Zihao Hu, Qianwei Ma, Huaming Lu, Xiangrui Xu, Guohui Zhao, Ningjun Jiang
This study presents a comprehensive investigation into the high-dosage utilization of phosphogypsum (PG) in conjunction with multiple industrial solid wastes, including fly ash, ground granulated blast furnace slag, and calcium carbide residue, to formulate fully waste-based subgrade fillers. The primary objective of this study is to promote the large-scale utilization of PG and facilitate its extensive application in road engineering. The research provides a thorough evaluation of the physical and mechanical properties, subgrade performance, microstructural mechanisms, and environmental safety of PG-based subgrade fillers. A novel method is proposed for preparing high-dosage PG-based subgrade fillers by synergistically integrating other industrial solid wastes to create a fully waste-derived cementitious material. The optimal mix proportions are determined to be P90S10 and P90S20, which denote that PG constitutes 90% of the stabilized PG, and soil accounts for 10% and 20% of the overall composition, respectively. After 28 d of curing, the unconfined compressive strength (UCS) reaches 1.94 MPa, the California bearing ratio (CBR) exceeds 80%, and the CBR swell rate is less than 1%. The microstructural evolution and reaction mechanisms were analyzed through X-ray diffraction (XRD), thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and 1 H low-field nuclear magnetic resonance (NMR). Toxicity and radioactivity tests confirmed that heavy metal and radioactive levels in PG-based subgrade fillers were consistent with established standards, thereby guaranteeing environmental compliance. This research delineates a technical pathway for large-scale PG utilization, supporting waste valorization and eco-friendly subgrade materials. The results highlight the potential of synergistically utilizing multiple industrial wastes and guide sustainable geotechnical engineering.