Research on rheological properties and modification mechanism of waterborne polyurethane modified bitumen

Polyurethane (PU) based materials are emerging as asphalt modifiers due to their unique molecular structure, but the production of commonly used PU prepolymers and PU elastomers might pose environmental and safety risks. In this work, environment-friendly waterborne polyurethane (WPU) additives were prepared and employed to modify bitumen. The properties of the WPU additive were characterized first. Then, the storage stability, workability, and rheological properties of the modified bitumen containing different dosages of WPU additives were investigated. The modification mechanism of the WPU on virgin bitumen was also analyzed. The Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC) experimental results indicate that WPU with two glass transition temperatures (Tg) without toxic terminal groups was successfully prepared. Additionally, the excellent storage stability and workability of the WPU modified bitumen can be observed with the dosages of WPU additives no more than 9 wt%. Dynamic shear rheometer results show that WPU additives enhanced the deformation resistance of bitumen in high-temperature environments. The improvement of the anti-cracking ability of WPU modified bitumen at low-temperature environments was also verified by the bending beam rheometer experiment. However, the fatigue resistance of bitumen was slightly weakened by WPU. FTIR analyses for modified bitumen prove that the incorporation of WPU additives didn't change the chemical structure of virgin bitumen. The enhanced high-temperature and low-temperature performance of the WPU modified bitumen can be attributed to the two-phase structure of the WPU molecular chain. Overall, the eco-friendly bitumen additive applied in this study has excellent application value and broad market prospects.