Aggregate Abrasion Value IS: 2386 PART- 4

Determine Aggregate Abrasion Value

Test - I
gm
gm
Test - II
gm
gm
 

Aggregate Abrasion Value

42 %
Abrasion Value %

Mean Aggregate Abrasion Value

Abrasion Value(Test-I)+Abrasion Value(Test-II)2

33.0+50.02

41.5 %

Result of Test - I

33.0 %
Abrasion Value %

Aggregate Abrasion Value

WA - WBWA×100

100-67100×100

33.0 %

Result of Test - II

50.0 %
Abrasion Value %

Aggregate Abrasion Value

WA - WBWA×100

200-100200×100

50.0 %

What is the need of Aggregate Abrasion value Test?

Due to the movement of traffic, the road stones and used in the surfacing course are subjected to wearing action at the top Resistance to wear or hardness is hence an essential property of road aggregate, especially when used in wearing course. Thus road stones should be hard enough to resist the abrasion due the traffic. When fast moving traffic fitted with pneumatic tyres move on the road, the sod particles present between the wheel and road surface causes abrasion on the road stone. Steel tyres of the animal drawn vehicles which rub against the stones can cause considerable abrasion of the stones on the road surface Hence in order to tests are carried out in the laboratory.


What is Los Angeles Abrasion Test?

The principle of Los Angeles Abrasion Test is to find the percentage wear due to the relative rubbing action between the aggregate and steel balls used as abrasive charge, pounding action of these balls also exist while conducting the test. Some investigators believe this test to be more dependable as rubbing and pounding action simulate the field conditions where both abrasion and impact occur. Los Angeles Abrasion Test has been standardized by the ASTM, AASHTO and also by the ISI Standard specifications of Los Angeles Abrasion Values are also available for various types of pavement constructions.


Appratus
  • Los Angeles Machine should have essential characteristics as under: The machine has hollow steel cylinder 700 mm in dia, and 500 mm in side length. A steel self-88 x 25 x 500 mm is projecting radially. It can be mounted on inside of the cover plate.
  • Sieve 1.70 mm and as given in Table 1. for different grades of aggregates
  • Abrasive charge: It consists of cast iron spheres or steel sphere app 48 mm in dia and weighing 390 to 446 gm No of spheres are chosen from Table - 2 as per the grade of aggregates.
  • Oven and accurate balance.

Sample Quantity

Sieve the sample of aggregate and refer to the "Grades of Test sample" to decide the grade and the weight of the aggregate to be taken. Take little пюге than the required quantity in the oven at 105 °C to 110 °C for 24 hours for drying. Allow it to cool to room temperature. From this sample, weigh the required quantity for the test.

Prodecure to conduct Los Angeles Abrasion Test

Apparatus

The apparatus shall consist of the following :

  1. Los Angeles machine - The Los Angeles abrasion testing machine, conforming in all its essential characteristics to the design shown in Fig, shall be used. The machine shall consist of a hollow steel cylinder, closed at both ends, having an inside diameter of 700 mm and an inside length of 500 mm. The cylinder shall be mounted on stub shafts attached to the ends of the cylinders but not entering it, and shall be mounted in such a manner that it may be rotated about its axis in a horizontal position. An opening in the cylinder shall be provided for the introduction of the test sample. The opening shall be closed dust-tight with a removable cover bolted in place. The cover shall be so designed as to maintain the cylindrical contour of the interior surface unless the shelf is so located that the charge will not fall on the cover, or come in contact with it during the test. A removable steel shelf, projecting radially 88 mm into the cylinder and extending its full length, shall be mounted along one element of the interior surface of the cylinder. The shelf shall be of such thickness and so mounted, by bolts or other approved means, as to be firm and rigid. The position of the shelf shall be such that the distance from the shelf to the opening, measured along the circumference of the cylinder in the direction of rotation, shall be not less than 1250 mm.
  2. Sieves - The 1.70-mm IS Sieve.
  3. Abrasive Charge -The abrasive charge shall consist of cast iron spheres or steel spheres approximately 48 mm i. diameter and each weighing between 390 and 445 g
Los Angeles machine for Abrasion Test

Los Angeles Abrasion Test Machine - Model

Los Angeles Abrasion Test Machine - Model
Diagram Los Angeles machine for Abrasion Test

Los Angeles Abrasion Test Machine - Diagram

Los Angeles Abrasion Test Machine - Diagram

Preparation of the Test Sample

The test sample shall consist of clean aggregate which has been dried in an oven at 105 to 110°C to substantially constant weight and shall conform to one of the gradings shown in Table. The grading or gradings used shall be those most nearly representing the aggregate furnished for the work.

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 gm samples and the finer ones using the 5000 gm samples.

Table - Grading of Test Samples for Los Angeles Abrasion Test
Grading Weight in grams of each lest sample in the size range mm (passing and retained on square holes) No. of spheres Weight of charge gms.
80-63 63-50 50-40, 40-25 25-20 20-12.5 12.5-10 10-6.3 6.3-4.75 4.75-2.36
A - - - 1250 1250 1250 1250 - - - 12 5000±25
B - - - - - 2500 2500 - - - 11 4584±25
C - - - - - - - 2500 2500 - 8 3330±2
D - - - - - - - - - 5000 6 2500+15
E 2500' 2500 » 5000 - - - - - - - 12 5000+25
F - - 5000" 5000 * - - - - - - 12 5000±25
G - - - 5000 * 5000 - - - - - 12 5000+25

Note: Tolerance of ±2 percent is permitted


Test Procedure
  • The test sample and the abrasive charge shall be placed in the Los Angeles abrasion testing machine and the machine rotated at a speed of 20 to 33 rev/min. For gradings A, B, C and D, the machine shall be rotated for 500 revolutions; for gradings E, F and G, it shall be rotated for 1000 revolutions. The machine shall be so driven and so counter-balanced as to maintain a substantially uniform peripheral speed. If an angle is used as the shelf, the machine shall be 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 shall be discharged from the machine and a preliminary separation of the sample made on a sieve coarser than the l.70-mm IS Sieve. The finer portion shall then be sieved on a 1.70-mm IS Sieve.
  • The material coarser than the 1.70-mm IS Sieve shall be washed dried in an oven at 105 to 110°C to a substantially constant weight, and accurately weighed to the nearest gram.

Note
Attention is called to the fact that valuable information concerning the uniformity of the sample under test may be obtained by determining the loss after 100 revolutions. When this determination is made, care should be taken to avoid loss of any part of the sample; the entire sample, including the dust of abrasion, shall be returned to the testing machine for the completion of the test.


Calculate Aggregate Abrasion Value

Difference between the original weight and the final weight of the test sample shall be expressed as a percentage of the original weight of the test sample. This value shall be reported as the percentage of wear.

Aggregate Abrasion Value = WA - WBWA×100

Where,

  • WA is Original weight of aggregate in gm
  • WB is Weight of material retain on 1.70 mm IS-sieve after test in gm
Reporting of Results

Difference between the original weight and the final weight of the test sample shall be expressed as a percentage of the original weight of the test sample. This value shall be reported as the percentage of wear.

Specifications: Los Angeles Abrasion Values

Maximum Permissible Aggregates Values for the different types of pavements
Sr. Type of Pavements Maximum Aggregates Value %
(IRC Recommendations)
1 Granular Sub Base (G.S.B.) Not Specified in MORT&H
2 Base course W.B.M (Water Bound Macadam) 40%
3 Base course W.M.M. (Wet Mix Macadam) 40%
4 Base course Crusher Run Macadam 40%
5 Base course / Binder course B.M. (Bituminous Macadam) 40%
5 Base course / Binder course D.B.M. (Dense Bituminous Macadam) 35%
6 Surface course / Wearing course S.D.B.C. (Semi Dense Bituminous Concrete) 35%
7 Surface course / Wearing course B.C. (Bituminous Concrete) 30%
8 Cement Concrete Pavement (Wearing Surface) 30%
9 Cement Concrete Pavement (Other than Wearing Surface) 16%