Ultrasound-assisted preparation of crumb rubber modified asphalt: Characterization and molecular dynamics simulation

The traditional method of crumb rubber modified asphalt (CRMA) preparation can improve the stability but is not conducive to cleaner production. From the perspective of process optimization, ultrasound is introduced into the crumb rubber modified asphalt preparation process, and the high temperature, high pressure and high energy accompanied by the cavitation effect are used to generate free radical triggering chemical effects at the two-phase interface between crumb rubber and asphalt. In this paper, the influence of ultrasound on the compatibility and stability of crumb rubber modified asphalt system was evaluated by combining experiment and molecular dynamics simulation. An experimental platform for ultrasound-assisted preparation of crumb rubber modified asphalt was established. The effects of ultrasonic on the physical properties of asphalt and crumb rubber modified asphalt were studied through Brookfield viscosity test, thin film oven aging test and Fourier infrared spectroscopy. The base, aged, and ultrasonically treated asphalt samples were simulated using molecular dynamics, and various parameters such as Cohesive Energy Density (CED), Mean Square Displacement (MSD), and Free Volume Fraction (FFV) of asphalt and its components were calculated and analyzed. The results showed that under the ultrasonic-assisted preparation, the agglomeration phenomenon of rubber particles is weakened, the particle size is reduced, the penetration degree is reduced, and the compatibility between rubber and asphalt is improved. Under the action of ultrasonic, the MSD and diffusion coefficient of crumb rubber modified asphalt are much higher than other kinds of asphalt, the dipole moment is increased, and the molecular motion range is wider. This indicates that the diffusion ability of crumb rubber modified asphalt is significantly enhanced under the external force of ultrasonic simulation. The molecular bonds of crumb rubber modified asphalt changes greatly, the energy decreases obviously, and the system stability increases. In conclusion, ultrasonic action on crumb rubber modified asphalt preparation is a green and effective way to improve system stability and compatibility.