# Experimental Study of Interfacial Bond Properties between CGM and Existing Concrete
## 2 General Conditions of the Experiment
### Specim Design and Preparation
#### 2.1.2 Specim Preparation  
Each test specimen was made of two materials; normal concrete was used as the substrate, and CGM was used as the reinforcement material. The cement, sand, and stones used to prepare the concrete were produced by Beijing Guoxingsheng Hardware and Building Materials Company, and their cement strengths were 32.5, 42.5, and 52.5 MPa, respectively. Medium sand with a fineness modulus greater than 2.8 and crushed stones with aggregate sizes ranging from 5 mm to 10 mm were used as fine aggregate and coarse aggregate, respectively. Potable tap water was utilized for mixing. According to the Chinese code _Specification for mix proportion design of ordinary concrete_[19], the materials and concrete mix procedure was designed. After many trials, the mixture proportions of each concrete strength were determined and are presented in Table 3. The CGM used as overlay materials in this study was CGM-I type commercial cementitious grouting material from Zhongde Xinya Company. In accordance with the instructions for use, the strength and fluidity of CGM were measured after trial preparation. The result showed that the water added to the dry material accounted for 11.9%.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Group No.** & **Concrete** & **Interface** & **Shear Angle** & **Shear Key** & **Number of Specimens** \\ \hline X-C35-30-W & C35 & smooth & 30\({}^{\circ}\) & without & 3 \\ X-C35-30-Y & C35 & smooth & 30\({}^{\circ}\) & with & 3 \\ X-C35-45-W & C35 & smooth & 45\({}^{\circ}\) & without & 3 \\ X-C35-45-Y & C35 & smooth & 45\({}^{\circ}\) & with & 3 \\ X-C45-45-Y & C45 & smooth & 45\({}^{\circ}\) & with & 3 \\ X-C55-45-Y & C55 & smooth & 45\({}^{\circ}\) & with & 3 \\ X-C55-45-Y & C55 & smooth & 45\({}^{\circ}\) & with & 3 \\ \hline \hline \end{tabular} Note: X denotes slant shear specimens, W denotes without shear key, and Y denotes with shear key.  
\end{table}
Table 2: Parameters of the specimens for the slant shear test.  
The preparation process of all test specimens was as follows. First, the normal concrete substrate was poured in accordance with the mix proportions listed in Table 3. Second, the mold was removed after 24 h of film curing and the concrete specimens were sent to the standard curing room for curing. Third, after 28 days of standard curing (at a temperature of 20 \(\pm\) 3 \({}^{\circ}\)C and relative humidity greater than 95%), the surface of the substrate was cleaned to remove dust and oil and then dried with a cloth. Fourth, the concrete substrate of the specimen was placed in the original mold with the contact surface perpendicular to the bottom surface. The remaining half of the mold was filled with CGM, and the mold was removed after 24 h and the concrete-CGM test specimens were sent to the standard curing room (at a temperature of 20 \(\pm\) 1 \({}^{\circ}\)C and relative humidity greater than 95%). Lastly, a loading test was conducted after the CGM standard curing for 28 days. While pouring the concrete substrate part of the test specimens, three concrete blocks with dimensions of 150 mm \(\times\) 150 mm \(\times\) 150 mm were cast at the same time, and when pouring the CGM part of the test specimen, three CGM blocks with dimensions of 100 mm \(\times\) 100 mm \(\times\) 100 mm were made at the same time. The measured average test-day compressive strengths of the concrete and CGM are listed in Table 4.