Los Angeles Abrasion Test

OBJECTIVES

        i.            To determine the Los Angeles abrasion value.

      ii.            To find out the suitability of aggregates for its use in road construction.

APPARATUS REQUIRED

As per IS 2386 (part IV)-1963 the apparatus required are:

1. Los Angeles Machine: It consists of hollow steel cylinder, closed at both the ends having internal diameter 700 mm and length 500 mm and capable of rotating about its horizontal axis. A removable cover for introducing sample is provided which when clamped is dust tight. A removable steel shaft projecting radially 88 mm into cylinder and extending full length (i.e. 500 mm) is mounted firmly on the interior of cylinder. The shelf is placed at a distance 1250 mm minimum from the opening in the direction of rotation.
2. Abrasive charges: Cast iron or steel balls, approximately 48 mm in diameter and each weighing between 390 to 445 gm; six to twelve balls are required.
3. Sieve: IS sieve size of order 40, 25, 20, 12.5 and 10 mm.

THEORY

     The aggregate used in the surface course of highway pavements are subjected to wearing due to the movement of the traffic. When vehicles move on the road, soil particles present between the pneumatic tires and roads surface cause abrasion of road aggregates. Therefore, road aggregates should be hard enough to resist the abrasion. Resistance to abrasion of aggregate is determined in laboratory by Los Angeles Test.

     The principle of Los Angeles Test is to produce the abrasive action by use of standard steel balls when mixed with aggregates ad rotated in drum for specific number of revolutions and also cause impact on aggregates. The percentage of wear on the aggregates due to the rubbing with the steel balls is determined and is known as Los Angeles Abrasion Value.

Table 1: Abrasion value for different pavement layer

S.N.	Type of pavement layer	Maximum permeable abrasion value in %
1.	Water bound macadam, sub bound 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
6.	Bituminous surface dressing, cement concrete surface course	35
7.	Bituminous concrete surface course	30

PROCEDURE

The Los Angeles test was performed by following way:

        i.            At first, the aggregates are sieve through the sieve of order 40, 25, 20, 12.5 and 10 mm. The aggregate sample weighing 1.25 kg was taken for passing through a sieve and retaining on the successive sieve with altogether of 5 kg

                       (W1) sample in weight.

    iii.            Then, the aggregate sample was poured into the Los Angeles abrasion testing machine.

    iv.            Taking grading as A, we had provided 12 nos. of abrasive charge.

      v.            Then the machine was revolved at 33 rev/min up-to 500 revolutions.

    vi.            Then, the tested samples were sieved through 1.7mm sieve and the weight of sample retained on 1.7mm weight was taken as W2 .

 vii.      Then, Los Angeles Abrasion Value =   ((W1-W2)/W1)*100

Table 2: Grading of Test samples

Sieve Size (Square Hole)		Weight in g of test sample for grade
Passing mm	Retained on mm	A	B	C	D	E	F	G
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	-	-	-

* Tolerance of + 2% permitted

Table 3:Selection of Abrasive Charge

Grading	No. of steel balls	Weight of charge, g
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

OBSERVATION

Table 4: Observation Table

Grading A	Sample
Original wt. of sample (W1)(kg)	5
Wt. of aggregate retained on 1.7mm sieve (W2)(kg)	2.692
Loss of weight (W1-W2)(kg)	2.308
Los Angeles Abrasion Value=((W1-W2)/W1)*100(%)	46.16

RESULT

Thus, the Los Angeles abrasion value of the aggregate sample=46.16%.

CONCLUSION AND DISCUSSION

The result shows the abrasion value of 46.16% for the given aggregate sample. From the table it shows that the aggregate can be used Bituminous Bound Macadam, WBM base course with bituminous surfacing, water bound macadam, sub bound course. The result may have contain some error due to the inaccuracy in weighing the samples correctly and inability to count the revolution accurately.

PRECAUTIONS

        i.            Weighing of the samples should be done carefully.

      ii.            The number of revolutions should be count carefully.