Investigation On Multi-scale Crack Resistance And Local Damage Characteristics Of Hot In-place Recycled Asphalt Mixture

As an economical and environmentally friendly road maintenance technology,geothermal regeneration can realize the efficient reuse of the original pavement materials and has become a good way of pavement maintenance.However,the problem of insufficient miscibility of new and old asphalt in the process of hot in-place recycling leads to the stiffness gradient between aged asphalt and blended asphalt,which greatly reduces the long-term service effect of recycled asphalt pavement.In this paper,the crack resistance and local damage characteristics of asphalt mixtures with different RAP contents are studied from the four scales of mixture,fine aggregate matrix(FAM),mortar and asphalt.Firstly,the key parameters such as RAP material gradation,old asphalt and old aggregate performance of the original pavement were tested,and the Marshall method was used to determine the amount of regenerant and the optimum oil-stone ratio of hot recycled asphalt mixture.According to the determined optimum asphalt content,the specific surface area method is used to calculate the mix ratio of hot recycled asphalt mixture,FAM,mortar and asphalt with different RAP content.Secondly,through laboratory tests,it is studied whether the road performance of hot inplace recycled asphalt mixture under different RAP content meets the specification requirements.The results show that with the increase of RAP content,its high temperature stability is continuously improved,while the low temperature crack resistance is rapidly reduced.When the RAP content is less than 90%,its low temperature performance still meets the minimum specification requirements.The water stability of hot recycled mixture with different RAP content meets the specification requirements.Then,the macroscopic crack resistance test of hot recycled asphalt mixture at different scales was designed,and the crack resistance performance parameters such as fracture energy and flexibility index were used to characterize its crack resistance.The results show that the test temperature greatly affects the fracture form of hot recycled asphalt mixture,and the fracture energy decreases with the increase of RAP content.By comparing the crack resistance of hot recycled asphalt mixtures at different scales,it is found that with the change of RAP content,the FAM and mixture scales have similar trends in the change of fracture energy.Finally,the ISDT in-situ tensile test of hot recycled asphalt FAM was designed to analyze the damage and fracture mechanism of hot recycled asphalt mixture from the mesoscopic level.The cracking process was observed by scanning electron microscopy.The results show that there are mainly two forms of bond failure and cohesive failure in the failure form of asphalt mortar,among which bond failure always dominates.The coupling analysis of damage and fracture process of asphalt mortar is carried out by load-CMOD curve.The results show that with the increase of CMOD,the number of microcracks increases,and the maximum microcrack length and maximum microcrack area increase significantly.In this paper,by studying the crack resistance and local damage characteristics of hot recycled asphalt mixture at different scales,it is of great significance to predict and control the crack resistance of hot recycled asphalt pavement and improve the long-term performance of recycled asphalt pavement.