Workability Of Concrete:
Workability in the ease
with the concrete can be handeled deposited or placed and spread into its final
location and compacted. It depends on the fluidity or weightness plasticity and
cohesiveness or harshness of concrete. Workability to be adopted also depends
upon the thickness of structural member where the concrete is placed. Thus for
thin member more fluid concrete is required. While for massive concrete work a
stiffer mix can be used. In heavily or conjected rainforce structure more
workable mixes required so as to ensure no hollows remains. Slump is the
vertical substidence of fresh concrete after the removal of cirtain mould
called a slump cone in which concrete is feel and compacted.
Purpose Of The Test:
The main purpose of this
test is to know that workability of fresh concrete. This test is used for
designing the concrete mix during the trial mixes. The application of this test
is realy to check uniformity of concrete in field by making regular test on
concrete.
The Apparatus Required
For Conduction The Slump Test:
- Slump Cone metal mould in the form of a frustum of a cone open on both ends. Made of sheet metal 1.6 mm thick with suitable guides for lifting vertically up.
- Metallic mould in the form of a frustum of a cone having the internal dimensions as under
- Bottom diameter 20cm
- Top diameter 10cm
- Height 30cm
- A steel tamping rod 16mm diameter, 0.6 meter or 60mm along with bullet end is used.
- Steel Rule.
- Tray.
Procedure:
- The internal surface of the mould is thoroughly cleaned and applied with 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 cross section).
- 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 measured.
- This difference in height in mm is the slump of the concrete.
Collapse Slump
Shear Slump True Slump
Reporting of Results
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.
Calculation for Slump of
concrete:
Slump
of concrete = Height of the mould – Height of the subsided concrete
