# Experimental Study of Interfacial Bond Properties between CGM and Existing Concrete
## 3 Results and Discussion
### Interfacial Bond Strength Analysis
#### 3.2.4 Influence of Shear Angle  
The comparison of the interfacial bond strengths of the specimens in the Z-C35-I, X-C35-30-W, and X-C35-45-W groups showed that when the shear key was not set, the interfacial bond strength of the slant shear specimen was greatly improved compared with that of the direct shear specimens; the larger the slant shear angle, the more the interface bond strength was improved. Compared with the direct shear specimen at a shear angle of 0\({}^{\circ}\), the interfacial bond strength increased by 409.73% when the shear angle was 30\({}^{\circ}\) and increased by 642.48% when the shear angle was 45\({}^{\circ}\). The presence of and the increase in pressure significantly improved the interfacial bond strength. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Group No.** & **Specimen No.** & \(\tau_{\text{max}}\)/**MPa** & **Discreteness /\%** & \(\tau_{\text{max}}\)/**MPa** \\ \hline \multirow{4}{*}{Z-C35-I} & Sample 1 & 1.09 & 4.39 & \multirow{4}{*}{1.13} \\  & Sample 2 & 1.16 & 1.75 & 1.13 \\ \cline{1-1}  & Sample 3 & 1.14 & & \\ \cline{1-1}  & Sample 1 & 2.89 & 0.00\% & \\ \cline{1-1}  & Sample 2 & 2.89 & & 2.90 \\ \cline{1-1}  & Sample 3 & 2.93 & 1.38\% & \\ \cline{1-1}  & Sample 1 & 3.17 & 0.00\% & \\ \cline{1-1}  & Sample 2 & 3.17 & & 3.15 \\ \cline{1-1}  & Sample 3 & 3.11 & 1.89\% & \\ \cline{1-1}  & Sample 1 & 3.36 & 5.08\% & \\ \cline{1-1}  & Sample 2 & 3.54 & & 3.50 \\ \cline{1-1}  & Sample 3 & 3.59 & 1.41\% & \\ \cline{1-1}  & Sample 1 & 3.59 & 5.28\% & \\ \cline{1-1}  & Sample 2 & 3.81 & 0.53\% & 3.73 \\ \cline{1-1}  & Sample 3 & 3.79 & & \\ \cline{1-1}  & Sample 1 & 5.79 & & \\ \cline{1-1} X-C35-30-W & Sample 2 & 5.94 & 2.59\% & 5.76 \\ \cline{1-1}  & Sample 3 & 5.56 & 3.97\% & \\ \cline{1-1}  & Sample 1 & 8.80 & 6.38\% & \\ \cline{1-1} X-C35-30-Y & Sample 2 & 9.40 & & 9.24 \\ \cline{1-1}  & Sample 3 & 9.52 & 1.28\% & \\ \cline{1-1}  & Sample 1 & 8.27 & 1.43\% & \\ \cline{1-1} X-C35-45-W & Sample 2 & 8.51 & 1.67\% & 8.39 \\ \cline{1-1}  & Sample 3 & 8.39 & & \\ \cline{1-1}  & Sample 1 & 10.62 & 6.76\% & \\ \cline{1-1} X-C35-45-Y & Sample 2 & 11.39 & & 11.52 \\ \cline{1-1}  & Sample 3 & 12.55 & 10.18\% & \\ \cline{1-1}  & Sample 1 & 14.30 & 1.31\% & \\ \cline{1-1} X-C45-45-Y & Sample 2 & 14.49 & & 14.47 \\ \cline{1-1}  & Sample 3 & 14.62 & 0.90\% & \\ \cline{1-1}  & Sample 1 & 14.65 & 5.61\% & \\ \cline{1-1} X-C55-45-Y & Sample 2 & 16.45 & 5.99\% & 15.54 \\ \cline{1-1}  & Sample 3 & 15.52 & & \\ \hline \hline \end{tabular} Note: The column “discreteness” in the table shows the absolute value of the ratio of the difference between the maximum or minimum value and the median value of the bond strength of the three specimens in the same group to the median value. When one of them is greater than 15%, the adopted interfacial bond strength value, \(\tau_{\text{max}}\), is taken as the minimum value of the three values; when both of them are less than 15%, the adopted interfacial bond strength value, \(\tau_{\text{max}}\), is the average of the three measured values.  
\end{table} 
Table 5: Interfacial bond strength of each specimen. The comparison of the interfacial bond strengths of the specimens in the X-C35-30-W, X-C35-45-W, X-C35-30-Y, and X-C35-45-Y groups revealed that when the shear angle increased from 30\({}^{\circ}\) to 45\({}^{\circ}\), the bond strength of the interface without shear keys increased from 5.76 MPa to 8.39 MPa (an increase of 45.66%), and the bond strength of the interface with shear keys increased from 9.24 MPa to 11.52 MPa (an increase of 24.68%). With the increase in the slant shear angle, the increase rate of the interfacial bond strength of the specimens with shear keys exhibited a decreasing trend, that is, the effect of shear key tended to decrease as the compressive stress on the specimen increased. According to the ACI standard [20], the interface bond strength of a direct shear specimen at 28 days should reach 3-4 MPa, and the interface bond strength of a slant shear specimen should reach 14-21 MPa.