OBJECT: To determine the compressive strength of a
sample cement.
APPARATUS: - Vibration machine cube moulds (70.60mm)
size area = 5000mm2 poking rod, container (basin) measuring cylinder, wash
bottle, trowel, etc.
EXTRACTS FROM IS: 4031-1968
1. Place on a non-porous container a mixture of cement
and standard sand (conform IS 650-1966) in the proportion of 13 by weight Mix
it dry with trowel for one minute and them with water until the mixture is of
uniform colour. 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 fresh quantity of cement,
sand and water.
2. The material for each cube shall be mixed
separately and the quantity of cement. standard sand and water shall be as
follows:
i) Cement: 200 gms
ii) Standard sand: 600 gms (IS: 650-1966)
The standard sand obtained from Ennore, Madras, shall
(100%) pass through 2 mm I.S. sieve and shall be (100%) retained on 90 micron
IS sieve with the following particle size distribution.
Particle
size
Percent
a)
Greater
than I mm
33.33
b)
Smaller
than 1 mm and greater than 33.33
c)
500
microns,
d)
Below
500 microns 33.33
The sieve shall conform to IS: 460-1962.
iii) Water (P/4+3) percent of combined weight of cement
and sand where P is the percentage of water required to produce a paste of
standard consistency.
3. Immediately after mixing the mortar place the
mortar in cube mould and prod with standard poking rod. The mortar shall be
prodded 20 times in about 8 seconds to ensure elimination of entrained air and
honey combing. Place the remaining quality of mortar in the hopper of the cube
mould and prod again as specified for the first layer and them compact the
mortar by vibration.
4. The period of vibration shall be two minutes (at
the specified speed 12000+ 400 vib./min).
5. At the end of vibration remove the mould together
with the base plate from the machine and finish the top surface of the cube in
the mould by smoothing the surface with the blade.
6. Curing Specimens: Keep the filled moulds at a
temperature of 27 ± 2° C in an atmosphere of at least 90% relative humidity for
24 hours 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. The water in which the cubes are
submerged shall be renewed every 7 days and shall be maintained at a temp of 27
+2°. After they have been taken out and until they are broken the cubes shall
not be allowed to become dry.
7. The load shall be steadily and uniformly applied
starting from zero at a rate of 350 Kg/cm /min.
8. Test three cubes for compressive strength at the
periods mentioned under the relevant specifications for different hydraulic
cements, the periods being reckoned from the completion of vibration. The
compressive strength shall be the average of the strengths of the three cubes
for each period of curing.
9. OBSERVATION:
|
S.No |
Identification Mark |
Age |
Crushing load (Kg) |
Compressive strength |
|
|
|
|
|
|
RESULT: The compressive strength of cement at
_____________(days)
_____________N/mm
DISCUSSION: - Cover the following points:
i)
Importance
of the test.
ii)
Normal
results expected
iii)
Reasons
for deviation of actual results from expected results
iv)
Sources
of errors.
NOTE: -
days =
1. LEAVE THE APPLICANCES USED BY YOU AND THEIR
SURROUNDINGS CLEAN.
2. RECORD YOUR OBSERVATIONS IN THE JOURNAL AND GET
THEM VERIFIED BY YOUR TEACHER
(i) AT THE TIME OF CASTING
(ii) AT THE TIME OF TESTING
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