Investigation on bitumen-epoxy interface in cold mixed epoxy bitumen using experimental observation and molecular dynamics simulation

Abstract Cold-mixed epoxy bitumen (CEB) has gained much importance due to the demand for high-performance materials in pavement construction. In addition to the curing process of epoxy bitumen, which has been comprehensively investigated, the bitumen-epoxy interface also critically influences the mechanical properties of CEBs. Therefore, this study explored the bitumen-epoxy interface based on experiments and molecular dynamic simulation. In the experiment part, the Fourier Transform Infrared Spectroscopy (FTIR) was adopted to characterize the chemical reaction that occurred in the epoxy bitumen. Besides, this study used the fluorescent microscope (FM) to experimentally observe the morphological evolution of CEBs as the curing proceeded. Concerning the molecular dynamic simulation, four simplified epoxy models with varying characteristics and their related bitumen-epoxy interface models were considered in the simulation. The results indicated that the curing process would increase the average molecular weight and the molecular polarity. Experimental observation of the bitumen-epoxy interface revealed that the formation of the bitumen-epoxy interface included two primary processes, which were the coarse-grained process and particle expansion process. Simulation results showed that the bonding between bitumen and epoxy was composed of van der Waals force and hydrogen force. Besides, the interphase distance was positively correlated with average molecular weight and reaction degree.