Abrasion Test is the measure of aggregate toughness and abrasion resistance such as crushing, degradation and disintegration. This test is suggested by AASHTO T 96 or ASTM C 131: Resistance to Degradation of Small-Size Coarse Aggregate by Abrasion and Impact in Los Angeles Machine.
The aggregates are used for the surface course of the highway pavements and they are subjected to wearing due to movement of traffic. (L
When vehicles travel on the road, the soil particles present between the pneumatic tyres of vehicle and road surface creates the abrasion effect on aggregates. The steel plate wheels of animal-driven vehicles also cause significant abrasion of the road surface.
Therefore, the aggregates used in road construction must be hard enough to resist abrasion. The resistance offered by aggregate to abrasion is determined in the laboratory by the Los Angeles test machine.
The Working principle of the Los Angeles abrasion test is to produce abrasive action by use of standard steel balls, which when mixed with aggregates and rotated in a drum for some specified time for a specific number of revolutions also causes an impact on aggregates.
The percentage wear of the sample aggregates due to rubbing with steel balls is determined and is known as Los Angeles Abrasion Value.
Los Angeles Abrasion Value Test:
The Los Angeles abrasion test on aggregates is done for the following purposes:
- To find out the Los Angeles abrasion value of aggregate.
- To find the suitability of aggregates for use in road construction projects.
Apparatus used for Los Angeles Abrasion Test:
The apparatus is standardized as per IS: 2386 (Part IV) – 1963 consists of:
- Los Angeles abrasion machine
- Abrasive charge balls: Cast iron or steel balls, approximately 48mm in diameter and each weighing between 390 to 445 gm; six to twelve balls are required
- Sieve: 1.70mm , 2.36mm, 4.75mm, 6.3mm, 10mm, 12.5mm, 20mm, 25mm, 40mm, 50mm, 63mm, 80mm IS Sieves.
- The balance of capacity 5 kg or 10 kg is used.
- Oven Drying.
- Miscellaneous elements like a tray.
Procedure for LA Abrasion Test:
The aggregates sample consists of clean aggregates dried in an oven at 105° – 110°C. The aggregates sample should conform to any of the grading shown in the below table.
- Select the size of aggregate to be used in the test such that it conforms to the grading to be used in construction, to the maximum extent possible.
- Take exactly 5 kg of the sample for grades A, B, C & D, and 10 kg for grading E, F & G.
- Choose the abrasive charge balls as per Table 2 depending on the grading of aggregates.
- Place the aggregates and abrasive charge balls on the cylinder and fix the cover.
- After that Rotate the machine at a speed of 30 to 33 revolutions per minute. The number of revolutions should be 500 for grades A, B, C & D and 1000 for grading E, F & G.
- The machine is stopped after the specified number of revolutions and the aggregate sample is discharged to a tray.
- The entire stone dust made from a machine is sieved on 1.70 mm IS sieve.
- The material size more than 1.7 mm size is weighed correct to one gram.
Table 1: IS Recommended Test Samples – *Tolerance of ± 12 percent permitted.
Table 2: Abrasive Balls Charge Selection
Read More: You can download the IS Codes of Aggregates for FREE Here: IS: 2386 (Part I-VII)
The original weight of aggregate sample = W1 g
The weight of the
Weight sample passing 1.7mm IS sieve = W1 – W2 g
Abrasion Value = (W1 – W2 ) / W1 X 100
Let the weight of the aggregate be W1 = 5000 gram
Weight of the aggregate sample retained W2 = 2100 gram
Weight sample passing 1.7mm IS sieve = W1 – W2 g = 2900 gram
Abrasion Value = (W1 – W2 ) / W1 X 100 = (2900/50000) X 100 = 58
Los Angeles Abrasion Value = 58
IS Recommended Los Angeles Abrasion Test Values for Pavements:
A Los Angeles test is performed to find the hardness of aggregates. On the basis of this value, the suitability of aggregates for different road constructions can be judged as per IRC specifications as given
Following the LA Abrasion Test as mentioned above, we derived the abrasion value of the sample as 58.
From the table given above, the suitability of aggregates used for the pavements can be known.
For the sample calculation done here having abrasion value of 58, the aggregates can be employed only for WBM sub base course. Its maximum permissible abrasion value is 60.
Watch Video: Los Angeles Abrasion Test
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