Research On Asphalt Aging And Self-Healing Properties Under Complex Environment

Transportation industry has been a basic and leading industry in China,with the rapid development of the national economy,which has achieved a historic breakthrough in recent years.Highway is an important index to measure transportation and even the national economy and among this the proportion of asphalt pavement has hit 90 percent.However,with the extension of the service period,asphalt pavement inevitably suffers from a serious of damage such as deformation,cracking and surface function attenuation,which seriously influences the service life of the highway.These pavement diseases come into being owing to the comprehensive influence of asphalt itself aging and external complex climate environment.As a viscoelasticity material,asphalt has the ability of selfrecovery(self-healing).This ability is always affected by other external environmental factors such as aging.Therefore,only to fully understand the aging mechanism of asphalt can we truly know the self-healing mechanism of asphalt.At present,the research on the thermal aging of asphalt has been quite mature.However,the research on composite water aging and composite ultraviolet aging which is based on the using stage of pavement is still in blank.On the basis of indoor thermal oxygen aging,this paper simulates composite water aging of road asphalt by adding moisture and composite ultraviolet aging through indoor accelerated ultraviolet aging equipment.Matrix asphalt and SBS modified asphalt that are commonly used in north area were selected and then applied to four different aging methods respectively.The physical and mechanical properties of asphalt before and after compound aging were tested and in combination with qualitative and quantitative analysis by microcosmic means.Finally the damage healing properties of aging asphalt were investigated,having found the key factors that affect self-healing and then provide reference for design and improvement of road asphalt materials.The study of conventional performance indexes indicates that the effect of composite aging on asphalt is much greater than that of thermal aging.Moreover,the effect of composite aging on low temperature performance is much higher than that of high temperature performance.It is found that viscosity ratio and aging index are suitable indicators for evaluating the degree of composite aging.As the degree of aging deepen,the low temperature rheological properties of two kinds of bitumen decrease before composite aging;The low temperature creep property of matrix asphalt and SBS modified asphalt after water aging is opposite to that of long term aging(PAV): The former is slightly improved and the latter is obviously reduced;The result of Burgers model fitting parameters show that UV aging leads to the least energy dissipation,the longest relaxation time and the worst temperature performance of two kinds of bitumen.Atomic force microscopy(AFM)was used to observe the change of micro-structure of asphalt before and after composite aging,it is observed that “bee-like structures” exist in most asphalt surface topographies and aging causes the changes of bee-like structures number and area;Two-dimensional surface topographies show that after the water aging,the number and area of bee-like structures of matrix asphalt decreased obviously while the phenomenon of cross-linking and highly gather between adjacent bee-like structures emerge in surface topographies of SBS modified asphalt;After UV aging,the number and area of two bee bitumen structures decreased significantly,which means ultraviolet radiation changes asphalt component and molecular structure;As is shown on amplitude parameter and function parameter,the surface roughness and apparent hardness of matrix asphalt decreased after water aging,which is opposite to that of SBS modified asphalt;Ultraviolet radiation makes the surface roughness and apparent hardness of two kinds of bitumen reach the lowest level.The phase diagram of matrix asphalt shows that the area of dispersed phase decreases and the area of continuous phase increases after water aging which is also opposite to that of SBS modified asphalt.After UV aging,the area of bee phase and dispersed phase of two bitumen decreased significantly.Pearson correlation analysis shows that the more particle number and the smaller the average particle size,the higher the aging degree,the poorer the stress relaxation ability and the worse the low temperature performance.The results of ductility tensile healing test(DTH)shows that the main factor affecting the self-healing properties of aging matrix asphalt is aging degree and it is more reasonable to select the ductility recovery rate(Drr)to evaluate its self-healing ability.While the self-healing ability of SBS modified asphalt is less influenced by the change of indexes.