Aggregate Abrasion Value Test (IS: 2386 (Part IV))
The abrasion value of coarse aggregate may be determined by either Deval Machine or by Los Angeles machine.
Using Deval Machine
Abrasive Charge: The abrasive charge consists of 6 cast iron or steel spheres approximately 48 mm in diameter, each weighing between 390 and 445 g. An abrasive charge of 6 spheres weighing 2500 ± 10 g is used with each test sample.
The test sample consists of dry coarse aggregate made up of percentages of the various sizes conforming to one of the gradings shown in Table 6.7. The grading used should be that most nearly representing the coarse aggregate furnished for the work.
Procedure: The test sample and the abrasive charge are placed in the Deval abrasion testing machine and the machine is rotated for 10000 revolutions at a speed of 30 to 33 rev/min. At the completion of the test, the material is removed from machine and sieved on a 1.70 mm sieve. The material retained on the sieve is washed, dried and accurately weighed to the nearest gram.
The loss by abrasion is considered as the difference between the original weight of the sample and the weight of the material retained on the 1.70 mm sieve, expressed as percentage of the original weight of the test sample.
In case of crushed gravel, the percentage by weight of crushed fragments is determined, and the permissible percentage or wear is calculated as:
W = AL (100 A)L / 100
Where W = permissible percentage of wear
A = percentage of uncrushed fragments
L= maximum percentage of wear permitted by the specifications for gravel consisting entirely of uncrushed fragments
100 - A = percentage of crushed fragments
L = maximum percentage of wear permitted by the specifications for gravel consisting entirely of crushed fragments
Using Los Angeles Machine
Abrasive Charge: The abrasive charge consists of cast iron spheres or steel spheres approximately 48 mm in diameter and each weighing between 390 and 445 g.
The abrasive charge, depending upon the grading of the test sample should be as given in Table 12.
The test sample consists of clean aggregate dried in an oven at 105 -110 o C to substantially constant weight.
Note: It is recognized that different specification limits may be required for gradings E, F and G than for A, B, C and D. It is urged that investigations be conducted to determine the relationship, if any, which exists between results for these coarse gradings using the 10000 g samples and the finer ones using the 5000 g samples.
The test sample and the abrasive charge is placed in the Los Angeles abrasion testing machine and the machine is rotated at a speed of 20 to 33 rev/min. For gradings A, B, C and D, the machine is rotated for 500 revolutions; for gradings E, F and G, it is rotated for 1000 revolutions. The machine is so driven and so counter-balanced as to maintain a substantially uniform peripheral speed. If an angle is used as the shelf, the machine is rotated in such a direction that the charge is caught on the outside surface of the angle. At the completion of the test, the material is discharged from the machine and a preliminary separation of the sample made on a sieve coarser than the 1.70 mm. The finer portion is then sieved on a 1.70 mm sieve.The material coarser than the 1.70 mm sieve is washed, dried in an oven at 105 -110 o C to a substantially constant weight, and accurately weighed to the nearest gram. The difference between the original and the final weights of the test sample expressed as a percentage of the original weight of the test sample gives the percentage of wear.
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