Semester

Spring

Date of Graduation

2020

Document Type

Thesis

Degree Type

MS

College

Statler College of Engineering and Mineral Resources

Department

Civil and Environmental Engineering

Committee Chair

John P. Zaniewski

Committee Member

Yoojung Yoon

Committee Member

Fei Dai

Abstract

Monitoring asphalt skid resistance in the laboratory could aid in improved friction prediction capabilities and provide insight for developing alternative asphalt mixture designs in the future. The West Virginia Department of Highways (WVDOH) sought the design of a laboratory accelerated asphalt polishing machine to further expand on current skid resistance measurement practices. The design is modeled after the North Carolina State University (NCSU) polishing machine detailed in ASTM E660. The purpose of this research was to develop a testing procedure for the polishing equipment. Friction was monitored with the British Pendulum Tester (BPT) according to ASTM E303.

Specimens were prepared using a Superpave Gyratory Compactor (SGC) at two air void contents (4% and 8%) using four asphalt surface course mixtures (JFA 12.5mm Skid-RAP, WVP W1-RAP, Greer W1, WVP 12.5mm Skid-RAP). Specimens were placed in the polishing machine for a minimum of 48,000 wheel passes and conditioned with silicon carbide abrasive powder for accelerated polishing. Tire toe angles were adjusted between low (4° toed in and 2° toed out) and high (8° toed in and 4° toed out) toe angles. Average BPN values were plotted and used for slope calculations to investigate asymptotic behavior. These trend lines were also used as prediction models to determine the number of wheel passes required to reach minimum BPN limits; a larger number of wheel passes indicates more polish resistance. Variables evaluated: specimen air void content (VTM), tire toe angles, tire type, nominal maximum aggregate size (NMAS), and asphalt production company were considered for analysis. Data were compared using t-tests at 95% confidence to determine statistical differences between average BPN measurements. The most polish resistant mixture was the WVP W1-RAP mix; JFA 12.5mm Skid-RAP was the least. T-tests concluded only statistically different results for toe angles and lab/field comparisons. Lower friction values for higher toe angles suggest increased polishing when using higher toe. These results could provide insight on polishing procedure optimization and skid resistant characteristics of asphalt mixtures.

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