Scope This test is used to determine the resistance of coarse aggregate to impact in a rotating cylinder containing metallic spheres. This test is known as the Los Angeles Abrasion Test. Sample - Using the Riffle Box obtain a representative sample of the aggregate. -Dirty or coated aggregate shall be washed, dried to constant mass at 110 +/- 5^0 C, and cooled to room temperature before preparing the test specimen. -Separate the aggregate on the required sieve sizes, and prepare the test specimen using the mass of each sieve size fraction specified for the grading selected. Determine and record the mass of the prepared test specimen to the nearest 1 g.
Required Materials and Equipment o Los Angeles Machine. o Balance. o Sieves. o Abrasive Charge. -A. Each abrasive charge shall consist of a solid, steel sphere having a mass between 390 and 445 g.
A solid, steel sphere with a diameter of 46. 5 +/- 0. 5 mm will typically meet this requirement Procedures 1. Place the test specimen and abrasive charge in the Los Angeles Abrasive Testing Machine and close the opening with the dust-tight cover 2 Start the testing machine and allow operating for the required number of revolutions. 3.
When the testing machine has completed rotating the required numbers of revolutions remove the cover and carefully empty the entire contents into a pan. Remove the abrasive charge from the pan. 4. Separate the test specimen on the 4.
75-mm sieve, then sieve the passing 4. 75-mm material on the 1. 70-mm sieve. Combine the material retained on the 4.
75 and 1. 70-mm sieves. Weigh and record these values to the nearest 1 g. 5. If the mass of material retained on the 1. 70-mm sieve was determined after 100 revolutions, return the entire test specimen, including the material passing the 1.
70-mm sieve, to the testing machine. Close the opening in the testing machine and operate for the required number of additional revolutions, then repeat Step 3 and 4 above... Calculation Calculate the "Percent loss" to the nearest % using the following equation: Percent loss = [ (A - B) /A) ] x 100 Where: A = Mass of original test specimen, to the nearest 1 g B = Mass retained on the 1. 70-mm sieve after the specified number of revolutions, to the nearest 1 g Result Type aggregate = 20 millimeters Grading = B # of spheres used = 11 Weight of specimen = 2500+2501 = 5001 g Weight of specimen after abrasion test, coarser than 1. 70 mm IS sieve = 3647 g % loss = 27. 07% Conclusion: The Los Angeles test is a measure of degradation of mineral aggregates of standard grading resulting from a combination of actions including abrasion, attrition, impact and grinding in a rotating steel drum containing, a specified number of steel spheres, the number depending upon the grading of test sample.
As the drum rotates, a shelf plate picks up the sample and steel spheres carrying them around until they are dropped to the opposite side of the drum, creating an impact crushing effect. The contents then roll with in the drum with an abrading and grinding action until the shelf plate impacts and cycle is separated. After the prescribed number of revolutions, the contents are removed from the drum and the aggregate portion is sieved to measure the degradation as percent loss. REFERENCED DOCUMENTS ASTM - C 131-90. Standard Test Method for resistance to Degradation of small-size coarse aggregate by abrasion and impact in Los Angeles Machine. Harold N.
Atkins, Highway Materials, Soil & Concretes, Prentice Hall Inc. 1987. AASHTO - T 96-87. Web page.