Chemical and Physical Effects of Polyurethane-Precursor-based Reactive Modifier on the Low-Temperature Performance of Bitumen

The use of novel polyurethane-precursor-based reactive modifier (PRM) to produce high-performance modified bitumen provides great benefits in terms of both performance improvement and environmental protection. Given the complexity of the chemical composition of bitumen, its chemical interaction with PRM and the modification effect on bitumen performance are of great interest. To fundamentally understand the chemical reactions and low-temperature behaviours of PRM-modified bitumen, physicochemical characterisations and quantum chemical calculations were performed from chemical, thermal, morphological, and mechanical aspects. The results were interpreted based on the reactions between PRM and bitumen model compounds. It shows that the carbamate, urea, and amide linkages are formed by the reactions of PRM with active sites in asphaltenes and resins, which eventually cause crosslinking polymerisation owing to the asphaltene fraction. The modification process promotes the conversion of the resin to asphaltene and reconfiguration of asphaltene, which accordingly increases the facilitation of the natural segregation of maltene and asphaltene. With the strengthening of the reconfiguration and crosslinking of asphaltene molecules, considerably improved stiffness and fracture resistance are observed. However, the concurrent changes in bitumen composition and chemical structures result in a slight increase followed by a decrease in the low-temperature properties with an increase in the PRM concentration. In the presence of excessive PRM, the modified bitumen becomes more susceptible to large deformations. This study not only provides a reference for understanding the PRM modification mechanism but could also serve as a guidance for the further application of PRM-modified bitumen.