An experimental study on the effect of loading history parameters on the resilient modulus of conventional and SBS-modified asphalt mixes

Test protocols commonly recommend measuring resilient modulus (Mr) of asphalt mixtures by applying a haversine waveform with a loading time (duration) of 0.1 s and a rest period of 0.9 s. These conditions may not necessarily simulate the actual loading history experienced by an asphalt layer in the field. This paper aims to investigate the effects of the loading history parameters such as the waveform, loading time and the ratio of rest period to loading time on the resilient modulus of the control and SBS-modified mixtures, experimentally. This study determined 9 as the minimum ratio of the rest period to loading time for measuring Mr accurately, especially for square waveforms. The results obtained from this study confirmed that the resilient modulus under square loading can be predicted when the resilient modulus under haversine loading is known by means of a calibrated quadratic polynomial with zero intercept. It was also observed that the beneficial effect of SBS-modified mixtures greatly depends on temperature, loading waveform and loading frequency. Finally, it was shown that the concept of master curve could be used successfully to represent resilient moduli of an asphalt mixture at a wide range of temperatures and loading frequencies.