Study On Performance Evaluation Of Recycled Asphalt And Microscopic Mechanism Of Asphalt Blends In Hot Recycled Asphalt Mixture

As the most advanced construction technology and the most controllable recycling technology,the hot-plant produced recycled asphalt pavement is one of the most promising asphalt pavement recycled technologies in the future.However,the lack of understanding of the performance of recycled asphalt/mixtures and the actual blending status of new and old asphalts still limits the proportion of reclaimed asphalt pavement(RAP)added in recycled asphalt mixtures.Based on this,a series of macroscopic and microscopic test methods were used to comprehensively study the performance and microstructure of recycled asphalt binder.At the same time,the degree of partial blending between RAP and virgin binder was accurately evaluated by utilizing microscopic tests and tracer method.First,based on the improved test method,the aged asphalt in the reclaimed asphalt pavement(RAP)was recovered,and the performance of the aged asphalt was restored with the new SBS modified asphalt + recycling agent.The optimal amount of recycling agent is determined by the target PG test.The basic performance tests,aging test,MSCR test,BBR test,and DSR frequency scanning test were conducted to comprehensively evaluate the high temperature anti-rutting performance,low temperature crack resistance,anti-aging performance,and master curve characteristics of recycled asphalt binder,and compared with the new SBS modified asphalt.Second,the microstructures of recycled asphalt binder with different aging degrees were tested by Fourier transform infrared spectroscopy(FITR),gel permeation chromatography(GPC),atomic force microscopy(AFM)experiments.The microstructure characteristics of recycled asphalt were analyzed and its differences with the new SBS modified asphalt were also investtigated.At the same time,combined witth the macroscopic properties of recycled asphalt,the microscopic mechanism of the performance change of recycled asphalt was further studied.Third,aiming at the key problem of hot recycled asphalt mixture,the degree of blending between reclaimed asphalt pavement(RAP)binder and virgin binder,a microscopic test method for evaluating the degree of blending based on scanning electron microscopy and energy dispersive spectroscopy(SEM/EDS)techniquesn was designed in this paper.The basic principles and operations of microscopic testing techniques,the implementation of new asphalt tracer methods,the selection of tracers,and the preparation of microscopic test samples are discussed in detail.It provides the experimental basis for the direct and accurate assessment of the actual blending state of old and new binder in hot recycled asphalt mixtures.At last,a series work was carried out to observe and evaluate the degree of blending between reclaimed asphalt pavement(RAP)binder and virgin binder in hot mixed asphalt mixture.The blending ratio was proposed as a quantitative indicator to accurately evaluate the degree of partial blending.And the influence of different handing process on the degree of blending has also been studied.The study shows that in the high RAP mixies,a certain amount of the aged binder is coated on the RAP aggregate in its original form,and with the increase of the RAP content in recycled mixture,the blending degree of virginand aged binder decreases rapidly and the homogeneity of blended binder is weakened.The blending process of the virgin and RAP binder mainly occurs during the long-term use of the recycled mixture pavement.Using recycling agent improved the efficiency RAP binder as it is blended with virgin binder.For high RAP content recycled asphalt mixture,it is ineffective and uneconomical to settle the influence of partial blending only by changing the addition of virgin binder.It is necessary to improve the utilization ratio of the aged binder and the properties of blended binder.