Study On Aging Behavior Of Asphalt And Asphalt Mixture In Northwest China

The climate conditions in the northwest region of our country are complex,with high altitude and large temperature differences,and characterized by strong UV intensity and long freeze-thaw cycles.These conditions cause severe aging damage to asphalt pavements in service,leading to diseases such as cracks and potholes.However,the conventional single-factor aging method currently used cannot accurately simulate the complex environment of the northwest region,which limits the analysis of the aging behavior of asphalt and asphalt mixtures.This article aims to study the aging mechanisms of base asphalt and SBS modified asphalt through UV aging,freeze-thaw aging,and UV-freeze-thaw coupling aging,providing detailed and scientific design basis for the wide application of asphalt mixtures in the northwest region.This article analyzes the climate characteristics of high altitude and large temperature differences in the northwest region and designs three aging methods: indoor simulation of UV aging,freeze-thaw aging,and UV-freeze-thaw coupling aging for asphalt and asphalt mixtures.The changes in the physical properties of asphalt before and after aging under different aging methods are analyzed by penetration,ductility,softening point,and Marshall stability tests.The changes in high-temperature rheological properties of asphalt before and after aging are analyzed using a dynamic shear rheometer(DSR).The changes in water stability,high-temperature performance,and low-temperature crack resistance of asphalt mixtures after environmental aging in the northwest region are analyzed.Fourier-transform infrared spectroscopy(FTIR),X-ray photoelectron spectroscopy(XPS),and gel permeation chromatography(GPC)are used to analyze the changes in functional groups and chemical composition of asphalt after aging in the simulated northwest environment.The main conclusions are as follows:(1)As aging time increases,the penetration and ductility of asphalt and SBS-modified asphalt decrease while the softening point gradually increases.The changes in physical properties of asphalt after UV-freeze-thaw coupling aging are greater than those after single-factor aging.The viscosity aging index of asphalt gradually increases with aging time,and the viscosity-temperature performance of asphalt gradually deteriorates.The rutting factor of asphalt gradually increases with aging time.The combined effects of freeze-thaw cycles and UV light cause a decrease in viscosity and an increase in hardness of the asphalt,leading to a significant reduction in conventional and rheological performance of asphalt.(2)During the UV-freezing-thawing coupling aging,although UV aging can improve the high-temperature performance of asphalt mixture,its impact on the mixture is limited,and freezing-thawing cycles will increase the cracks in the mixture,gradually reducing its high-temperature performance.Compared with single-factor aging methods,the coupled aging leads to a significant decrease in the road performance of asphalt mixtures after aging.(3)After aging by different methods,the C=C and C-H bonds in the asphalt are quickly cleaved and oxidized,leading to an increase in the oxygen content in the asphalt and a higher abundance of carbonyl and sulfoxide functional groups.Cross-linking reactions occur between asphalt molecules after aging,resulting in an increase in the content of large molecular weight species(LMS)in the asphalt.Freeze-thaw cycles can accelerate the chain scission and oxidation reactions of asphalt molecules under UV radiation,resulting in a rapid increase in the content of LMS in the asphalt.