Evolution of a Filling Paste Cementitious System and Impact Patterns of Sulfate Mine Water Erosion on Filling Paste Performance

To assess the impact of sulfate mine water on filling material performance, an accelerated sulfate erosion process was used to analyze the effects of various erosion concentrations, aging periods, and cation types on the macroscopic properties of the filling paste. These properties encompassed apparent phenomena, mass changes, and alterations in the uniaxial compressive strength. Observations revealed sulfate erosion, causing the formation of white substances and salt crystals on specimen surfaces. Initially, all solution-eroded specimens exhibited increased mass and strength. Over time, specimens in 5 and 10% MgSO4 solutions displayed the first signs of decline, while variations in other solutions were relatively small. Increasing the erosion concentration led to greater variations in mass and strength during the initial erosion phase. Specimens in 5 and 10% MgSO4 solutions initially peaked in mass and compressive strength, followed by a decline, while other filling paste specimens continued slow increases. Under equivalent conditions, the MgSO4 solution exhibited stronger erosion than the Na2SO4 solution. Composite erosion by Na2SO4 and MgSO4 involved initial strengthening and gel pore filling, intermediate expansion and crystallization, and late-stage substantial degradation, with MgSO4 exhibiting a more pronounced and complex impact. Gray relational analysis ranked factors affecting mass and uniaxial compressive strength variations as erosion concentration > erosion ion type > erosion aging period. Correlation degrees for factors influencing mass variations were 0.8822, 0.8714, and 0.4754, while for factors influencing uniaxial compressive strength variations, the correlation degrees were 0.8336, 0.7943, and 0.6125, respectively.