Los angeles test

About

This test use Los Angeles testing machine for determining sizes of course aggregate smaller than 3/2” for resistance to degradation.

Our standard was ASTM C131.

Aggregates in excavation works

Objectives

The purpose of this test is to find the resistance of coarse aggregate to abrasion and attrition and to take an over view on the strength of aggregate for compressive one.

Equipment & Apparatus

1. Los Angeles machine. 
   
2. Sieves ( for 1st part the sample must be sieved on sieve 20 mm & retained 14 mm , and for the 2nd one it must be sieved on sieve 14 mm & retained on sieve 10 mm). 
   
3. Balance – Accurate within 0.1 %
   
4. Charge – With a steel spheres averaging on diameter approximately 46.8 mm and each having a mass of between 395 and 440 gram.
   

Procedure

- Summary:

As the drum rotates, a shelf plate picks up the sample and the steel spheres, carrying them around until they arc dropped to the opposite side of the drum, creating an impact-crushing effect.

- We have two parts of this test ( the 1st was at 100 revolutions and the 2nd at 400 revolutions).

- Place the test sample (which is should be washed and oven dried) for 1st part and with weight 2500g and the charge ( 11 balls) in the Los Angeles testing machine and rotate the machine at a speed of 30 to 33 r/min for 100 revolutions. Wash the material coarser than the 1.70- mm sieve and oven-dry at 110 ± 5°C (230 ± 9°F) to substantially constant mass and determine the mass to the nearest 1 g. For the 2nd part we put 2500g and added to the mass retained from part one in the Los Angeles machine and rotate the machine at a speed of 30 to 33 r/min for 400 revolutions. Then we take the crushed aggregate in sieve No. 12 then we weight the retained in the sieve.

Data & Calculation

- We calculate the loss (difference between the original mass and the final mass of the test sample) as a percentage of the original mass of the test sample. Report this value as the percent loss.

- For the 1st part:

➤ Weight before = 2500g. 
➤ Weight after = 2286g.

- For the 2nd part: 

➤ Weight before = 2500 + 2286 = 4786g. 
➤ Weight after = 3568g.

So:

( Passing Wagg. / Main Wagg. ) X 100 % = ( 5000 – 3568 ) / 5000 X 100 % 
= 28.64 %

Comment& Conclusion:

The Los Angeles test which combines the processes of abrasion and attrition gives results that shows the correlation not only with actual wear of the aggregate in concrete.

To asses any possibility of degradation of an unknown fine aggregate on prolonged mixing of fresh concrete, the Los Angeles test is not very suitable for this latter requirement and in fact no standard apparatus is available.