Preparation and Performance Characterization of Phosphogypsum Whisker Composite Modified Asphalt Binder

Solid waste recycling and reuse have attracted great interest as environmentally friendly modifiers for asphalt pavements in recent years, and phosphogypsum whiskers (PSWs) synthesized by phosphogypsum (PSP) wastes were used as the main modifying material to develop an environmentally friendly asphalt binder in this study. PSWs could significantly enhance the deformation resistance and fatigue performance of asphalt binder but were prone to cracking at low temperature. To alleviate this problem, the novel idea of developing a PSW composite modified asphalt binder was proposed in this study. The organic coating method was used to surface modify PSWs by using surfactants and ultrasonic vibrator to enhance the compatibility of PSWs with asphalt binder. Then a composite modifier containing modified PSW (MPSW) was developed by the uniform design method (UDM), and the preparation process of the modifier was investigated by response surface method (RSM) on this basis. The physical performance of modified asphalt binder was investigated by conventional performance tests; the high-temperature performance, rutting resistance, and fatigue performance were investigated by several rheological tests; and the low-temperature performance was evaluated by the force ductility test (FDT). The microstructure and modification mechanism were characterized by the Fourier transform infrared spectroscopy (FTIR) test and differential scanning calorimetry (DSC) test. The results showed that the self-developed modifier (MPGJ-I) could effectively reduce the negative effects of MPSW on conventional physical properties, and it exhibited a significant aging resistance compared with other commonly used modifiers. In addition, the modified asphalt binder showed a significant enhancement in high-temperature performance, rutting resistance, and fatigue performance. The MPGJ-I not only solved the adverse effect of MPSW on low-temperature performance, but also enhanced the low-temperature performance to a certain degree. The MPGJ-I was only physically mixed with asphalt binder and did not change its chemical structure. The MPGJ-I reduced the influence of MPSW on glass transition temperature (Tg) and improved the thermodynamic properties of asphalt binder at low temperatures. The comparison study revealed that the MPGJ-I could comprehensively enhance the service performance of virgin asphalt binder, and the recommended dosage of MPGJ-I was 6%.