In 1997 the Indiana Department of Transportation adopted the Superpave mixture design method and attendant specifications for hot-mix asphalt pavements. Prior to Superpave, the Indiana Department of Transportation aggregate frictional requirements were based on average daily traffic volumes and were divided into low, medium, and high volume categories. With the implementation of Superpave in Indiana, aggregate frictional requirements were reassigned to categories based on equivalent single axle load values. The purpose of the research is to determine whether average daily traffic or equivalent single axle load has a greater effect on the frictional resistance of a hot-mix asphalt pavement, to confirm and update, if necessary, the current equivalent single axle load based breakpoints for aggregate frictional requirements, and to evaluate the effects of aggregate physical properties on frictional resistance.

Statistical analyses were conducted on inventory skid data to observe the effects of average daily traffic and equivalent single axle loads. It was determined that average daily traffic may have a greater effect on frictional resistance than equivalent single axle load. Additional statistical analyses were conducted to verify categorical breakpoints which indicated that the former average daily traffic breakpoints are correct and that the upper bound equivalent single axle load breakpoint may need some modification.

Aggregates were tested for acid insolubility, differential wear, and frictional resistance. Acid insolubility results and physical property data obtained from quality assurance files were correlated to aggregate frictional resistance. Collected quality assurance data included bulk specific gravity, percent absorption, percent loss from impact, and percent loss from brine freeze/thaw. It was observed that the aggregates used in this study had a negligible amount of insoluble material and therefore had an insignificant effect on the frictional resistance. Terminal frictional resistance increased with decreasing bulk specific gravity, and increased with increasing percent absorption and percent loss from impact. Correlation between terminal frictional resistance and brine loss was very weak. Differential wear measurements were taken on stone-slag aggregate blends to determine the effectiveness of blends used in pavement mixtures. Differential wear results indicated that the high friction component of each blend could be improved by blending with softer carbonate aggregates, which also may be more cost effective.

Report Number



pavement friction, skid resistance, polish resistance, aggregate, hot-mix asphalt, SPR-2665

SPR Number


Performing Organization

Joint Transportation Research Program

Publisher Place

West Lafayette, IN

Date of this Version