As specified in IS 2386 (Part IV): 1963, which of the following set of sieves are used to find the crushing value of coarse aggregates?
Correct Answer: D. 2.36 mm, 10 mm, 12.5 mm
🧱 Detailed Explanation: Sieve Sizes for the Aggregate Crushing Value Test
The Aggregate Crushing Value (ACV) test, specified in IS 2386 (Part IV): 1963, measures how much an aggregate breaks down under a gradually applied compressive load of 40 tonnes. Three specific sieves are involved at different stages of the test.
Why these three sieves?
Role of each sieve in the ACV test:
1. 12.5 mm sieve (upper limit): The test sample must pass through this sieve — oversized particles that are retained are discarded.
2. 10 mm sieve (lower limit): The sample must be retained on this sieve. The 10–12.5 mm single-sized fraction is then filled into the steel test mould.
3. 2.36 mm sieve (post-crush): After the 40-tonne load is applied, the crushed aggregate is sieved on this sieve. The fraction passing 2.36 mm represents the crushed fines.
1. 12.5 mm sieve (upper limit): The test sample must pass through this sieve — oversized particles that are retained are discarded.
2. 10 mm sieve (lower limit): The sample must be retained on this sieve. The 10–12.5 mm single-sized fraction is then filled into the steel test mould.
3. 2.36 mm sieve (post-crush): After the 40-tonne load is applied, the crushed aggregate is sieved on this sieve. The fraction passing 2.36 mm represents the crushed fines.
ACV formula: (Mass passing 2.36 mm ÷ Original mass) × 100 = ACV (%)
Sieve Roles in the ACV Test
| Sieve Size | Stage | Purpose |
|---|---|---|
| 12.5 mm IS sieve | Sample preparation | Remove oversized particles (retained = discarded) |
| 10 mm IS sieve | Sample preparation | Define test fraction (retained material = test sample) |
| 2.36 mm IS sieve | Post-crushing | Quantify the fines produced = indicates crushing damage |
ACV Limit Values (IS 2386 / IS 383)
| Application | Maximum ACV |
|---|---|
| Wearing course of pavement | 30% |
| WBM base course | 40% |
| Building concrete aggregates | 45% |
Key Concepts for Students
- The ACV test uses a static 40-tonne load (gradual compression) — not a hammer or rotating drum. It measures resistance to crushing, not impact or abrasion.
- The 2.36 mm sieve is the most critical sieve — it separates intact aggregate (retained) from crushed fines (passing) to calculate the ACV percentage.
- Options A, B, and C are wrong because they substitute incorrect sieve sizes: 6.3 mm has no role in ACV; 20 mm is too large for the test cylinder.
- A lower ACV means the aggregate is stronger and more resistant to crushing under load.