Why to do Los Angeles abrasion test?
Los Angeles abrasion test of aggregate is necessary because aggregates are used on the surface layers of the road pavement are subjected to bear load due to vehicle moving over it.
The friction between the vehicles moving tyre and the road surface results in the tear or abrasion of aggregates.
This affects the durability of road and loss of economy. Therefore aggregates should be hard enough to bear resistance against abrasion. And this property of aggregates is evaluated by the help of loss angles abrasion test.
Method to test the abrasion value of aggregates
- Los Angeles abrasion value test
- Deval abrasion test
- Dorry abrasion test
Currently about 47 countries are using the Los Angeles abrasion value test for aggregate. In this post we will talk about the Los Angeles abrasion test. So, let’s start.
- Abrasion machine
- It has a hollow steel cylinder having an internal diameter of 17 centimeters and length 50 centimeters.
- The machine can rotate about the horizontal axis.
- The removable cover is provided to the cylindrical machine with a clamp.
- A steel shelf has provided for the full length of the steel cylinder and kept at the distance of a minimum 125 cm from the opening from the direction of rotation.
- Abrasive machine ball having diameter 4.8 mm and weighing between 390 to 445 grams.
It requires 12 such balls. It depends upon the type of grading used.
- Weighting machine having capacity 5 to 15 kg.
- IS sieve of size 1.7 mm.
The aggregate used for the test compressed of a grading as specified in this table.
Grading of test sample (Table)
Tolerance of 12 % permitted.
The selection of grading is dependent on its designated use.
For WBM we shall select grading E for use in SDBC grading B, C or D are selected.
We shall be conducting the test using grading B.
So, well shall require IS sieve of size 20 mm, 12.5 mm and 10 mm.
A total of 2.5 kg of materials passing 20 mm sieve retained on 12.5 mm sieve is taken and also 2.5 kg of materials passing 12.5 mm sieve and retained on 10 mm sieve is taken.
Procedure for Los Angeles abrasion test
- First of all dry, the materials in an oven maintained at 105 degrees centigrades to 110 degrees centigrade for four hours.
- Take out the material after the required time and allow it to cool at room temperature.
- Now, measure the exact weight of the materials as per the grading specified and note down the exact weight of the sample (w1).
- Now, take the abrasive charge steel ball corresponding to the grading.
- For grading B we need 11 balls. Take the help of the table below.
Selection of abrasive charge (Steel Ball)
|Grading||No. of steel balls||Wt. of charging|
- Clean the cylinder of the abrasion machine.
- Now, place the abrasive charge steel ball into the abrasive machine.
- Now, close the lid of the cylinder at machi9ne tightly.
- Set the reading of the machine to all zero.
- Now, switch on the machine and allow the machine to rotate at the speed of 30 to 32 revolutions per minute.
- Provide 500 revolutions for grades A, B, C, or D and 1000 revolutions for grading E, F, or G.
- Since, we are using grading B we will subject the sample to 500 revolutions.
- Abrasive and impact of aggregates occur repeatedly during this revolution in the machine.
- After completed 500 revolutions the revolution of the machine is stopped and a sample of aggregates are taken out.
- Now, sieve the materials through 1.7 mm sieve.
- Take the weight of both passed samples (w2) and retained samples on 1.7 mm sieve.
- Now, calculate the Los Angeles abrasion value with the formula given by,
= (Weight of fraction passing 1.7 mm sieve / Weight of total sample)
Let, the passed sample be 1120 gm and total sample weight be 5000 gm.
Los Angeles abrasion value = (1120/5000) * 100%
= 22.4 %
- Repeat the test and take the mean value of two sample to get accurate value of abrasion test.
List of abrasion values for different types of road construction.
|S.N.||Types of pavement layers||Maximum possible abrasion value in percentage (%)|
|1||WBM Base course with bituminous surfacing||50|
|2||Water bound macadam, sub base course||60|
|3||WBM surfacing course||40|
|4||Bituminous bound macadam||50|
|5||Bituminous penetration macadam||40|
|6||Bituminous concrete surface course||30|
Report of Los Angeles test
Weight of sample (w1) =
Weight of sample retained (On 1.70 mm IS sieve) (w2) =
Loss of weight (w1-w2) =
Percentage of wear [(W1 – W2)/W1)]* 100 =
Significance of Los Angeles abrasion test
These Procedures follows IS Code As per I386 part 4
- Lower the percentage of test greater the strength of aggregate toward abrasion.
- The test determines the quality and strength of aggregates.
- The maximum value for the road pavement should be 60%.
Precaution of test
- The machine should be revolved at uniform speed.
- The sample of aggregate should be carefully chosen according to the IS code.
- The aggregates should be washed clearly before testing of aggregate.