Research on the time-dependent stability of filling paste under the action of different concentrations of chloride salts

In order to study the time-dependent characteristics of filling paste under the action of mine water, chloride salt solutions with mass fraction of 0%, 5%, 10%, and 15% were prepared, and chloride salt dry wet cycle tests with erosion cycles of 4, 8, 12, and 16 times were carried out. The macroscopic and microscopic characteristics of the filling paste were analyzed, the damage curve of the filling paste was obtained based on the constructed compaction-elastoplastic constitutive model, and the stress evolution mechanism of the filling paste under the action of chloride salt was discussed. The results indicate that the mass of filling paste shows a sharp increase, a slow increase, and a slow decrease trend with the increase of chloride erosion cycles. High-concentration chloride salt solution accelerate the quality change of filling paste. As the cycles of chloride erosion increase, the filling paste exhibits a macro-mechanical characterized by high stress-low strain, low stress-high strain, and low stress-low strain. The compaction degree exhibits a dynamic evolution characterized by an initial sharp decrease followed by a stable variation, the plasticity factor demonstrates a developmental trend of initial stability followed by a sharp change. The chloride salt promotes the stable development of the damage process of filling paste and inhibits the surge of damage in the later stage of plasticity. The development curvature of the damage curve after 16 dry-wet cycles in 5% and 10% chloride salt solution is relatively small, and the development curvature of the damage curve after 12 dry-wet cycles in 15% chloride salt solution is relatively small. Chemical corrosion is a significant factor leading to the deterioration of the binding properties of filling paste. The salt corrosion products from chemical corrosion partly originate from the chemical combination of chloride and unreacted tricalcium aluminate(C3A), and another portion arises from the chemical bonding of chloride with the hydration product ettringite(AFt). The coordination deformation between salt corrosion products and internal structure is a key factor causing the alienation of the bearing performance of filling paste. The crystalline expansion force of salt corrosion products resists internal stresses of filling paste, resulting in a reduction in compaction performance and crack propagation ability. This study can provide a theoretical basis for the analysis of the time-dependent stability of filling paste in mine water, and this study is of great significance for maintaining the long-term stability of filling paste.