## 3 Results and Discussion
### Analysis of Mechanical Properties  
In order to further explore the C-S-H/SiO\({}_{2}\) system of mechanical properties subject to the interfacial water content, uniaxial tensile simulation experiments were conducted along the direction of the \(Z\) axis in this study. In Figure 8, the C-S-H/SiO\({}_{2}\) system stress-strain relation curves obtained for varying water-layer thicknesses are plotted, while the variation in the tensile strength \(\sigma_{\rm c}\) and the residual strength \(\sigma_{\rm r}\) are discussed. The C-S-H/SiO\({}_{2}\) systems stress-strain curves with different water-layer thicknesses were all divided into two stages: the elasticity (OA) stage and the failure (AB) stage (Figure 8a). During the OA stage, the stress values of all C-S-H/SiO\({}_{2}\) systems gradually increased and reached a peak value, as the strain increased. During the AB stage, the stress dropped sharply as the tensile strain increased, and then gradually flattened out.  
Figure 8b demonstrates that as the interfacial water layer thickened, the C-S-H/SiO\({}_{2}\) system tensile strength \(\sigma_{\rm c}\) showed a downward trend, indicating that the water molecules presented a weakening effect on the bonding performance. Whilst 1 A-thick interfacial water molecules were introduced, the decrease in tensile strength \(\sigma_{\rm c}\) was smaller, and the strength value decreased from 1.31 GPa to 1.18 GPa. As the water-layer thickness increased to 3 A and 5 A, the tensile strength \(\sigma_{\rm c}\) decreased significantly, and the strength values decreased to 0.92 GPa and 0.68 GPa, respectively. Visible lower water content had a limited impact on the interfacial bonding strength, while the weakening effect enhanced with the increase in the interfacial water content. This result is consi  
Figure 6: (**a**) Interaction energy of C-S-H/SiO\({}_{2}\); (**b**) energy ratio (ER).  
Figure 7: Schematic diagram of interfacial connection (**a**) 0 Å water; (**b**) 1 Å water.  
from the interaction energy (as shown in Figure 6). The simulation results are similar to the mechanisms by which water molecules weaken the adhesive performance of the asphalt-quartz [36], and the effect of the ITZ thickness and strain rate on the mechanical properties of C-S-H/SiO\({}_{2}\) systems [37].  
However, the tensile strength obtained from the MD simulations is much greater than the experimental results. [PERSON] et al. [38] examined the mechanical properties of the interface between cobblestone aggregate and mortar, and found that the tensile strength of the interface was 1.8 MPa. [PERSON] et al. [39] obtained a tensile strength of 1.75 MPa for the cement-aggregate interface, after a hydration time of 90 days. This large difference was attributed to the time and space constraints of the MD simulations [40]. Furthermore, the actual influencing factors, such as porosity, were not considered in this simulation.  
The residual strength \(\sigma_{\mathrm{r}}\) exhibits of the material tended to decrease in the case of increasing water-layer thickness (Figure 8b). During the event of a low water content, the C-S-H/SiO\({}_{2}\) system exhibited an excellent interfacial bonding performance, and the structure showed good resistance to loading, even after the structure was damaged. As the interfacial water content grew, the interfacial bonding performance of the system was weakened, causing a further reduction in the material residual strength \(\sigma_{\mathrm{r}}\), with the strength value decreasing from 0.37 GPa to 0.18 GPa. The simulation results are similar to the mechanisms by which water molecules weaken the adhesive performance of the C-S-H-graphene-oxide [41] and asphalt-aggregate [42] interfaces. Moreover, this phenomenon was verified in the concrete interfacial bond strength experiments by [PERSON] et al. [43].