EFFECT OF QUANTITY AND SIZE DISTRIBUTION OF THE PLUS #200 ACID-INSOLUBLE RESIDUE ON THE SKID RESISTANCE CHARACTERISTICS OF THE LOYALHANNA LIMESTONE

摘要

The Materials and Testing Division (MTD) of the Pennsylvania Department of Transportation has recently re-evaluated the Skid Resistance Level (SRL) rating of nineof the existing Department-approved aggregate sources in the Loyalhanna limestone. For the first six of these aggregate sources whose SRL ratings were re-evaluated, the MTD also cored a number of the skid-tested asphalt wearing courses. The aggregate extracted from these bituminous wearing courses was then subjected to an acid digestion, and the amount and size distribution of the plus #200 acid insoluble residue (AIR) for each of the extracted aggregate samples was determined. Inserting the plus #200 AIR results of the extracted aggregates onto a skid number vs. ADT graph for the roads from which the aggregates were derived demonstrated that the SRL characteristics of the Loyalhanna limestone depend on the amount of the plus #200 AIR, and that below a certain critical value of plus #200 AIR, the Loyalhanna limestone should not be rated as an SRL "E" aggregate for use on roads with greater than 20,000 ADT, but as an SRL "H" aggregate for use only on roads with less than 20,000 ADT. The amount of AIR within a certain size range also becomes important in determining the SRL characteristics of the Loyalhanna limestone the closer the total plus #200 AIR comes to the critical minimum.