Research On The Rheological Chacrateristics Of Fiber Modified Asphalt Binder And Mixtures

Fiber modified asphalt concrete is a kind of composite which can enhance the performances of asphalt pavement by using some fiber materials. The prominent features of fiber modified asphalt concrete include the prevention of crack propagation, reduction of permanent deformation and fatigue damage in asphalt pavement structure, which are significant for prolonging the service life of asphalt pavement. The profound researches on the rheological properties, service performance and mechanical characteristics of fiber modified asphalt binder and mixtures are important for the application of fiber modified asphalt concrete in practice projects.The rheological characteristics of fiber modified asphalt bind are study by some methods in rheology firstly in this research. The effects of fiber type, concentration, temperature and loading frequency on the viscosity, complex shear modulus and phase angle of fiber modified asphalt binder are investigated. Test results indicate that the viscosity of asphalt binder are increased by the addition of different types of fiber, the viscosity enhancement of fibers represent more significantly when the fiber concentration is up to 0.5 % and at lower temperatures. The structure of asphalt binder can be changed and most portion of stress concentration can be released by the use of fibers, which result in the reinforcement of bearing forces and elastic properties of fiber modified asphalt binder. The complex shear modulus is increased and the phase angle is decreased for asphalt binder containing various fibers.Secondly, the Simple Performance Test commented by SHRP is conducted to study the dynamic rheological properties of fiber modified asphalt mixtures. Test results show that the frequency dependence and temperature dependence are remarkable for dynamic modulus and phase angle of fiber modified asphalt mixtures. The dynamic modulus of asphalt mixtures with fibers is increased and the phase angle is decreased. The dynamic modulus master curves of fiber modified asphalt mixtures can be obtained by adopting the Time-Temperature equivalence principle. Such master curves of fiber modified asphalt mixtuers prove that the dynamic modulus is increased and the amplitude of variation of dynamic modulus is decreased in the whole working frequency or temperature range, which indicate the decrease of sensitivity to temperature for asphalt mixtures. The relationship between dynamic modulus and phase angle can be characterized by a semilog model, which further verified the reinforcement of fiber modified asphalt mixtures. The fatigue property and high temperature stability of fiber modified asphalt binder can be improved greatly. The improvement of fatigue property is more significant at lower stress lever, and the resistance to permanent deformation can be evaluated by the rutting parameters for fiber modified asphalt mixtures.Thirdly, the viscoelastic characteristics of fiber modified asphalt binders and mixtures are investigated by creep test, and proper rheological models are employed to describe such characteristics. Results indicate that the viscoelastic properties of asphalt binders and mixtures can be changed by the use of fibers. The total deformation of fiber modified asphalt binders and mixtures are decreased during loading period, and the elastic and retardant elastic deformations are increased, which lead to the reduction of permanent deformation for asphalt binder and mixtures. The relationship of creep stiffness modulus and loading time can be characterized by a power function for fiber modified asphalt binders and mixtures, and a relationship between the stiffness and temperature and loading time can be established for asphalt binders. Burgers model can be used to describe the viscoelastic characteristics for fiber modified asphalt binders, which reveal that the elastic and viscous property of asphalt binders can be affected by various fibers and all mechanical parameters are increased. The revised Burgers model is more suitable for the viscoelastic property research of fiber modified asphalt mixtures, the model demonstrate that the retardant viscoelastic property and viscous property of asphalt mixtures containing different types of fibers can be improved, which result in the enhancement of resistance to permanent deformation for fiber modified asphalt mixtures.Finally, some conclusions obtained from the test section for the application of fiber modified asphalt mixtures in practice projects, including the optimization of fiber type and concentration, mixture design method, control measures and technology for construction.