Engineering Performance and Activation Mechanism of Asphalt Modified by Microwave and Diesel Pre-Processed Waste Crumb Rubber

In order to enhance the performance of waste crumb rubber modified asphalt (WCRMA) and expand its engineering application, this study applied three methods to activate waste crumb rubber, containing diesel pre-swelling, microwave radiation, and composite activation. Activated waste crumb rubber modified asphalt samples under 4 diesel pre-swelling content and 6 microwave radiation intensities were prepared, respectively. Fourier Transform Infrared Spectrometer (FTIR), Thermogravimetric (TG) test, and Dynamic Mechanical Analysis (DMA) were used to characterize the influence of activation on the functional groups, crosslinking, and viscoelasticity of crumb rubber. Viscosity was employed to illustrate the engineering performance of modified asphalt, while the phase angle and complex modulus in the Dynamic Shear Rheometer (DSR) test were recorded to identify rheological properties. The distribution of rubber in asphalt and the interaction with asphalt were observed by Gel Permeation Chromatography (GPC), electron microscope, and Scanning Electron Microscope (SEM) tests. Results demonstrated that diesel pre-swelling was beneficial to the synthesis of C=C, microwave radiation and composite activation had a positive effect on breaking the main chain and crosslinking bonds of rubber. As for modified binders, three activation treatments decreased the viscosity. The control of microwave radiation equivalent intensity and diesel content had an important signification on alleviating the damage to the ability of WCRMA to resist deformation. In addition, Diesel pre-swelling supplemented the light components in the asphalt and helped to reduce the size of rubber particles combined with the secondary swelling. Microwave radiation was related to the pyrolysis of rubber particles. Furthermore, the rubber core phenomenon disappeared under 1.8 kJ/g composite activation and the rubber was distributed in the modified asphalt system evenly.