Research On Performance And Security Evaluation Of Pavement Based On Three-Dimensional Microscopic Structure Of Asphalt Concrete

Asphalt concrete is a composite material that contains aggregate, air-void and asphalt mastic, the randomness and irregularity of micro-structure sharp and distribution cause a comprehensive mechanical state in asphalt concrete. The research on damage mechanism and effective prediction of asphalt concrete are investigated by the foundation that accurately and objective characteristics of inner structure, and interactions between micro-structures are also considered. The traditional researches regard asphalt concrete as a homogeneous material, the effect of micro-structures, such as aggregate and air-void, on performance of asphalt concrete are neglected usually, resulting a significant different between theoretical study and practical conclusions. In this paper, X-Ray CT scanning device with high precision was used to acquire the cross-sectional image of asphalt concrete, digital image processing, numerical finite element simulation and fractal dimension technology were also used to study the macroscopic properties prediction and damage mechanism considering the effect of micro-structure on asphalt concrete, and fuzz mathematics analytic hierarchy process was developed to calculate the comprehensive influence weight that represented as micro-structure indicators, such as aggregate sharp, size and air-void distribution et al. The research conclusion establishes the initial impact mechanisms between micro-structure and macro-properties, improves the research system of asphalt concrete performance at micro-scale, and supports the theoretical foundation to optimize the design of micro-structure material.First of all, the gray image data of inner micro-structure in asphalt concrete with different gradations before and after damage were acquired by X-Ray CT scanning device, and according to the inhomogeneity state of gray value distribution, maximum classes square error with different regions was developed as a dynamic calculation method of the threshold between aggregate, mastic and air-void, the topography characteristics of micro-structure can be effective represented by binary image data; Based on the reverse stereological theory, the spatial model of micro-structure was created by triangle piece element, and microscopic morphology characteristics of aggregate, mastic and other inner structure were developed accurately, the model formed by triangle piece element can be used as numerical calculation after materialization operation.Secondly, the dynamic modulus master curves of different mastic at several temperature and loading frequency were determined by dynamic modulus test, the viscoelastic material property of mastic at widely loading frequency can be acquired from the data that after smooth and extend processing, and then, viscoelastic property of mastic can be expressed as Prony series derived by generalized Maxwell constitutive model; The spatial numerical finite element model of asphalt concrete was developed to investigate the stress and strain field state in aggregate system and mastic, the hierarchical characteristics of asphalt concrete during high-temperature creep deformation was determined, and the development situation of elastic and creep strain in each layer were also investigated.Thirdly, according on the binary image data of aggregate and air-void structure, MATLAB software was used to compile relative image processing program to investigate the monograph and distribution change of micro-structure in asphalt concrete before and after the compress damage and high-temperature rheological deformation, aggregate sharp, edge and corner, coarse aggregate content, air-void rate, air-void volume and air-void distribution were selected as research objection, investigating the variation law of displacement, monograph and rotate situation of each micro-structure factor, and the sensitivity effect of micro-structure on damage situation of asphalt mixture was determined. Besides, the damage mechanism of the inner material system of asphalt concrete was also study by visualization of image data; Fractal dimension was used to quantify the complexity of individual aggregate monograph, the cross-sectional weight dimension conception was prepared to predict the initial air-void distribution state in different part in asphalt concrete, and the damage index of asphalt concrete cross-section was also used to investigate the damage rate of air-void after high-temperature rheological deformation.Finally, considering the fuzziness of subjective judgment, and combining the research conclusions of image processing and numerical simulation, analytic hierarchy process based on fuzz mathematics was utilized to developed the relationship between micro-structure factor and performance of asphalt concrete, comprehensive evaluation index system for pavement safety performance was proposed though hierarchy system analysis, this will provide information to develop the relation between micro-scale and macro-scale, and also provide a theoretical basis to improve the match and design of asphalt concrete materials.