Los Angeles Abrasion test is to measure the abrasion resistance value of aggregates. Aggregate is the fundamental and essential component of concrete, flexible pavements, etc. More than 70 to 80 percent of the volume of concrete is aggregate. Aggregates are the main ingredients of concrete, flexible pavements, etc., so quality matters when it comes to aggregates.
Tests on aggregates
Different types of tests are done to determine their properties like
- Water Absorption etc.
Following are the types of aggregate tests conducted to ascertain the suitability of aggregates.
- Crushing test
- Abrasion test
- Impact test
- Water absorption test
- Flakiness index test
- Elongation index test
- Bulk specific gravity test
- Polishing test
Los Angeles Abrasion test on aggregates
Los Angeles Abrasion test determines the wearing resistance and hardness properties of aggregate. The wearing action on aggregate by the movement of vehicles is known as abrasion. Hence the aggregate should have adequate abrasion value to resist abrasion. The abrasion test value can ensure the quality and suitability of aggregates. Moreover, aggregate with good abrasion resistance has a good life span.
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Codes and standards
ASTM C 131: Resistance to Degradation of Small-Size Coarse Aggregate by Abrasion and Impact in Los Angeles Machine.
The relevant Indian code is (IS: 2386 part-IV)
There are 3 tests commonly used to test aggregates for its abrasion resistance. (a) Deval Attrition Test (b) Dorry Abrasion Test (c) Los Angeles Abrasion Test. Los angeles abrasion test values are more realistic and correct.
Working principle of Los Angeles Abrasion test
The principle of this test is to produce abrasive action using steel balls mixed with aggregates. The aggregate and steel balls are rotated in a drum for a specific number of rotations. The percentage wear due to relative rubbing action between the aggregate and steel balls are recorded. This value is the Los Angeles Abrasion value.
The Los Angeles abrasion testing machine consist of a hollow steel cylinder, closed at both ends, having an inside diameter of 700 mm and an inside length of 500 mm. The abrasive charge shall consist of cast iron spheres or steel spheres approximately 48 mm in. diameter and each weighing between 390 and 445 g. The number of balls to be placed shall be as per IS 2386.
The test sample shall consist of clean aggregate which has been dried in an oven at 105 to 110°C to substantially constant weight. They shall confirm to one of the gradings shown in Table II.
- Firstly, place the specimen inside the horizontal drum.
- Then, put the steel balls and rotate the cylinder for a total of 500-1000 revolutions at the speed of 30-33 rpm about its horizontal axis. For gradings A, B, C and D, the machine shall be rotated for 500 revolutions. However for gradings E, F and G, it shall be rotated for 1000 revolutions.
- After completing the specific rotations, collect the specimens from the cylinder.
- Then sieve on 1.7 mm IS sieve and weigh the specimen.
- Lastly, calculate the abrasion value using the formula below.
Formula for Los Angeles Abrasion Test
Original weight of aggregate sample = W1 g
Weight of aggregate sample retained = W2 g
Weight passing 1.7mm IS sieve = W1 – W2 g
Abrasion value = [(weight of sample taken – weight of sample retained on IS sieve) / weight of sample taken ] x 100
The difference between the original weight and the final weight (sieved through 1.7mm) is expressed as % of the original weight of the sample aggregate. Similarly this value is called as Los Angeles abrasion value.