| Due to economic and environmental benefits,the production of waste resins and rubber into bitumen is currently receiving widespread attention.In order to solve the problem of waste resin and rubber reuse and provide systematic and comprehensive theoretical guidance for the design of resin/rubber composite modified asphalt.In this thesis,combining macro and microscopic tests to reveal the modification mechanism by studying the evolution of the properties of recycled polyethylene(RPE)/waste rubber(WTR)composite modified bitumen under different mixing ratios of RPE and WTR.Firstly,Fourier Transform Infrared Spectroscopy(FTIR)was used to analyze the change of the absorption peak of each feature,and clarify the physical blending and chemical reaction during the modification process.Secondly,through Gel Chromatography(GPC),the molecular structure of modified bitumen was further clarified,and the influence of modifier on bitumen molecular weight and molecular weight distribution was clarified.Then,the Laser Scanning Confocal Microscope(LSCM)was used to analyze the changes of the micromorphology of modified asphalt.Finally,through solubility test,the effects of modifier content,swelling time and temperature on the swelling and degradation behavior of modified bitumen were explored,and the swelling and degradation behavior of modified bitumen were revealed by combining FTIR,GPC and LSCM results.The main conclusions are as follows:The macroscopic test results show that after adding RPE and WTR,the penetration degree of modified asphalt decreases,the value of softening point and viscosity increase,and the ductility decreases.Compared with WTR,RPE has a greater impact on penetration and has a better effect on viscosity.For single RPE-modified asphalt,adding an appropriate amount of WTR can increase its ductility,indicating that WTR can improve the low temperature performance of RPE-modified bitumen to a certain extent.The FTIR results showed that the modification process of RPE/WTR composite modified asphalt was mainly based on physical modification,and chemical modification was mainly oxidation of weak bonds and polymer degradation.Due to poor stability,aromatic phenols are also prone to polycondensation and chain breakage by oxidation.GPC results showed that RPE and WTR increased the weight-average molecular weight(Mw)and numerical average molecular weight(Wn)of modified bitumen,and the molecular weight distribution area was expanded and the dispersion degree was higher.The depolymerization of large molecular size coexists with the polymerization of small molecular size.The LSCM results showed that the modified asphalt underwent swelling and degradation reactions during the modification process.RPE and WTR influence each other during the modification process and promote each other’s reactions.A gel film forms on the surface of RPE that promotes overlapping,and the polymer molecular chains break and aggregate.RPE/WTR composite modified asphalt forms a relatively stable filamentous and network structure,which prevents the movement of the macromolecular chain of asphalt binder,thereby improving the stability of the modified asphalt and effectively improving the low-temperature flexibility of asphalt.The solubility test results showed that the modifier,modification temperature and modification time all affected the swelling and degradation behavior of the polymer.When the RPE content is4.5% and the WTR content is 10%,the bitumen can reach the best solubility;The critical temperature at which polymer particles can undergo degradation reactions is 180°C,at which time a relatively stable filamentous and network structure is formed.In order to ensure the stability of asphalt,the modification time of 120 min-150 min is just enough to meet the needs of full degradation of polymer particles.The swelling and degradation behavior of polymer modifier is divided into three stages,the first stage polymer modifier and bitumen are only sheared at short time and low speed,at which time some polymers undergo swelling reaction;In the second stage,the polymer and bitumen are sheared at high speed,and the polymer gradually breaks under high temperature and external force to form a chain,and the swelling reaction occurs with the light components in the surrounding asphalt,at which time the swelling reaction occurs simultaneously with a small amount of polymer degradation reaction;In the third stage,the swelling state of the polymer tends to be saturated,and then it is gradually decomposed by the expansion and decomposed,and degradation occurs. |
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