## 3 Results and Discussion  
### Stress-Strain Curve  
Figure 6 displays the stress-strain curve of HBPRGC. Notably, when the matrix strength is constant, the overall shape of the stress-strain curve undergoes significant changes with the addition of BF and PF. At a 0.1% fibre volume content, the addition of fibres minimally impacts the initial elastic deformation stage preceding the peak stress but markedly enhances the rate of stress reduction after the peak stress is reached, which indicates that it improves the ductile deformation of coal-gangue concrete. Comparatively, when either BF or PF is added individually, although the difference in strain corresponding to the HBPRGC compressive strength is marginal, BF exhibits a greater influence on the strength of coal-gangue concrete than PF. After reaching the same postpeak strain, coal-gangue concrete mixed with BF shows slightly lower strength than its PF-mixed counterpart, implying that PF enhances the ductility deformation slightly more than BF. The combination of BF and PF has the most pronounced effect on coal-gangue concrete ductility deformation among the tested specimens. At a 0.2% hybrid-fibre volume content, during the front elastic deformation stage of the peak stress, the slope of the stress-strain curve decreases, and the ductile deformation of gangue concrete increases significantly. However, excessive hybrid-fibre volume can lead to reduced fibre-dispersion uniformity in the coal-gangue concrete matrix, resulting in the stacking, gathering, and introduction of air bubbles during mixing, thereby increasing the internal defects in the coal-gangue concrete and reducing deformation resistance. As matrix strength increases in HBPRGC, the influence of fibres on the initial elastic deformation stage of the stress-strain curve diminishes as the matrix strength increases. In contrast, for the reference group of coal-gangue concrete, a higher matrix strength leads to higher stress-reduction rates and more pronounced brittle failure characteristics after reaching the peak stress on the stress-strain curve. Notably, the addition of fibres  
Figure 6: Stress–strain curves of the compression test. (**a**) C20; (**b**) C30. \begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Mixture**} & **BF/** & **PF/** & **Cement/** & **Water/** & **Slag/** & **Silica** & **Fly Ash/** & **Sand/** & **Coarse Ag-** & **Water** \\  & **(kg/m3)** & **(kg/m3)** & **(kg/m3)** & **(kg/m3)** & **(kg/m3)** & **Fume/** & **(kg/m3)** & **(kg/m3)** & **(kg/m3)** & **gege/** & **Reducer/** \\ \hline \multirow{4}{*}{C30 Group} & 0C-30 & / & / & 234.2 & 161 & 36.6 & 22 & 73.2 & 583.0 & 1162.9 & 3.66 \\  & BC-30-0.1 & 2.56 & / & 234.2 & 161 & 36.6 & 22 & 73.2 & 583.0 & 1162.9 & 3.66 \\  & PC-30-0.1 & / & 0.910 & 234.2 & 161 & 36.6 & 22 & 73.2 & 583.0 & 1162.9 & 3.66 \\  & HBPRGC-30-0.1 & 1.28 & 0.455 & 234.2 & 161 & 36.6 & 22 & 73.2 & 583.0 & 1162.9 & 3.66 \\  & HBPRGC-30-0.2 & 2.56 & 0.910 & 234.2 & 161 & 36.6 & 22 & 73.2 & 583.0 & 1162.9 & 3.66 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: _Cont._significantly mitigates the impacts of matrix strength on the brittle failure characteristics of coal-gangue concrete, underscoring the benefits of BF and PF in enhancing the ductile deformation of coal-gangue concrete. Figure 7a illustrates variations in the compressive strength of HBPRGC with the fibre volume content, type, and matrix strength. Notably, for coal-gangue concrete with differing matrix strengths, the influences of fibre type and volume content on compressive strength are consistent. At a 0.1% fibre volume content, the compressive strengths of BC-20-0.1 and BC-30-0.1 increase by 14.12% and 4.78%, respectively, relative to the base group coal-gangue concrete. Additionally, PC-30-0.1 and PC-30-0.1 exhibit respective increases of 1.68% and 1.25% in compressive strength. Similarly, HBPRGC-20-0.1 and HBPRGC-30-0.1 demonstrate increases of 4.92% and 2.00% in compressive strength.