The Hamburg Rutting Test (HWTT) alternative data analysis methods and HMA screening criteria

Abstract

The Hamburg Wheel Tracking Test (HWTT) is a widely used routine laboratory test for identifying and screening hot-mix asphalt (HMA) mixes that are prone to rutting. The standard HMA pass-fail screening criterion under the current HWTT protocol is 12.5 mm rutting at 50°C. However, Texas has experienced record high summer temperatures in the recent years (i.e., over 122°F), and several rutting failures have occurred in the field with some surface HMA mixes that had passed the HWTT in the laboratory. These failures occurred mostly in high shear-stress locations, in particular with slow moving (accelerating/decelerating) traffic at controlled highway intersections, stop-go sections, in areas of elevated temperatures, heavy/high traffic loading, and/or where lower performance grade (PG) of asphalt binders have been used. This laboratory hybrid study was thus initiated to explore new data analysis methods and introduce new alternative rutting parameters to supplement the traditional HWTT pass-fail screening criteria (= 12.5 mm rut depth at 50°C) for surface HMA mixes. Several HMA mixes commonly used in Texas were evaluated in the laboratory and new HWTT analysis parameters, such as the rutting area ( A), the normalized rutting area (Rut ), and the shape factor (SF) with the potential to capture the HMA rutting path-history, were formulated. In addition, a comparison between the newly formulated and traditional rutting parameters with field performance observations was conducted and yielded plausible results in terms of predicting the early-life rutting performance of HMA mixes.