Compressive strength test of cement

The compressive strength of cement is found by crushing standard mortar cubes made from cement and standard sand (IS 4031 Part 6, IS 650).

Apparatus

Cube moulds of 70.6 mm side (area 5000 mm²), vibrating machine, standard (Ennore) sand, graduated cylinder, balance, curing tank, compression testing machine.

Procedure

1. Take 200 g cement and 600 g standard sand for each cube, a 1:3 mix (for 3 cubes: 600 g cement + 1800 g sand). Mix dry for about one minute.
2. Add water equal to (P/4 + 3)% of the combined weight of cement and sand, where P is the percentage of water for standard consistency. Mix for 3-4 minutes until uniform in colour.
3. Place the mortar in the mould immediately and vibrate for 2 minutes at the specified speed; level and smooth the top.
4. Keep the moulds in a moist chamber at 27 ± 2 C and at least 90% relative humidity for 24 hours.
5. Remove the cubes and cure them in clean water at 27 ± 2 C until the test date.
6. Test the cubes at 3, 7 and 28 days after casting, on their sides, with a load rate of 35 N/mm² per minute.
7. Compressive strength = failure load / cross-section area (5000 mm²). The average of three cubes is the result.

Minimum strength (53 grade OPC, IS 12269)

For 43 grade (IS 8112) the values are 23, 33 and 43 MPa.