Abstract Manager

Regulations concerning the operation of Autonomous Vehicles (AVs) and Connected Autonomous Vehicles (CAVs) are evolving in North America.  From a pavement perspective, these technologies will increase traffic volumes and weights, reduce lateral wheel wander, and permit platooning of truck traffic.  Collectively, these new conditions will focus and intensify the applied loading with significant consequences to the structural and functional performance of our pavements. 

Maintaining adequate friction between the tire and pavement surface is critical to the safe operation of all vehicles.  Greater surface polishing effort from AVs and CAVs may therefore accelerate friction loss.  Historically, many road agencies have identified sources of polish-resistant aggregates from legacy data or multi-year monitoring efforts.  Unfortunately, these approaches may no longer be feasible to accurately or rapidly evaluate polish resistance for the “road ahead.”

To accelerate the evaluation process, the use of the NCAT Three-Wheel Polishing Device (TWPD) and Dynamic Friction Tester (DFT) offers a promising laboratory approach.  The test is tortuous – with three polishing tires at 87 psi (600 kPa) turning on the wetted HMA surface.  At present, 150,000 cycles are used to assess the polish resistance of aggregates in compacted HMA samples.  As an exercise, extended TWPD to 1,000,000 cycles was utilized to compare the polish resistance of HMA mixtures produced with varying percentages of two different aggregate sources. 

Of interest, HMA produced with silica-based aggregates started with lower friction values than HMA produced with dolomite limestone yet had greater polish resistance after 1 million polishing cycles yet this was not apparent at 150,000 polishing cycles.  The use of the slope of the DFT friction versus the number of polishing cycles curve appears to have promise for identifying aggregate polish resistance and should be considered during the evaluation process. 

The study also provided insights into the use of Acid Insoluble Residue (AIR) testing.  Based on results obtained, it is recommended to use AIR as an index test to be reported but waived if the TWPD and DFT results are acceptable. 

While routine TWPD polishing to 1 million cycles is not recommended due to excessive time and machine wear, the results did suggest that long-term polishing performance of aggregates is complex.  Overall, the use of the TWPD and DFT in the laboratory presents a promising approach for the accelerated evaluation of HMA mixtures and new aggregate sources, with the ultimate goal of better managing pavement friction and saving lives on North American roadways.