Submitted by:
Roll No:
Semester:
Date of Experiment:
Date of Submission:
1. Objective
To determine the compressive strength of concrete cubes as per IS 516:1959.
2. Theory
The compressive strength of concrete is one of the most important properties that determines its quality and suitability for construction purposes. It is defined as the capacity of concrete to resist loads without failure.
The compressive strength is calculated using the formula:
Compressive Strength (MPa) = Maximum Load (N) / Cross-sectional Area (mm²)
As per IS 456:2000, concrete is classified based on its characteristic compressive strength at 28 days:
- M10: Characteristic strength of 10 MPa
- M15: Characteristic strength of 15 MPa
- M20: Characteristic strength of 20 MPa
- M25: Characteristic strength of 25 MPa
- M30: Characteristic strength of 30 MPa
- M35: Characteristic strength of 35 MPa
- M40: Characteristic strength of 40 MPa
Standard cube sizes for testing are 150mm × 150mm × 150mm or 100mm × 100mm × 100mm. The test is typically conducted at 7 days and 28 days of curing to assess the strength development.
3. Apparatus Used
- Compression testing machine
- Cube molds (150mm or 100mm)
- Tamping rod
- Weighing balance
- Curing tank
4. Test Parameters
| Concrete Grade |
M20 |
| Cube Size |
150 × 150 × 150 mm |
| Testing Age |
28 days |
| Testing Standard |
IS 516:1959 |
5. Procedure
- Prepare the concrete mix as per the specified mix design.
- Fill the cube molds with concrete in three layers, compacting each layer with 35 strokes of the tamping rod.
- Level the top surface and allow the cubes to set for 24 hours at room temperature.
- Remove the cubes from the molds after 24 hours and place them in a curing tank with water at 27±2°C until the testing age.
- After the specified curing period (7, 28, 56, or 90 days), remove the cubes from water and wipe off surface moisture.
- Measure the dimensions of the cube to the nearest 0.2mm.
- Place the cube in the compression testing machine with the cast face in contact with the platens.
- Apply the load continuously at a rate of 14 N/mm² per minute until failure occurs.
- Record the maximum load at which the cube fails.
- Calculate the compressive strength for each cube.
- Take the average of compressive strengths of all tested cubes as the compressive strength of the sample.
6. Observations
| Sample No. |
Dimensions (mm) |
Cross-sectional Area (mm²) |
Max Load (kN) |
Compressive Strength (MPa) |
| 1 |
150×150×150 |
22500 |
675 |
30.00 |
| 2 |
150×150×150 |
22500 |
690 |
30.67 |
| 3 |
150×150×150 |
22500 |
705 |
31.33 |
7. Sample Calculations
Calculation of Compressive Strength:
Compressive Strength (MPa) = Maximum Load (N) / Cross-sectional Area (mm²)
For Sample No. 1:
Cross-sectional Area = 150mm × 150mm = 22,500 mm²
Maximum Load = 675 kN = 675,000 N
Compressive Strength = 675,000 N / 22,500 mm² = 30.00 MPa
Average Compressive Strength:
Average = (30.00 + 30.67 + 31.33) / 3 = 92.00 / 3 = 30.67 MPa
8. Results
The average compressive strength of the tested concrete cubes at 28 days was found to be 30.67 MPa.
As per IS 456:2000, this concrete sample exceeds the characteristic strength requirement for M20 grade concrete (20 MPa).
9. Conclusion
The compressive strength test conducted on the concrete cubes showed satisfactory results with an average strength of 30.67 MPa at 28 days, exceeding the specified requirement for M20 grade concrete.
10. Precautions
- Ensure proper compaction of concrete in molds to avoid honeycombing.
- Maintain consistent curing conditions (temperature and humidity).
- Measure cube dimensions accurately to calculate the correct cross-sectional area.
- Apply load uniformly without any shock or impact.
- Ensure proper alignment of cube in the testing machine.
- Record the maximum load accurately at the point of failure.
Student's Signature
Instructor's Signature