The Los Angeles abrasion test is used to determine the toughness and abrasion resistance of aggregates against crushing, deterioration, and disintegration. AASHTO T 96 or ASTM C 131: Resistance to Degradation of Small-Size Coarse Aggregate by Abrasion and Impact in the Los Angeles Machine are used to conduct this test. The aggregate used in the surface course of highway pavements is susceptible to wear as a result of vehicular movement. When cars travel on the road, the soil particles between the pneumatic tyres and the road surface cause the road aggregates to abrade.
Additionally, the steel-rimmed wheels of animal-driven vehicles abrade the road surface significantly. As a result, road aggregates should be sufficiently resistant to withstand abrasion. The resistance of aggregate to abrasion is evaluated in the laboratory using the Los Angeles test equipment. The Los Angeles abrasion test is based on the concept of producing abrasive action via the use of ordinary steel balls that, when mixed with aggregates and spun in a drum for a predetermined number of revolutions, also generate impact on the aggregates. The Los Angeles Abrasion Value is used to measure the percentage wear of aggregates caused by rubbing against steel balls.
Table of Contents
Obtaining the Los Angeles Abrasion Value
The Los Angeles abrasion test is performed on aggregates for the following reasons:
- To estimate the abrasion value.
- Determine the appropriateness of aggregates for use in roads.
Apparatus for the Abrasion Test
The equipment is comprised of the following:
- Los Angeles Machine
- Cast iron/steel balls, around 48mm in diameter and each weighing between 390 to 445 g; 6 to 12 balls are required.
- Sieves: 1.70, 2.36, 4.75, 6.3, 10, 12.5, 20, 25, 40, 50, 63, 80 mm.
- Scale
- Oven for drying
- Trays
Procedure
The test sample comprised of cleaned aggregates that have been dried in an oven at a temperature of 105° – 110°C. The sample should fall into one of the grading categories listed in table 1.
- Choose the grading to be applied in the test so that it is as close as feasible to the grading to be used in construction.
- 5 kilogram for gradings A, B, C, and D; 10 kg for gradings E, F, and G.
- Select the appropriate abrasive charge from Table 2 based on the aggregates’ grade.
- Fix the lid to the cylinder and add the aggregates and abrasive charge.
- At a speed of 30 to 33 revolutions per minute, rotate the machine. For grades A, B, C, and D, the number of revolutions is 500; for grades E, F, and G, the number of revolutions is 1000. The machine should be balanced and operated in such a way that the peripheral speed is consistent.
- After the required number of revolutions, the machine is stopped and the material is dumped onto a tray.
- On a 1.70 mm IS sieve, the whole stone dust is sieved.
- Material coarser than 1.7mm in size is accurately weighed to the nearest gram.
Table 1: Grading of Test Samples – *Within a tolerance of 12%.
| Sieve size (square hole) | Weight of test sample in gm | |||||||
| Passing (mm) | Retained on (mm) | A | B | C | D | E | F | G |
| 80 | 63 | 2500* | ||||||
| 63 | 50 | 2500* | ||||||
| 50 | 40 | 5000* | 5000* | |||||
| 40 | 25 | 1250 | 5000* | 5000* | ||||
| 25 | 20 | 1250 | 5000* | |||||
| 20 | 12.5 | 1250 | 2500 | |||||
| 12.5 | 10 | 1250 | 2500 | |||||
| 10 | 6.3 | 2500 | ||||||
| 6.3 | 4.75 | 2500 | ||||||
| 4.75 | 2.36 | 5000 | ||||||
Table 2: Charge Selection
| Grading | No of Steel balls | Weight of charge in gm. |
| 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 |
Abrasion Test Observations
Weight of the aggregate sample at its start =W1 g
Retained sample weight of aggregate= W2 g
Weight passing 1.7mm  = W1 – W2 g
Abrasion Value = (W1 – W2 ) / W1 X 100
Results
Los Angeles Abrasion Value =
Recommended Abrasion Values for Pavements
The Los Angeles test is a widely used method for determining the hardness of aggregates. The test is more acceptable since it determines both abrasion and impact resistance concurrently. The appropriateness of aggregates for various road projects may be determined as follows:
| Sl. No. | Type of Pavement | Max. permissible abrasion value in % |
| 1 | Water bound macadam sub base course | 60 |
| 2 | WBM base course with bituminous surfacing | 50 |
| 3 | Bituminous bound macadam | 50 |
| 4 | WBM surfacing course | 40 |
| 5 | Bituminous penetration macadam | 40 |
| 6 | Bituminous surface dressing, cement concrete surface course | 35 |
| 7 | Bituminous concrete surface course | 30 |