Procedure

Preparation of test specimen -

1. Use clean appliance and the room temperature shall be 27º ± 2º C. Take 200 g of cement and 600 g of standard sand ( ratio of cement to sand is 1:3). Place it on a non-porous plate and mix it with a trowel for one minute. The material for each cube shall be prepared separately.
2. Add water {(P/4) +3}% of the combined weight of cement and sand, where P is the consistency of cement. Mix it with cement and sand thoroughly such that the mixture attains a uniform colour. The mixing time should be less than 3 minutes and not exceed 4 minutes.
3. Hold the cube mould of size 70.6 mm (coated with a thin film of petroleum jelly between it's bottom surface and its base plate) firmly in the vibrating machine using appropriate clamps. Attach the hopper at the top of the mould.
4. Fill the mixed mortar in the hopper of the cube mould and then compact it by vibrations. The duration of vibration should be of two minutes at the speed of 1200 ± 1400 vibrations per minute.
5. Then place the moulds at a temperature of 27º ± 2º C and 90% relative humidity for 24 hours.
6. Remove the cubes from the mould and submerge them in fresh water for curing. This water shall be restored after every seven days and maintained at a temperature of 27º ± 2º C.

Testing of cement mortar cubes -

7. Take out three cubes from the water at the end of 3 days respectively. Wipe them with a dry cloth and measure their dimensions.
8. Place the cube inside the compression testing machine and apply the load uniformly at the rate of 14 N/mm²/ min. Note the load at which the cube fails.
9. Compute the compressive strength of the cube by using the formula Load/Area.
10. The average of all three readings gives the compressive strength of cement mortar at the end of 3 days.
11. Perform the same procedure (steps 7 to 10) to calculate the compressive strength of cement mortar at the end of 7 days and 28 days respectively.