Objective: The Los Angeles Abrasion Test is a crucial examination carried out to assess the hardness of aggregates. Its fundamental principle involves measuring the percentage wear resulting from the friction between the aggregate and steel balls used as an abrasive charge.

Apparatus Required for Abrasion Test of Aggregate :

Balance: You will need a precision balance that can accurately measure weights up to 1 gram. This balance is essential for weighing the test samples accurately.

Sieves: Several sieves with specific sizes are required for grading the aggregate. The sieves needed include sizes such as 80 mm, 63 mm, 50 mm, 40 mm, 25 mm, 20 mm, 12.5 mm, 10 mm, 6.3 mm, 4.75 mm (these sizes are chosen based on the gradation of the aggregate), and 1.7 mm.

Los Angeles Testing Machine:

This machine is the primary apparatus used for conducting the Los Angeles Abrasion Test. It has specific dimensions, with an inside length of 50 cm and an inside diameter of 70 cm. The machine rotates the test samples and abrasive charges to simulate abrasion conditions.

Abrasive Charges: These are steel balls used as the abrasive charge in the Los Angeles Abrasion Test. Each abrasive charge should have a diameter of 48 mm and a weight ranging from 390 to 445 grams. The number of abrasive charges used depends on the grading of the aggregate, as specified in the testing procedure.

Reference:

This test adheres to the guidelines specified in IS 2386(Part 4):1963, titled “Methods of Test for Aggregates for Concrete- Mechanical Properties.”

Procedure of Abrasion Test of Aggregate :

A. Gradation of Aggregate:

  1. Determine the gradation of the aggregate to assess its grade (A to G) as per the specified sieve sizes and weights. Refer to the table for the grading details in the testing procedure.

B. Procedure for Los Angeles Abrasion Test:

  1. Prepare a test sample of clean aggregate, dried in an oven at 105 to 110°C until it reaches a substantially constant weight. Choose the grading that best represents the aggregate to be tested.
  2. Place the test sample and the appropriate number of abrasive charges into the Los Angeles abrasion testing machine based on the grading (as per the table in the testing procedure).
  3. Rotate the machine at a speed between 20 to 33 revolutions per minute (RPM):
    • For gradings A, B, C, and D, rotate for 500 revolutions.
    • For gradings E, F, and G, rotate for 1000 revolutions (as indicated in the table).

Table: Number of Charges as per Grading of Aggregate

GradingNumber of SpheresWeight of Charge (grams)
A125000 ± 25
B114584 ± 25
C83330 ± 20
D62500 ± 15
E125000 ± 25
F125000 ± 25
G125000 ± 25
  1. Ensure that the machine operates and is counter-balanced to maintain a uniform peripheral speed. If an angle is used as the shelf, rotate the machine in a direction that causes the charge to be caught on the outside surface of the angle.
  2. After completing the test, discharge the material from the machine and perform an initial separation of the sample using a sieve coarser than the 1.70 mm IS Sieve.
  3. Wash, dry, and weigh the material retained on the sieve coarser than 1.70 mm to the nearest gram (B).

Calculation:

Calculate the Los Angeles Abrasion Value using the formula:

Aggregate Abrasion Value =((AB​)/A)×100

Where:

  • A = Weight in grams of the oven-dried sample.
  • B = Weight in grams of the fraction retained on 1.70 mm IS Sieves after washing and oven-drying to a constant weight.

This procedure enables the assessment of aggregate hardness and, subsequently, helps in selecting suitable materials for construction projects.

(Know about specific gravity test of aggregate .)

FAQs:

What is the value range of abrasion test?

The value range of abrasion tests typically represents the percentage of wear that an aggregate undergoes during the test. The minimum abrasion value is 30% and the maximum abrasion value is 50%.

How do you test for abrasion?

Abrasion tests are conducted by subjecting an aggregate sample to abrasive forces, often using specialized equipment like the Los Angeles Abrasion Testing Machine. The sample is rotated with abrasive charges, simulating wear and tear. After a specific number of revolutions, the material is separated, and the percentage of wear is calculated.

What unit of measure is abrasion?

The unit of measure for abrasion in the context of abrasion tests for aggregates is typically expressed as a percentage. It represents the percentage of weight loss or wear experienced by the aggregate during the test compared to its original weight.