The properties of aggregates used in asphalt concretes are very important to the performance of the pavements in which the asphalt concretes are used. Often pavement distress, such as stripping and rutting, can be traced directly to the aggregates used. Clearly, proper aggregate selection is necessary for attaining desired performance. The aggregate used in surface course of the highway pavements are subjected to wearing due to movement of traffic. When vehicles move on the road, the soil particles present between the pneumatic tyres and road surface cause abrasion of road aggregates. The steel reamed wheels of animal driven vehicles also cause considerable abrasion of the road surface. Therefore, the road aggregates should be hard enough to resist abrasion. Resistance to abrasion of aggregate is determined in laboratory by Los Angeles test machine.
Many tests have been developed to empirically characterize aggregate properties without, necessarily, strong relationships to the performance of final products incorporating an aggregate. The Los Angeles (L.A.) abrasion test is a common test method used to measure of degradation of mineral aggregates of standard grading resulting from a combination of action including abrasion and grinding. The standard Los Angeles abrasion test is ASTM C131: Resistance to degradation of small-size coarse aggregate by abrasion and impact in the Los Angeles Machine. Aggregate abrasion characteristics are important because the constituent aggregate in HMA (Hot Mix Asphalt) must resist crushing, degradation and disintegration in order to produce a high quality HMA.
The standard L.A abrasion test subjects a coarse aggregate sample (retained on the No. 19.0 mm sieve) to abrasion, impact, and grinding in a rotating steel drum containing a specified number of steel spheres. As the drum rotates, a self-plate picks up the sample and the steel spheres, carrying them until they are dropped to the opposite site of the... [continues]
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