A Research On The Prediction Models Of Pavement Performance Of Asphalt

Nowadays, there are many early destructive phenomena occurred in asphalt pavement of high-type highway in our country. The main destructive formals are fatigue cracking, thermal cracking and permanent deformation. Except for the results of construction and materials, this situation can be explained that the design method used deflection as design index is not able to control diseases in asphalt pavement effectively. Also, the rapid arise of traffic volume and the rate of heavy tracks challenge the current asphalt pavement design method. Thus this paper prompted new thought using fatigue cracking, permanent deformation and thermal cracking as indices to design asphalt pavement based on the theory analysis and test research, and discussed on asphalt pavement design method.Asphalt is a kind of complicate engineering materials. There are many factors that will affect it. Theory method or empirical method can not represent its character well. So selecting and modifying proper theory based on former research results will be a good idea to gain achievements reality. Based on the existing achievements, the author selected Burger's visco-elastic model as constitute model, and modified it according to specified property of each index. After that the author put forward test scheme for fatigue cracking, permanent deformation and thermal cracking. The author performed research on data analysis method to processing mass testing data. Among this, B-spline based on unequal node was introduced to screen test data series, and Levenberg-Marguardt method of nonlinear least square method to fit asphalt constitute. Finally, the author used visco-elastic layered system program to analysis conventional asphalt pavement structure, and achieved performance evaluation model of each index.This paper proved energy dissipation existing in the process of fatigue of asphalt by the visco-elastic analysis and test research, also the accumulation of dissipation energy relating to fatigue cracking of asphalt. Thus dissipation energy was used as criterion to evaluate the fatigue cracking potential of asphalt. By the beam bending fatigue test research, asphalt fatigue was proved to be process of damage occur, develop and cracking in the asphalt cement. Thus the damage evolution should be considered in the research of asphalt fatigue. This paper defined the change of strain amplitude in the stress control fatigue test as fatigue damage function. The function could be obtained by analyzing the process of beam bending fatigue test which was stress and load time related. Then the function could be used to modify fatigueequation. The visco-elastic parameters were obtained by splitting creep test and Levenberg-Marguardt method. Thus the fatigue equation considering damage was constituted to evaluate the fatigue potential of asphalt pavement. This paper used the fatigue equation evaluating the conventional asphalt pavement successfully after analyzing the structure by visco-elastic layered system program. Finally, the design method of fatigue cracking of asphalt pavement method was discussed.The author introduced Norton rule into Burger's model to attribute the permanent deformation of asphalt well. The visco-plastic parameters were received by uniaxial static creep test combining Levenberg-Marguardt method. Then the parameters were introduced into evaluation model based on Shell method to predicting permanent deformation. After that, the author used the modified Burger's viscoelasticplastic model as constitute model, analyzed the conventional pavement structure by visco-elastic layered system theory, and predicted permanent deformation. Finally, the permanent deformation design method was discussed.In the research of thermal cracking performance of asphalt, energy criterion was introduced to judge whether asphalt crack or not. That is, when the energy produced by temperature dropped was larger than the energy needed by asphalt to crack, the crack would occur. Then the method to calculate asphalt cracking energy by asphalt bending test was put forward, also the method to gain the visco-elastic parameters of Burger's model by asphalt bending creep test at low temperature accompany with Levenberg-Marguardt method. After that, the author gave the calculation formula of asphalt thermal stress based on Burger's visco-elastic model and boundary conditions, and the method to calculating stain energy produced by thermal stress. Thus the method was established using energy creation to evaluate the crack potential of asphalt pavement. Finally, an example was gave to illustration the method.Finally, the author generalized the whole paper, gave some advice to asphalt pavement design used pavement performance of asphalt as design indices, and put forward tentative ideas to future research.