Swelling and chemical degradation of sulfur-bearing fillers in high-speed railway subgrade: Effect of pH on ion release and material deterioration

The deformation and degradation of sulfur-bearing fillers are critical factors affecting the long-term performance of high-speed railway subgrade materials. This study investigates the swelling and chemical degradation behavior of sulfur-bearing fillers under different pH environments (acidic pH = 2.03, neutral pH = 6.97, and alkaline pH = 11.95). Advanced analytical methods, including Scanning Electron Microscopy (SEM), X-Ray Diffraction (XRD), and Ion Chromatography (IC), were utilized to explore the structural and chemical changes in these materials. Results demonstrate that alkaline conditions significantly accelerate degradation, characterized by a higher rate of SO₄²⁻ release and an increase in porosity to 25.65 %, compared to 12.87 % in acidic conditions. The degradation process comprises three distinct stages: rapid initial degradation, intermediate deceleration, and final stabilization. Under alkaline conditions, the formation of white precipitates and increased fissures were observed, indicating severe structural deterioration. Conversely, acidic environments exhibit an inhibitory effect on filler degradation, characterized by reduced ion release rates and lower total ion concentrations. These findings enhance the understanding of the degradation mechanism of sulfur-bearing fillers and provide a basis for improving subgrade material selection and durability design in high-speed railway projects.