# Mechanical Behavior of Carbon Fiber-Reinforced Concrete Structures After Structural Failure
## 3 Results y Analysis
A compressive strength increase of 464% was achieved in concretes without polypropylene fibers (SA-5-U600) and 393% in concretes with polypropylene fibers (PP-4-U600). \begin{table}
\begin{tabular}{l l c c c c c c c c} \hline  & **Specimens** & \(\sigma_{\text{max}}\) & **(\%)** & \(\sigma_{\text{ult}}\) & **(\%)** & \(\varepsilon_{\text{max}}\) & **(\%)** & \(\varepsilon_{\text{ult}}\) & **(\%)** \\ \hline \multirow{4}{*}{Type I} & PP-3-U 300 & 46.45 \(\pm\) 0.26 & 229 & 46.45 \(\pm\) 0.26 & 992 & 0.009 \(\pm\) 0.014 & 120 & 0.009 \(\pm\) 0.014 & 120 \\  & PP-1-U 600 & 52.86 \(\pm\) 1.57 & 211 & 52.86 \(\pm\) 1.57 & 937 & 0.016 \(\pm\) 0.028 & 187 & 0.016 \(\pm\) 0.028 & 187 \\  & PP-1-BI 230 & 29.98 \(\pm\) 0.59 & 31 & 29.98 \(\pm\) 0.59 & 328 & 0.006 \(\pm\) 0.017 & 27 & 0.006 \(\pm\) 0.017 & 27 \\  & PP-1-BI 360 & 28.28 \(\pm\) 0.7 & 34 & 28.28 \(\pm\) 0.7 & 345 & 0.005 \(\pm\) 0.018 & \(-\)13 & 0.005 \(\pm\) 0.018 & \(-\)13 \\ \hline \multirow{4}{*}{Type II} & PP-4-U 300 & 45.15 \(\pm\) 0.68 & 214 & 45.15 \(\pm\) 0.68 & 942 & 0.010 \(\pm\) 0.027 & 103 & 0.010 \(\pm\) 0.027 & 103 \\  & PP-4-U 600 & 64.24 \(\pm\) 0.66 & 393 & 64.24 \(\pm\) 0.66 & 1539 & 0.018 \(\pm\) 0.035 & 270 & 0.018 \(\pm\) 0.035 & 270 \\  & PP-6-BI 230 & 29.95 \(\pm\) 0.22 & 125 & 29.95 \(\pm\) 0.22 & 645 & 0.006 \(\pm\) 0.001 & 51 & 0.006 \(\pm\) 0.001 & 51 \\  & PP-4-BI 360 & 35.88 \(\pm\) 0.61 & 160 & 35.88 \(\pm\) 0.61 & 762 & 0.008 \(\pm\) 0.017 & 86 & 0.008 \(\pm\) 0.017 & 86 \\ \hline \end{tabular}
\end{table} 
Table 4: Test results of specimens reinforced with the addition of polypropylene fibers. Figure 5: _Cont._  
Figure 6 shows the maximum stresses reached in concretes with and without polypropylene fibers for each type of reinforcement. For bidirectional reinforcements, the behavior is similar regardless of whether the concrete contains polypropylene fibers or not. In the case of unidirectional reinforcements, the best stress performance is observed in concretes without polypropylene fibers, except for the U-300 reinforcement in Type I concretes. Table 5 shows the percentage variation in stresses and strains among the different reinforced specimens, depending on whether or not they contain polypropylene fibers. As can be observed, the addition of fibers does not generally improve performance in terms  
Figure 5: Maximum compressive stresses. (**a**) Type I specimens; (**b**) Type II specimens. Figure 6: Maximum compressive stress in concretes with and without polypropylene fibers and different types of reinforcement. of stress. However, an improvement is evident in the increase in maximum and ultimate strains when the concrete contains polypropylene fibers, which enhances ductility. Figure 7 shows the maximum stresses achieved in concretes with and without polypropylene fibers as a function of the type of reinforcement. As can be observed, the highest strengths were achieved with unidirectional U-600 reinforcements in concretes with strengths below 15 N/mm\({}^{2}\), reaching strength increases of over 450% [36]. Reinforcements with unidirectional U-300 fabrics also achieved significant strength increases on the order of 220%. Although lower than those achieved by the fabric with a higher weight, reinforcing concrete with the unidirectional fabric of 600 g/m\({}^{2}\) results in a 22% increase in strength compared to the 300 g/m\({}^{2}\) fabric in Type I reference concretes and a 52% increase in Type II reference concretes. In concretes with polypropylene fibers, the increase in fabric weight leads to a 13% increase in strength in Type I concretes and a 42% increase in Type II concretes. The bidirectional fabrics studied achieved much smaller strength increases compared to the unidirectional fabrics. In the case of the BI-230 reinforcement, the strength increase was similar across all specimens, regardless of their initial strength or whether the concrete contained polypropylene fibers. For the BI-360 reinforcement, the behavior was similar to the previous case, but better performance was observed in Type II concretes.