Viscoealstic Characterization And Mesomechanical Prediction Of Asphalt Mixture

Asphalt mixture is a typical particulate-filled composite.Under most wheel loadings,it exhibits very small strains and can be assumed to be a linear viscoelastic(LVE)material in engineering applications.On the basis of this assumption,the Mechanistic-Empirical Pavement Design Guide(MEPDG)2002 adopted the uniaxial asphalt mixture dynamic modulus(|E*|)master curve in the form of the Sigmoidal function as one of the basic material characterization parameters of asphalt structural layers.The utilization of dynamic modulus represented a transition of asphalt pavement design from an elastic method to a viscoelastic method.Essentially,however,the MEPDG is still an elastic design method based on the layered system theory.This is because the dynamic modulus,representing the stiffness of asphalt structural layers,can only characterize the frequency and temperature dependence of asphalt mixture,but cannot take into account its realistic mechanical behavior related to a loading history.To achieve a completely viscoelastic asphalt pavement design,a systematic investigation into the viscoelastic characterization methods and mesomechanical complex modulus(E*)prediction methods are needed for asphalt mixture.To this end,the following research efforts were made in this dissertation:(1)Uniaxial complex modulus tests within the small strain range were performed on two asphalt mixtures at different temperatures and loading frequencies.A viscoelastic characterization method of asphalt mixure based on the Havriliak-Negami(HN)complex modulus model was developed in accordance with the characteristics of the dynamic modulus,phase angle,storage modulus and loss modulus.The HN model parameters were determined by using the direct method and the Wicket diagram method,respectively.The fitting results from the HN method were compared with those from the conventional Sigmoidal method in detail,demonstrating the advantages of the HN method.(2)Considering the remarkable computational efficiency of the generalized Maxwell(GM)model and the generalized Voigt(GV)model,unified algorithms for determining the viscoelastic discrete and continuous time spectra were presented based on the developed HN complex modulus master curves and the test data characteristics of asphalt mixture.The results indicated that both the two presented algorithms were able to accurately characterize the viscoelastic behavior of asphalt mixture in the time and frequency domains.For practical considerations,the dissertation also discussed how to transform the continuous time spectra into the corresponding discrete ones.In addition,a method for determining reduced master curves was presented.(3)To better characterize the viscoelastic behavior of asphalt mixuture in triaxial stress states,the effect of confining pressure on the time-temperature shift factors and complex modulus of asphalt mixture were investigated.A confinement dependent triaixal HN complex modulus model was developed by using the derived HN continuous relaxation spectrum model and an existing equilibrium modulus model.The results showed that the developed triaixal HN model could not only accurately and completely characterize all the triaixal complex modulus components in the frequency domain but also be conveniently converted into the corresponding triaxial relaxation modulus in the time domain without performing any complicated conversion operations.(4)Besides,considering the importance of the rheological properties of asphalt binder(or mastic)to the material design and performance prediction of asphalt mixture,a unified approach that could rapidly combine the LVE information from the bending beam rheometer(BBR)and dynamic shear rheometer(DSR)tests that cover different temperature ranges and different loading modes was developed,achieving LVE characterization of the material over a complete range of pavement service loading frequency and temperature.(5)Finally,the influency of aggregate interlocking reinforcement on the master curves of the complex modulus components of asphalt mixture was analyzed:in detail,and the deficiencies of the traditional mesomechanical models in predicting asphalt mixture complex modulus was revealed.Based on the discussion,a method that could consider the aggregate interlock effect in the traditional mesomechanical prediction models of asphalt mixture complex modulus was presented.The results showed that the presented method overcame the deficiencies of underprediction of the traditional models under the conditions of high temperatures and low loading frequencies;also,without changing any original geometries,the advantages of simplicity and practicability of the traditional mesomechanical models remained in the presented method.