Laboratory Investigation Of Dynamic Modulus Of Modified Asphalt Mixtures Under Biaxial Loading

Asphalt pavement in service was subjected to the interaction of normal and shear stresses,especially in the starting and braking,accelerating and decelerating or uphill sections.Current pavement design methods only consider dynamic modulus of asphalt mixture under uniaxial vertical load,which is different from the stress state of real asphalt pavement.In this paper,the dynamic modulus test on SBS modified asphalt mixture with three gradations commonly used under biaxial loading were carried out to investigate the dynamic performance of the mixture under the compression-shear stress state.It can be used as a reference for the design and research of mixture in crossing,uphill and other special road sections.The main contents of this paper are as follows:The experiment scheme of biaxial dynamic modulus test was designed with reference to a variety of dynamic modulus test methods and existing works at home and abroad.Proportioning design of AC-13,AC-16 and AC-20 graded SBS modified asphalt mixtures were determined by Marshall test and the specimens were formed by gyratory compactor.The dynamic modulus test under uniaxial compression and biaxial loading were carried out with different temperature and loading frequency,and master curves of dynamic modulus were constructed by time-temperature equivalence principle to investigate the influence of temperature,loading frequency,mixture gradation,loading mode and shear stress on the dynamic modulus of mixture.It was found that the effects of temperature and loading frequency on the dynamic modulus of SBS modified asphalt mixture under two loading modes were similar,but compared with uniaxial compression mode,the influence of temperature and loading frequency on the dynamic modulus under biaxial loading modes decreased.The gradation of mixture had less effect on dynamic modulus than temperature and loading frequency.Loading mode had a certain effect on the dynamic modulus of the asphalt mixture.The dynamic modulus under biaxial loading were almost less than dynamic modulus under uniaxial compression loading at each temperature and load frequency.The difference in modulus between two loading modes gradually decreases with increasing temperature.The addition of shear stress has a certain weakening effect on the dynamic performance of the asphalt mixture,meanwhile the larger the shear stress,the smaller the dynamic modulus of the mixture.