Study On Viscoelastic Properties Of Asphalt Mixtures Based On Micromechanics

Traditional design and research focused on the relationship between macro index and performance of asphalt mixtures through phenomenological and experiential methods, which is difficult to reveal physical mechanism of material deformation and distress. However, the microstructure of asphalt mixtures is far more complicated. Asphalt mixtures is one of typical viscoelastic materials, there are close relations between its viscoelasticity and road performance. In this paper, asphalt mixtures are treated as a multiphase composite, the effect of material properties and internal structure on its viscoelasticity is researched based on micromechanics.Firstly, creep performance and dynamic modulus test of asphalt mixtures and asphalt mortar are conducted to analyze variations of viscoelasticity respectively, and the factors which affect the viscoelasticity are discussed. Secondly, using micromechanics of composite materials, Hashin composite spheres model is improved and simplified, and based on the elasctic-viscoelastic correspondence principle, a micromechanical model is developed to predict the viscoelasticity of asphalt mixtures. In this model, asphalt mixtures are regarded as a three-phase composite by embedding the coarse aggregate and air void into the asphalt mortar. Effect of aggregate size, aggregate gradation and air void distribution are taken into account in this model. Creep and relaxation properties of asphalt mixtures are predicted with the newly developed model, and the factors affecting the viscoelasticity are also explored. Laboratory experiments results are used to verify the developed model. Results show that a discrepancy exists between the predicted and measured viscoelasticity, the reasons for the discrepancy may be attributed to the differences between assumption of model and internal structure, interface interaction of each phase. Thus, the intermediate transition layer (ITL) is proposed, and the model is modified based on the analysis above. It can be found that the predicted results agree reasonably well with the measured ones using the modified model. Moreover, the viscoelasticity of granulated crumb rubber (GCR) modified asphalt mixtures is also investigated in this paper, the effect of GCR content on viscoelasticity of asphalt mixtures is analyzed through creep performance and dynamic modulus test, and the mechanism of GCR are also researched. Results indicate that this types of asphalt mixture has better low temperature relaxation property than high temperature creep performance, the reasonable content of GCR by weigh of asphalt mixture is 2% considered the factors above. The viscoelastic micromechanical model of GCR modified asphalt mixtures is also created based on the Mori-Tanaka method, and predicted precision of the model is verified and analyzed compared with the tested results.