## 2 Materials and Methods  
### Test Materials  
This section briefly describes the physicochemical properties of materials, mix design, and experimental methodologies. The particle size distributions (Figure 1) and chemical compositions of bentonite, cement, and steel slag were determined using a laser particle size (Mastersizer 2000. The instrument is manufactured in Nanjing, China) and X-ray fluorescence spectroscopy. These data underpin the analysis of mechanical and permeability performance. All tests followed the Standard for Geotechnical Test Methods (GB/T50123-2019) and ASTM specifications to ensure reproducibility and engineering relevance.  
The test was conducted using a yellowish-white powder, which was bentonite produced by Suzhou Jigeao, and the particle size of the material can be seen in Figure 1. According to the soil classification system [17], this bentonite belongs to high-liquidity clay. The chemical composition of bentonite is shown in Table 1, and the basic physical index of bentonite is shown in Table 2.  
The cement used in the test of this paper is 42.5-grade ordinary silicate cement. The chemical composition of the cement was analyzed using X-ray fluorescence spectrometer; the chemical composition is shown in Table 3, and the main performance indexes are shown in Table 4.  
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \begin{tabular}{c} **Chemical** \\ **Components** \\ \end{tabular} & \begin{tabular}{c} **SiO2** \\ **SiO2** \\ \end{tabular} & \begin{tabular}{c} **Al2O3** \\ \end{tabular} & \begin{tabular}{c} **Fe2O3** \\ \end{tabular} & \begin{tabular}{c} **CaO** \\ \end{tabular} & \begin{tabular}{c} **Na2O** \\ \end{tabular} & \begin{tabular}{c} **MgO** \\ \end{tabular} & \begin{tabular}{c} **SO3** \\ \end{tabular} & \
\begin{tabular}{c} **K2O** \\ \end{tabular} &
\begin{tabular}{c} **Other** \\ **Components** \\ \end{tabular} \\ \hline Mass percentage (\%) & 59.76 & 16.13 & 5.55 & 4.92 & 4.73 & 3.99 & 1.93 & 1.45 & 1.54 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Main chemical composition and percentage of bentonite.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
\begin{tabular}{c} **Physical Indicator** \\ \end{tabular} & \multicolumn{3}{c}{**Measurement Results**} \\ \hline Loss on filtration (mL) & \multicolumn{3}{c}{\(\leq\)18} \\ Liquid limit (\%) & \multicolumn{3}{c}{169} \\ Plastic limit (\%) & \multicolumn{3}{c}{20} \\ Plasticity index & \multicolumn{3}{c}{149} \\ Expansion index (mL/2g) & \multicolumn{3}{c}{24} \\ \hline \hline \end{tabular}
\end{table}
Table 2: Basic physical indexes of bentonite.  
Figure 1: Particle size distribution.  
The formula for calculating the alkalinity of steel slag is shown in Equation (1). This equation can be used to calculate the steel slag alkalinity in this study. [PERSON] [18] classified the alkalinity of steel slag, and the relationship between the alkalinity of steel slag and its mineral composition is shown in Table 6. The alkalinity of steel slag can evaluate the activity of steel slag, and greater activity corresponds to higher alkalinity [19]. The alkalinity of the steel slag used in this study is calculated as 1.68, which falls under the dicalcium silicate slag category according to the classification.  
\[\mathrm{P}=\mathrm{CaO}/(\mathrm{SiO}_{2}+\mathrm{P}_{2}\mathrm{O}_{5}) \tag{1}\]