EFFECT OF AGGREGATE MINERALOGY ON POLISHING RATE AND SKID RESISTANCE IN PENNSYLVANIA

A PILOT STUDY ON SKID RESISTANCE IN 1960 CLASSIFIED 11 OF THE 19 SELECTED TEST SITES AS SLIPPERY. THESE SLIPPERY PAVEMENTS EXHIBITED POLISHED CARBONATE AGGREGATE. A CONTINUING PROGRAM OF MEASURING SKID RESISTANCE ON PENNSYLVANIA HIGHWAYS WAS CONDUCTED IN ANNUAL SKID SURVEYS. DATA REVIEWED INDICATED THAT THERE WAS NO SATISFACTORY CONSTRUCTION OR MATERIAL SPECIFICATION TO ENSURE PERMANENT ADEQUATE SKID RESISTANCE ON THE LIFE OF A BITUMINOUS PAVEMENT SURFACE. THE SKID RESISTANCE OF BITUMINOUS PAVEMENT SURFACE IN PENNSYLVANIA IS GENERALLY RELATED TO THE TYPE OF COARSE AGGREGATE USED. THE GRAVEL AND SAND-STONE SURFACES HAVE HIGHER AVERAGE SKID RESISTANCE THAN THE CARBONATE SURFACES. SLAG AND OTHER AGGREGATE TYPE SURFACES GIVE INTERMEDIATE SKID MEASUREMENTS. A SERIES OF TEST SECTIONS WAS CONSTRUCTED TO EVALUATE THE CONTROLLING PARAMETERS IN CARBONATE AGGREGATES. A NUMBER OF BLENDS OF CARBONATES WITH OTHER AGGREGATES WERE ALSO INCLUDED TO DETERMINE THE EFFECT OF BLENDING ON SKID RESISTANCE. A MINIMUM OF 1000 FT. WAS SET FOR EACH SKID TESTING SECTION. THE TEST STRIP AGGREGATES (CARBONATE, SLAGS, GRAVELS, BLENDS AND OTHERS) WERE IDENTIFIED PETROGRAPHICALLY, AND THEIR PROPERTIES DETERMINED. CONTINUED EXPOSURE TO TRAFFIC AND PERIODIC SKID TESTING ARE BEING DONE TO PROVIDE AN EVALUATION OF THE SKID RESISTANCE POTENTIAL OF ROCK FORMATION IN PENNSYLVANIA, SO THAT SUITABLE AGGREGATE SPECIFICATIONS CAN BE PREPARED TO PROVIDE PERMANENT ADEQUATE SKID RESISTANCE THROUGHOUT THE PAVEMENT'S LIFE. THE SUPPLEMENTARY LABORATORY TESTING OF THESE AGGREGATES IS DIRECTED AT DEVELOPING A METHOD OF PREDICTING FIELD PERFORMANCE OF AGGREGATES TO BE USED. /AUTHOR/