Properties enhancement of asphalt mortar incorporating phosphogypsum based on surface activation

To broaden the utilization of Phosphogypsum (PG), this paper involves the deployment of a silane coupling agent (SCA) to enhance the surface reactivity of PG, thereby evaluating its potential to serve as a viable alternative to traditional limestone filler within asphalt mortar compositions. Through dynamic shear rheological test , it observed a significant increase in the complex modulus of asphalt mortar containing activated PG, ranging from 25.2 % to 41.7 %, coupled with a decrease in irrecoverable compliance by 46.8–51.4 % compared to traditional asphalt mortar. Thermal analysis via thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) indicated that activated PG asphalt mortar possesses the highest thermal decomposition temperature and the lowest total heat absorption, suggesting enhanced compatibility with asphalt. Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDX) confirmed that SCA treatment induces dehydration condensation reactions with the hydroxyl groups on the PG surface, forming new Si-O-Si chemical bonds and altering the surface acidity. Molecular simulations revealed that activated PG forms the thickest interfacial transition zone with asphalt, measuring 9.82 Å, which is a 546 % increase over untreated PG. These results underscore the potential of activated PG as an environmentally friendly alternative to conventional limestone filler in asphalt mixtures , offering a promising solution for waste utilization and improved asphalt pavement performance.