Los Angeles abrasion test on aggregate

Test Specifications

AASHTO: T 96-02 ASTM C-131 ASTM C-535

Apparatus

1. Los Angeles abrasion machine,
2. Sieves conforming to ASTM standards.
3. Balance.
4. Abrasive charge i.e. steel spheres  inches in diameter and each weighing 390-445 gram.

Related Theory

This test is used to assess the hardness of aggregate used in road construction. The road aggregate is subjected to wearing action by the moving traffic and therefore resistance to wear or hardness is an essential property of the aggregate should be hard enough to resist abrasion due to traffic.

Los Angeles abrasion test is used to find out percentage wear due to relative rubbing action between aggregates and steel balls used as abrasive charges. Pounding action of these balls also exits while conducting the test. The test is considered more dependable as rubbing and pounding action simulate field conditions.

The test has been standardized by ASTM and AASHTO. FHWA recommendations are that coarse aggregate for dense graded mixes have a percent wear of 50% or less. For open graded mixes or where requirements are more exacting, the requirement is of 40% or less.

Procedure

The sample taken should be representative and conforming to any of the grading given in the table attached.

The sample is placed in the cylinder along with the abrasive charges and the machine is rotated for required number of revolutions (500-1000). After the required number of revolutions the material is discharged from the machine and sieved through # 12 US sieve. Wash the material coarser than # 12 sieves, oven dry and weigh.

Los Angeles Abrasion Value =  x100

Table 4.1:       Grading of Test Samples

Sieve size	Weight of test sample in (gm)
Passing (mm)	Retained on (mm)	A	B	C	D
40	25	1250
25	20	1250
20	12.5	1250	2500
12.5	10	1250	2500
10	6.3			2500
6.3	4.75			2500
4.75	2.36				5000

Table 4.1:       Selection of Abrasive Charge

Grading	No of Steel Balls	Weight of Charge (gm)
A	12	5000 ± 25
B	11	4584 ±25
C	8	3330 ± 20
D	6	2500 ± 15

Observations and Calculations

Grading used for the test                                            =                     

Material taken for the test:

                                                                                    =                     

                                                                                    =                     

Number of abrasive charges used                               =                     

Original weight of the test sample, W₁                       =                     

Final weight after test (retained on # 12), W₂            =                     

Los Angeles Abrasion value,                                      =                     

Results

Los Angeles Abrasion value                                       =         

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