The Crushing test of aggregate is used to test crushing strength of pavement materials.
IS code Recommendation:
IS: 2386 Part IV (Method of test for Aggregates)
Crushing Test of Aggregate
- 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.
- To know more about shape & size of aggregates click here>>>>
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 cylnder
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)
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 than 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 |
