Optimized Test Procedures for Measurement of Aggregates and Asphalt Mixtures Friction Performance for Routine Test Purposes

AASHTO recently approved Provisional Practice Specifications PP-103, Standard Practice for Sample Preparation and Polishing of Unbound Aggregates for Dynamic Friction Testing, and PP-104, Standard Practice for Sample Preparation and Polishing of Asphalt Mixture Specimens for Dynamic Friction Testing for evaluating the frictional resistance of aggregates and asphalt mixtures, respectively, using the three-wheel polishing device (TWPD) and dynamic friction tester (DFT). One of the concerns of highway agencies with these specifications has been the duration of sample preparation and polishing. This study aims to address these concerns by proposing steps to reduce the test duration without sacrificing the accuracy and repeatability of these test procedures. The feasibility of using a faster setting material for preparing specimens to accelerate the sample preparation process was examined. Uncertainties in friction measurements during polishing were evaluated. The long-term repeatability of the DFT device was assessed. The feasibility of estimating the long-term friction values with a reduced number of polishing cycles was evaluated. This study indicates that using quick-setting cement for sample preparation, followed by dry polishing with 25,000 polishing cycles, can potentially accelerate the test protocol from 43 h to 15 h for both aggregate and asphalt mixtures. Optimized test procedures with recommended modifications to the current PP-103 and PP-104 specifications are summarized for consideration by highway agencies and researchers.