of the subsided concrete.
Types of Slump:-
The slump is termed as three types
1) Collapse slump 2) Shear Slump 3)True Slump
If the Slump is termed as shear or collapse slump, a fresh sample should be taken and the test repeated.
Result of Slump Test
0 – 25 mm = very dry mixes = used in road making.
10 – 40 mm = low workability mixes = used for foundations with light reinforcement
50 – 90 mm = medium workability mixes = used for normal reinforced concrete
100+ mm high workability concrete.
Limitation of the slump test:The slump test is suitable for slumps of medium to high workability, slump in the range of 25 – 125 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.