Compressive strength test of cement

AIM:

Determine the compressive strength of cement as per IS 4031 (Part 6) 1988.

APPARATUS:

1. Vibrating machine confirming to IS: 10080 – 1982.
2. Poking rod confirming to IS: 10080-1982.
3. Cube moulds shall be of 70.60 mm
4. size confirming to IS: 10080-1982.
   Gauging trowel having steel blade 100 to 150 mm in length with straight edge
   weighing 210 + 10 gms.
5. Balance of capacity 10 Kg and sensitivity 1 gram.

AGE AT TEST:

Tests should be done at recognised ages of the test specimens, usually being 7 and 28 days. The ages should be calculated from the time of the addition of water to the drying of ingredients.

PROCEDURE:

• Unless otherwise specified this test shall be conducted at a temperature 270 + 20C.
• Weigh the material required for each cube separately.
• The quantity of cement, standard sand and water required for each cube are as follows
  Cement = 200gms
  2mm to 1mm – 200gms
  Standard Sand = 600gms 1mm to 500mic – 200gms
  Conforming to IS: 650 –1991. 500mic to 90mic – 200gms
  Water =(P/ 4+ 3) Percentage of combined mass of cement and sand.
  P is the consistency of cement as per IS: 4031 (Part 4) 1988.
• Place on a nonporous plate, a mixture 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 time of mixing shall in any event be not less than 3 minutes and should be the time taken to obtain uniform colour exceeds 4 minutes.
• In assembling the moulds ready for use, cover the joints between the halves of the
  mould with a thin film of petroleum jelly and apply a similar coating of petroleum jelly between the contact surface of the bottom of the mould and base plate in order to ensure that no water escapes during vibration.
• Place the assembled mould on the table of the vibration machine and hold it firmly
  in position by means of suitable clamp, attach a hopper of suitable size and shape
  securely at the top of the mould to facilitate filling and hopper shall not be removed until the completion of vibration period.
• Immediately after fixing the mould in the vibrating machine, place the mortar in the cube mould and prod with the rod.
• Prod the mortar 20 times in about 8 seconds to ensure elimination of entrapped air
  and honey combing.
• Place the remaining mortar in the cube mould and prod again as specified for the
  first layer and then compact the mortar by vibration.
• The period of vibration shall be two minutes at the specified speed of 12000 + 400
  vibrations per minute.
• Remove the mould from the vibrating machine and cut of the excess mortar with a
  straight edge.
• Store the test specimens in a place free from vibration, in moist air of at least 90
  percent relative humidity and at a temperature of 27 + 20C for 24 + 1/2 hours from
  the addition of water to the dry ingredients.
• After this period, mark the specimens and remove from the moulds and unless
  required for test within 24 hours.
• Immediately submerge the cubes in a clean, fresh water or saturated lime solution
  and keep there until taken out just prior to test.
• Renew the water or solution in which the specimens are submerged for every seven days, and the temperature of water is maintained with the specified limits.
• Conduct testing at recognized ages of the specimens, the most usual being 7 and
  28 days.
• When it may be necessary to obtain the early strength, tests may be conducted at
  the age of 72 + 2 hours.
• Calculate the ages from the addition of water to the dry ingredients.\Test at least three specimens preferably from different batches at each selected
  age.

CALCULATIONS:

Compressive strength =(Load/Cross sectional area of the specimen)/N / mm²

RESULTS:

Report the individual and the mean results to the second decimal and express in N/ mm²

PRECAUTIONS:-

• The time of mixing is very important and in no case shall not be less than 3minutes. 
• Apply the Greece to the mould (inner side of mould)
• The Temperature of water should be maintained at 27 +/- 2 oC.
• Mould should be immersed in water fully.
• The cube should be tested immediately after taking out of water. 
• Cube should be tested on their side not on their face. 

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