# Research and Application of Foam Filling Material in Soft Rock Roadways
## 4 Foam Filling Material Performance Index Test
### Material Swellability and Foam Loss Percentage Test  
If the selected filling material decreases in volume after solidification, this may cause the filling material to detach from the surface of the filling bag, leading to the formation of unfilled spaces. Therefore, to ensure the effective sealing of the filling bag, the filling material must have volume swellability capability.  
The formula for calculating the swellability percentage of foaming material slurry is given in Equation (2).  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Water–Solid Ratio** & \begin{tabular}{c} **Foam** \\ **Content/\%(C)** \\ \end{tabular} & \
\begin{tabular}{c} **Initial Setting** \\ **Time/min** \\ \end{tabular} &
\begin{tabular}{c} **Final Setting** \\ **Time/min** \\ \end{tabular} \\ \hline \hline
1:1 & 1.5 & 6 & 14 \\  & 2 & 7 & 15 \\
1:1 & 2.5 & 8 & 18 \\  & 3 & 9 & 18 \\  & 3.5 & 9 & 19 \\ \hline
1.5:1 & 1.5 & 10 & 16 \\  & 2 & 10 & 18 \\  & 2.5 & 11 & 20 \\  & 3 & 11 & 22 \\ \hline
2:1 & 1.5 & 12 & 19 \\  & 2 & 12 & 20 \\
2:1 & 2.5 & 14 & 22 \\  & 3 & 16 & 24 \\  & 3.5 & 16 & 25 \\ \hline
2.5:1 & 1.5 & 28 & 32 \\  & 2 & 29 & 34 \\
2.5:1 & 2.5 & 31 & 37 \\  & 3 & 32 & 40 \\  & 3.5 & 33 & 40 \\ \hline
3:1 & 1.5 & 37 & 53 \\  & 2 & 38 & 55 \\
3:1 & 2.5 & 42 & 57 \\  & 3 & 44 & 58 \\  & 3.5 & 47 & 60 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Test results of material slurry setting time.  
\[V_{s}=\frac{V_{2}-V_{1}}{V_{1}} \tag{2}\]  
where \(V_{s}\) is the volume swellability percentage of the material; \(V_{1}\) is the initial slurry volume; and \(V_{2}\) is the volume after mixing and solidifying with foam.  
The formula for calculating the foam loss percentage is provided in Equation (3).  
\[\eta=\frac{V_{\text{f}}+V_{1}-V_{2}}{V_{\text{f}}} \tag{3}\]  
where \(\eta\) is the foam loss percentage of high-water and high-foaming material, and \(V_{f}\) is the volume of added foam.  
Based on the cement ratio, water-solid ratio, foam content, and fly ash content, 25 sets of orthogonal experiments were designed and carried out to evaluate the swellability percentage of the material slurry. According to the results shown in Figure 10, it can be observed that the swellability percentage of the foaming material increases with the foaming content, while the growth rate of the swellability percentage gradually decreases. When the content of the foaming agent reaches 3.5%, the slope of the curve approaches 0. This is due to excessive foam content, which makes the foam more likely to break. Therefore, considering all factors, it is advisable for the foaming content to not exceed 3%.  
The test results of the foam loss percentage of material slurry are shown in Figure 11. When the water-solid ratio is 1.0:1 and 1.5:1, the foam loss percentages are between 80 and 90% and 70 and 80%, indicating relatively high foam loss. This can be attributed to the lower moisture content, which leads to a higher particle concentration in the slurry. The increased \"extrusion\" between particles makes it more likely for the foam to break.  
Figure 11: Test results of foam loss percentage of material slurry.  
Figure 10: Test results of material slurry expansivity.  
From the tests, it can be seen that at the water-solid ratios of 2.0:1, 2.5:1, and 3.0:1, when the foaming agent content is 1.5%, the foam loss percentages are 40%, 78.6%, and 89%. These percentages are significantly lower compared to those at a water-solid ratio greater than 1.5:1. This analysis indicates that as the water content in the slurry increases, the concentration of particles decreases, reducing the impact of \"extrusion\" and allowing the foam to be better preserved. Additionally, when the water-solid ratio is between 2.5:1 and 3.0:1, the foam loss percentages remain below 44%.