Research On 3D Reconstruction And Digital Test Of Asphalt Concrete Based On X-ray CT And Finite Element Method

Asphalt mixture is composed of aggregates, sand matrix and air voids. volume compositions of three parts and viscoelastic properties of sand matrix make the mechanical properties of asphalt mixture complex. In practical engineering field, loading frequency, loading magnitude, and environment change exacerbate complexity. Because of the limitation of traditional methods, combining with digital image processing and numerical simulation technology, X-ray CT(X-ray Computerized Tomography) was used to study the microstructure of asphalt mixture for analyzing internal structure of asphalt mixture. Virtual mechanics test namely digital test was performed as hot research focus at home and abroad in recent years.However, the most research about microstructure of asphalt mixture focused on following two aspects: (1) quantitatively or qualitatively analyzing the internal structure of asphalt mixture; (2) Based on one or several two-dimensional cross-sections of specimen, combining with digital image processing technology , two-dimensional numerical model was established for mechanics simulation. It is obvious that the research is limited. Oppositely, The research about digital test based on the model for real three-dimensional micro-samples is few, mainly because it is difficult for reconstructing three-dimensional model and mechanical numerical simulation, these two points are the key to achieve a virtual test.This paper attempts to challenge the research limits, not only qualitatively but also trying to solve the problem quantitatively. According to principles of three-dimensional reconstruction of asphalt mixture, grasping the essential characteristics from three-dimensional visualization model transformation to three-dimensional numerical model, analyzing difficult problems in-depth: three-dimensional reconstruction of digital specimen. Based on CT technology, numerical reconstruction algorithm was proposed and program was developed for reconstructing digital specimen. After three dimensional model reconstruction, the most important step is choosing appropriate constitutive model that reflecting viscoelastic properties of asphalt sand matrix. On this basis the viscoelastic constitutive relationship of asphalt mixture was systematically expounded and FEM realization of viscoelastic constitutive of asphalt mixture was discussed. Using Dynamic Shear rheometer (DSR), creep test of sand matrix was conducted. Through different stress level creep test, the relationship between model parameters and loading stress function was established. Creep equation general expression of Burgers model was obtained and impact for the model parameters on creep process was analyzed.Currently, most reconstruction model for uniaxial creep of numerical simulation is continuous homogeneous, which is difficult to simulate actual situation. After model reconstruction based on real microcosmic distribution of specimen, uniaxial static load creep numerical simulation of digital specimen was conducted for three different gradations of FAC-13: fine, middle course and coarse gradation. The purpose of simulation is to reflect different deformation response of three different gradations. The simulation results truly reflected actual experimental results.To further verify the feasibility of the methods and program, combining with indoor indirect tensile test, X-ray CT was used to scan the FAC-13 specimen. Under low-temperature and rapid loading conditions, digital test of indirect tensile test was conducted for evaluating inhomogeneity of stress distribution qualitatively;Under three different temperatures and six different frequencies conditions, digital test of dynamic modulus was conducted. The simulation results were compared with actual experimental results. It was found that the whole methods and procedures were validated practical.