Macro And Micro Characterization Of Reversibility Between Aging And Recycling Of Asphalt

During the construction and service of asphalt pavement,its life will decrease due to the external environment effect.In order to recover the performance of asphalt pavement,hot recycling is a common method for maintenance.Nowadays,the mechanism of hot recycling of asphalt pavement is not clear,and the selection of rejuvernator and recycling parameters relies on experience.There is not a recognized evaluation method and criterion.Therefore,the recycling effect cannot be guaranteed.In order to evaluate the recycling behavior of aged asphalt effectively,this paper carried out research contents are as follows.Firstly,the effects of aging-recycling on high-temperature performance,low-temperature performance and viscoelastic properties at full temperature were investigated.The macro reversibility index of virgin asphalt(ARIV)was put forward.The effect of different rejuvenators on macro properties of virgin asphalt was quantitatively analyzed.It was found that the ultraviolet aging and water damage are coupled with each other,which will aggravate the performance degradation of asphalt.With the intensifying of aging,the softening point and the stiffness modulus of virgin asphalt increased,while the changing rate of stiffness modulus–m value decreased.The lower the temperature was,the weaker the aging effect will be.The virgin asphalt has strong reversibility between aging and recycling in macro performance.Different rejuvenators reduced the softening point,stiffness modulus and complex modulus of aged virgin asphalt.The lighter the aging,the better the recycling effect.The quantitative evaluation result of ARIV was similar to that of qualitative analysis,which showed that the reversibility of aging and recycling of virgin asphalt was good in macro mechanical behavior.Based on the analysis of asphalt macro performance,the micro characterization and simulation methods were used to study the aging and recycling of virgin asphalt,mainly including the effect of aging-recycling on molecular distribution,chemical composition,micro characteristics.The relationship between the micro performance and the macro performance of virgin asphalt during the aging-recycling process was established,and the aging-recycling mechanism was revealed.The micro reversibility index of virgin asphalt(IRIV)was put forward.The effect of different rejuvenators on micro properties of virgin asphalt was quantitatively analyzed.It was found that with the intensifying of aging,the number-average molecular weight of virgin asphalt increased,and the polydispersity of molecular weight increased.Some rejuvenators can recover the number-average molecular weight of aged asphalt,and decrease the polydispersity of molecular weight.In addition,the chemical composition of asphalt varies with different aging methods.The effect of rotating film aging test(RTFOT)on carbonyl group and sulfoxide group was not significant,while ultraviolet aging and pressure aging were particularly obvious.Finite element modeling results show that the aging made the gap phase change to the honeycomb and the shell phase,which leaded to the weakening of the overall resistance and early failure.The quantitative evaluation result of IRIV showed that the average value R_{molecular weight} was 0.32,and the average value of R_C=O was 0.43,which were all less than 0.5.It was similar to that of qualitative analysis,which showed that the reversibility of aging and recycling of virgin asphalt was poor in micro mechanical behavior.In order to explore the influence of modification on the aging-recycling of virgin asphalt,the reversibility between aging and recycling of SBS modified asphalt,rubber powder modified asphalt and high viscoelaticity modified asphalt was further studied.Viscoelasticity and phase state analysis were conducted to explore the effect of different modifications on macro performance of asphalt binder during aging and recycling.The macro reversibility index of modified asphalt(ARIM)was put forward.The effect of different rejuvenators on macro properties of modified asphalt was quantitatively analyzed.It was found that three modifications all cannot affect the complex modulus increasing resulted from aging.But the modification will reduce the increase of modulus.SBS modification and rubber powder modification effected the changing of glass transition temperature due to short-term aging.But rubber powder didn't effect the changing of glass transition temperature due to long-term aging.The rejuvenator reduced the modulus of the aged asphalt,but has no obvious effect on the temperature recovery of the virgin asphalt,rubber powder modified asphalt and SBS modified asphalt.The reversibility of the macro properties of three modified asphalts was similar,which were more significant than that of virgin asphalt.The ARIM of the three modified asphalts was greater than 1,and the mean values were 3.62 and3.83.Rejuvenators had strong regeneration effect on macro performance of asphalt,but over recovery phenomenon was severe.So it can be considered to reduce the amount of rejuvators.Based on the analysis of modified asphalt macro performance,the effects of aging and recycling on the distribution of four fractions,micro morphology and surface adhesion of SBS,rubber powder and high viscosity modified asphalt were analyzed qualitatively.The influence of micro characteristics on the macro performance was determined.The aging and recycling mechanism of modified asphalt was revealed and compared with virgin asphalt.The micro reversibility index of modified asphalt(IRIM)was put forward.Furthermore,the correlation between the reversibility indexes at different scales was analyzed and the comprehensive evaluation reversibility index of asphalt aging and recycling(RI)was put forward.It was found that the surface adhesion force of three modified asphalt all decreased after aging.Three recover agents can recover the adhesion force of high viscoelasticity modified asphalt,but cannot recover the SBS and rubber powder modified asphalt.Both aging and modification can change the aromactics to asphaltene and reduce the colloidal structure stability.To a certain extent,recover agents can recover the fractions'change of asphalt binder due to aging.(Rsoftening point,RS,RM,RV complex modulus,RC=O,RS=O,Rmolecular weight,RVDMT)can be calculated by RI.Among them,the indexes of warm mixing agent were(1.41,5.33,1.2,1.03,0.51,1.53,0.39,1.03).It was found that the regeneration effect of warm mixing agent on the high temperature performance,the viscoelastic properties and the micro mechanical properties.The regeneration effect of chemical composition and molecular weight distribution was general,but the low temperature performance was over recovered.From qualitative analysis to quantitative evaluation,the reversibility between aging and recycling of virgin asphalt,SBS modified asphalt,rubber powder modified asphalt and high viscosity modified asphalt was comprehensively evaluated in multi-scale.The mechanism of aging and recycling of asphalt was analyzed,and the quantitative evaluation method of aging asphalt regeneration was determined.Results can establish a theoretical foundation for developing the high-performance rejuvenator and anti-aging agent,optimizing the recycling technology,proposing the evaluation method and criterion of recycling and increasing the content of recycled asphalt in pavement.