Micromechanical Analysis Of Equivalent Mechanical And Thermal Properties Of Asphalt Mixture

In recent years asphalt mixture is widely used in pavement engineering because of its advantages, such as high strength, smooth and comfortable driving. However, a number of distresses, including cracks, rut, layer-segregation and so on, take place in asphalt pavement with the increase in traffic volume and heavy vehicle percentage. These distresses reduce the service capacity of asphalt pavement. The investigation of mechanical behaviors of asphalt mixture is very important for distress control, and design and life prediction of asphalt pavement. The constitutive relations of asphalt mixture have been a crucial issue for application of the materials. The researches on the constitutive model of asphalt mixture are very important for understanding the deformation law of the road pavement, predicting the permanent deformation of pavement structure and lifetime, and suppressing the road failure.In this dissertation, based on the micromechanical theory, with the elastic-viscoelastic correspondence principle, the micromechanical constitutive models of asphalt mixture are proposed, the constitutive relations are researched. The main works are as follows.Based on the micromechanical theory, a two-phase and a three-phase model for the asphalt mixture are developed, in which the material is considered as matrix phase and inclusion phase or matrix phase, inclusion phase and interface phase. From the micromechanical analysis, the macroscopic mechanical properties are derived.The equivalent inclusion method was used to investigate the viscoelastic problem of asphalt mixture. The creep constitutive relations of asphalt mixture were investigated by Laplace transformation. The uniaxial creep experiments of asphalt sand under different test temperatures and stresses were conducted. The viscoelastic model parameters were fitted by the creep curves of asphalt sand. Based on this, the creep curves of asphalt mixture under different stresses and test temperatures were predicted. The results show that the strains and the rates of increased strain of asphalt mixture increase with the temperature under the same loading stress, they obviously mutate near the softening point; the strains and the rates of increased strain of asphalt mixture increase with the loading stress under the same temperature.Based on the self-consistent method and elastic-viscoelastic correspondence principle, the creep constitutive relations of asphalt mixture were proposed, with the uniaxial creep experiments of asphalt sand, the creep curves of asphalt mixture under different stresses and test temperatures were predicted. It’s near to the experimental data of asphalt mixture. The work is helpful to design the material.According to the elastic-viscoelastic correspondence principle, an elastic micromechanical framework taking the inclusion-matrix interface effect into account is extended for predicting viscoelastic properties of asphalt mixture, which is simply treated as elastic coarse aggregate inclusions periodically and isotropically embedded into viscoelastic asphalt mastic matrix. The Burgers model is adopted for characterizing the matrix mechanical behavior, so that the homogenized relaxation modulus of asphalt mixture in compression creep is derived. After a series of uniaxial compression creep tests are performed on asphalt mastic in different temperature and stress conditions in order to determine the matrix constitutive parameters, the presented framework is validated by comparison with the experiment, and then some predictions to uniaxial compression creep behavior of asphalt mixture in different temperature and stress conditions are given.Based on the micromechanical theory, a two-phase model for thermal expansion coefficient is developed. With the micromechanical analysis, the common expression for thermal expansion coefficient of asphalt mixture is derived. The results are compared with others’ used other methods from the literatures, and are found to be in good agreement with them.