## 3 Results and Discussion
### Mechanical Characterization of Specimens
#### 3.1.3 Saltwater (SW)  
Tensile strength values are reported in Figure 13a for UN-FREI and UR-FREI specimens exposed to saltwater for 500% and 7% strains, respectively. In the first days of immersion, the UN-FREI specimens exhibited a decrease in tensile strength of 0.92% (day 5), followed by an increase of 22.82% due to the drying process (day 12). However, with further immersion in saltwater, the strength gain was reduced to 7.09% (day 16). This suggests that the drying process increases stiffness at 500% deformation, likely due to the test temperature, whereas immersion in saltwater decreases tensile strength as the material becomes more flexible due to water absorption.  
In contrast, the UR-FREI specimens displayed the opposite behavior. Initial immersion led to an increase in tensile strength of 48.56% (day 5), followed by a decrease of 3.69% after drying (day 12), and finally, with re-immersion, the strength gain was reduced to 12.93% (day 16). Overall, repeated cycles of saltwater immersion and drying could increase the material's tensile strength over time, but its deformation capacity would be reduced [58].  
Figure 13b shows the compressive stress required to achieve 70% deformation in the UN-FREI and UR-FREI specimens. Contrary to the compressive values observed in specimens exposed to RH, the UR-FREI specimens exhibited higher strength than the UN-FREI specimens. The UN-FREI specimens exposed to saltwater experienced a strength loss of 34.38%, 41.56%, and 41.05% at 5, 12, and 16 days of testing, respectively. However, the strength values of UR-FREI followed an increasing trend, transitioning from a loss of 14.23% at day 5 to a gain of 8.39% at day 16.  
Regarding residual compression (Figure 13c), exposure to saltwater increased the deformation of both the UN-FREI and the UR-FREI specimens, reaching a CB of 34% and 46% at the end of the exposure period, respectively.  
The cyclic shear test was conducted with a period of 9 s due to the capacity limitations of the laboratory machine used. With increased saltwater exposure, the shear modulus increased by 12.84% in UN-FREI and 3.62% in UR-FREI at 16 days of exposure (Figure 14a).  
Figure 12: UV radiation results for the cyclic shear test: (**a**) shear modulus (G), and (**b**) damping ratio (\(\beta\)).  
Regarding the damping ratio, it is evident that increasing the test period decreased the damping ratio of both materials compared to the tests conducted under RH and UV radiation exposure, which were performed with a period of 5 s. At 30% strain, the difference  
Figure 14: Saltwater exposure results for the cyclic shear test: (**a**) shear modulus (G), and (**b**) damping ratio (\(\beta\)).  
Figure 13: Saltwater exposure results for: (**a**) tension, (**b**) monotonic compression, and (**c**) residual compression (CB) tests.  
in damping between the reference samples tested at 5 and 9 s was 21%. FEMA 450 [54] specifies a maximum difference of 15% in properties to demonstrate the independence of rubber behavior from the test period. Therefore, under the conditions of this study, the observed difference is slightly higher.  
This behavior is similar to that reported by [PERSON] et al. [1], who concluded that as the test period increased, the damping ratio decreased by up to a maximum of 8%. With increased exposure to saltwater, the damping ratio decreased by 25.77% in UN-FREI and 11.57% in UR-FREI (Figure 14b) compared to the reference value.