Preparation of calcium sulphate whiskers from phosphogypsum for asphalt modification: rheological properties and microscopic mechanisms

This study aimed to explore the efficient utilisation of phosphogypsum and the improvement of asphalt performance by producing and organically modifying anhydrous calcium sulphate whiskers (CSW). The 'dissolution-recrystallisation' method was employed to derive CSW from phosphogypsum, followed by treatment with a silane coupling agent, KH-550, for improved compatibility with asphalt. Indoor experiments were conducted to investigate the microscopic characteristics of anhydrous CSW and organically modified CSW (MCSW), as well as the storage stability, rheological properties, and microscopic mechanisms of asphalt modified with MCSW. The results demonstrated that anhydrous CSW produced from phosphogypsum formed a silane coupling film on the surface after organic treatment, effectively improving their compatibility with asphalt. The optimal dosage when used as an asphalt additive was determined to be 8%. Furthermore, the use of MCSW in asphalt significantly enhanced high-temperature performance while slightly decreasing low-temperature performance. Under 3.2 kPa, compared to virgin asphalt, the R of 8% MCSW-modified asphalt increased by 495.12%, and the Jnr decreased by 98.69%. When MCSW was used for asphalt modification, physical blending was the primary mechanism, allowing for the absorption of light components in the asphalt and inducing swelling, thereby enhancing the asphalt's resistance to permanent deformation.