The machine used for testing abrasion resistance of coarse aggregate is
Correct Answer: C. Los Angeles abrasion machine
📚 Detailed Explanation: Los Angeles Abrasion Test
The abrasion resistance of coarse aggregate is a critical property in concrete and road construction, as aggregates in pavements and floors experience repeated wear and impact loads. The Los Angeles (LA) abrasion test is the internationally accepted standard for measuring this property.
Why C (Los Angeles abrasion machine) is correct: The LA abrasion machine is a hollow steel cylinder (710 mm diameter, 508 mm inside length) that rotates about a horizontal axis. The coarse aggregate sample is placed inside with a prescribed number of steel balls (abrasive charge). After 500 revolutions at 30–33 rpm, the material is sieved on a 1.7 mm sieve. The percentage of fines generated (loss) is the LA Abrasion Value. Option A (Dorry machine) is used for fine aggregate abrasion; there is no “Dewal” machine in standard Indian/international testing.
LA Abrasion Test Summary
| Parameter | Value |
|---|---|
| Standard | IS 2386 (Part IV) / ASTM C131 |
| Drum diameter | 710 mm |
| Revolutions | 500 at 30–33 rpm |
| Sieve for loss | 1.7 mm (retained = sound material) |
| LA Value limit (roads) | ≤30% (IS 383) |
| LA Value limit (concrete) | ≤50% (IS 383) |
Key Concepts for Students
- LA Abrasion Value = (mass lost after 500 revs / initial mass) × 100; lower value = harder aggregate.
- The steel balls provide impact as well as abrasion, so the test measures combined impact and wear resistance.
- For concrete structures, aggregate with LA value ≤50% is acceptable; for pavements, ≤30% to ≤40% is required.