Research On Fatigue Damage Self-healing Capability Of Asphalt Mixture Under The Condition Of Thermal Aging

With the rapid development of highway construction in china,selecting more durable asphalt pavement materials is a common research direction for current road researchers.Fatigue cracking is one of the main damage forms of asphalt pavement today,road researchers have been working on solving the problem of pavement cracking on the road surface for a long time,but they haven't been solved fundamentally so far.Based on the previous research results,it can be concluded that asphalt mixture have self-healing ability after fatigue damage,and studying on the self-healing ability of asphalt mixture have important significance for optimizing asphalt pavement design and prolonging the service life of the pavement.In this paper,the four-point bending fatigue test was used to analyze the fatigue damage performance and self-healing properties of matrix asphalt mixture,styrene-butadiene-styrene triblock copolymer(SBS)modified asphalt mixture and rubber powder modified asphalt mixture under the thermal aging condition,scanning electron microscopy(SEM)and nuclear magnetic resonance apparatus(NMR)were used to analyze the microstructure and pore structure of asphalt mixture before and after aging,the main conclusions are as follows:(1)Through analyzing the results of the four-point bending fatigue test of asphalt mixture:as the degree of aging deepens,the asphalt mixture becomes brittle and its fatigue resistance deteriorates.The damage factor D and the fatigue damage factor D_f can reflect the fatigue resistance of asphalt mixture,but the fatigue damage curve D_f can't describe the evolution of the damage process.The rubber powder modified asphalt mixture have the best anti-fatigue performance,followed by SBS modified asphalt mixture,matrix asphalt mixture under the different aging conditions;With the loading times increase,the dissipation energy decrease.With the aging degree increase,the dissipating energy of the asphalt mixture increase,and the dissipating energy of the matrix asphalt mixture is larger than the other asphalt mixture under the same strain condition;The fatigue damage degree of asphalt mixture can be reflected by the change rate of dissipation energy.(2)Through the phenomenal method and energy method of self-healing evaluation index HI~1 and HI~2 can be evaluated to the same conclusion that the original asphalt mixture with less damage at 50°C for 6 hours have the best healing.Using grey relational entropy analysis and range analysis to study the influence of multiple factors on the self-healing ability of asphalt mixture,it can be concluded that the aging degree affects the self-healing ability of asphalt mixture significantly;In the unaged condition,the self-healing ability of the matrix asphalt mixture is better than the modified asphalt mixture.In the aging state,the self-healing ability of the modified asphalt mixture is better than matrix asphalt mixture,and the healing ability of the SBS modified asphalt mixture is better than rubber powder modified asphalt mixture.(3)The microstructure of the asphalt mixture was analyzed before and after aging by scanning electron microscopy(SEM),the matrix asphalt mixture and the SBS modified asphalt mixture have micro cracks between asphalt and aggregate interface after the short-term aging,and there is no obvious cracks at the interface of the mixture after the long-term aging;There is no obvious change on micro-morphology of rubber powder modified asphalt mixture before and after aging,because its high temperature performance and anti-aging performance are better.There is no obvious crack at the interface of the rubber powder modified asphalt mixture before and after aging,which indicates that rubber powder modified asphalt has stronger cohesiveness with aggregate,and its fatigue resistance is more better.The porosity of matrix asphalt mixture was analyzed under the different aging conditions by nuclear magnetic resonance apparatus(NMR),and it can be concluded that short-term aging matrix asphalt mixture have the biggest porosity,followed by unaged matrix asphalt mixture,long-term aging matrix asphalt mixture;Thermal aging has a little effect on the micro-porosity of asphalt mixture,but it has great influence on its large and medium pores.the pores of matrix asphalt mixture are mainly large and medium pores with 10-100?m before and after aging.