Effect of Phosphogypsum Whiskers as a Sustainability Modifier on the Performance of Asphalt and Asphalt Mixtures: Insights from an Organic Coating Method

The development of modern chemical technology has raised the production of phosphogypsum (PSP) to a new level, while its inappropriate disposal would have a significant risk to the natural environment as hazardous solid waste. As a by-product of PSP refining, the incorporation of phosphogypsum whiskers (PSW) into hot mix asphalt not only mitigates the negative environmental effects of PSP accumulation but also improves the service performance of the modified asphalt, yielding considerable environmental benefits. To facilitate the use of PSW in asphalt pavements, this study employed four surfactants to apply organic coatings to PSW and investigated the surface modification process of PSW. Additionally, rheological tests under different temperatures and stress conditions were conducted to investigate the effects of PSW with modification on the functional properties of asphalt. These tests include the performance grade test, multiple stress creep recovery test, frequency sweep test, time sweep test, linear amplitude sweep test, and bending beam rheometer test. The test results indicated that the incorporation of modified PSW (MPSW) effectively improved the high temperature performance and rutting resistance, and enhanced the fatigue performance to a certain degree, but it also affected the low temperature performance. Moreover, there were some differences in the modification effects for several surfactants, and the aminopropyltriethoxysilane (KH550) exhibited a superior modification effect on PSW compared to other surfactants, and PSW + 10% KH550 + ultrasonic vibration was suggested as the optimal combination. The Fourier transform infrared spectroscopy (FTIR) test results revealed that only physical modification involved in the MPSW modified asphalt. The pavement performance test results showed that the high temperature performance and moisture stability of MPSW modified asphalt mixtures were improved, while the low temperature performance was attenuated, but it was satisfied with the utilization requirement. This study offers a sustainable method for consuming significant quantities of PSW, thereby promoting the resourceful utilization of solid waste and contributing to the sustainable development of asphalt pavement.