The Consistency of cement test is performed to determine the
amount of water content that is to be added in cement to attain Standard
consistency or normal consistency of cement.
When water is mixed with cement, it starts hydration.
Excessive addition of water in cement results an increase in Water cement ratio
& ultimately cement loses its strength when it hardens. If Less water is
added than required, Cement isn’t properly hydrated and results in loss of
strength.
AIM:
To determine the normal consistency of a given sample of
cement.
Apparatus:
· Vicat apparatus conforming to IS : 5513-1976,
· Balance,
· Gauging Trowel,
· Stop Watch.
FIGURE:
Procedure:
1.
The standard consistency of a cement paste is
defined as that consistency which will permit the Vicat plunger to penetrate to
a point 5 to 7 mm from the bottom of the Vicat mould.
2.
Initially a cement sample of about 300 g is
taken in a tray and is mixed with a known percentage of water by weight of
cement, say starting from 26% and then it is increased by every 2% until the
normal consistency is achieved.
3.
Prepare a paste of 300 g of Cement with a
weighed quantity of potable or distilled water, taking care that the time of
gauging is not less than 3 minutes, nor more than 5 min, and the gauging shall
be completed before any sign of setting occurs. The gauging time shall be
counted from the time of adding water to the dry cement until commencing to
fill the mould.
4.
Fill the Vicat mould with this paste, the
mould resting upon a non-porous plate. After completely filling the mould,
smoothen the surface of the paste, making it level with the top of the mould.
The mould may be slightly shaken to expel the air.
5.
Place the test block in the mould, together
with the non-porous resting plate, under the rod bearing the plunger; lower the
plunger gently to touch the surface of the test block, and quickly release,
allowing it to sink into the paste. This operation shall be carried out
immediately after filling the mould.
6.
Prepare trial pastes with varying percentages
of water and test as described above until the amount of water necessary for
making up the standard consistency as defined in Step 1 is found.
Observation:
Express
the amount of water as a percentage by mass of the dry cement to the first
place of decimal.
Sr. No.
|
Weight of cement
(gms)
|
Percentage by
water of dry
Cement (%)
|
Amount of
water added
(ml)
|
Penetration
(mm)
|
1
|
||||
2
|
||||
3
|
||||
4
|
Conclusion:
Standard
consistency (%)= Weight of water added/Weight of cement x 100
The
consistency of a given sample of cement is _ _ _ _ %.
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