Multidimensional insights into recycling fine solid waste into asphalt mastic: interfacial characteristics, microstructural evolution and mechanical properties

The phosphogypsum (PSP) and coal-based synthetic natural gas slag (CNS) had been recognized as one of the solid wastes with huge reserves, and to provide an effective method of treating the two solid wastes, this study investigated the feasibility of using CNS powder (CNP) and phosphogypsum whiskers (PSW) as fillers in asphalt mastic. For this, this study prepared sixteen asphalt mastics by selecting two traditional fillers (limestone and PC42.5 cement) and two solid wastes (CNP and PSW), and then the feasibility of CNP and PSW as substitute fillers in asphalt mastic was verified by multi-scale tests, and its microscopic properties, mechanical properties and asphalt-filler interaction mechanism were analyzed. The results showed that the bee-shaped structure of CNP asphalt mastic (CNAM) and PSW asphalt mastic (PSAM) was significantly less than limestone asphalt mastic (LAM), but their adhesion properties were more excellent. In addition, the interaction of CNP and PSW with asphalt was significantly higher than limestone and PC42.5 cement (PCC), and the mechanical properties of CNAM and PSAM were superior to LAM and PCC asphalt mastic (PCAM) due to their rougher surface morphology and higher particle size, density, and specific surface area. In addition, the strong interaction of CNP and PSW with asphalt was exhibited in the chemical structure of asphalt mastic by the attenuation of the characteristic peak intensity. This study explored an effective option to utilize CNS and PSP as substitute fillers for sustainable asphalt pavements, which could promote the resourceful use of solid waste to a certain degree.