## 3 Results
### Effect of the Mechanical Properties of PET Fiber  
Since the PET fiber in the concrete matrix acts as a bridge to improve the consistency of the concrete mass, the mechanical properties of these fibers have an essential influence on the compressive strength of PFRC. Therefore, the effect of the mechanical properties of PET fiber in terms of tensile strength (f\({}_{\rm f}\)) and modulus of elasticity (E) on the compressive strength of PFRC is discussed. The generalization results are depicted in Figure 7. According to the initial dataset and based on Figure 2h,g, the tensile strength and modulus of elasticity of PET fiber are determined to be in the range of [100, 550] and [200, 12,000], respectively. As can be seen from the results, the PET fiber shapes have an important impact on the compressive strength of PFRC. For fiber with a string shape, the most essential parameter is the PET fiber modulus of elasticity (E), as in a higher E, the compressive strength has its maximum values. This trend is not in accordance with the other fiber shapes, as in other fiber shapes, the maximum compressive strength occurs in higher tensile strengths of PET fibers. This can be attributed to the fact that the string shape fiber has a lower bond strength and the fiber pull out during the loading before they reach  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Water (kg/m\({}^{3}\))** & **Binder (kg/m\({}^{3}\))** & **Fine Aggregate (kg/m\({}^{3}\))** & **Coarse Aggregate (kg/m\({}^{3}\))** \\ \hline
150 & 500 & 900 & 750 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Assumed mix design for generalization analysis.  
maximum tensile strength. However, the lower tensile strength of fiber results in a lower compressive strength in all fiber shapes. For shapes of fiber with higher bond strengths, the tensile strength of PET fibers plays an important role by bridging the concrete mass and limiting crack formation and propagation [56; 57; 58]. Therefore, according to the results of the ANN model for unseen data, it is strongly recommended to deform the shape of PET fiber into some patterns to enhance its bond strength.  
In addition, the higher compressive strength of PFRC is related to PET fibers with deformed shapes. Furthermore, the concrete made with this type of fiber has a wider region of high strength, meaning that the maximum compressive strength occurs for a higher number of specimens. Moreover, the variation of the compressive strength is independent of the modulus of elasticity, which indicates that this type of fiber is cut during loading due to the applied tensile strength. The same experimental results were obtained by [PERSON] et al. [44], showing the slipping of PET fibers with string shapes from the concrete matrix and the suitable bond strength of deformed PET shapes. It can be concluded that the most effective PET fiber shape is deformed, followed by embossed and irregular. This is in accordance with the experimental research of [PERSON] et al. [42], [PERSON] et al. [59], and [PERSON] [60]. Furthermore, the deformed PET fiber shape improves the shrinkage behavior of PFRC by limiting micro-c  
Figure 6: The variation of the 28-day compressive strength for different PET fiber content, aspect ratios, and fiber shapes. (**a**) String shape, (**b**) Irregular shape, (**c**) Deformed shape, and (**d**) Embossed Shape.