Los Angeles Abrasion Test and Impact Test

Introduction

Aggregates used on highway surface pavement are subjected to impact and abrasion due to traffic movement. Thus, the road aggregate have to be tough to resist disintegration due to impact and abrasion. Both abrasion and impact of the pavement aggregates were determined in this experiment. The aim of the first experiment was to determine the Los Angeles value of the pavement aggregate using Los Angeles test machine. The principle of this machine is generate abrasive action using standard aluminium balls which are mixed together with the aggregate and rotated in the machine for a specific number of revolutions. The balls cause impact on the aggregate and the percentage ware, which is the Los Angeles Value, is determined.

The second experiment involved impact test on the sample. The aim of this test was to determine the toughness of the aggregate sample to resist disintegration due to impact. This was measured by the impact value which is the resistance of the aggregate to sudden shock or impact, which is different from the resistance due to gradual applied compressive force.

Apparatus and samples

Los Angeles Abrasion Test

  1. 20mm aggregate sample

  2. 1.7mm IS sieve

  3. Weight machine and other supporting apparatus

  4. Los Angeles Machine – it has a hollow cylinder with closed ends and with the length of 500mm and diameter of 700mm. It can rotate about its horizontal axis. The machine is shown in figure 1 and 2 below.

Los Angeles Abrasion Test and Impact Test

Figure 1: Los Angeles Machine

Los Angeles Abrasion Test and Impact Test 1

Figure 2: Cross sectional view of Los Angeles test machine (Australian Standard, 2009)

Impact Test

  1. Aggregate impact test machine is shown in figure 3 below.

Los Angeles Abrasion Test and Impact Test 2

Figure 3: Impact test machine

  1. Weight machine and other supporting apparatus

  2. 2.36mm Sieve

Safety and precautions

Los Angeles machine test

  1. Ear protection are worn when operating the machine, because it produce a lot of noise

  2. The mask must also be worn when retrieving the sample since the dust was present

Impact test

  1. The plunger was placed at the central location so that it felt directly on the sample and could not touch the cylinder walls.

  2. Tampering was done properly by dropping the tamping rod gently and through hammering.

  3. Precaution is taken when operating the machine since the hammer is very heavy.

  4. Mask must be worn as the dusts are present

Procedures

Los Angeles Abrasion Test

  1. Measure 5kg sample of 20mm single-sized aggregate.

  2. The test machine and the steel sample were ensured they were clean

  3. The test sample and 12 steel balls were placed in Los Angeles Test machine and the cover plate was tightened and clamp secured.

  4. Then the machine was rotated at constant speed for 500 revolutions.

  5. After the completion test, the material sample is discharged from the test machine and sieved through 1.7mm sieve.

  6. The weight of the materials passing through the 1.7mm IS sieve was recorded.

  7. The materials which passed through the 1.7mm sieve were weighted and recorded as mp, and those that remained were recorded as mw.

  8. The result was excepted if the difference between mp + mw and mT exceeded 25g.

Impact test

  1. After making sure that the safety switch was installed, the mold was removed from the impact test machine and weighed.

  2. The aggregate sample was filled in the mold and weighed and the weight of the mold was deducted to obtain the weight of sample, mT.

  3. The cylindrical mold was then installed at the base of the impact test machine.

  4. The hammer was raised until the lower face was 380mm from the surface of the aggregate and release to fall on the sample. 25 such blows were given at a time interval of one second.

  5. The crushed aggregate was removed from the impact test machine and sieved through 2.36mm sieve. The fraction passing through the sieve, mp, and those that remained were weighed, mR.

  6. It was made sure that the difference between mp + mR and mT did not exceed 25g.

Los Angeles Abrasion Test

Before abrasion

Total mass of test portion (20mm Aggregate), mT

After abrasion

Mass passing 1.7mm sieve, mP

Mass retained on 1.7mm sieve, mw

Check mP + mw = mT ± 25g

Los Angeles Abrasion Test and Impact Test 3Loss Angeles value =

Impact test

Before Impact Test

Mass of sample (10mm aggregate), mT

After Impact Test

Mass passing 2.36mm sieve, mp

Mass retained on 2.36mm sieve, mR

Check mp + mR = mT±25g

Los Angeles Abrasion Test and Impact Test 4Impact text value =

Discussion

Los Angeles abrasion test

Los Angeles abrasion test is used to determine the resistance of the pavement surface to wear because of the moving traffic. The standard balls produce abrasive action on the aggregate when the mixture was rotated in the drum. The particles in between the road surface and the pneumatic tyres cause abrasion on the aggregate surface. It is important to have tough materials which can resist abrasion.

The Los Angeles value or the percentage wear for the pavement aggregate due to rubbing with the metal balls is 75.15%. This mean that the aggregate material that has been tested is weak for road surfacing as it wear out easily. It is therefore not suitable for use in the highway pavement.

Impact test

Toughness of material is the property to resist impact. The aggregate on the road are subjected to impact due to the movement of vehicles, making the pavement aggregate to break down to pieces. Thus the aggregate should be tough in order resist disintegration. The impact value which is the resistance to disintegration due to sudden impact for the current materials is 12.12%. This means that the aggregate materials are sufficiently strong and can be used for road pavement.

From the Los Angeles test and impact test, it has been shown that the materials both weak and tough. This means that although the material has low abrasiveness or soft because of ductility, but difficult to grind or is tough (Weimer, 1996).

Conclusion

The two tests have given us the values used to determine the properties of the aggregate pavement. Los Angeles value indicates the hardness of the material and the impact test indicates its toughness. The material is weak but is tough. This means that although the material has low abrasiveness or soft because of ductility, but difficult to grind or is tough. Therefore, the material is not suitable to be used in the road surface pavement.

References

Australian Standard. (2009). AS1141.23-2009.Sydney: Australian Standard.

Weimer, A. W. (1996). Carbide, Nitride and Boride Materials Synthesis and Processing. Dordrecht: Springer Netherlands.