Effect of Waveform, Duration and Rest Period on the Resilient Modulus of Asphalt Mixes

Resilient modulus (Mr) of asphalt mixtures in laboratory tests is usually measured by applying a haversine pulse with a specific duration and rest period which may not simulate the actual stress pulse occurring in field. In this paper, the effect of various parameters of loading pulse consist of the waveform, duration as well as the ratio of rest period to loading time (R/D) on the resilient modulus of asphalt concretes is investigated. For this purpose, complex modulus of four different asphalt mixtures were utilized and after validating results of numerical method for determining Mr, based on linear viscoelastic theory, resilient moduli of these mixtures were computed under different conditions. The results of this research showed that the waveform and duration of loading pulse affect the resilient modulus of asphalt concrete significantly and these two parameters should be considered in analysis and design of flexible pavements. The study showed that the ratio of rest period to loading time (R/D) should be equal to 9 or greater values to achieve an acceptable range of error in measurement of resilient modulus. This study proposes a good relation between the resilient modulus under haversine waveform and resilient modulus under square waveform which can be calibrated and used for prediction of Mr under square pulse by knowing Mr under haversine waveform. Also it was shown that the concept of the resilient modulus master curve can be used successfully to represent the resilient modulus of asphalt mixtures in a wide range of mix temperatures and frequencies.