Rheological properties and aging durability of in-situ synthesized SMC-g-TPU modified asphalt

Styrene–maleic anhydride copolymer-grafted thermoplastic polyurethane (SMC-g-TPU) modified binders with various dosages were prepared through an in-situ grafting synthesis approach. The high- and low-temperature performances of the modified asphalts were systematically evaluated using conventional tests, dynamic shear rheometry (DSR), and bending beam rheometry (BBR). In addition, the modification mechanism of SMC-g-TPU was elucidated through Fourier transform infrared spectroscopy (FTIR), fluorescence microscopy (FM), and environmental scanning electron microscopy (ESEM). The results demonstrated that the rigid SMC segments effectively enhanced the thermal stability of the modified asphalt while maintaining the low-temperature toughness imparted by TPU. The incorporation of SMC enhanced the polarity of TPU, thereby improving its compatibility with asphalt and strengthening its self-healing capability. Meanwhile, the resulting grafted structure reduced the high-temperature aging sensitivity of the modified asphalt, although slight increases were observed in its low-temperature aging sensitivity and in the fatigue factor after long-term aging. Notably, when the SMC-g-TPU dosage reached 5 wt%, uniformly dispersed microaggregates formed within the asphalt matrix, providing a microstructural basis for the enhanced functional performance of the modified binder.