The microstructure and dynamic rheological characteristics of asphalt containing different polymer modifiers (crumb rubber, styrene-butadiene-styrene and crumb rubber mix with styrenebutadiene-styrene) at mid and high service temperature levels were investigated by using scanning electron microscopy(SEM), dynamic shear rheometer(DSR) and repeat creep test. The main objective of the investigation was to rank the modifiers based on their effect on performance characteristics of asphalt under service conditions. To evaluate the effect of different modifiers on the viscoelastic response of asphalt, the temperature and frequency dependences of the dynamic viscoelastic properties were compared. The mid-temperature fatigue resistance and high-temperature rutting resistance of three polymer modified asphalts were evaluated to predict their field performance in roads. Based on the current results, an improved rutting factor was proposed to determine the rutting resistance of asphalt pavements. In addition, the viscous stiffness (Gv), defined as the reciprocal of viscous compliance, was used to evaluate the high-temperature deformation resistance of asphalt mixtures. The experimental results indicate that the asphalt containing crumb rubber only shows superior performance at mid and high service temperatures in all three modified asphalt binders due to the action of the crumb rubber.

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Crumb rubber modified asphalt containing 20 percent crumb rubber particles of 30 mesh has been examined by Scanning Electron Microscope (SEM) to observe the microcosmic appearance and the characteristic distribution of crumb rubber particles in asphalt. The SEM pictures reveal that the crumb rubber particles distribute evenly in the asphalt and they are compatible well with asphalt. The shear creep test of crumb rubber modified asphalt was carried out at -10 ℃ and 40 ℃ by Dynamic Shear Rheology (DSR). The shearing deformation at different temperature and creep stiffness modulus curve at loading stage of crumb rubber modified asphalt have been measured. The stiffness modulus of crumb rubber modified asphalt is much temperature sensitive and it decays much quick at the early stage of loading than normal asphalt. The rate of decay of stiffness modulus is slow at the subsequent stage and stiffness modulus approaches to a stable value at the final stage at a higher temperature. In addition, Burgers model is suitable to describe and simulate experimental results of viscoelastic properties of the crumb rubber modified asphalt.

A test for crumb rubber modified asphalt containing 20% crumb rubber particles (30 mesh) was performed using a scanning electron microscope (SEM). The experimental results indicate that the crumb rubber particles are evenly distributed in the asphalt. Shear rate sweep and shear-temperature sweep tests on the crumb rubber modified asphalt at -20-80 ℃ using a dynamic shear rheology (DSR) instrument, were carried out. The tests show that the complex modulus decreases with increasing temperature; at equivalent temperature, higher load frequencies lead to a larger complex modulus, and this value increasingly decreases as the temperature increases; the phase angle increases with temperature and decreases as the load frequency increases. It can be concluded that the rutting resistance limiting temperature of crumb rubber modified asphalt is 78 , and the anti ℃ -fatigue limiting temperature is 16 ℃, which shows that the asphalt has preferable rutting resistance characteristics at high temperature, as well as anti-fatigue characteristics. In addition, the complex modulus master curve at different temperatures was plotted according to the time temperature equivalence principle, which allows the study of the dynamic state behavior of crumb rubber modified asphalt at a wide range of load frequency.

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