## 3 Results and Discussion
### Mechanical Characterization of Small-Scale Prototypes  
#### 3.2.1 Shear Compression Test  
The shear compression test was conducted on small-scale prototypes under two exposure conditions available at Pankow Materials Laboratories: (i) a 20% CO\({}_{2}\) environment for 10 days, followed by an 85% RH environment for another 7 days. In each case, three prototypes of each material were tested. The nomenclature used was CO\({}_{2}\) for the first phase and CO\({}_{2}\)+RH for the combined exposure. And (ii) a constant 85% RH environment. Three prototypes of each material were tested at 14 and 31 days. The nomenclature used was RH-14d and RH-31d, respectively. The loading protocol (Figure 6a) was also applied to reference prototypes, designated as REF. Figure 15 summarizes the results obtained for damping as a function of horizontal displacement and exposure type. For UR-FREI, the damping and stiffness values were limited to 50% deformation due to the lack of flexibility of the prototypes beyond that level.  
In general, the damping of UN-FREI decreased as the shear strain increased up to 67%, but then increased when reaching 100% and 75% strain in both exposure conditions (Figure 15a,b). Regarding the effect of the environmental conditions evaluated, the greatest deviation from the reference value was observed with CO\({}_{2}\) exposure, resulting in a damping loss of 3.43% and 3.63% at 67% and 75% deformation, respectively. In contrast, the combination of CO\({}_{2}\)+RH resulted in less than a 1% difference from the reference value (Figure 15a).  
Figure 15: Damping (\(\beta\)) vs. shear deformation (\(\gamma\)): (**a**) CO\({}_{2}\)+RH UN-FREI, (**b**) constant RH UN-FREI, (**c**) CO\({}_{2}\)+RH UR-FREI, and (**d**) constant RH UR-FREI.  
Exposure to constant RH led to an increase in damping at almost all strain levels in UN-FREI, with the greatest gain occurring after 31 days of exposure. At 67% and 75% strain, damping increased by 2.12% and 2.60%, respectively (Figure 15b).  
Contrary to the behavior of UN-FREI, the damping value of UR-FREI increased with increasing strain levels in all evaluated cases. However, exposure to CO\({}_{2}\) and CO\({}_{2}\)+RH led to a reduction in damping at 50% strain, with values 3.80% and 5.99% lower than the reference value, respectively (Figure 15c).  
Exposure to constant RH initially caused a decrease in damping of 8.96% at 14 days, followed by an increase of 12.12% at 31 days at 50% strain. Although both materials exhibited higher damping at 31 days of constant RH exposure, a difference was observed at 14 days: while damping increased in UN-FREI, it decreased in UR-FREI (Figure 15d).  
Figure 16 presents the results for horizontal stiffness as a function of horizontal displacement and each type of exposure.  
The horizontal stiffness of UN-FREI decreased as the shear strain increased in both exposure conditions (Figure 16a,b). Among the evaluated environmental conditions, all resulted in an increase in stiffness compared to the reference value, except for RH at 14 days, which caused a slight stiffness reduction of 0.42% at 100% strain (Figure 16b). The greatest increase occurred after 31 days of RH exposure, with gains of 10.60% and 7.22% at 100% and 75% strain, respectively.  
Similar to UN-FREI, the horizontal stiffness of UR-FREI also decreased as the strain level increased. However, in contrast to the reference value, stiffness decreased under all  
Figure 16: Horizontal stiffness (kh) vs. shear deformation (\(\gamma\)): (**a**) CO\({}_{2}\)+RH UN-FREI, (**b**) constant RH UN-FREI, (**c**) CO\({}_{2}\)+RH UR-FREI, and (**d**) constant RH UR-FREI.  
evaluated environmental conditions, except for the CO\({}_{2}\)+RH combination, which led to a slight increase of 0.50% at 25% strain (Figure 16c). Exposure to RH for 14 days resulted in a stiffness reduction of 8.40% and 8.49% at 25% and 50% strain, respectively.