Performance and modification mechanism investigation of polyurethane prepolymer system modified bitumen for 100 % reclaimed asphalt pavement (RAP) application

The recycling and reusing of reclaimed asphalt pavement (RAP) are generally restricted by the limited integration of RAP and the insufficient service life of recycled products. This research incorporated the polyurethane prepolymer (PUP) system into bitumen, creating an innovative bonding material to develop a fully reclaimed asphalt pavement (FRAP) mixture including 100 % RAP. The performance and modification mechanism of the PUP system modified bitumen (PUPB) binder, PUPB-RAP interface, and PUPB/FRAP mixture were systematically investigated. The permanent non-deformability of PUPB was effectively enhanced due to the formation of carbamide and amide, whereas the soft segment increment contributes to a slight improvement in low-temperature cracking resistance. Compared to the neat bitumen-RAP interface, the PUPB-RAP interface possessed greater adhesion and cohesion properties based on the free-surface energy measurement. The PUPB/FRAP mixture demonstrated its application prospect in regions with heavy vehicle loads, low temperatures, or dramatic seasonal variations, especially for damaged upper surface courses. The efficient utilization of RAP with the addition of a small amount of PUPB creates significant new opportunities for sustainable development and environmental footprint reduction associated with road construction and maintenance.