Strain and Pulse Duration Considerations for Extended-Life Hot-Mix Asphalt Pavement Design

In the design of extended-life hot-mix asphalt pavements (ELHMAP or perpetual pavements), the fatigue endurance limit is the key element. Thus, horizontal tensile strain at the bottom of the hot-mix asphalt layer is the critical design parameter. This paper presents results of a study performed at the University of Illinois test facility that focused on the evaluation of the most critical pavements responses for ELHMAP design. Longitudinal and transverse tensile strain pulses were measured in four sections tested with the accelerated pavement testing machine. A very strong relationship between the longitudinal and transverse pulse durations was found. In general, the transverse pulse durations were about three times those in the longitudinal direction. A relationship between longitudinal and transverse tensile strains was also found. Generally speaking, the transverse tensile strains were about 1.5 times greater than those in the longitudinal direction. The haversine function was the best representation for the longitudinal and the transverse strain pulses. The transverse pulse is very sensitive to the lateral position of the moving load. As the offset of the moving load increases, the rate at which the transverse tensile strain decreases is considerably greater than that of the longitudinal tensile strain. Moreover, if the moving load passes far enough from the strain gauge location, the transverse strain pulse reverses from tension to compression.