Compressive Strength Test of Cement Mortar Cubes – IS 4031 (Part 6) | Step-by-Step with ExamplesCompressive Strength Test of Cement Mortar Cubes
(IS: 4031 – Part 6)
1. Object of the Test
To determine the compressive strength of hydraulic cement using
standard cement mortar cubes (70.6 mm) compacted by a
standard vibration machine as per IS 4031 (Part 6).
Quick Summary:
IS:4031 (Part-6) specifies the
method for determination of compressive strength of cement using
standard mortar cubes of size 70.6 mm.
Cubes are prepared in a
1:3 cement–standard sand mix, compacted by vibration, cured for
3, 7 and 28 days, and tested at a loading rate of
35 N/mm²/min.
The test ensures that cement meets the
minimum strength requirements prescribed for OPC-43 and OPC-53 grades.
See calculation & examples →
Example:
This test is used to check whether an OPC 43 or OPC 53 cement bag supplied to site
meets BIS strength requirements at 3, 7 and 28 days.
2. Apparatus
- Vibration machine (12,000 ± 400 vibrations/min)
- Cube moulds – 70.6 mm × 70.6 mm × 70.6 mm
- Standard sand (IS 650 : 1966)
- Prodding rod
- Non-porous mixing plate
- Weighing balance
- Cube crushing testing machine (CTM)
- Mould oil, petroleum jelly
- Potable / distilled water
Example:
If your CTM capacity is 2000 kN and vibration machine speed is calibrated annually,
the setup satisfies IS requirements.
3. Standard Sand (IS 650)
| Particle Size Range | Percentage |
|---|
| 2.0 mm – 1.0 mm | 33.33% |
| 1.0 mm – 500 micron | 33.33% |
| 500 micron – 90 micron | 33.33% |
Example:
If 900 g of standard sand is tested for gradation,
each fraction should weigh approximately 300 g.
4. Mix Proportion
| Material | Quantity |
|---|
| Cement | 200 g |
| Standard Sand | 600 g |
| Water | (P/4 + 3)% |
P = % water required for standard consistency (IS 4031 Part 4)
Example:
If standard consistency P = 26%
Water = (26/4 + 3)% = 9.5%
Total mass = 800 g
Water = 0.095 × 800 = 76 g
5. Mixing Procedure
- Dry mix cement + sand for 1 minute.
- Add calculated water.
- Mix for minimum 3 minutes.
- Reject mix if uniform colour is not achieved within 4 minutes.
Example:
Dry mixing from 10:00–10:01 AM
Wet mixing ends at 10:04 AM → ACCEPTABLE
If mixing continues beyond 10:05 AM → REJECT batch
6. Moulding of Specimens
- Oil mould and base plate.
- Fix mould firmly on vibration table.
- Fill mortar in layers.
- Prod each layer 20 times in ~8 seconds.
- Vibrate for 2 minutes.
- Finish surface using trowel.
Example:
1st layer: 20 rod blows in 8 s
2nd layer: 20 rod blows in 8 s
Vibration time: 2 minutes exactly
7. Curing of Specimens
- Keep moulds in moist room for 24 hours.
- Demould and immerse in water.
- Maintain water temperature at 27 ± 2°C.
- Renew water every 7 days.
Example:
Casting completed at 4 PM on Day-0
Demould at 4 PM on Day-1
3-day test conducted at 4 PM on Day-3
8. Testing of Specimens
- Test cubes on their sides.
- Load rate: 35 N/mm² per minute.
- Test minimum three cubes.
Example:
For cube area 50 cm² (=5000 mm²),
Load rate ≈ 175 kN per minute
9. Calculation of Compressive Strength
Compressive Strength = P / A
Example (kg-machine):
Crushing load = 7200 kg
Area = 50 cm²
Strength = 7200 / 50 = 144 kg/cm²
Example (kN-machine):
Load = 720 kN
Equivalent load = 720 × 101.97 = 73418 kg
Strength = 73418 / 50 = 1468 kg/cm²
10. Minimum Strength Requirements
OPC 43 Grade Cement
| Age | Strength (MPa) | kg/cm² |
|---|
| 3 Days | 23 | 235 |
| 7 Days | 33 | 337 |
| 28 Days | 43 | 438 |
OPC 53 Grade Cement
| Age | Strength (MPa) | kg/cm² |
|---|
| 3 Days | 27 | 275 |
| 7 Days | 37 | 377 |
| 28 Days | 53 | 540 |
⬇ Download Cement Mortar Cube Test – Excel Sheet
