AGGREGATE ABRASION TEST (AASHTO T 96, ASTM C 131)
OBJECT: TO DETERMINE THE LOS ANGELES ABRASION VALUE (% WEAR) OF THE GIVEN AGGREGATE SAMPLE.
PERFORMANCE OBJECTIVE:
To determine the Los Angeles abrasion value.
EQUIPMENT: Los Angeles machine, Abrasive charge, Sieves, balance, etc.
Los Angeles machine: Consists of a hollow steel cylinder, closed at both ends, having an inside diameter of 70 cm and inside length of 50 cm, mounted on slab shafts about which it rotates on a horizontal axis.
Abrasive charge: Consists of cast iron spheres Approximately 4.7 cm in diameter and 390 to 445 g in weight. The number of spheres used depends on Sample grading.
THEORY
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Due to traffic movements, the road aggregates are subjected to wearing action. Resistance to wear or hardness is an essential property of road aggregates, especially when used in the wearing course. Therefore the aggregates should be hard enough to resist abrasion due to traffic. Abrasion is a measure of resistance to wear or hardness. It is an essential property for road aggregates, especially when wearing course.
The principle of the Los Angeles abrasion test is to produce the abrasive action by use of standard steel balls which when mixed with the aggregates and rotated in a drum for a specific number of revolutions also cause impact on aggregates. The percentage wear of the aggregates due to rubbing with steel balls is determined and is known as the Los Angeles Abrasion Value.
PROCEDURE
- Wash the test sample conforming to any of the sample grading and dry at 105°C – 110°C to constant weight. Take the weight of the sample in gm (W1).
- Place the sample in the cylinder along with the specified charge. Fix the cover of the machine and rotate it at a speed of 30 to 33 rpm for a specified no. of revolutions.
- Take out the material from the machine and make a preliminary separation of the sample on a sieve coarser than 1.70 mm and then sieve the remaining portion from a 1.70 mm sieve.
- Wash the material coarser than 1. 70 mm and oven dry at 105°C -110°C to constant weight in gm (W2).
GRADING OF TEST SAMPLES
Sieve Size (Square Openings) | Weight of Indicated Sizes, gm | ||||
Passing on | Retained on | A | B | C | D |
37.5 mm (1 ½ in) | 25.0 mm (1 in) | 1250 ± 25 | |||
25.0 mm (1 in) | 19.0 mm ( ¾ in) | 1250 ± 25 | |||
19.0 mm ( ¾ in) | 12.5 mm ( ½ in) | 1250 ± 10 | 2500 ± 10 | ||
12.5 mm ( ½ in) | 9.5 mm (3/8 in) | 1250 ± 10 | 2500 ± 10 | ||
9.5 mm (3/8 in) | 6.3 mm (¼ in) | 2500 ± 10 | |||
6.3 mm (¼ in) | 4.75 mm (No. 4) | 2500 ± 10 | |||
4.75 mm (No. 4) | 2.36 mm (No. 8) | 5000 ± 10 | |||
Total | 5000 ± 25 | 5000 ± 10 | 5000 ± 10 | 5000 ± 10 | |
No. of Spheres | 12 | 11 | 8 | 6 | |
Wt. of Charges (gm) | 5000 | 4584 | 3330 | 2500 | |
GRADING OF TEST SAMPLES
Sieve Size (Square Openings) | Weight of Indicated Sizes, GM | |||
Passing on | Retained on | E | F | G |
76 mm (3 in) | 63 mm (2 ½ in) | 2500 ± 25 | ||
63 mm (2 ½ in) | 50 mm (2 in) | 2500 ± 25 | ||
50 mm (2 in) | 37.5 mm (1 ½ in) | 5000 ± 25 | 5000 ± 25 | |
37.5 mm (1 ½ in) | 25.0 mm (1 in) | 5000 ± 25 | 5000 ± 25 | |
25.0 mm (1 in) | 19.0 mm ( ¾ in) | 5000 ± 25 | ||
Total | 10000 ± 25 | 10000 ± 25 | 10000 ± 25 | |
No. of Spheres | 12 | 12 | 12 | |
Wt. of Charges (gm) | 5000 | 5000 | 5000 | |
RESULT OF TEST
S. No. | Description | Sample | |
1 | 2 | ||
1 | Weight of specimen = W1 | ||
2 | Weight of specimen after abrasion test, particles coarser than 1.70 mm IS sieve = W2 | ||
3 | Percentage wear = WI – W2 x 100 WI | ||
The Average value of both samples is __________________
RECOMMENDED VALUE:
The Los Angeles test is commonly used to evaluate the hardness of aggregates. The test has more acceptability because the resistance to abrasion and impact is determined simultaneously. Depending upon the value, the suitability of aggregates for different road constructions can be judged as per IRC specifications as given:
S.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 |
