Los Angeles Abrasion test on Aggregates

AIM:

To determine the abrasion value of coarse aggregates as per IS: 2386 (Part IV) – 1963.

APPARATUS: 

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i) Los Angles abrasion testing machine
ii) IS Sieve of size – 1.7mm
iii) Abrasive charge – 12 nos. cast iron or steel spheres approximately 48mm dia. and each weighing between 390 and 445g ensuring that the total weight of charge is 5000 + or – 25g
iv) Oven 

PREPARATION OF SAMPLE:

The test sample should consist of clean aggregates which has been dried in an oven at 105 to 110ºC to a substantially constant weight and should conform to one of the gradings shown in the table below: 

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PROCEDURE:

  1. Clean and dry aggregate sample confirming to one of the grading A to G is used for the test. 
  2. Aggregates weighing 5 kg for grading A, B, C or D and 10 kg for gradings E, F or G may be taken as test specimen and placed in the cylinder.
  3. The abrasive charge is also chosen in accordance with table no.1 and placed in the cylinder of the machine, and cover is fixed to make dust tight.
  4. The machine is rotated at a speed of 30 to 33 revolutions per minute.
  5. The machine is rotated for 500 revolutions for gradings A, B, C and D, for gradings E, F and G, it shall be rotated for 1000 revolutions.
  6. After the desired number of revolutions, the machine is stopped and the material is discharged from the machine taking care to take out entire stone dust.
  7. Using a sieve of size larger than 1.70 mm I.S sieve, the material is first separated into two parts and the finer position is taken out and sieved further on a 1.7 mm I.S sieve.
  8. Let the original weight of aggregate be W1 gm, weight of aggregate retained on 1.70 mm I.S sieve after the test be W2 gm.

RESULTS:

i) The material coarser than 1.70 mm IS Sieve should be washed, dried in an oven at a temperature of 100 to 110ºC to a constant weight and weighed (Weight ‘B’).
ii) The proportion of loss between weight ‘A’ and weight ‘B’ of the test sample should be expressed as a percentage of the original weight of the test sample. This value should be
reported as,

Aggregate abrasion value = {(A-B)/A} x 100%
A sample proforma for the record of the test results is given in the below table

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Recommended Values of Los Angeles Test:

Maximum Allowable Los Angeles Abrasion Values of Aggregates in Different types of pavement layers as per Indian Road Congress (IRC) are:-

  1. For sub-base course a value of 60%.
  2. For base course such as WBM, Bituminous Macadam (B.M.), Built – Up spray grout base course and etc. value of 50%.
  3. For surface course such as WBM, BM, Bituminous Penetration Macadam,Built-Up spray grout binder course and etc. a value of 40%.
  4. If aggregates are used in surface course as bituminous carpet, bituminous surface dressing, single or two coats, cement concrete surface course and etc. a value of 35%.
  5. If aggregates are used for bituminous concrete, Cement concrete pavement as surface coarse than aggregate abrasion value of 30% maximum.

DISCUSSION:

The principle of Los Angeles abrasion test is to find the percentage wear due to the relative rubbing action between the aggregates and steel balls used as abrasive charge pounding action of these balls also exist while conducting the test.

Due to the movements of traffic, the road stones used in the surfacing course are subjected to wearing actions at the top. When traffic moves on the road the soil particle (sand) which comes between the wheel and road surface causes abrasion on the road stone.

Why are steel balls used in the Los Angeles abrasion test?
  • To produce the abrasive action by use of standard steel balls which when mixed with the aggregate and rotated in a drum for specific number of revolution cause impact on aggregate.
  • The %age wear due to rubbing with steel balls is determined later on.

ALSO READ:-

  1. Penetration test of Bitumen
  2. Bitumen content test
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