# Effect Mechanism of Material Ratio on Ultrasonic P-wave Velocity in Coal Based Paste Fill Materials
## 2 Experimental Procedures
### Characteristics of Experimental Raw Materials
#### 2.1.2 Characteristics of High-Water Materials  
Two constituents form the high-water materials referenced in sources [37; 38; 39]: material A and material B. Comprising sulfoaluminate cement clinker, a suspending agent, and a super retarder, material A is the primary composition. Conversely, material B is mainly constructed of plaster and lime, along with a suspending agent and a rapid-setting hardening accelerator. Their unique behavior upon mixing with water distinguishes these materials. Individual mixing of either material A or B with water yields a slurry that remains unset. Nonetheless, a rapid solidification occurs when these components are merged. This unique solidification property is crucial for coal based paste fill materials. The introduction of  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Apparent Density/kg m\({}^{-3}\)** & **Moisture Content/\%** & **Unidirectional Compressive Strength/MPa** & **Unidirectional Tensile Strength/MPa** & **Modulus of Elasticity/GPa** & **Poisson’s Ratio** & **Cohesive Force/MPa** & **Angle of Internal Friction/\({}^{e}\)** \\ \hline
1296.37 & 7.19 & 20.13 & 1.39 & 2.88 & 0.33 & 4.31 & 37.00 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Orthogonal test factor table (designed by mass scale).  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Group** & **Uniaxial Compressive Strength/MPa** & **Uniaxial Tensile Strength/MPa** & **Elastic Modulus/GPa** & **Poisson’s Ratio** & **Cohesive Force/MPa** & **Internal Friction Angle/\({}^{\circ}\)** \\ \hline
1 & 23.79 & 1.58 & 3.09 & 0.34 & & \\
2 & 24.27 & 1.41 & 2.97 & 0.29 & & \\
3 & 17.35 & 1.77 & 2.58 & 0.37 & & \\
4 & 16.46 & 1.31 & - & - & & \\
5 & 18.79 & 0.89 & - & - & & \\ Average & 20.13 & 1.39 & 2.88 & 0.33 & & \\ \hline \hline \end{tabular}
\end{table}
Table 2: Physical properties of coal samples.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Carbon** & **Hydrogen** & **Nitrogen** & **Sulfur** & **Oxygen** & **Moisture** & **Ash** \\ \hline
80.03 & 3.01 & 1.36 & 1.12 & 6.17 & 3.30 & 5.01 \\ \hline \hline \end{tabular}
\end{table}
Table 4: Relative contents of various main minerals in coal samples (mass fraction) %.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Group** & **Apparent Density/kg m\({}^{-3}\)** & **Moisture Content/\%** \\ \hline
1 & 1297.85 & 7.23 \\
2 & 1301.59 & 6.76 \\
3 & 1289.68 & 7.57 \\ Average & 1296.37 & 7.19 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Mechanical properties of coal samples.  
sulfoaluminate into these materials accelerates the solidification, imparting a measure of strength to the resultant cementitious substances. This expedited solidification is vital for the enhancement of the coal based paste fill materials' efficiency and stability. The primary chemical constituents of the high-water material are listed in Tables 5 and 6.  
As shown in Figures 2 and 3, the blue line in the figures are the results of the first particle size scanning results, the red lines and green lines are the second and third respectively, and the particle size of high-water materials is mainly between 1 and 100. Specifically, the particle size mostly falls within the range of 10 to 100, constituting the major proportion of the overall distribution. It is observed that there exists a relatively clear centralized trend, indicating that this range accommodates the majority of particle sizes. The density of the fill can be effectively enhanced by smaller particle sizes, leading to a reduction in particle voids and thereby improving the material's uniformity and stability.