Los Angeles Abrasion Test
Abrasion test, also known as Los Angeles abrasion test, is widely used to check the relative quality of aggregates. It is used to measure the hardness and abrasion resistance of aggregates such as crushing, degradation and disintegration.
The aggregates used in road pavement should have some properties such as resistance to abrasion, wear and tear, and hardness. So the aggregates should be hard, tough, and strong enough to withstand the loads and effects acting on them. So before using the aggregates, their abrasion and other such properties shall be checked.
The resistance to abrasion offered by the aggregates is determined using the Los Angeles equipment in the lab. This is known as the Los Angeles abrasion test.
Following are the objectives of the Los Angeles abrasion test:
- To find the Los Angeles abrasion value of the aggregates.
- To check if the particular aggregate sample is suitable for use in road construction.
According to IS: 2386 (part 4) – 1963 the apparatus consists of:
1. Los Angeles abrasion machine.
2. Abrasive charge balls – Cast iron or steel balls having diameter of approximately 48 mm and weighing between 390 grams to 450 grams. On average 6 to 12 balls are required for this test.
3. Sieve (IS standard) –1.70 mm, 2.36 mm, 4.75 mm, 6.3 mm, 10 mm, 12.5 mm, 20 mm, 25 mm, 40 mm, 50 mm, 63 mm, and 80 mm, respectively.
4. A balance of 5 kg or 10 kg capacity.
5. An oven for drying.
Los Angeles Abrasion Test Procedure
The procedure of the abrasion test is given below:
1. First, select the grading size of aggregates to be used in the test such that it conforms to the grading to be used in construction.
2. The sample of aggregates is separated according to individual size fractions of the required masses.
3. Place the aggregate sample in the Los Angeles abrasion machine and start rotating at a speed of 30 to 33 rotations per minute (rpm).
4. Now remove the aggregate sample from the Los Angeles machine and wash over a 1.70 mm (no. 12) sieve and place it in the oven to dry.
5. Calculate the loss of mass of aggregates (difference between the original mass and the final mass) in percentage.
6. This calculation indicates the quality of aggregates in context to their ability to resist abrasion.
Following are the observations acquired from the Los Angeles abrasion test:
Original weight of aggregate sample = W1 grams
Weight of aggregate sample retained on the sieve = W2 grams
Weight passing through 1.7 mm Indian standard sieve = W1 –W2 grams.
Abrasion value = (W1 – W2) / W1 x 100.
The abrasion value is expressed in percentage (%).
Indian Standard Recommended Los Angeles Abrasion Value For Road Pavements
Indian standard codes have determined maximum permissible abrasion values for different types of road pavements. So, It should not exceed the maximum permissible abrasion value, given by IS codes. If the value exceeds the maximum permissible abrasion value, then that particular sample of aggregates is rejected and is considered unsuitable for using pavements.
The maximum permissible abrasion values are expressed in percentage (%). Let us see the maximum permissible abrasion values for various types of pavements, specified by Indian standards. They are as given below:
|Sl. No.||Type Of Pavement||Maximum Los Angeles Abrasion Value (%)|
|1.||Water bound macadam sub base course||60 %|
|2.||Water bound macadam base course with bituminous surfacing||50 %|
|3.||Bituminous bound macadam||50 %|
|4.||Water bound macadam surfacing course||40 %|
|5.||Bituminous penetration macadam||40 %|
|6.||Bituminous surface dressing, cement concrete surface course||35 %|
|7.||Bituminous concrete surface course||30 %|