# Research on Key Parameters and Engineering Experiments of Coal Gangue Slurry Filling Technology
## 3 Research and Development of Millimeter-Grade Gangue Grouting Filling Material
### The Bleeding Performance of Different Gangue Grades and Slurry Concentrations  
Based on the physical significance of the concrete bleeding rate, the bleeding rate of the gangue slurry was used to characterize the water retention properties of different gangue grades and slurry concentrations. Then, a reasonable range of the slurry concentration was determined. The bleeding rate of gangue slurry refers to the ratio of water secreted from the gangue slurry to the total amount of water in the gangue slurry. The formula for calculating the bleeding rate of the slurry is as follows:  
\[B_{m}=\frac{m_{m}}{m_{0}+m_{1}\omega} \tag{1}\]  
In the above formula, \(B_{m}\) is the bleeding rate of the gangue slurry, %; \(m_{m}\) is the total amount of bleeding in the slurry, g; \(m_{0}\) is the total amount of water added during the preparation of the slurry, g; \(m_{1}\) is the amount of gangue added during the preparation of the slurry, g; and \(\omega\) is the moisture content in the gangue, %. The upper limits of the gangue particle size controlled in this experiment were \(-\)5 mm, \(-\)3 mm, \(-\)2.5 mm, \(-\)1.25 mm, and \(-\)0.63 mm, respectively. The slurry concentrations were set to 60%, 65%, 70%, 75%, and 80%, respectively. A total of 25 sets of experiments were conducted, and the moisture content of the gangue under different gradations was measured before the experiment. The overall plan of this investigation was to keep the total amount of 200 g of gangue unchanged and to prepare 60%, 65%, 70%, 75%, and 80% gangue slurries by controlling the different water amounts in sequence. Then, the gangue slurry was allowed to stand still, and the water released from the surface of the gangue slurry was sucked out using a rubber-tipped dropper at different times. After 90 min, the mass of accumulated water released was calculated [26; 27; 28]. Finally, the bleeding rate of the gangue slurry was calculated according to Formula (1), and the data were processed, as shown in Table 2 and Figure 3. \begin{table}
\begin{tabular}{c c} \hline
**Particle Size** & **Proportion** \\ \hline \(>\)5.0 mm & 5.25\% \\
3.0–5.0 mm & 10.03\% \\
2.5–3.0 mm & 8.95\% \\
1.25–2.5 mm & 13.35\% \\
630 \(\upmu\)m–1.25 mm & 12.95\% \\
315–630 \(\upmu\)m & 10.70\% \\ \(<\)315 \(\upmu\)m & 38.77\% \\ \hline \end{tabular}
\end{table} 
Table 1: Particle size distribution of original gangue samples after crushing. \begin{table}
\begin{tabular}{c c c c c c} \hline
**Upper Limit of Particle Size** & **60\%** & **65\%** & **70\%** & **75\%** & **80\%** \\
**Mass Fraction** & & & & & \\ \hline
5.00 mm & 33.76\% & 29.71\% & 4.93\% & 2.25\% & 0\% \\
3.00 mm & 23.26\% & 13.93\% & 2.92\% & 1.50\% & 0\% \\
2.50 mm & 13.50\% & 6.50\% & 1.75\% & 0\% & 0\% \\
1.25 mm & 2.50\% & 1.10\% & 0.20\% & 0\% & 0\% \\
0.63 mm & 0\% & 0\% & 0\% & 0\% & 0\% \\ \hline \end{tabular}
\end{table} 
Table 2: Bleeding rate of gangue slurry with different concentrations and particle size gradations. Figure 3 shows three main aspects: (1) As the upper limit of the gangue particle size increased, the bleeding rate of the gangue slurry showed an upward trend. As the concentration of the gangue slurry increased, the bleeding rate of gangue slurry showed a downward trend, that is, the gangue particle size was inversely proportional to the water retention performance of the slurry, and the slurry concentration was directly proportional to the water retention performance of the slurry. (2) Based on the standard that the bleeding rate of qualified paste is between 1.5% and 5.0% [29], a reasonable gangue particle size grading and an appropriate gangue slurry concentration were a variable interval, and the gangue particle size grading and gangue slurry concentration interacted with each other. (3) From the perspective of the variable interval, there was a corresponding  
Figure 3: Bleeding experiment of different gangue slurry gradations and concentrations. relationship between a reasonable gangue particle size grading and an appropriate slurry concentration.