Fatigue Shift Factors to Predict HMA Performance

Abstract

Hot-mix-asphalt (HMA) fatigue failure is achieved much faster under a laboratory setting than in the field. The difference between laboratory and field conditions is related to loading, material properties and specimen preparation. This difference has typically been accounted for by using a single shift factor based on engineering experience. Four shift factors can be identified: stress state, traffic wander, HMA healing and material properties. In this paper, approaches are presented to determine the stress-state and traffic-wander shift factors. Both field-measured critical strains and strain energy exerted during truck loading were used to determine the stress-state shift factor. Strain measurements for truck-loading distribution (wander) were used to determine the wander shift factor. Although the derived shift factors utilize the measured stresses and strains at the Virginia Smart Road, the approach may be used to determine the stress state and traffic wander shift factors utilizing appropriately calculated strains and stresses.

Keywords:

• Flexible pavement instrumentation
• HMA fatigue
• Shift factors
• Field-laboratory correlation
• Critical strain

Acknowledgements

The authors wish to acknowledge the financial support by the Virginia Transportation Research Council (VTRC) of the Virginia Department of Transportation (VDOT). The help provided by Tom Freeman of the VTRC in this project is acknowledged. Gerardo Flintsch, Amara Loulizi, Samer Lahouar, Stacey Reubush, Brian Diefenderfer, Alexander Appea, Robin Davis, Kenneth Taylor and Kevin Light assisted in the field instrumentation. The technical assistance of Mostafa Elseifi in this paper is greatly appreciated.