Study On Fusion Behavior And Characterization Of Old And New Asphalt During Regeneration

With the development of current asphalt recycling technology,more and more waste asphalt mixture is recycled.However,the lack of understanding of the fusion behavior of new and old asphalt makes the degree of fusion of new and old asphalt low,and the performance of recycled asphalt cannot reach a high level,which results in low regeneration efficiency of recycled asphalt mixture.In this paper,dynamic shear rheological test(DSR),infrared spectroscopy(FTIR),gel permeation chromatography(GPC),atomic force microscopy(AFM),and molecular dynamics simulation techniques were used to analyze the fusion behavior of new-old asphalt from macro,micro,and molecular simulation perspectives.Firstly,the variation law of complex shear modulus of new-old asphalt composite samples under different environments is analyzed by the DSR test.Based on Fick’s theory,a quantitative evaluation index of new-old asphalt fusion behavior was obtained,and the influences of asphalt grade,time,temperature,and rejuvenator on the fusion rate and diffusion activation energy of new-old asphalt were analyzed.The results show that the fusion rate of 90# asphalt is greater than that of 70# asphalt.With the increase of time,the diffusion activation energy of asphalt molecules increases,while the fusion rate decreases and gradually reaches stability.With the increase of temperature,the transition probability of asphalt molecules increases,and the fusion rate accelerates.With the addition of XT-2,the diffusion activation energy of bitumen decreases and the fusion rate increases significantly.Then,the changes of asphalt microstructure during the fusion process of new-old asphalt were analyzed by microscopic experiments such as FTIR,GPC,and AFM.The results show that with the fusion of new asphalt and old asphalt,the content of aging asphalt molecules measured by the new asphalt increases,the index of hydroxyl and sulfoxide group increases,the content of macromolecules increases,the "bee structure" develops further,the roughness increases,the energy required for the diffusion of asphalt molecules increases,and the fusion rate decreases.At the same time,the microstructural indicators and the characterization indicators of macro integration behavior are analyzed,and the correlation between macro and micro indicators is good.Finally,the fusion process of new and old asphalt is simulated by the molecular simulation method,the macro-micro-simulation results are linked,and the previous macro-micro conclusions are verified.The simulation results show that with the extension of simulation time,the diffusion coefficient decreases rapidly and reaches stability.With the increase of temperature,the degree of agglomeration of aged asphalt molecules decreases,the distribution is more uniform,and the cohesive energy density decreases,which makes the diffusion coefficient increase significantly.After adding the rejuvenator,the diffusion coefficient increases significantly.Paraffins with low molecular weight,low benzene ring content,and low polarity can accelerate the fusion of new and old asphalt.According to the multi-angle analysis of the macro-micro-simulation results,it is found that the transition of asphalt molecules can be promoted by controlling the relevant influencing factors,and the fusion rate and degree of new-old asphalt can be improved.