Los Angeles Abrasion Test – Step-by-Step Procedure (IS 2386 Part IV)
The Los Angeles Abrasion Test determines the resistance of aggregates to abrasion, wear and impact. It is one of the most important quality control tests for highway pavements and concrete works. The test is carried out as per IS 2386 (Part IV) and referenced in MoRTH Specifications (5th Revision, 2013).
Step 1 – Purpose of the Test
To assess the toughness and abrasion resistance of aggregates when subjected to mechanical wear. Aggregates with lower abrasion values are stronger and more durable.
Step 2 – Apparatus Required
- Los Angeles Abrasion Machine – steel drum rotating at 30–33 rpm
- Steel Balls (Abrasive Charge)
- Diameter: 48 ± 2 mm
- Weight per ball: 390–445 g
- Hardness: 400–450 HB
- IS Sieves: 80, 63, 50, 40, 25, 20, 12.5, 10, 6.3 and 1.70 mm
- Balance: accuracy up to 1 g
- Oven: capable of maintaining 105–110°C
Step 3 – Sample Preparation
- Take clean aggregates of the required size as per grading.
- Dry the sample in an oven at 105–110°C to constant weight.
- Weigh a total of 5000 g of aggregates.
Step 4 – Selection of Grading (A–G)
Aggregates are classified into grading groups based on nominal size. The grading determines the number of revolutions and steel balls used.
| Grading | Aggregate Size (mm) | Sample Weight (g) | Revolutions | Typical Use |
|---|---|---|---|---|
| A | 63–50 | 5000 | 500 | GSB / Sub-base |
| B | 50–40 | 5000 | 500 | WMM Base |
| C | 40–25 | 5000 | 500 | DBM Base |
| D | 25–20 | 5000 | 500 | Bituminous Macadam |
| E | 20–12.5 | 5000 | 1000 | Bituminous Concrete |
| F | 12.5–10 | 5000 | 1000 | SMA / OGPC |
| G | 10–6.3 | 5000 | 1000 | Seal Coat |
Step 5 – Steel Ball Requirement
| Grading | No. of Steel Balls | Total Weight (g) |
|---|---|---|
| A | 12 | 5000 ± 25 |
| B | 11 | 4584 ± 25 |
| C | 8 | 3330 ± 20 |
| D | 6 | 2500 ± 15 |
| E | 12 | 5000 ± 25 |
| F | 12 | 5000 ± 25 |
| G | 12 | 5000 ± 25 |
Step 6 – Test Procedure
- Place aggregates and steel balls into the drum.
- Rotate the drum at 30–33 rpm.
- Run for the specified number of revolutions.
- Discharge the material and sieve through 1.70 mm sieve.
- Weigh material retained on sieve (B).
Step 7 – Calculation
Los Angeles Abrasion Value (%) = ((A − B) / A) × 100
A = Original weight of sample (g)
B = Weight retained on 1.70 mm sieve (g)
Step 8 – Interpretation
Lower abrasion value indicates tougher aggregates with better resistance to wear and longer pavement life.
Step 9 – Permissible Limits (MoRTH 2013)
- Base / Sub-base: ≤ 45%
- Bituminous Layers: ≤ 35%
- Wearing Courses: ≤ 30%
Frequently Asked Questions (FAQ)
- Which IS code specifies this test? IS 2386 (Part IV).
- What is sample weight? 5000 g.
- Machine speed? 30–33 rpm.
- Final sieve size? 1.70 mm.
- Lower value means? Better quality aggregate.
