LAB TEST FOR DETERMINATION OF COMPRESSIVE STRENGTH OF CEMENT
OBJECTIVE: To determine the cement
compressive strength of mortar cubes compacted by means of standard vibration
machine.
APPARATUS: balance of 0.1gm
accuracy: standard vibration machine, standard weights, gauging trowel, standard
sand conforming to zone-1,2 and 70.6mm square cube mold, poking rod with
rounded at one end, evaporation dish and graduated glass measuring jar.
PROCEDURE:
1. Take
a representative cement sample to be tested with a sample driver.
2. Take
200gm of cement and mix with 200gm each of the zones of standard testing sand
which make quantity to cast one cube.
3. Place
it on non porous plate and mix it dry for one minute with trowel until the mix
is of uniform colour.
4. Take
water content of (p/4+3) percent, where p is the water required to prepare a
paste of standard consistency.
5. Mix
it well for three minutes to obtain a uniform colour of mixture, if this time
exceeds 4 minutes reject the mixture and take a fresh one.
6. Apply
a thin coating of petroleum jelly to the cube moulds and all faces of corners.
7. Place
the mould on the vibrating machine and clamp it top hold firmly.
8. Attach
a hopper of suitable size securely at the top of the mould to facilitate
filling of mould.
9. Immediately
after mixing place the mortar in the mould, prod the mortar at the edge for 20 times
to eliminate entrapped air and honey combing.
10. Place
the remaining mortar in the hopper of the cube mould, prod again ,and then
compact the mortar by vibration for two times.
11. Remove
the mould together with base plate from vibrating machine and finish the top
surface by smoothening with trowel.
12. Keep
the filled moulds in moist closet or moist room for 24 hours after completion of
vibration.
13. After
the time elapsed, de-mould the cubes and submerge immediately in water for the
specified/required time of curing.
14. Test
three moulds for each age of testing as specified in the relevant
specification.
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