The Los Angeles abrasion test is used to evaluate the toughness and abrasion resistance of aggregates, specifically their ability to withstand crushing, degradation, and disintegration. This test is conducted according to the standards set by AASHTO T 96 or ASTM C 131, which involve subjecting small-sized coarse aggregates to abrasion and impact in a Los Angeles machine. In highway pavement construction, the aggregates used in the surface course are exposed to continuous wear and tear from the movement of vehicles. The soil particles between the road surface and pneumatic tires, as well as the steel rimmed wheels of animal-drawn vehicles, contribute significantly to the abrasion of road aggregates. As a result, road aggregates must be hard enough to resist abrasion. The Los Angeles abrasion test machine is used in laboratories to determine the resistance of aggregates to abrasion. The test involves introducing standard steel balls into a drum containing the aggregates and rotating it for a specified number of revolutions to produce abrasive action and impact on the aggregates. The percentage of wear on the aggregates due to rubbing with steel balls is then calculated and referred to as the Los Angeles Abrasion Value.
Determination of Los Angeles Abrasion Value
The purpose of conducting the Los Angeles abrasion test is twofold. Firstly, it aims to determine the Los Angeles abrasion value of the aggregates being tested. This value is a measure of the resistance of the aggregates to wear and tear caused by abrasion, impact, and grinding. The higher the value, the greater the resistance of the aggregates to such wear and tear.
Secondly, the Los Angeles abrasion test is conducted to assess the suitability of the aggregates for use in road construction. Roads are subjected to various types of stresses, including traffic loads, weathering, and erosion, which can cause damage to the road surface over time. Therefore, it is essential to use aggregates that can withstand these stresses and maintain their integrity and durability over the long term.
By determining the Los Angeles abrasion value of the aggregates, engineers and construction professionals can make informed decisions about their suitability for use in road construction. If the value is too low, it may indicate that the aggregates are not strong enough to withstand the stresses of road traffic and other factors. Conversely, a high value suggests that the aggregates are robust and can withstand wear and tear, making them suitable for use in road construction.
Apparatus for Los Angeles Test
The IS: 2386 (Part IV) – 1963 apparatus includes several components. One of them is the Los Angeles Machine, which is used for testing the abrasion resistance of aggregates. Another component is the abrasive charge, which consists of cast iron or steel balls that are about 48mm in diameter and weigh between 390 to 445 g. To conduct the test, between six to twelve balls are needed.
The apparatus also includes a set of IS Sieves with varying mesh sizes ranging from 1.70 to 80 mm. The sieve sizes are 1.70, 2.36, 4.75, 6.3, 10, 12.5, 20, 25, 40, 50, 63, and 80 mm. These sieves are used to separate the aggregate samples into different sizes for further analysis.
The apparatus also requires a balance with a capacity of either 5 kg or 10 kg to accurately measure the weight of the aggregates. Additionally, a drying oven is needed to dry the aggregates before conducting the test. Finally, miscellaneous items like trays may also be needed during the testing process.
Procedure for Los Angeles Test
For conducting a test on aggregates, a clean sample of aggregates should be used, which has been dried in an oven at a temperature of 105°C to 110°C. The sample selected for the test should conform to any of the gradings specified in Table 1. It is important to choose a grading that aligns with the grading to be used in construction as much as possible.
The quantity of sample to be taken for gradings A, B, C, and D is 5 kg, while for gradings E, F, and G, it is 10 kg. The selection of the abrasive charge should be made based on the grading of the aggregates and in accordance with the values listed in Table 2. The aggregates and abrasive charge are to be placed inside the cylinder, and the cover should be fixed securely.
The machine used for the test should rotate at a speed of 30 to 33 revolutions per minute, with 500 revolutions for gradings A, B, C, and D, and 1000 revolutions for gradings E, F, and G. The machine’s rotation must be balanced and uniform, ensuring a consistent peripheral speed. After the desired number of revolutions, the machine should be stopped, and the material discharged into a tray.
The entire stone dust material is then passed through a 1.70 mm IS sieve, and the coarser material that remains on the sieve is weighed, with precision to one gram.
Table 1: Grading of Test Samples – *Tolerance of ± 12 percent permitted.
| 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: Selection of Abrasive Charge
| 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 |
Observations of Los Angeles Test
The given context appears to be a brief set of instructions or information related to a test that involves measuring the abrasion value of an aggregate sample. The context outlines the various components of the test, including the original weight of the aggregate sample (W1), the weight of the aggregate sample that is retained (W2), and the weight of the aggregate sample that passes through a 1.7mm IS sieve (W1 – W2).
The context goes on to provide a formula for calculating the abrasion value of the aggregate sample, which is (W1 – W2) / W1 X 100. Finally, the context mentions the specific result that is obtained from the test, which is the Los Angeles Abrasion Value.
To summarize, the given context provides instructions and information related to a test that measures the abrasion value of an aggregate sample, including the components of the test, the formula for calculating the abrasion value, and the specific result that is obtained.
Recommended Los Angeles Test Values for Pavements
The Los Angeles test is a widely recognized method for evaluating the hardness of aggregates. This test is preferred because it can determine both the resistance to abrasion and impact simultaneously, providing a more comprehensive evaluation. The test results are used to determine the suitability of aggregates for different types of road construction projects in accordance with the specifications set forth by the Indian Roads Congress (IRC).
Based on the value obtained from the Los Angeles test, the IRC specifications provide guidelines for determining whether the aggregates are suitable for use in different types of road construction. This helps to ensure that road construction projects use the appropriate type of aggregate to achieve optimal results. Overall, the Los Angeles test is an important tool for evaluating the quality of aggregates and ensuring that they meet the necessary standards for use in road construction.
| 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 |