The Los Angeles Abrasion test is carried out on aggregates in order to determine the hardness and abrasion characteristic i.e. ability to resist degradation due to imposed wheel load.
The principle of this test is to determine the percentage of wear due to deliberate rubbing action between aggregates.
Steel balls are used as an abrasive charge for creating the rubbing action in the test.
The percentage wear of the aggregates due to rubbing with steel balls is taken as abrasion value.
Apparatus Required :
Sieves as per gradation of aggregate 80mm, 63mm, 50mm, 40mm, 25mm, 20mm, 12.5mm, 10mm, 6.3mm, 4.75mm and 1.7mm.
Abrasion testing machine with inside diameter 70cm and inside length 50cm
Steel balls (abrasive charge) of diameter 48mm and weighing between 390g to 445g.
Selection of Abrasive Charge for Los Angeles Abrasion Test
|Grading||No of Steel balls||Weight of charge in gm.|
|A||12||5000 ± 25|
|C||8||3330 ± 20|
|D||6||2500 ± 15|
|E||12||5000 ± 25|
|F||12||5000 ± 25|
|G||12||5000 ± 25|
Grading of Test Samples – *Tolerance of ± 12 %permitted
|Sieve size (square hole)||Weight of test sample in gm|
|Passing (mm)||Retained on (mm)||A||B||C||D||E||F||G|
Procedures in Los Angeles Abrasion Test:
1. The test sample must contain clean well-graded aggregates that have been oven-dried at a temperature ranging from 105 degrees to 110 degree Celsius.
2. Then, the aggregates along with the abrasive charges are placed in the Los Angeles Abrasion testing machine.
3. The machine is then rotated at a speed of 20 to 33 rev/min.
4. The machine shall be driven such that a substantially uniform peripheral speed is maintained.
5. After the completion of the test, the coarse aggregate is removed and passed through sieves.
6. The aggregates coarser than 1.7mm IS sieve is then separated.
7. The retained aggregates are then oven-dried at temperature 105 degree Celsius to 110 degree Celsius and finally weighed.
8. The Los Angeles Abrasion Value is then calculated using the following formula:
Abrasion value = ((A-B)/A) * 100
A= weight in gm of oven-dried sample
B= weight in gm of the fraction of aggregate retained on 1.7mm sieve after oven-dried
Suitable Abrasion Value for Pavements
|Sl. No.||Type of Pavement||Max. permissible abrasion value in %|
|1||Water bound macadam sub base course||60|
|2||WBM base course with the 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|
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