# Impact Analysis and Optimization of Key Material Parameters of Embedded Water-Stop in Tunnels
## 3 Optimization of the Bonding between the Water-Stop and Concrete
### Test Method  
The experimental equipment used was a tensile testing machine (0-5000 N), with specific fixtures to fix the specimens. The fixation of rubber-cement tensile and shear specimens is shown in Figure 19. Due to the rectangular shape of the rubber-cement specimens and the brittleness of the bonding interface, the selected tensile speed was 5 mm/min. The maximum stress sustained during the process of bonding failure caused by external forces was taken as the tensile or shear strength. The average strength of three specimens in each group was taken as the measured result.  
Figure 17: Cement casting.  
Figure 18: Casted rubber-cement coated specimens.  
The tensile bond strength test results of the rubber-cement specimens are shown in Table 4 (the symbol \"/\" indicates that the cement block broke during the tensile process, and no specific value was measured). From the table, it can be seen that the tensile bond strength measured for conditions 1, 2, 5, 6, 7, 9, and 10 are all greater than 0.9 MPa, while the bond strength for the remaining conditions is less than 0.8 MPa and greater than 0.6 MPa. This indicates that the epoxy-quartz sand coating can indeed enhance the tensile bond strength between rubber and concrete. The degree of enhancement is relatively small concerning the thickness of the epoxy resin layer but more significant concerning the particle size of the quartz sand. When the thickness of the epoxy resin layer is 2 mm, the tensile bond strength is larger, and when the particle size of the quartz sand is larger (such as 40-80 mesh, 80-120 mesh), the tensile bond strength is smaller. Among them, the tensile bond strength of condition 6 is the largest.  
The shear bond strength test results of the rubber-cement specimens are shown in Table 5. It can be observed from the tables that the shear bond strength measured for conditions 1, 2, 5, 6, 7, 9, and 10 are all greater than 0.3 MPa, while the remaining conditions have bond strengths less than 0.3 MPa and greater than 0.2 MPa. This indicates that the epoxy-quartz sand coating can also enhance the shear bond strength. When the quartz sand particle size is larger, the bond strength is smaller, and when the epoxy resin layer thickness is 2 mm, the bond strength is larger. Among them, the shear bond strength of condition 6 is the largest.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Working Condition** & **Test 1/MPa** & **Test 2/MPa** & **Test 3/MPa** & **Tensile Bond Strength/MPa** \\ \hline
1 & 1.160 & 1.089 & / & 1.125 \\
2 & 1.140 & 1.067 & 0.976 & 1.061 \\
3 & 0.571 & 0.643 & 0.740 & 0.651 \\
4 & 0.654 & 0.638 & 0.584 & 0.625 \\
5 & 0.947 & 0.863 & / & 0.919 \\
6 & 1.157 & 1.260 & 1.227 & 1.215 \\
7 & 1.050 & 1.128 & 1.212 & 1.130 \\
8 & 0.502 & 0.693 & 0.678 & 0.624 \\
9 & 1.120 & 0.989 & 1.243 & 1.117 \\
10 & 0.876 & / & 0.958 & 0.917 \\
11 & 0.715 & 0.806 & 0.763 & 0.761 \\
12 & 0.505 & 0.602 & 0.689 & 0.600 \\ \hline \hline \end{tabular}
\end{table}
Table 4: Tensile bond strength of cement-rubber coated specimens.  
Figure 19: Schematic diagram of specimen fixation. (**a**) tensile specimen. (**b**) shear specimen.  
In summary, the epoxy-quartz sand coating on the surface of the water-stop can enhance the bonding strength between the water-stop and the concrete. There is a certain relationship between the thickness of the epoxy resin layer, the particle size of the quartz sand, and the enhancement of the bonding strength. When the thickness of the epoxy layer is 2 mm, and the particle size of the quartz sand is 26-40 mesh, the bonding strength is the greatest.