TESTS ON FRESH CONCRETE
AIM: To determine the workability of fresh concrete by slump test as per IS: 1199 - 1959.
APPARATUS
i) Slump cone
ii) Tamping rod
PROCEDURE
i) The internal surface of the mould is thoroughly cleaned and applied with a light coat of oil.
ii) The mould is placed on a smooth, horizontal, rigid and nonabsorbent surface.
iii) The mould is then filled in four layers with freshly mixed concrete, each approximately to one-fourth of the height of the mould.
iv) Each layer is tamped 25 times by the rounded end of the tamping rod (strokes are distributed evenly over the crosssection).
v) After the top layer is rodded, the concrete is struck off the level with a trowel.
vi) The mould is removed from the concrete immediately by raising it slowly in the vertical direction.
vii) The difference in level between the height of the mould and that of the highest point of the subsided concrete is measured.
viii) This difference in height in mm is the slump of the concrete.
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.
2. COMPACTING FACTOR
AIM: To determine the workability of fresh concrete by compacting factor test as per IS: 1199 - 1959.
APPARATUS
i) Compacting factor apparatus
PROCEDURE
i) The sample of concrete is placed in the upper hopper upto the brim.
ii) The trap-door is opened so that the concrete falls into the lower hopper.
iii) The trap-door of the lower hopper is opened and the concrete is allowed to fall into the cylinder.
iv) The excess concrete remaining above the top level of the cylinder is then cut off with the help of plane blades.
v) The concrete in the cylinder is weighed. This is known as weight of partially compacted concrete.
vi) The cylinder is filled with a fresh sample of concrete and vibrated to obtain full compaction. The concrete in the cylinder is weighed again. This weight is known as the weight of fully compacted concrete.
REPORTING OF RESULTS
Compacting factor =
Weight of partially compacted concrete
Weight of fully compacted concrete
It should normally be stated to the nearest second decimal
place.
3.VEE-BEE
AIM: To determine the workability of fresh concrete by using a Vee-Bee consistometer as per IS: 1199 - 1959.
APPARATUS
i) Vee-Bee consistometer
PROCEDURE
i) A conventional slump test is performed, placing the slump cone inside the cylindrical part of the consistometer.
ii) The glass disc attached to the swivel arm is turned and placed on the top of the concrete in the pot.
iii) The electrical vibrator is switched on and a stop-watch is started, simultaneously.
iv) Vibration is continued till the conical shape of the concrete disappears and the concrete assumes a cylindrical shape.
v) When the concrete fully assumes a cylindrical shape, the stop-watch is switched off immediately. The time is noted.
REPORTING OF RESULTS
The consistency of the concrete should be expressed in VB-degrees, which is equal to the time in seconds, recorded above.