Laboratory Investigation of PPG-TDI Polyurethane–Modified Asphalt Binders and Mixtures

Considering the defects of insufficient low-temperature flexibility and high cost of epoxy asphalt binder, low-cost polypropylene glycol (PPG) and toluene diisocyanate (TDI) were used to synthesize two polyurethane (PU) prepolymers (PTPU) with different isocyanate group (─ NCO) contents, and the properties of PTPU-modified asphalt binders and mixtures were studied. First, the mixing parameters of the PTPU-modified asphalt binders were determined through tests, and its storage stability, high- and low-temperature creep characteristics were studied. Then the microscopic modification mechanism of PTPU-modified asphalt binders was explored. Finally, the PTPU-modified asphalt binders were used to prepare mixtures, and the application performance in bridge deck pavement was evaluated. The results showed that PTPU-modified asphalt binder has satisfactory storage stability and high- and low-temperature performance. Chemical reactions occur during the modification process which change the micromorphology of the asphalt binder, and its high-and low-temperature performance and the adhesion to the aggregates are improved. The increase of -NCO content improves the high-temperature stability and mechanical strength of the PTPU-modified asphalt binder but reduces the flexibility. Hence, the ─ NCO content in PTPU can be adjusted according to actual needs during application. The PTPU-modified asphalt mixture has a good comprehensive performance, its low-temperature anticracking performance is improved greatly compared with that of epoxy asphalt mixture, and the lower price gives it good promotion and application prospects in engineering applications.