**COMPRESSIVE STRENGTH OF CEMENT**

The compressive strength of the cement cubes is the maximum load applied to the cubes during the test divided by its cross-sectional area. The average of the three specimens at each specified age shall be calculated. This method covers the method of compressive strength test of cement motor cubes compacted by means of standard vibration machine.

**Test standard :** IS 4031-Part VI : 1988

**Test Apparatus : **

- Balance of accuracy 0.01gm
- Standard vibration machine
- 70.6 mm size cube moulds
- Gauging trowels
- Standard sand of grade I, II and III,
- Pocking rod rounded at one end
- Evaporation dish
- Graduated measuring jar

**Test Procedure :**

- Maintain the laboratory at a temperature and relative humidity of 27±2 °C and 65±5%.
- Take the cement sample to be tested and test sample shall be prepared by adding 200 gm of cement and mix with 200 gms of each grade of standard sand, which make quantity to cast one cube.
- Place it on a non-porous plate and mix it dry for one minute with trowel until the mix is of uniform colour.
- Take water content of (P/4 + 3) percent, where P is the water required to prepare a paste of standard consistency.
- Mix it well for 3 minutes to obtain a uniform colour of mixture, if this exceeds 4 minutes reject the mixture and take a fresh one.
- Apply a thin coating of oil to the cube mould on all faces and corners. Place the mould on the vibrating machine and clamp it. Attach a hopper at the top of mould to facilitate filling of mould.
- Immediately after mixing place the mortar in the mould, prod the mortar at the edge for 20 times in 8 sec to eliminate entrapped air and honey combing.
- Place the remaining mortar in the hopper of the cube mould, prod again and then compact the mortar by vibration for two minutes.
- Remove the mould together with base plate from the vibrating machine and finish the top surface of cube by smoothening with a trowel.
- Keep the filled moulds in moist closet or moist room for 24 hours after completion of vibration. After the time elapsed, de-mould the cubes and submerge immediately in water at a temperature of 27±2 °C.
- Three cube specimens shall be tested for each period of testing as specified in the relevant specification.
- 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**

Compressive strength of the cubes is the maximum load applied to the cubes during the test divided by its cross-sectional area. Average of the three specimens at each specified age shall be calculated and reported to the nearest 0.5N/mm2

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