Aim
To determine the compressive strength sample of
cement.
Apparatus
The standard sand to be used in the test shall
conform to IS : 650-1966, Vibration Machine, Poking Rod, Cube Mould of 70.6 mm size conforming to IS :
10080-1982, Balance, Gauging Trowel, Stop Watch, Graduated Glass Cylinders, etc.
Theory
The compressive strength of hardened cement is
the most important of all the properties. Therefore, it is not surprising that the cement is always tested
for its strength at the laboratory before the cement is used in important works. Strength tests are
not made on neat cement paste because of difficulties of excessive shrinkage and subsequent
cracking of neat cement.
Procedure
1. Preparation of test
specimens - Clean appliances shall be used for mixing and the temperature of water and that of the test room at the time when the above
operations are being performed shall be 27 ± 2°C. Potable/distilled water shall be used in preparing the cubes.
2. The material for each cube shall be mixed
separately and the quantity of cement, standard sand and water shall be as follows:
Cement 200 g and Standard Sand 600 g
Water per cent of combined mass of cement and sand, where P is the percentage
of water required to produce a paste of standard consistency determined as described in
IS : 4031 (Part4)-1988 or as taken in Normal consistency of Cement.
3 .Place on a nonporous plate, a mixture of
cement and standard sand. Mix it dry with a trowel for one minute and then with
water until the mixture is of uniform colour. The quantity of water to be used
shall be as specified in step 2. The time of mixing shall in any event be not
less than 3 min and should the time taken to obtain a uniform colour exceed 4
min, the mixture shall be rejected and the operation repeated with a fresh
quantity of cement, sand and water.
4. Place the assembled mould on the table of the vibration machine and hold it
firmly in position by means of a suitable clamp.
5. Immediately after mixing the mortar in
accordance with step 1 & 2, place the mortar in the cube mould and prod with the rod. Place the mortar in the hopper of the cube
mould and prod again as specified for the first layer and then compact the mortar by
vibration.
6. The period of vibration shall be two minutes
at the specified speed of 12 000 ± 400 vibration per minute.
7. Curing Specimens - keep the filled moulds in moist closet or moist room for
24 ± 1 hour after completion of vibration. At the end of that period, remove them from the
moulds and immediately submerge in clean fresh water and keep there until taken out just
prior to breaking and shall be maintained at a temperature of 27 ± 2°C
8. Test three cubes for compressive strength for
each period of curing mentioned under the relevant specifications (i.e. 3 days, 7 days, 28 days)
9. The cubes shall be tested on their sides
without any packing between the cube and the steel plattens of the testing machine. One of the plattens shall be carried on
a base and shall be self-adjusting, and the load shall be steadily and uniformly applied, starting
from zero at a rate of 40N/mm2/min
Observation
|
Sl.
NO.
|
Age of
Cube
|
Wt of Cement
Cube
|
Cross sectional
Area (mm2)
|
Load (N)
|
Compressive
strength (N/mm2 )
|
|
1
|
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2
|
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3
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4
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5
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6
|
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Compressive strength is reported to the nearest 0.5 N/mm2
Specimens that are manifestly faulty, or that give strengths
differing by more than 10% from the average value of all the test specimen
should not be considered.
Test three cubes for compressive strength for each period of
curing.
Result
i) The average 3 Days
Compressive Strength of given cement sample is found to be ________
ii) The average 7 Days Compressive Strength of given cement sample is found to
be ________
iii) The average 28 Days Compressive Strength of given cement sample is found
to be_______
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