Los Angeles abrasion test

The Los Angeles abrasion test measures the resistance of road aggregate to wear through the combined action of abrasion, attrition and impact in a rotating drum. It follows IS:2386 (Part IV) / AASHTO T96 / ASTM C131 and is used in NRS 2070.

Apparatus

• Los Angeles machine: hollow steel cylinder 700 mm in diameter and 500 mm long, closed at both ends, rotating about a horizontal axis, with one internal shelf (steel plate) 90 mm wide.
• Abrasive charge: cast iron or steel balls about 48 mm in diameter, each 390-445 g.
• IS sieve 1.7 mm, balance (accuracy 1 g), oven, tray.

Procedure

1. Take a clean, oven-dried (105-110 degrees C) sample of 5 kg (gradings A to D) or 10 kg (gradings E to G), according to the grading of the aggregate in IS:2386.
2. Select the number of balls by the grading: A - 12, B - 11, C - 8, D - 6 balls, and 12 balls for gradings E, F and G.
3. Place the sample and the charge in the drum, fix the cover, and rotate at 30-33 rpm for 500 revolutions (gradings A to D) or 1000 revolutions (E to G).
4. Remove the material, separate the balls, and sieve the aggregate on a 1.7 mm IS sieve.
5. Wash and oven-dry the retained portion and weigh it.

$$\text{LA abrasion value} = \frac{W_1 - W_2}{W_1}\times 100\%$$

where $W_1$ = original weight and $W_2$ = weight retained on the 1.7 mm sieve after the test.

Significance

• It indicates the hardness and toughness of the aggregate and its ability to resist crushing, wear and abrasion under traffic.
• A low value means a strong aggregate. Desirable limits (IRC/NRS 2070, MoRTH): not more than 30% for wearing course/bituminous concrete, not more than 35% for dense bituminous macadam, 40% for bituminous macadam and WBM base courses (up to 50% for lower layers such as the granular sub-base).
• The test is quick and repeatable, and it is widely used for quality control of aggregate sources.