The Los Angeles testing machine is commonly used to determine which property of the coarse aggregate?
🧱 Detailed Explanation: The Los Angeles Abrasion Test
The Los Angeles (LA) abrasion test is the industry-standard procedure for measuring the hardness and abrasion resistance of coarse aggregates, codified in IS 2386 (Part IV): 1963. It simulates the mechanical degradation that aggregates endure during handling, compaction, and service life.
How the test works: A weighed aggregate sample (passing 12.5 mm, retained on a specified lower sieve) is placed in a rotating steel drum with a given number of hardened steel balls. After 500 revolutions at 30–33 rpm, the material is sieved through a 1.7 mm IS sieve. The percentage of fines produced is the LA Abrasion Value — the lower the value, the harder the aggregate.
Comparison of Key Aggregate Tests — IS 2386
| Test | Property Measured | Mechanism |
|---|---|---|
| Los Angeles Abrasion | Abrasion resistance / hardness | Rotating drum + steel balls |
| Aggregate Crushing Value (ACV) | Resistance to gradual compressive load | Static 40-tonne press |
| Aggregate Impact Value (AIV) | Toughness (sudden dynamic load) | Repeated hammer drops |
| Specific Gravity & Water Absorption | Density and porosity | Water immersion + weighing |
Key Concepts for Students
- Lower LA value = more durable aggregate. IS 383 specifies ≤30% for pavement wearing course, ≤35% for non-wearing pavement layers, and ≤50% for general building concrete.
- The test applies both impact and abrasion simultaneously — making it a comprehensive, realistic simulation of aggregate wear under traffic or construction loads.
- Do not confuse with the AIV test: the Impact Value test uses a drop hammer (15 blows), while the LA test uses a rotating drum with steel balls (500 revolutions). They measure different properties.
- The same IS 2386 (Part IV) standard governs the LA test, ACV test, and AIV test — but each uses a completely different apparatus.