The Crushing test is used to test crushing strength of pavement materials.
This test is very important test for road works as it specifies the crushing strength of aggregates.
IS code: IS: 2386 Part IV (Method of test for Aggregates)
Crushing Test on Aggregates:
- The Crushing test is used to test crushing strength of pavement materials.
- The crushing test of aggregate is used to determine the resistance to crushing under gradually applied load.
- This test is performed on aggregates used for road works.
Apparatus:
- A 15 cm dia. Steel cylinder with plunger and base plate.
- A straight metal tamping rod 16mm diameter and 45 to 60cm long rounded at one end.
- A Weigh balance of accuracy up to 1 gam.
- IS sieves of sizes 12.5mm, 10mm, and 2.36mm
- A compression testing machine.
- Cylindrical measure having a diameter of 11.5 cm and 18cm height.
Sampling:
- Take the coarse aggregates passing through 12.5mm IS sieve and retained on 10mm IS sieve
- Heat dry the aggregates in oven at temperature 110°C for 4 hours and cooled to room temperature.
- Take the quantity of aggregate in such a way that the complete cylinder fill after tamping. Approximately 6.5 kg of sample is sufficient to fill the cylinder completely.
- Fill the depth of cylinder in 3 equal layers with aggregates and tamp each layer 25 times and finally leveled off using the tamping rod.
- The weight material in cylinder shall be determined ( W1), and same weight is to be taken to repeat the test.
W1 = weight of cylinder with material – weight of empty cylinder
Procedure for Aggregate Crushing Test:
- Prepare the sample and cylinder as stated in sampling procedure.
- Place the cylinder in testing machine, level the sample surface and place cylinder with plunger.
- Apply load 40 Tones at the uniform rate in 10 minutes.
- Release the load and remove the material from the cylinder.
- Sieve all removed material with 2.36mm IS sieve.
- Weight the fraction of material passing through IS sieve (W2)
- Test on Aggregates
- Stripping Value Test, Bitumen Adhesion Test
- Specific gravity and water absorption of aggregates
- Soundness test of aggregate
- Los Angeles Abrasion test
Calculations:
Crushing value = (W2/W1) x 100
Result:
If W1 = 6.5Kg
W2 = 1.5kg
Crushing value = (W2/W1) x 100
= (1.5 x 100) /6.5
= 23.07
Conclusion:
| Aggregate Crushing Value | Type of aggregates |
| Less tha 10 | Exceptionally strong aggregates |
| Above 35 | Weak aggregate |
| 30 or higher | Result may be mistaken |
Aggregate Crushing Value Limits for road Pavements:
The below table shows the aggregate crushing value limits for different types of roads
| Types of Roads / Pavements | Aggregate Crushing Value Limit |
| Flexible Pavements | |
| Soling | 50 |
| Water bound macadam | 40 |
| Bituminous macadam | 40 |
| Bituminous surface dressing or thin premix carpet | 30 |
| Dense mix carpet | 30 |
| Rigid Pavements | |
| Other than wearing course | 45 |
| Surface or Wearing course |