Study On Mesoscopic Fatigue Mechanism And Fatigue Prediction Model For Asphalt Mixture

Fatigue damage is one of the critical and major distresses in asphalt pavement, therefore studying on fatigue performance of asphalt pavement under certain traffic and environmental conditions is extremely important, and this study has been the subject of road workers all over the world. In order to ensure good service performance and durability of asphalt pavement, studying on fatigue performance of asphalt mixture and establishing appropriate fatigue prediction model is meaningful and significant.Asphalt mixture is a multi-phase composite material with complex physical and mechanical properties and its fatigue performance is affected both by the material and external factors, thus that fatigue performance of asphalt mixture could not be completely presented simply by macroscopic laboratory fatigue test analysis. In this dissertation,based on the notched semi-circular bending fatigue test, fatigue performance of asphalt mixture was studied from both macroscopic and microscopic levels by combining the laboratory test and numerical simulation. According to the research results, a fatigue prediction model with crack for asphalt mixture is proposed and established with considering multiple impact factors including stress, resilient modulus of asphalt mixture, volume of air voids, and temperature. The fatigue prediction model for asphalt mixture is meaningful both theoretically and practically for providing technical support for the asphalt pavement service performance and durability.Various fatigue test methods were first analyzed here, and based on which the semi-circular bending fatigue test was selected as the fatigue test method in this study. The development and application of corresponding equipment for semi-circular bending fatigue test were carried out, to establish a good technical support for the smooth conduct of asphalt mixture fatigue test. And then the fatigue tests at different temperatures and different asphalt mixture gradations were carried out, and the test results were analyzed.According to the mechanics characteristic of the asphalt mixture and specialties of various contact and bond models in discrete element method, appropriate contact and bond models were selected for the asphalt mixture discrete elements. A relationship between microscopic parameters of contact constitutive models and macroscopic performance was deduced consequently, and microscopic parameters of the contact and bond models in discrete element method were determined, through the transformation of the relationship between microscopic parameters and macroscopic performance.A notched semi-circular specimens discrete element model of irregular shape aggregate were constructed according to the design of asphalt mixture gradation and with considering the calculation parameters in discrete element method, and a numerical simulation method of the notched semi-circular bending fatigue test for asphalt mixture was determined. After the simulation of the notched semi-circular bending fatigue test, the rationality and feasibility of numerical simulation for the notched semi-circular bending fatigue test was proved to be reasonable and practicable by comparing results from the laboratory fatigue test and the numerical simulation.Based on the numerical simulation fatigue test, fatigue performance of asphalt mixture was studied on aggregates and voids in specimen for the influence of the mesoscopic structure on asphalt mixture fatigue performance, and the relationships between fatigue life and aggregate, and between fatigue life and void were analyzed respectively. Moreover,fatigue failure mechanisms were revealed from a view of mesoscopic structures.The basic form of the asphalt mixture prediction model was determined by comparing different asphalt mixture fatigue prediction models, and influence parameters of fatigue prediction model were determined with considering both laboratory test results and a large number of fatigue prediction models. Further, a fatigue prediction model with crack is established for asphalt mixture based on laboratory notched semi-circle bending fatigue test in consideration of multiple impact factors including stress, resilient modulus of asphalt mixture, volume of air voids, and temperature. Besides, the prediction effect of the laboratory fatigue prediction model was evaluated as well.