## 2 Study on Physical Properties of Materials
### Experimental Analysis on Physical Properties of Coal Ganguue  
(1) To examine the influence of coal gauge reactivity on the structure and performance of cement-based materials, an acid-alkali leaching method was employed using a 1.25 mol/L NaOH solution to dissolve the coal ganguue aggregates. The experimental results are presented in Table 4.  
As indicated by the data in Table 4, the concentrations of leached Si\({}^{4+}\) and Al\({}^{3+}\) ions in coal ganguue aggregates are relatively low, with the levels of active ion dissolution substantially below those required for cementitious reactivity. Therefore, in this study, the pozzolanic activity of coal ganguue is not considered, and is investigated solely as a concrete aggregate. (2) Quantitative analytical methods were employed to examine the differences between coal ganguue and natural aggregates, and to quantify the percentage content of individual \begin{table}
\begin{tabular}{c c c} \hline \hline
**Style** & \
\begin{tabular}{c} **Dissolution of Si\({}^{4+}\)** \\ **(mg/L)** \\ \end{tabular} &
\begin{tabular}{c} **Dissolution of Al\({}^{3+}\)** \\ **(mg/L)** \\ \end{tabular} \\ \hline coal ganguue aggregate & 0.933 & 2.574 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Elution concentrations of Si\({}^{4+}\) and Al\({}^{3+}\) in 1.25 mol/L NaOH solution from coal ganguue. \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline
**Chemical Composition** & **SiO\({}_{2}\)** & **Al\({}_{2}\)O\({}_{3}\)** & **Fe\({}_{2}\)O\({}_{3}\)** & **CaO** & **K\({}_{2}\)O** & **TiO\({}_{2}\)** & **MgO** & **Na\({}_{2}\)O** & **SO\({}_{3}\)** & **P\({}_{2}\)O\({}_{5}\)** \\ \hline W/\% & 54.91 & 30.19 & 4.11 & 4.06 & 2.08 & 1.37 & 0.91 & 0.88 & 0.77 & 0.72 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Chemical composition and content of fly ash. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Main Ingredients** & **SiO\({}_{2}\)** & **CaCO\({}_{3}\)** & **Fe\({}_{2}\)O\({}_{3}\)** & **CaSO\({}_{4}\)** & **Clay** \\ \hline content & 82.1\% & 6.8\% & 3\% & 2.3\% & 5.8\% \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Content of medium sand composition components. Figure 2: Fly ash samples and fly ash diffraction patterns. (**a**) Fly ash samples. (**b**) Diffraction pattern of fly ash. chemical components within the aggregates. An XRD-7000 diffractometer was utilized, and the corresponding experimental results are presented in Table 5.  
Among the coal gangue produced in Liangshuijing coal mine, SiO\({}_{2}\) and Al\({}_{2}\)O\({}_{3}\) are the main chemical components, accounting for up to 73.45%. The content of this component in coal gangue produced in North China mining area is generally high, mainly concentrated in the range of 65-85%, which is highly consistent with the coal gangue in this study. The content of this component in coal gangue produced in Shendong mining area is also generally above 70%. Therefore, the coal gangue produced in Liangshuijing coal mine can well characterize Shendong mining area and North China mining area. In contrast, these two constituents comprise only 6.66% of natural crushed stone. The dominant chemical constituent of natural crushed stone is calcium oxide (CaO), comprising 64.23%, whereas in coal gangue, calcium oxide accounts for only 2.34%. This compositional disparity is primarily attributed to the contrasting geological environments and formation processes of coal gangue and natural crushed stone. (3) The physical properties of coal gangue and natural crushed stone were evaluated, including particle size distribution, crushing index, apparent density, bulk density, needle- and flake-shaped particle content, and water absorption rate. Representative samples of coal gangue aggregate and natural crushed stone are depicted in Figure 3, while the corresponding test results are presented in Table 6.  
Figure 4 is the classification of coal gangue aggregate and natural gravel aggregate according to different particle sizes.