Study On Multi-scale Behavioral Characteristics Of Asphalt Before And After Aging

Aging is one of the main causes of various diseases of asphalt pavement,which profoundly affects the road performance of asphalt.At present,the research on asphalt aging mainly focuses on the influence of aging on its road performance and chemical composition.However,the change of micro-properties of asphalt before and after aging is still unclear,and it is impossible to establish the relationship between chemical composition,micro-properties and macroscopic properties for exploring the aging mechanism of asphalt deeply.By analyzing the micro-performance of asphalt,this paper proposed a method to evaluate the micro-properties and establish a connection to link chemical composition and macro properties.Meanwhile,the aging mechanism and the interaction relationship between the properties of asphalt at different scales were thoroughly explored.The research provides scientific theoretical basis for improving the anti aging performance,regeneration and recovery of asphalt,and it also can be used to effectively optimize the production conditions of bitumen and select suitable modifiers for asphalt modification,so as to improve the road performance of asphalt.In this paper,the changes of element composition,chemical functional group,molecular weight and its distribution of asphalt before and after thermal-oxygen aging were analyzed by using element analysis,infrared spectroscopy(FTIR)and gel permeation chromatography(GPC),and the mechanism of chemical composition on macro performance was also explored.The results indicated that the content of oxygen elements of aphalt is greatly increased after thermal-oxygen aging,and the increase of the polar functional groups such as carbonyl and sulfoxide groups can promote the intermolecular association and interaction between molecules,thus the high temperature stability of asphalt is improved.Meanwhile,the principal component analysis(PCA)showed that different chemical functional groups had synergistic effect on base asphalt and promoted the changes of road performance together.In addition,the molecular weight of asphaltene moves towards macromolecule after thermaloxygen aging,and the weight-average molecular weight and its distribution coefficient increase significantly.The effect of aging on the chemical functional group and molecular weight of SBS modified asphalt shows that the aging of SBS modified asphalt is the comprehensive embodiment of the aging of base asphalt and SBS modifier,and the SBS modifier degrades in the aging stage and mainly occurs in the PAV stage.Statistical regression analysis indicated that the chemical component of asphalt has a significant correlation with its macro-performance.The analysis of the changes in chemical components before and after aging can effectively predict the effect of aging on the performance of asphalt.The changes of microstructure and micro mechanical properties of asphalt before and after aging can be effectively analyzed by using atomic force microscopy(AFM).In order to ensure the accuracy and rationality of AFM test,a new AFM sample preparation device which can be used for asphalt was invented and a new method for preparing AFM bitumen sample was proposed.AFM analysis indicated that the asphalt surface has a special structure which called bee structure,the number of bee structure decreased and the total area ratio increased significantly after PAV aging.The research shows that the bee structure is the wax crystallization which was formed by the wax molecules and long-chain alkyl eutectic of macromolecules,such as asphaltenes.Meanwhile,the study of the micro mechanical properties and its distribution of asphalt surface shows that aging could increase the its elastic properties significantly,promote the increase of the dispersion of micro mechanical properties,which could affect the macro properties of asphalt.The micromorphology of asphalt surface has good structural similarity with its distribution of micro mechanical properties.The correlation analysis between chemical components and micromechanics indicated that they have significant correlation.The micro mechanical properties of asphalt surface are influenced by its chemical components,and the formation mechanism of micro mechanical properties before and after aging was explored.The micromorphology and micro mechanical properties of asphalt indicated that asphalt structure is a colloid structure.However,the AFM study shows the colloid polarity,which is different from the traditional colloid theory,is gradually decreasing,and the different phases of the asphalt have distinct boundary layers,both morphology and mechanical properties.This research supplement and promote the development of asphalt colloidtheory effectively.The dynamic shear rheometer(DSR)was used to analyze the changes of the viscoelastic properties of the asphalt before and after aging.The results indicated that the SBS modified asphalt has a better stability and anti-aging ability than the base bitumen.The viscosity temperature curve indicated that aging leads to the reduction of temperature sensitivity.Meanwhile,the master curve was established by the principle of time temperature equivalence principle to analyze the changes of the asphalt viscoelastic properties with frequency in the wider frequency domain.The statistical regression analysis indicated that the micro mechanical properties of asphalt have a significant influence on the macro mechanical behavior.The macro mechanical behavior is the embodiment of micromechanics at the macro level,and the two values are at the same magnitude by eliminating the influence of the different frequency and action mode of the AFM and DSR.The analysis can effectively predict the change of macroscopic road performance.