Compressive Strength Test of Cement
Ref : IS : 4031 (part VI)
Purpose : To determine the compressive strength of cement
Significance : Compressive strength of cement helps in determining grade of cement, in
calculations of mix designing proportioning of concrete etc.
Apparatus:
Vibration machine
Poking rod
Cube mould of 70.6mm size
Gauging trowel
Balance, weights and tray
Graduated glass cylinder
Test Procedure:
Take cement 200gm, standard sand 600gm and 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 IV) – 1988
Place mixture of above cement and sand (1:3) on a tray, mix it dry with a trowel for one minute and then with water (as per step (1) of procedure) until the mixture of uniform colour
Note: The time of mixing shall in any event be not less than 3 minutes and should the time taken to obtain a uniform colour exceed 4 minutes, the mixture shall be rejected and the operation repeated with a fresh quantity of cement, sand and water
Properly oil the interior faces and bottom of mould which should be water tight
Place the assembled mould on the table of 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 vibration period
Immediately after mixing the mortar as in step (2) of procedure, place the mortar in the cube mould and rod with the poking rod 20 times in about 8 seconds to ensure elimination of entrapped air to prevent honey combing. Place the remaining quantity of mortar in the hopper of the cube mould and rod again as done for the first layer
Compact the mortar by vibration machine for 2 minutes at the specified speed of 12000 ± 400 vibration per minute
At the end of vibration, remove mould together with the base plate from the machine and finish the top surface of the cube in the mould by smoothening the surface with the blade of trowel
Keep the filled mould in moist cloth for 24 hours after completion of vibration
At the end of this period remove them from the mould and immediately submerge in clean fresh water
Test sets of three cubes for compressive strength at 3, 7 & 28 days in compression testing machine. The cubes shall be tested on their sides without any packing between the cube and the steel platens of the testing machine. Load shall be steadily and uniformly applied at the rate of 35 N/mm2 per minute
The load when the cube fails shall be noted and divided by cross sectional area of the cube and record the results.
Observation Table:
Limit: Minimum compressive strength in N/mm2 for different type of cement at different ages:
Frequency: For every batch received at site.
