Los Angeles Abrasion Resistance Test

Abrasion is known as process of scraping or wearing something away, technically speaking; abrasion in geology is the mechanical scraping of a rock surface by friction between rocks and moving particles during their transport by wind, waves, gravity, running water or erosion. The intensity of this erosion effect depends on the hardness, concentration, velocity and mass of the moving particles.

Los-Angeles Abrasion Resistance Test

What is abrasion, wear and tear?

Pavements in transportation engineering, either rigid or flexible have aggregates of specific sizes. These aggregates throughout their life are subjected abrasive effect of moving traffic vehicles. Whether it is sub-base, base or wearing course the aggregates are subjected to wear and tear. Aggregates transfer their loads from vehicles to ground through the interlock and toughness of their rigid surface.
The aggregates, thus, must be hard enough to resist crushing, degradation and disintegration from any associated activities. While fine aggregates are used among the coarser aggregates the load transferring mechanism is bit easy due to the cushioning effect of the fine aggregates, in case of gap or open graded Hot mix asphalt (HMA), where there are no such fines or some are missing, toughness of aggregates play a pivotal role in defining the life of a pavement.

Resistance to Abrasion?

Absence of abrasion resistance, hardness or toughness in aggregates would result in premature degradation, dust pollution early loss of skid resistance and many other problems as well.
Extent of Resistance to abrasion is measured in laboratory by a test called “Los Angeles Abrasion test” or L.A Test. Los Angeles abrasion test is an empirical test; meaning that it doesn’t have a numerical or analytical concept as its base. Though it relates and defines well with the toughness of the aggregates but generally do not show a good relationship with the field performance of the subject sample.

Background

Theory of Los Angeles abrasion test is to produce the abrasive action by use of standard steel balls which when mixed with aggregates and rotated in a drum for specific number of revolutions also causes impact on aggregates. The percentage wear of aggregates due to rubbing with steel balls is determined and is known as Los Angeles Abrasion value.

Summary

Based on grading of aggregates select the number of steel balls and respective sieve sizes are arranged and total of 5000g sample is prepared. The sample is placed in a steel rotating drum along with the steel spheres or “charge”. As the drum rotates the drum picks up the aggregates and steel spheres and then drops them on the opposite end. This rotating, crushing and impact generates the abrasive effect. After specific number of revolutions, aggregates are removed from the drum and sieved on No. 12 (1.70 mm) sieve. The aggregate that is retained on the sieve is weighed and the difference between the weight is reported as percentage and given as Los Angeles Abrasion value.

Procedure

1) The sample obtained is cleaned and dried in oven at 105 to 110 degree Celsius.
2) Select the grading of the aggregates such that it suits best with the grading to be used in construction as shown in the table;
3) Arrange the sieves as per grading and weight the material retained on specific sieves such that the total weight becomes 5000 g.
4) Select the charge or steel balls for the Los Angeles Abrasion test as per the grading.
5) Place the aggregates and the charge in to the steel drum.
6) Rotate the Los Angeles Abrasion testing machine at a speed of 30 to 33 revolutions per minute (rpm). The revolutions is also dependent on the grading of the aggregates, it is 500 for grading A, B, C and D while 1000 for E, F and g.
7) The machine after specific revolutions is stopped and material is discharged to a tray.
8) The material is then sieved from Sieve No. 12 or 1.70 mm.
9) The material that would retained on sieve No. 12 is weighed and noted.

Table 1 : Grading of Aggregates

Sieve size (square hole)	Weight of test sample in gm
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

Table 2 – Grading with no of charge and weight of sample in gm.

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

Observations and calculations

Original test sample mass = M(original) = ____________ g
Final test sample mass = M(final)= ________________ g
Loss = ((Mo – Mf)/Mo) x 100
Los Angeles Abrasion value (L.A Value) = _______________ %

Determination of field density of soil by Sand Replacement Method

Sand replacement test method is used to determine the field density or in-place density of earth embankments, road fills, sub-grade, sub-base or any of compacted material. This method serves as base upon which one can accept the density of a compacted material to a specified magnitude or to a percentage of maximum unit dry density determined as proctor.

As we know that moisture content of the soil vary from time to time and hence the field density also, so we are required to report the test result in terms of dry density. In order to determine the dry density we must have to examine the moisture content in the soil by using general method.
Moisture content (%) = m = ((wt. of wet soil – wt of dry soil) / wt of dry soil)  x 100
Dry density = (bulk density ) / (1 + w)

Apparatus Required

Sand pouring cylinder
Calibrating
Metal tray
Excavating tool
Balance
Glass plate
Metal tray
Clean uniform sand (1mm pass 600 mirco retain)
Water content determination apparatus

Theory

The dry density of the sample obtained as a result is divided by the proctor test result i.e. the maximum dry obtained of the sample that can be obtained in the laboratory by using standard AASHTO compaction test or Modified AASHTO compaction test and the result is reported as percentage.

The acceptance criteria for these percentages depend on the specification requirements and generally following rules is followed;

No less than 98% within 150 mm below formation level
No less than 95% between 150 mm and 1200 mm below formation
No less than 90% beyond 1200 mm below formation level

Background

As we know density means weight per unit volume or in other words how much mass is being enclosed in a specific quantum of volume. We can easily determine the mass of soil by using the physical balance or digital balance, but the problem lies in finding the volume of the hole dug.
This problem is solved with the help of a calibrated sand whose unit weight or density is already being determined and thus if we could determine how much weight of calibrated sand is going to rest in the dug hole we can find the volume of the hole by using following formula;
Volume of dug hole = weight of soil in hole dug  / unit weight of calibrated soil

Procedure

The standard procedure of this test is being divided in two parts in first part we will find the unit weight of the standard soil by calibration process described  as follows;

Calibration

1. Determine the internal volume of the calibrating container by using the dimensions as follows;
                                                    V = ((Pi) d^2 / 4) x h
2. Now fill the sand pouring cylinder with the sand to be calibrated within about 10 mm of its top left vacant and then determine the mass of the sand pouring cylinder along with sand and note it as w1.

3. Now place the sand pouring cylinder on top of calibrating cylinder of known volume and open the shutter to allow the sand to fall in to the cylinder after no more sand is falling close the shutter and determine the mass of the calibrating cylinder filled with sand and note it as W2

4. Now as we also have the weight of the sand in the conical portion of the sand pouring cylinder, we must subtract the weight of sand that can accumulate within that conical portion. For that take a flat glass plate and place the sand pouring cylinder. Open the shutter till no more sand falls and determine the mass of sand in the conical portion and note it as W3.

5. Now the weight of the sand in the calibrating cylinder is determined as
                        Wa = W1 – W2 – W3

6. The bulk density of the sand is determined by dividing the mass of sand in the calibrating cylinder with the volume of the calibrating cylinder.

Determine the Dry density of the soil under sample

1. Prepare the area of the embankment subject to test, level the top of the soil using the scrapper tool.

2. Place the metal tray on the flat surface, if required insert the nails into the small holes of the metal tray.

3. Trace the circular hole of the tray on the ground and excavate the soil carefully without loosing any of
the soil fragment. Dig a hole of approximately 150 mm in the ground.

4. Collect all the excavated material in a metal container and clear the hole using a brush.

5. Determine the mass of this soil as weight of wet soil from hole Ww.

6. Fill the sand pouring cylinder with the calibrated sand and determine its mass as W1.

7. Place the cylinder directly over the excavated hole. Allow the sand to run out the cylinder by opening the shutter. Close the shutter when the hole is completely filled and no further movement of sand is observed.

8. Now weigh the remaining sand in the sand pouring cylinder and note it as w4.

9. Take a sample of the excavated soil in an air tight sampler for the determination of the water content or moisture content.

10. Volume of the hole is determined by using the unit weight of the calibrated sand already known;

Observations and Calculations

Volume of calibrating container = V Cm3 = 1000 cm3
Weight of cylinder + sand (before pouring) , W1 g = 7476 g
Mean weight of cylinder + sand (after pouring), W2g = 5610 g
Mean weight of sand in cone (of pouring cylinder), W3 g = 436 g
Weight of sand to fill calibrating container Wa = w1 – w2 – w3 g = 1430 g
Bulk density of sand = Gamma b = Wa / v g/cm3 = 1.43

Dry Density

Weight of calibrated sand in hole wb = W1 – W4 – W2
Volume of hole = Vh = Wb  / Unit weight of sand
Dry density of soil = ww / vh
% compaction = (dry density / proctor density )  x 100