Study on dynamic adhesion and crack growth characteristics of <scp>Puhpc‐Nc</scp> interface

Abstract The interface formed by the combination of ultra‐high performance concrete (UHPC) and normal concrete (NC), a material for repairing and strengthening concrete structures, not only has various defects but also easily leads to stress concentration and residual stress at high temperature, which affects the overall structural safety of the repaired and strengthened concrete. Therefore, it is extremely important to study the mechanical properties and crack propagation behavior of the bonding interface between cast‐in‐place UHPC and old concrete after high temperature. Therefore, in this paper, ordinary concrete (NC) with C40 and C60 strength grades is used as old concrete (precast concrete), and plain ultra‐high performance concrete (PUHPC) without micro steel fiber is used as post‐pouring concrete. Bi‐material notched semi‐circular bend (BNSCB) and double‐sided cutting (DSC) specimens were designed and adopted. Three different temperatures (100°C, 200°C, and 300°C), one strain rate (255S‐1), and four bonding schemes were considered. The crack initiation toughness and crack propagation velocity at the interface of bonded samples were obtained by the experimental‐numerical method and crack propagation meter, respectively. The effects of different temperatures and strength differences of bonding materials on the crack growth rate, initiation toughness, failure mode, and interface strength of the bonded interface were analyzed, and the change characteristics of interface properties of PUHPC‐NC bonded samples under dynamic load at room temperature and after high temperature were compared and analyzed. The results show that under the influence of shock wave and temperature, the bonded sample has been endowed with great kinetic energy at the crack initiation, and it continues to expand at a relatively fast speed even though it is hindered by aggregate particles at the interface. After being burned at low temperature (100–200°C) for a short time (3 h), the resistance of PUHPC‐NC bonded samples to crack initiation was not weakened, but gradually increased. However, after being burned at a high temperature(300°C or above) for a short time, the resistance of the bonded samples to crack initiation was gradually weakened.