## 3 Results and Discussion
### The Residual Flexural Tensile Strength  
Figure 10 shows the \(f_{R,j}\)-CMOD curves obtained from the three-point flexural test on notched prisms. Firstly, no significant differences can be observed between the concretes in terms of the flexural tensile strength at the peak load (i.e., \(f_{LOP}\)), Table 5. This is in line with previous literature results, pointing to no significant effect of RA on the tensile strength of concrete [32]. Figure 10: \(f_{R,j}\)-CMOD curves of three-point bending tests: 3 kg/m\({}^{3}\) (**up**); 9 kg/m\({}^{3}\) (**below**); each line represents an average of 2 or 3 specimens. However, after cracking, the curves can be divided into two groups: concretes N-3, RF-3, R3-3, and R9-3 in one group, and concretes N-9, RF-9, R3-9, and R9-9 in the other. It can be clearly seen that fiber content has a strong influence on residual tensile strength, regardless of whether virgin or recovered fiber is used, or natural or recycled aggregate. The results of the residual tensile strength tests are given in Table 5. The table provides the average of the three specimens with the coefficient of variation (CoV) in parentheses (in %), except for R9-3 and R9-9, for which the number of specimens was two because of the availability of the R9 aggregate (hence, no CoV is reported). There are five special points in the testing process: \(f_{LOP}\), \(f_{R1}\), \(f_{R2}\), \(f_{R3}\), and \(f_{R4}\). The \(f_{LOP}\) is the flexural tensile strength when the load reaches the cracking load, and \(f_{R1}\), \(f_{R2}\), \(f_{R3}\), and \(f_{R4}\) are the residual flexural tensile strengths corresponding to the CMOD at 0.5, 1.5, 2.5, and 3.5 mm. Figure 11 shows the \(f_{R1}\) and \(f_{R3}\) residual strengths of the parent concrete, PPRAC and Re-PPFRC, respectively. Maintaining the same theoretical fiber content (disregarding fibers embedded in RA), the values are higher when RA is used. This is because these concretes contain not only virgin fibers, but also fibers embedded in the aggregate. As for concretes with RF, they experience a clear loss in strength relative to the parent concrete, which can be attributed to a combination of the reduced average length of RF (see Table 3) and the degradation of their surface (important for anchorage) and mechanical properties. It can also be clearly seen that the concrete with a fiber content of 9 kg/m\({}^{3}\) has a residual strength higher than that of concrete with 3 kg/m\({}^{3}\) of fiber content, both for different aggregates and different types of fibers. For \(f_{R1}\), PPRAC has higher values than Re-PPFRC. At a fiber content of 9 kg/m\({}^{3}\), R9 has the highest value, reaching 3.2 MPa. This is 10.7% higher than for R3 and PC. Likewise, the Re-PPFRC concrete with 9 kg/m\({}^{3}\) of fiber content experienced a decrease in \(f_{R1}\) of 54.0% relative to its companion PC. The results are also similar for a fiber content of 3 kg/m\({}^{3}\). The flexural tensile residual strength of PPFRC is higher than RF and RC, but R3 is the highest at 1.48 MPa, which is 20.3% higher than R9. For \(f_{R3}\), the results are similar to \(f_{R1}\). The Re-PPFRC concretes have the lowest values \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Concrete** & \(f_{LOP}\) & \(f_{R1}\) & \(f_{R2}\) & \(f_{R3}\) & \(f_{R4}\) \\ \hline N-3 & 4.00 (5.1\%) & 0.97 (19.0\%) & 1.06 (24.3\%) & 1.12 (24.4\%) & 1.13 (24.1\%) \\ N-9 & 3.78 (1.6\%) & 2.89 (13.7\%) & 3.54 (16.2\%) & 3.75 (15.0\%) & 3.80 (14.0\%) \\ \hline RF-3 & 3.54 (4.9\%) & 0.53 (34.2\%) & 0.45 (44.5\%) & 0.44 (40.0\%) & 0.43 (35.1\%) \\ RF-9 & 3.15 (3.6\%) & 1.56 (20.5\%) & 1.81 (23.8\%) & 1.87 (23.0\%) & 1.93 (24.4\%) \\ \hline R3-3 & 3.34 (14.0\%) & 1.48 (53.3\%) & 1.62 (53.1\%) & 1.64 (47.3\%) & 1.09 (70.4\%) \\ R3-9 & 3.23 (2.2\%) & 2.89 (11.3\%) & 3.62 (10.3\%) & 3.87 (10.6\%) & 3.79 (10.8\%) \\ R9-3 & 3.36 (–) & 1.18 (–) & 1.29 (–) & 1.31 (–) & 1.28 (–) \\ R9-9 & 3.43 (–) & 3.20 (–) & 3.99 (–) & 4.03 (–) & 3.90 (–) \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Residual flexural tensile strength results.