## 3 Results and Discussion
### Influence of RS Fibers on the Tensile Peak Strain of CPB  
According to Table 5, the peak strain of group A ranged from 0.86% to 4.56% after curing for 3 days, and 3.74-5.87% and 1.38-3.67% after curing for 7 and 28 days, respectively. The peak strains of CCPB (group B) were 2.38-4.64%, 2.15-5.91%, and 2.67-5.82% when the curing ages were 3, 7, and 28 days, respectively. The relative errors of tensile peak strains of RSCPB compared with the CCPB are shown in Figure 9. In this section, the same method as that used for the calculation of \(Re_{\sigma}\) was used to calculate \(Re_{\varepsilon}\). The \(Re_{\varepsilon}\) of the different specimens varied from \(-76.88\%\) to 120.93%. According to the different curing ages, \(Re_{\varepsilon}\) varied from \(-76.88\%\) to 16.03% on the 3 rd day, from \(-36.72\%\) to 120.93% on the 7 th day, and from \(-70.67\%\) to 12.73% on the 28 th day. The results showed that the RS fibers did not significantly enhance the tensile peak strain of the CPB. Moreover, most of the data showed a decrease in peak strain.  
To investigate the effects of RS fiber length and content, the average peak strains of the RSCPB at different contents and lengths are plotted in Figure 10. Figure 10a shows the effect of the added content of RS fibers on the peak strain of the RSCPB, which indicated that the peak strain had the same changing rule under the influence of different fiber lengths when the curing ages were 3 days and 28 days. With the increase in RS fiber content, the average \(\varepsilon\) of the RSCPB decreased and then increased. The peak strain reached the maximum value when the fiber content was 1 kg/m\({}^{3}\), and the peak strains on the 3 rd day and 28 th day were 3.300% and 2.583%, respectively. At 7 days of curing age, the peak strain decreased continuously with the increase in fiber content. The maximum \(\varepsilon\) was 4.840% at a fiber content of 1 kg/m\({}^{3}\).  
Figure 10b shows the effect of RS fiber length on the peak tensile strain of the RSCPB. It can be seen that when the curing age is 3 days and 28 days, the peak strain trend is similar. As the fiber length increased, the peak strain of the RSCPB increased initially and decreased afterwards. The peak strain reached the maximum at fiber lengths of 1-3 cm, and the peak strain at 3 and 28 days of curing was 3.023% and 3.007%, respectively. At 7 days of curing age, the peak strain increased by 14.22% continuously with the increase in fiber length. The maximum peak strain was 4.764% when the fiber length was 3-5 cm. According to the analysis of the above data, the tensile peak strain trend of RSCPB with the addition of RS fibers is opposite to the trend with the fiber length.  
The data in Figure 10c,d show that \(Re_{\varepsilon}\) shows a \"V\" shape as the RS fiber content changes from 1 to 3 kg/m\({}^{3}\) on the 3 rd day and 28 th day, however, ultimately it is less than 0%. On the 7 th day, \(Re_{\varepsilon}\) keeps decreasing close to 0%. As the length of the RS fibers increases, \(Re_{\varepsilon}\) has an inverted \"V\" shape similar to the \(Re_{\sigma}\) with fiber length. With the addition of RS fibers, only a few RSCPB specimens increased in \(\varepsilon\) compared with CCPB. In terms of improving the strain of RSCPB, the RS fibers addition amount of 1 kg/m\({}^{3}\) and the length of 1-3 cm are the best values.  
Figure 9: \(Re_{\varepsilon}\) of RSCPB for 3 days, 7 days, and 28 days curing ages.