DETERMINATION OF COMPRESSIVE STRENGTH OF CEMENT

Compressive strength test of cement is conducted at 3 days, 7 days and 28 days. The cubes of size 70.6 mm are made. Each test requires 3 cubes to be tested. For casting one cube, 200gm of cement and 600gm of standard sand is used.

DETERMINATION OF COMPRESSIVE STRENGTH OF HYDRAULIC CEMENT OTHER THAN MASONRY CEMENT

• Overview:

Compressive strength test of cement is conducted at 3 days, 7 days and 28 days. The cubes of size 70.6 mm are made as per procedure laid here and complying with IS 4031: Part-6. Each test requires 3 cubes to be tested. For casting one cube, 200gm of cement and 600gm of standard sand is used.

• Codes – IS 4031: Part 6,  ASTM C109

• SAMPLING:

The samples of the cement shall be taken in accordance with the requirements of IS: 3535- 1986 and the relevant standard specification for the type of cement being tested. The representative sample of the cement selected as above shall be thoroughly mixed before testing.

• TEMPERATURE AND HUMIDITY:

The temperature of moulding room, dry materials and water shall be maintained at 27 ± 2°C. The relative humidity of the laboratory shall be 65 ± 5 percent.

• MATERIALS REQUIRED: Cement, Standard Sand and Water.

• APPARATUS: –
  • Vibration Machine
  • Poking Rod
  • Cube Mould- The mould shall be of 70.6 mm size.
  • Graduated Glass measuring cylinder, 150 or 200ml capacity
  • Gauging Trowel
  • Balance
  • Standard Weights

 

• PREPARATION OF TEST SPECIMENS
• Mix Proportions and Mixing:

1. 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              –    200g
Standard Sand –   600 g
Water                 –   (P/4 + 3.0) percent 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 (Part 4) – 1988

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.
4. The quantity of water to be used shall be as specified in step 2.
5. 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.

• Moulding Specimens 

1. 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 surfaces of the bottom of the mould and its base plate in order to ensure that no water escapes during vibration. Treat the interior faces of the mould with a thin coating of mould oil.

2. Place the assembled mould on the table of the vibration machine and hold it firmly in position by means of a suitable clamp. Attach a hopper of suitable size and shape securely at the top of the mould to facilitate filling and this hopper shall not be removed until the completion of the vibration period.

3. Immediately after mixing the mortar in accordance with 6.1, place the mortar in the cube mould and prod with the rod specified in 5.2. The mortar shall be prodded 20 times in about 8s to ensure elimination of entrained air and honeycombing. Place the remaining quantity of mortar in the hopper of the cube mould and prod again as specified for the first layer and then compact the mortar by vibration.

4. The period of vibration shall be two minutes at the specified speed of 12,000 ± 400 vibration per minute.

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 of a trowel.

 

• Curing Specimens

1. Keep the filled moulds in moist closet or moist room 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.
2. The water in which the cubes are submerged shall be renewed every 7 days and shall be maintained at a temperature of 27 ± 2°C.
3. After they have been taken out and until they are broken, the cubes shall not be allowed to become dry.

 

• TESTING:

1. Test three cubes for compressive strength for each period of curing mentioned under the relevant specifications for different hydraulic cements, the periods being reckoned from the completion of vibration.

2. 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 35 N/mm2/min.

 

• CALCULATION

1. The measured compressive strength of the cubes shall be calculated by dividing the maximum load applied to the cubes during the test by the cross-sectional area, calculated from the mean dimensions of the section and shall be expressed to the nearest 0.5 N/mm”.

             Compressive strength of cement cube = Maximum load applied to the cube/ Cross sectional area of cube

                                                                                    = Breaking load of cube(in KN)/ 5.0 mm2

2. In determining the compressive strength, do not consider specimens that are manifestly faulty, or that give strengths differing by more than 10 percent from the average value of all the test specimens.
3. After discarding specimens or strength values, if less than two strength values are left for determining the compressive strength at any given period, a retest shall be made.