Multiscale damage evolution and chemo-mechanical constitutive modeling of acid-corroded sandstone

This study investigated time-dependent chemo-mechanical deterioration of fine-grained sandstone exposed to dilute sulfuric acid representing the proton-sulfate component of acid mine drainage. Specimens were corroded for 0-20 days and examined by X-ray diffraction, scanning electron microscopy, endpoint solution chemistry, and triaxial compression at 20, 30, and 40 MPa. Results showed cumulative carbonate dissolution, cement degradation, microstructural deterioration, and mechanical weakening. After 20 days, Ca²⁺ and Mg²⁺ concentrations reached 156 and 25.3 mg/L, while peak strength decreased by 33.3%, 26.6%, and 29.9%, respectively. A nested Mohr-Coulomb comparison yielded F(4,5) = 1.284 and p = 0.388, supporting downward envelope translation but not statistically detectable slope variation. A time-dependent damage model reproduced pre-peak responses across all 15 conditions, with R ² = 0.767-0.961. The framework links mineral alteration and microstructural damage to mechanical degradation but requires further validation for multicomponent field acid mine drainage and long-term engineering service.