Recycling of waste tire rubber and polyethylene plastic in asphalt: Microstructural evolution and quantitative relationship with rheological behavior

Mismanagement of waste tires and plastics has resulted in environmental pollution globally. The sustainable reuse of waste tire crumb rubber (CR) and recycled polyethylene (RPE) plastic as modifiers can improve asphalt properties and reduce the environmental burden. To clarify the relationship between the micro-multiphase and rheological performance, this paper investigated the impact of modifier content on the microstructure, physical and rheological properties of CR and RPE modified asphalt (RPEA), and quantitatively analyzed the relationship between microstructure and macroscopic properties. The area and shape indicators through fluorescence microscope (FM) were adopted to evaluate the microscopic three-phase structure. It is illustrated that the shape indicators, including the mean of aspect ratio (L a ) and the mean of roundness (R a ), can precisely characterize the microphase state, categorized into scattered, transitional, and continuous states. Microscopic morphology analysis showed a mutual adhesion between CR and RPE without embedding with each other. Physical and rheological analysis demonstrated that the increased viscosity, elastic response and better deformation resistance of RPEA are mainly dominated by RPE. Benefiting from CR, RPEA exhibits favorable low-temperature creep behavior, while RPE has the opposite effect. Spearman’s correlation analysis showed strong monotonic correlations between composition parameters, microstructural indicators and macro-performance of RPEA. Furthermore, the linear regression and polynomial regression between strongly correlated parameters were established to provide a prediction for RPEA proportioning optimization. The outcome of this study can guide the efficient recycling of CR and RPE for asphalt modification, to promote the sustainability of transportation infrastructure. • The evolution of the three-phase structure of RPEA can be categorized into three states. • CR and RLDPE are physically combined and have a balanced modification effect. • Found R a and L a are the pivotal mediator variables between content and performance. • Built prediction by linear and polynomial regression from microstructure views.