## 3 Results and Discussion
### Statistical Analysis  
In order to highlight the impact of environmental conditions (A--temperature and B--solution type) on the mechanical properties, the Pareto charts' and main effect plots' graphical representations are used.  
The Pareto charts presented in Figure 12 indicate that the environmental conditions (temperature and solution type) have a marked effect on the mechanical properties of the GFR pipe, with temperature being the more significant factor in influencing the tensile strength, modulus, and Poisson's ratio. The solution type also impacts the strength and modulus, but it seems to have little effect on the Poisson's ratio. The findings from [2; 28] also demonstrate that the temperature has a pronounced effect on both the compressive and tensile strength of GFRP material.  
Figure 12: _Cont._The main effects plots from Figure 13a show that there is a clear decrease in the tensile strength as the temperature increases from 20 \({}^{\circ}\)C to 50 \({}^{\circ}\)C. The reduction is quite significant, indicating that elevated temperatures weaken the material considerably. The tensile strength decreases significantly in alkaline and saltwater environments compared to air, but the reduction is less pronounced than that caused by the temperature. Like the tensile strength, the tensile modulus decreases notably with an increase in the temperature from 20 \({}^{\circ}\)C to 50 \({}^{\circ}\)C, indicating that the stiffness of the GFRP pipe decreases at higher temperatures. Alkaline solutions also negatively affect the modulus but to a lesser extent. Regarding the Poisson's ratio, it can be observed from Figure 13c that it also decreases with an increase in the temperature, indicating that the material becomes less ductile as the temperature rises. The Poisson's ratio is lowest in alkaline solutions, showing a distinct V-shaped trend.  
Figure 12: Pareto charts for the following: (**a**) tensile strength; (**b**) tensile modulus; (**c**) Poisson’s ratio (factors: A—temperature \({}^{\circ}\)C, B—solution type).  
Figure 13: _Cont._  
The interaction plots (Figure 14) demonstrate how the temperature and solution type together affect the mechanical properties of GFRP pipes under aggressive environments. For the tensile strength (UTS), at the reference condition (20 \({}^{\circ}\)C and air), the material has its highest strength. However, as the temperature rises to 50 \({}^{\circ}\)C, the tensile strength decreases across all solution types, with the most severe reduction occurring in saltwater. This suggests that exposure to higher temperatures significantly weakens the material, and the aggressive nature of saltwater exacerbates this effect. While the alkaline solution also reduces the tensile strength, its impact is less severe compared to saltwater at elevated temperatures. A similar pattern is observed for the tensile modulus (E). As the temperature increases to 50 \({}^{\circ}\)C, the tensile modulus drops noticeably, especially in the alkaline solution, which has the most detrimental impact. For the Poisson's ratio, it can also be seen that, as the temperature rises to 50 \({}^{\circ}\)C, the Poisson's ratio decreases in both the air and alkaline solutions, with alkaline conditions showing the most pronounced drop, indicating a loss of ductility.  
Figure 13: Main effect plots for the following: (**a**) tensile strength; (**b**) tensile modulus; (**c**) Poisson’s ratio.