# Experimental Study of Interfacial Bond Properties between CGM and Existing Concrete
## 1 Introduction  
When an existing concrete structure's load-bearing capacity no longer meets the design requirements due to the increase in service time and the effects of natural environmental factors, repair and reinforcement are necessary to avoid costly reconstruction. The limitations of traditional approaches using fresh concrete as the repair material, such as long wet working time and difficulties associated with concrete pouring and vibration, have become increasingly prominent. A cementitious grouting material (CGM) is formulated with a high-strength material as the aggregate and cement as the binder, and it has high fluidity, micro-expansion, and anti-segregation capability. It also has good self-flow (vibration free), fast hardening, high early strength, stable performance, and convenient construction [1, 2]. Using CGM instead of new concrete as a reinforcement material can overcome the limitations of traditional concrete methods [3]. Moreover, with the vigorous promotion and construction of prefabricated buildings, CGM is often used as a bonding material for connecting prefabricated concrete components. Whether for the retrofitting of concrete structures or as a bonding material for connecting assembly components, the reliability of the interfacial adhesive properties between CGM and concrete should be guaranteed to form a whole, and the two should work together. Statistics show that many concrete reinforcement structures develop cracks on the bonding surface during their service period, and the overall structure is damaged due to the cracking of the bonding surface, resulting in the failure of repair and reinforcement [4]. Therefore, the bond properties of the interface between CGM and existing concrete must be studied to maximize the excellent performance of CGM and ensure that the CGM layer and existing concrete work together. Thus far, scholars have studied the interfacial bond of the repair layer and existing concrete and have achieved useful results [5, 6, 7, 8, 9, 10, 11, 12]. [PERSON] [5] investigated the influence ofshear angle on the interfacial bonding performance of new and old concrete and found that failure occurred along the interface when the shear angle was not more than 40\({}^{\circ}\), and the weaker concrete was crushed when the shear angle was more than 40\({}^{\circ}\). [PERSON] et al. [6] studied the influence of interface roughness on the interfacial bond strength between recycled aggregate concrete and natural aggregate concrete and found that the interfacial bond strength increased with an increase in roughness. [PERSON] et al. [7] studied the bond strength between ultra-high-strength fiber reinforced cementitious mortar and conventional concrete. Their results showed that the bond strength depended greatly on the method of substrate surface treatment and pointed out that sandblasting was the best method for interface treatment and preparation. [PERSON] et al. [8] examined the influence of interface treatment methods on the interfacial bond strength of normal concrete reinforced with metakaolin containing concrete and showed that the grooved acid etching treatment method provided the highest bond strength compared with other types of interface treatment techniques. [PERSON] et al. [11] studied the interfacial bond strength between cementitious grouting material and ordinary concrete by using 30\({}^{\circ}\) slant shear specimens and drilling holes at the interface and concluded that the bond strength increased with an increase in roughness. [PERSON] et al. [12] conducted a direct shear test to investigate the bond strength between cementitious grouting material and existing concrete and declaimed that the strength of cementitious grouting material had little influence on the interfacial bond strength. As mentioned above, current studies on the interfacial bond properties of CGM and concrete is very limited, and the influence of different shear angles, different interface structures, and interface shear key settings remains unclear.