## 3 Results and Discussion
### Influence of RS Fibers on the Tensile Strength of CPB  
According to Table 5, the peak tensile strengths of CCPB were 0.10-0.23 MPa, 0.12-0.22 MPa, and 0.16-0.26 MPa at 3, 7, and 28 days, respectively. The strength changed after adding RS fibers. When cured for 3 days, the peak tensile strengths of RSCPB were 0.28-0.50 MPa, 0.23-0.58 MPa for 7 days, and 0.11-0.32 MPa for 28 days. The relative errors (\(Re\)) of the tensile strength of RSCPB compared to CCPB were calculated according to Equation (2) [10]. Figure 6: The influences of cement content and solid mass concentration on ITS and \(\varepsilon\). (**a**) Average \(\sigma_{t}\) at different cement contents; (**b**) average \(\sigma_{t}\) at different solid mass concentration; (**c**) average \(\varepsilon\) at different cement contents; (**d**) average \(\varepsilon\) at different solid mass concentration. \[Re_{\sigma}=\frac{\sigma_{t-A}-\sigma_{t-B}}{\sigma_{t-B}}\times 100\% \tag{2}\]  
where \(\sigma_{t-A}\) and \(\sigma_{t-B}\) represent the peak tensile strength of specimens in groups A and B, respectively, and \(Re_{\sigma}\) represents the percentage of increase in the peak tensile strength of specimens in group A relative to group B. It can be seen from Figure 7 that RS fibers can significantly increase the peak tensile strength of CPB in the first 7 days. A higher initial strength is beneficial to shorten the mining cycle of adjacent stopes and improve production efficiency [39; 40]. Due to the differences in preparation formulas and curing ages between group A and B, \(Re_{\sigma}\) varied from \(-38.10\%\) to \(346.15\%\). Depending on the curing age, the increase in ITS of RSCPB ranged from \(115.38\%\) to \(300.00\%\) at 3 days curing age, \(40.91\%\) to \(346.15\%\) at 7 days, and \(-38.10\%\) to \(28.00\%\) at 28 days. The enhancement in the ITS of CPB was evident, although the curing ages were only 3 and 7 days. For the 28-day curing age, the effect of adding RS fibers on the tensile strength of CPB is not significant. The single factor analysis of the ITS of RSCPB was carried out for fiber content and length. Based on the results of the analysis, the effects of different RS fiber contents and lengths on the average ITS of the RSCPB are plotted in Figure 8. Figure 8a shows the average ITS of the RSCPB at different RS fiber addition masses. When the curing age was 3 days, the average ITS of the RSCPB decreased slightly with the increase in RS fiber content, and then increased by 30%. At the curing age of 7 days, the average ITS of the RSCPB first increased by 0.016 MPa and then decreased by 9.2% with the increase in RS fiber content. At 28 days of curing age, the average ITS of the RSCPB continued to increase slightly with the increase in fiber content. Figure 8b shows the effect of RS fiber length on the average ITS of the RSCPB. It can be seen that after being cured for 3 days, the average ITS decreased and then increased with the increase in the RS fiber length, and the tensile strength enhancement effect of the RSCPB with 3-5 cm RS fibers is the best. When the curing ages were 7 days and 28 days, the average ITS was affected by different fiber lengths in the same trend: the tensile strength of the RSCPB first increased and then decreased with increasing fiber length, and the specimens reached the maximum when the fiber length was 1-3 cm. Figure 7: \(Re_{\sigma}\) of RSCPB for 3 days, 7 days, and 28 days curing ages. Figure 8c,d show the effects of RS fibers on \(Re_{\sigma}\). When the curing ages were 3 and 28 days, as the content of RS fibers increased, \(Re_{\sigma}\) continued to increase; however, they gradually decreased at 7 days. Although the \(Re_{\sigma}\) with an RS fiber addition of 3 kg/m\({}^{3}\) was lower than 2 kg/m\({}^{3}\) cured for 3 days, the average tensile strength was still more than 100% higher than 0.173 MPa when no RS fiber was added. \(Re_{\sigma}\) increased first and then decreased with the increase in RS fiber length during the entire curing period.