## 3 Experimental Analysis of Mountain Sand Paste Filling Material
### Analysis of Performance Testing for Filling Materials  
The filling materials used for sealing the corners in working faces should have reasonable flowability to ensure rapid accumulation in the corners and efficient blockage to prevent air leakage. They also need to exhibit good self-supporting characteristics, short-term solidification, and a certain degree of expansiveness to reach the roof and prevent airflow leakage into the goat. Analyzing the flowability, setting time, and expansiveness of the mountain sand-based paste filling material through slump tests, viscosity tests, and quantitative tests for accelerators and expanders aims to determine the optimal ratio for the filling material applicable to the corners of the 22,122 working face [28; 29; 30]. The typical range of slump for a mine filling system paste is 15 to 25 cm. Pasets with slumps between 16 and 20 cm exhibit good self-supporting properties, but they require specific capabilities from pumping equipment. Considering that the mine uses an HBMD-30/9-45S mine filling pump, capable of handling paste within a slump range of 120 to 200 mm, it is recommended to maintain a slump range of 16 to 20 cm for the filling slurry to ensure the effective pipeline transport of high-concentration pastes. Based on the physicochemical properties of the mountain sand-based paste filling material, various mix ratios (cement: fly ash: mountain sand) and mass concentrations of the mountain sand-based paste were prepared. Slump, slump spread, and viscosity tests were carried out on slurries with different ratios using a slump cone and an SC145 mortar viscometer. The test results, depicted in Figure 4, indicate a decrease in the slump, slump spread, and viscosity values of the mountain sand-based filling slurry with an increase in the mass concentration. Using a slump range of 16 to 20 cm as the standard, the optimal concentration for the 1:2:6 mountain sand ratio is 83%, with a slump of 17.8 cm; for the 1:2:10 ratio, the optimal concentration is 84.5%, with a slump of 18.2 cm; for the 1:4:15 ratio, the optimal concentration is 84%, with a slump of 19.1 cm; and for the 1:4:20 ratio, the optimal concentration is 84.5%, with a slump of 16.3 cm. A series of quantitative tests were carried out on a J85 rapid-setting agent by adding 3%, 6%, and 9% to different proportioned slurries. The initial setting time of the sand-based growth was measured using a Vicat apparatus. The results, presented in Table 2, show that the initial setting time of the slag-based paste filling material fluctuated with the amount of the J85 rapid-setting agent, initially decreasing and then increasing, across different mix ratios and concentrations. The shortest initial setting time occurred when the rapid-setting agent was added at 9%, with a mix ratio of 1:4:15 and a mass concentration of 84% for the mountain sand-based paste filling slurry. Additionally, a quantitative selection test was conducted on the sand-based paste filling material using a UEA-type expansion agent at dosages of 0.25%, 0.5%, 0.75%, and \begin{table}
\begin{tabular}{c c c c c} \hline \hline  & **Cement:Fly** & **Mass Con-** & **Addition** & **Initial Setting** \\
**Ash:Mountain Sand** & **centration/\%** & **Amount of J85/\%** & **Time/min** \\ \hline  & 1:2:6 & 83 & 3 & 145 \\  & 1:2:6 & 83 & 6 & 139 \\  & 1:2:6 & 83 & 9 & 150 \\ \cline{2-5}  & 1:2:10 & 84.5 & 3 & 152 \\ Mountain sand-based filling material & 1:2:10 & 84.5 & 6 & 143 \\ \cline{2-5}  & 1:4:15 & 84 & 3 & 145 \\  & 1:4:15 & 84 & 6 & 144 \\  & 1:4:15 & 84 & 9 & 135 \\ \cline{2-5}  & 1:4:20 & 84.5 & 3 & 162 \\  & 1:4:20 & 84.5 & 6 & 148 \\  & 1:4:20 & 84.5 & 9 & 179 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Quantitative test results of J85 rapid-setting agent. 1%. The expansion rates before and after the test samples were calculated, and the results, presented in Figure 5, show that the maximum expansion rate initially increased and then decreased with the increase in the UEA expansion agent dosage.