Determination Of Compressive Strength

STANDARD

  • IS 403l (Part6)1988.

DEFINITION

  • Compressive strength is defined as the ratio of the load per unit area.

APPARATUS

  • Vibrating machine conforming to IS: 10080— 1982.
  • Poking rod confirming to IS: 10080-1982.
  • Cube moulds shall be of 70.60 mm size confirming to IS: 10080-1982.
  • Gauging trowel having steel blade 100 to 150 mm in length with straight edge weighing 210± 10gm.
  • Balance of capacity 10 kg and sensitivity l gram.

PROCEDURE

  • Unless otherwise specified this test shall be conducted at a temperature 27° ± 2 °C.
  • Weigh the material required for each cube separately.
  • The quantity of cement, standard sand and water required for each cube are as follows
    Cement = 200 gm
2mm to 1 mm – 200gms
Standard Sand = 600gms 1mm to 500 – 200 gms 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 arid 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 ± 2°C 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

REPORT

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

PRECAUTION

  • The time of mixing is very important and in no case shall not be less than 3 minutes and not to exceed 4 minutes.

DETERMINATION OF COMPRESSIVE STRENGTH
IS:4031(
Part 6)1988

Cube No Weight in grams Size of Cube Load in mm2 Load in KN Stress in N/mm2
1
2
3
Average
1
2
3
Average
1
2
3
Average
Average Compressive strength:                                                               Required Strength :                43 N/mm2
Remarks :

 

 

 

 

 

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