| Road construction will consume resources and produce a large amount of waste and other pollutants,With the emergence of resources and energy crisis,how to utilize Recycled Asphale Pavements(RAP)efficiently has become the focus of scientific research workers.Most studies have considered the effect of material gradation and bitumen marking on the performance of Reclaimed Asphalt Pavement,and put forward the corresponding control indexes,but the early damage problem still exists in the paved road,which is because without considering the influence of the diffusion and diffusion degree between virgin binder and RAP binder.Therefore,it is of great theoretical significance for the accurate evaluation and design of RAP to fully understand the effect of the external field on the diffusion and to carry out the study of the macro and micro mechanism of the diffusion.Firstly,in order to study the diffusion law of between virgin binder and RAP binder under different external fields,the existing state of new a nd old bitumen in RAP was analyzed,and the suitable method of specimen preparation was selected.According to the significant viscoelastic properties of the asphalt material,the complex shear modulus G* was determined as the characterization parameter of the diffusion degree of new and old binder,the variation law of G* under different factors is analyzed,and the main factors affecting the diffusion are analyzed by variance analysis.The results show that the diffusion phenomenon can occur at 80℃ between virgin binder and RAP binder,but the diffusion equilibrium state is basically achieved after diffusion at 120 ℃ for two hours.Time and temperature have a significant effect on the diffusion between new and old asphalt,and the influence of temperature is more significant,the influence of asphalt variety on diffusion is small.At the same temperature,the curve of G* with time has the same rule.It first increases rapidly and then slows down gradually.In order to characterize the variation of G* with time,Fick’s law is chosen as the diffusion model in this paper.The results show that,for the given diffusion coefficient D,the calculated values of Fick’s law are in good agreement with the experimental values,and the diffusion of new and old bi tumen in RAP agrees with the Fick’s law.The diffusion effect of 70# is better than that of 90# asphalt of the two kinds of base asphalt in macroscopic experiment.In order to study the reason,the microcosmic experiment is used to analyze the composition,molecular structure and molecular size of the two kinds of asphalt.The experiments were carried out by Thin Layer Chromatography(TLC),Fourier Transform Infrared spectroscopy(FTIR)and Gel Permeation chromatography(GPC).The results showed that the colloidal structure of 70# base asphalt was more than that of sol type,the content of saturates and aromatics was higher,the content of benzene ring in asphalt was small,and the number of molecular branching chain was less.To a certain extent,the effect of molecular structure and the proportion of four components on diffusion effect is greater than that of molecular size on diffusion effect.In order to explore the microscopic diffusion process of new and old asphalt and verify some macroscopic conclusions by means of molecular simulation,the diffusion of new and old asphalt was simulated by molecular simulation technology.The results show that the diffusion coefficient obtained by the simulation technique is related to the total simulation time,and the NPT ensemble is more suitable for the diffusion phenomenon studied in this paper.The temperature has a significant effect on the diffusion under the simulated total time.The diffusion rate of the four components into the ol d asphalt is aromatics > saturates > resins> asphaltenes respectively.This conclusion also verifies the conclusion that when the content of aromatics and saturates is higher,the diffusion rate to aging asphalt is faster. |
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