## 2 Materials and Methods  
### Materials and Preparation of Specimens  
The CG used in this experiment was sourced from Xuzhuang Coal Mine in Xuzhou City, Jiangsu Province, China (Figure 1). X-ray diffractograms of coal gangue aggregate (CGA) were obtained with a Bruker AXS D8 Advance instrument with Cu anode (40 kV, 40 mA) (Billerica, MA, USA). Samples were step-scanned at a rate of 2\({}^{\circ}\)/min, with 2\(\theta\) in the range 5-70\({}^{\circ}\), with a step size and 2s/step count time. The results, shown in Figure 2, revealing that the primary mineral components are kaolinite, quartz, and feldspar, consistent with previous studies. The chemical composition of CGA was determined using X-ray fluorescence spectroscopy (XRF, AXIOSmAX, Panalytical B.V., Alemelo, The Netherlands). The results, presented in Table 1, reveal that the primary constituents of CGA are SiO\({}_{2}\) and Al\({}_{2}\)O\({}_{3}\), accounting for 62.113% and 28.169%, respectively. The preparation of the CGCMs also involved the use of 42.5 ordinary Portland cement (PC), fine silica fume, polycarbonate superplasticizer (SP), and potable water. Table 2 provides the chemical composition and physical characteristics of both the PC and silica fume. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline
**Material Type** & **SiO\({}_{2}\)** & **Al\({}_{2}\)O\({}_{3}\)** & **Fe\({}_{2}\)O\({}_{3}\)** & **K\({}_{2}\)O** & **CaO** & **TiO\({}_{2}\)** & **MgO** & **Na\({}_{2}\)O** \\ \hline CGA & 62.113 & 28.169 & 3.508 & 2.231 & 1.224 & 0.981 & 0.667 & 0.400 \\ \hline Material Type & SO\({}_{3}\) & Others & & & & & & \\ \hline CGA & 0.379 & 0.328 & & & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: The chemical composition of CGA. Figure 1: The crushed CGA. Figure 2: XRD result sheet for CGA. Fillers used to improve conductivity in cement-based composites include carbon fibers (CFs), steel fibers (SFs), and carbon black (CB). Among these, CB is a powder filler, whereas CFs and SFs serve as flexible and rigid fiber fillers, respectively. CFs have a length of 12 mm, a diameter of 7 \(\upmu\)m, 95% carbon content, 1.53% elongation, a tensile strength of 3500 MPa, an elastic modulus of 230 GPa, and a density of 1.75 g/cm\({}^{3}\). SFs, on the other hand, have a diameter of 200 \(\upmu\)m, a length of 6 mm, a tensile strength of 2060 MPa, and an elastic modulus of 200 GPa. For CB, the surface area is 254 m\({}^{2}\)/g, the average particle size is 30 nm, and the density is 0.0961 g/cm\({}^{3}\). The CF content in this study matched that used by [PERSON] and [PERSON] (2016), while the SF and CB content was based on the findings of [PERSON] et al. (2017) and [PERSON] et al. (2018), respectively, both of which reported satisfactory mechanical performance. The names and proportions of the CGCM mixtures are listed in Table 3, with each mixture named according to the specific functional additive it contained. The water-to-binder ratio was maintained at 0.4, and workability was enhanced using polycarboxylic acid SP (Feike Ltd., Yuncheng, China) at a dosage of 0.25%. The mass ratio of CFs to PC was set at 0.08, while the volume percentages of SFs and CB were 2% and 9%, respectively, and these proportions were converted to mass ratios in Table 3. Additionally, a control CGCM mixture without any functional fillers was also prepared for comparison. A 60 L mixer was used to prepare the CGCM specimens. First, 30% of the total water and the SP were added and allowed to sit for 20 min to ensure complete dissolution. The functional filler was then manually incorporated. Next, the remaining water and silica fume were added, and the mixer operated at a slow speed for about 1 min. Finally, PC and CGA were added, and mixing continued for an additional 2 min. Cubic specimens measuring 100 mm \(\times\) 100 mm \(\times\) 100 mm were then cast, with nine specimens produced for each mix. After 24 h, the specimens were demolded and placed in a moist-curing room for curing durations of 7, 14, and 28 days, respectively.