Khwopa College Of Engineering Lab Report on Transportation Engineering
DETERMINATION OF LOS ANGELES ABRASION VALUE
1. Objectives
To determine the Los Angeles abrasion value
To find out the suitability of the aggregates for use in road construction
2. Apparatus Required
Los Angeles Machine
Abrasive Charge i.e Cast
iron or steel balls
Sieves
Weighing machine
Aggregates
Miscellaneous like tray
etc. Figure 1:- Los Angeles Machine
3. Theory
Aggregates undergo substantial wear and tear throughout their life. In general, they
should be hard and tough enough to resist crushing, degradation and disintegration from
any associated activities including manufacturing, stockpiling, production, placing and
compaction. Furthermore, they must be able to adequately transmit loads from the
pavement surface to the underlying layers and eventually the subgrade. These
properties are especially critical for open or gap graded HMA, which do not benefit
from the cushioning effect of the fine aggregate and where coarse particles are subjected
to high contact stresses. Aggregates not adequately resistant to abrasion and polishing
may cause premature structural failure and/or a loss of skid resistance. Furthermore,
poor resistance to abrasion can produce excessive dust during HMA production
resulting in possible environmental problems as well as mixture control problems.
Because of the preceding issues, a test to predict aggregate toughness and
abrasion resistance is valuable. The L.A. abrasion test is the predominant test.
The L.A. abrasion test measures the degradation of a coarse aggregate sample
that is placed in a rotating drum with steel spheres. As the drum rotates the aggregate
degrades by abrasion and impact with other aggregate particles and the steel spheres
(called the “charge”). Once the test is complete, the calculated mass of aggregate that
has broken apart to smaller sizes is expressed as a percentage of the total mass of
aggregate. Therefore, lower L.A. abrasion loss values indicate aggregate that is
tougher and more resistant to abrasion.The L.A. Abrasion test is an empirical test; it is
Khwopa College Of Engineering Lab Report on Transportation Engineering
not directly related to field performance of aggregates. Field observations generally do
not show a good relationship between L.A. abrasion values and field performance. Wu
et al. (1998[2]) found that L.A. abrasion loss was unable to predict field performance.
Specifically, the test may not be satisfactory for some types of aggregates. Some
aggregates, such as slag and some limestones, tend to have high L.A. abrasion loss but
perform adequately in the field. L.A. abrasion loss seems to be reasonable well
correlated with dust formation during handling and HMA production in that aggregates
with higher L.A. abrasion loss values typically generate more of dust.
Table 1: Grading of Test Samples – *Tolerance of ± 12 percent permitted.
Sieve size
(square Weight of test
sample in gm
hole)
Passing
Retained on (mm) A B C D E F G
(mm)
80 63 2500*
63 50 2500*
50 40 5000* 5000*
40 25 1250 5000* 5000*
25 20 1250 5000*
20 12.5 1250 2500
12.5 10 1250 2500
10 6.3 2500
6.3 4.75 2500
4.75 2.36 5000
Khwopa College Of Engineering Lab Report on Transportation Engineering
Table 2: Selection of Abrasive Charg
Grading No of Steel balls Weight of charge in gm.
A 12 5000 ± 25
B 11 4584 ±25
C 8 3330 ± 20
D 6 2500 ± 15
E 12 5000 ± 25
F 12 5000 ± 25
G 12 5000 ± 25
4. Procedure
Los Angeles test was done for Grade A in which 5 kg of sample was taken as
W1.
The abrasive charge was choosen as A (i.e. 12 steel balls).
The cover of Los Angeles machine was opened and the aggregates and steel
balls were fed into the cylinder. Cover was replaced tightly.
The machine was rotated at uniform speed 30-33 revolutions per minute.
The machine was revolved for 500 revolutions for grading A.
Dust cover was removed and material was taken out carefully.
The steel ball was separated and the material was sieved on 1.7 mm IS sieve
and weighted as W2.
The percentage of loss of material was calculated as follows.
5. Observation and Calculation
Grade of aggregates = A
Original weight of sample (W1) = 5 kg
Weight of sample retained on 1.75 mm IS sieve (W2) = 2.680 kg
Loss in weight (W1-W2) =2.320 kg
Percentage wear or LA value= (W1-W2)/W1 *100% = 46.40%
6. Result
Thus the Los Angeles value of the aggregate was found to be 46.40%.
Khwopa College Of Engineering Lab Report on Transportation Engineering
7. Discussion And Conclusion
Los Angeles test is commonly used to evaluate the hardness of aggregates. The test
has more acceptability because the resistance to abrasion and impact is determined
simultaneously. Similarly the test can also be used to determine the performance of
the aggregate in pavement, aggregate must be sufficiently hard to resist the abrasive
effect of traffic over a long period of time. The soft aggregates will quickly ground
to dust, while the hard aggregates are quite resistance to the crushing effect. With
the help of the Los Angeles test we can easily determine the suitability of the
aggregate for the road construction.
Depending upon the value, the suitability of aggregates for different road constructions
can be judged as per IRC specifications as given:
Max. permissible
Sl.
Type of Pavement abrasion value in
No.
%
1 Water bound macadam sub base course 60
2 WBM base course with bituminous surfacing 50
3 Bituminous bound macadam 50
4 WBM surfacing course 40
5 Bituminous penetration macadam 40
Bituminous surface dressing, cement concrete surface
6 35
course
7 Bituminous concrete surface course 30
And since the Los Angeles Value was determined to be 46.40 which lies between
40-50%. Thus the aggregate we choose for the practical was found suitable for three
types of pavements namely 1. Water bounded macadam sub base course 2. WBM
Base course with bituminous surfacing and 3. Bituminous bound macadam.
Hence the practical related with the determination of the Los Angeles value of the
aggregate was performed.
8. Precautions
Instruments must be handled with care.
Proper counting of the no. of revolutions must be done
Aggregate must be properly sieve.
