Research On Fatigue Damage Of Asphalt Mortar And Asphalt Mixture Based On Viscoelastic Continuous Damage Model

As a coarse dispersion system in which coarse aggregate is dispersed in asphalt mortar according to specific spatial distribution law,the fatigue performance of asphalt mixture is closely related to the fatigue performance of asphalt mortar.To explore the correlation between fatigue performance of asphalt mortar and asphalt mixture,the fatigue damage of asphalt mortar and asphalt mixture is studied based on viscoelastic continuous damage model.Firstly,the common asphalt mixture AC-20 was selected as the research object,and the asphalt-aggregate ratio of No.70 base asphalt mixture and SBS modified asphalt mixture was determined by Marshall test method.According to the principle of removing coarse aggregate from the mixture and keeping fine aggregate unchanged,the aggregate amount and asphalt amount of each grade in matrix asphalt mortar and SBS asphalt mortar were calculated.At the same time,on the basis of No.70 base asphalt mixture and mortar,high modulus modified asphalt mixture and asphalt were obtained by directly adding high modulus agent by dry method.Then,the uniaxial compression dynamic modulus test was carried out on three asphalt mixtures and corresponding asphalt mortar,including No.70 base asphalt,SBS modified asphalt and high modulus modified asphalt,the influence of test temperature and loading frequency on dynamic characteristics(dynamic modulus and phase angle)of asphalt mortar and asphalt mixture was analyzed,and the correlation between dynamic characteristics of asphalt mortar and asphalt mixture was explored.Then,based on the results of dynamic modulus test,the master curves of dynamic modulus and phase angle of asphalt mortar and asphalt mixture were established,and the variation laws of master curves of asphalt mortar and asphalt mixture were analyzed and compared.Finally,based on AASHTO TP 107,the direct tensile cyclic fatigue test under displacement control mode was carried out by MTS.Based on the dynamic modulus test results and fatigue test results,the virtual secant modulus C and internal state variable S of different asphalt mortar or asphalt mixture in the fatigue test process were calculated,and the fatigue damage characteristic curve of asphalt mortar and asphalt mixture was established,and the damage evolution law was analyzed,the fatigue performance of different asphalt mortar and asphalt mixture was evaluated by using the average reduction in virtual secant modulus up to failure(DR)in fatigue process,and the correlation between fatigue performance of asphalt mortar and asphalt mixture was explored.The results show that with the increase of test temperature or the decrease of loading frequency,the dynamic modulus of asphalt mortar and asphalt mixture has a similar downward trend.In the same temperature range,the dynamic characteristics of asphalt mixture are significantly affected by the dynamic characteristics of asphalt mortar,and there is a strong correlation between them.The dynamic modulus main curve and phase angle main curve between asphalt mixture and asphalt mortar prepared by the same asphalt binder have high shape similarity and change similarity.The position distribution of fatigue damage characteristic curve and the distribution of DR value of asphalt mortar and asphalt mixture keep good consistency,and there is a strong power function correlation between their fatigue performance.