Los Angeles Abrasion Test – Step-by-Step Procedure (IS 2386 Part IV)
The Los Angeles Abrasion Test is one of the most important laboratory tests in highway and civil engineering. It measures the resistance of aggregates to abrasion and impact and ensures that the aggregates used in road construction are strong and durable. The test is conducted as per IS: 2386 (Part IV) – 1963 and referenced in MoRTH 5th Revision (2013).
Step 1 – Purpose of the Test
To determine the aggregate toughness and abrasion resistance when subjected to mechanical wear. Aggregates with lower abrasion values are more resistant and hence more suitable for road construction.
Step 2 – Apparatus Required
- Los Angeles Abrasion Machine – A hollow steel cylinder mounted on a horizontal shaft, rotating at 20–33 rpm.
- Steel Balls (Abrasive Charge):
- Diameter: 48 ± 2 mm
- Weight per ball: 390–445 g
- Hardness: 400–450 HB (Brinell)
- IS Sieves: 80 mm, 63 mm, 50 mm, 40 mm, 25 mm, 20 mm, 12.5 mm, 10 mm, 6.3 mm, and 1.70 mm
- Balance: with accuracy up to 1 g
- Oven: capable of maintaining 105–110°C
Step 3 – Sample Preparation
- Obtain clean and dry aggregates conforming to the required size range (refer grading table below).
- Dry the aggregates for 4 hours in an oven at 105–110°C to a constant weight and after that remove from the oven.
- Weigh a total of 5000 g of aggregates for the test.
Step 4 – Selection of Grading (A–G)
Aggregates are classified into different grading groups (A–G) based on their nominal size. The grading determines the number of steel balls and total revolutions.
| Grading | Aggregate Size (mm) | Sample Weight (g) | Revolutions | Application |
|---|---|---|---|---|
| A | 63–50 | 5000 | 500 | Heavy-duty base/sub-base |
| B | 50–40 | 5000 | 500 | WBM Grade I base |
| C | 40–25 | 5000 | 500 | WBM II / DBM base |
| D | 25–20 | 5000 | 500 | DBM / Bituminous macadam |
| E | 20–12.5 | 5000 | 1000 | Bituminous Concrete (BC) |
| F | 12.5–10 | 5000 | 1000 | SMA / Wearing course |
| G | 10–6.3 | 5000 | 1000 | Seal coat / Surface dressing |
Step 5 – Adding the Steel Balls
| Grading | Number 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 the prepared aggregate sample and the required number of steel balls into the Los Angeles machine.
- Close the cover tightly and rotate the drum at 20–33 revolutions per minute.
- Operate for the required number of revolutions as per the grading (500 or 1000).
- After completion, discharge the material and sieve it through a 1.70 mm IS sieve.
- Weigh the material retained on the sieve (Weight B).
Step 7 – Calculation
Los Angeles Abrasion Value (%) = ((A - B) / A) × 100
A = Original weight of sample (g)
B = Weight of retained material on 1.70 mm sieve (g)
Step 8 – Interpretation of Result
The smaller the Los Angeles Abrasion Value, the tougher the aggregate. A low value indicates higher resistance to abrasion and better performance in road layers.
Step 9 – Requirement of Grading for different Layers
| Pavement Layer | Nominal Size | Suggested Grading |
|---|---|---|
| GSB / WMM Sub-base | 53 mm | A or B |
| WMM Base Course | 40 mm | C |
| DBM Base Course | 25 mm | D |
| Bituminous Concrete (BC) | 19 mm | E |
| SMA / OGPC | 12.5 mm | F |
| Surface Dressing / Seal Coat | 10 mm | G |
Step 10 – Typical Acceptable Limits Requirements (MoRT&H 2013 Edition – 5th Revision)
- Base / Sub-base: ≤ 45%
- Bituminous Layers: ≤ 35%
- Wearing Courses: ≤ 30%
Frequently Asked Questions (FAQ)
- Which IS code specifies the Los Angeles test? IS 2386 (Part IV): 1963.
- What is the weight of the test sample? 5000 grams.
- At what speed should the machine rotate? 20–33 rpm.
- What is the final sieve size used? 1.70 mm.
- What does a lower L.A. value mean? Greater resistance to wear and better quality aggregate.
