LA abrasion test|Los Angeles Abrasion Test|LAA Test on Aggregates for Pavement

Los Angeles Abrasion test (LA abrasion Test) is normally used to measure aggregate hardness, toughness, and abrasion resistance with respect to scuffing, scratching, wearing, marring, rubbing, and disintegration. This test is suggested by AASHTO T 96 or ASTM C 131

Highway pavement is constructed with different aggregates, due to the movement of traffic, it is subjected to wearing. The moving action of vehicle pneumatic tire causes abrasion of the road surface. So, it is designed to use sufficient hard aggregates on the road surface to resist abrasion.

There are two methods to calculate the abrasion value of coarse aggregate they are: Los Angeles abrasion testing machine and Devil abrasion testing machine. Many practices show that the Los Angeles abrasion testing machine gives a better result of the abrasion resistance of the aggregate.

LA abrasion test is briefly described here:

Principle of LA abrasion test:

The main principle of the Los Angeles abrasion test is to develop an abrasion action between mixed aggregate and standard steel balls that is rotated in a drum with a specific number of revolutions that also cause an impact on aggregates. The weight of the wear of aggregate with the steel ball is measured and is expressed in percentage that is known as the Los Angeles abrasion value. Hence, the main objective of this test is to find the LAA value and judge it’s suitability for Road construction.

Apparatus Used In LA abrasion test:

Following apparatus are used for the Los Angeles abrasion test:

Los Angeles abrasion machine: LAA Machine is a 700 mm diameter, 500 mm length hollow cylinder with closed at both ends. It is fitted in such a way that it can rotate about a horizontal axis. A cover of movable type is provided to feed the sample, and it is clamped for dust-tight. A removable steel shaft projecting radially 88 mm in the cylinder and extending full length (i.e. 50 mm) is mounted firmly on the interior of the cylinder.
Abrasive Charge: Abrasive charge is generally 6 to 12 balls having approximately 48 mm diameter cast iron or steel balls each weighing in the range of 390 to 445 gm.
Sieve: sieve of size 1.70, 2.36, 4.75, 6.3, 10, 12.5, 20, 25, 40, 50, 63, 80 mm IS sieve.
A weighting balance having a capacity of 5 kg to 10 kg.
Oven drying machine.
Other tools like collecting tray, cup, etc.

Also read: Aggregate Impact value Test Apparatus, Procedure and uses

Steel Balls used for Abrasive Charge in LA abration test — **Fig. 3 Steel Balls used for Abrasive Charge in LA abration tes**t

Detail parts of - LA abrasion testing — **Fig.2. Detail parts of – LA abrasion testing Machine**

Procedure for Abrasion Test:

Followings steps are follows during LAA test:

Selection of Sample: the selection of samples is clean gravel coarser than 1.7 mm sieve and is dried in over dry to 105 ⁰C – 110 ⁰C. The test sample should be in the following adding given in table 1.

Table1. Grading chart of Test Samples – *Tolerance permitted is ± 12 percent.

Sieve size (mm)		Weight in gm. of the sample used
Passing mm	Retained on in 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

Table1. Grading chart of Test Samples – *Tolerance permitted is ± 12 percent.

According to the grading desire of our construction, grading is selected from the table.
The sample from grading A, B, C, or D 5 kg of sample is taken and for grading E, F, G 10 kg of sample is taken.
Abrasion charge according to our grading is selected from the given table (2) below is taken.
The sample aggregates and steel balls are applied in the cylinder by opening the cover of the LAA machine. after that cover is tighter.
After that, the Los Angeles abrasion test machine is uniformly rotated at a speed of 20 to 33 revolution per minute.
For grading A, B, C, or D machine is run for 500 revolutions per minute and for grading E, F, G 1000 revolution per minute after that the machine is stopped.
After that, the machine cover is opened and material is taken out.
Steel all’s are separated from the crushed stone and sieve the material on 1.7 mm IS sieve.
The material coarser than 1.7 mm is washed and makes dry in the oven at 105 to 110 ⁰C and is weighted to the accuracy level of one gm.

Then the percentage of loss of material is calculated by dividing the loss of weight by the original weight of the test sample. This value is the Los Angeles Abrasion value of the sample aggregate.

The values the percentage of the wear of a sample and should not be more than 16 percentage for concrete aggregates.

Table 2: Suitable Abrasive Charge according to Grading

Grading	No of Sphere balls	Charge Weight (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

Suitable Abrasive Charge according to Grading

Observations of Los Angeles Abration Test

Original weight of aggregate sample = A g

Weight of aggregate sample retained after sieving = B g

Weight passing 1.7mm IS sieve = Ag – B g

Abrasion Value = (Ag– Bg) / AgX 100

Uses of Los Angeles Test Values for Road Design

Los Angeles Abrasion test is normally used to measure aggregate hardness, toughness, and abrasion resistance with respect to scuffing, scratching, wearing, marring, rubbing, and disintegration.

The table below suggests the type of pavement layer according to abrasion value.

Table. 3. Types of pavement suitable for permissible abration value

Sr. No.	Type of Pavement	Max. permissible abrasion value in %
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
6	Bituminous surface dressing, rigid pavement like cement concrete surface course	35
7	Bituminous concrete surface course	30