Experimental Study On Interface Shear Performance Between Self-compacting HPC And Old Concrete

With the development of building industrialization,a large number of prefabricated concrete structures are applied in construction projects.Prefabricated construction is the important development trend in China.The prefabricated members need to be connected by post-cast concrete,therefore,a large number of interfaces between the old and new concrete are formed.The shear resistance of the interfaces is the key to ensure structural safety.Self-compacting concrete has good fluidity,which is suitable for dense reinforcement and inconvenient construction.In this paper,self-compacting HPC used as post-cast concrete was taken as the research object,and 12 specimens are designed with the influence factors of interface treatment method,concrete strength and shear reinforcement ratio.The static shear loading test were carried out.The failure mechanism and influencing factors of the interface between old and new concrete were analyzed.Relevant design suggestions are proposed.The specific research is as follow:Based on the interface treatment method,concrete strength and interface shear reinforcement ratio,12 specimens were designed for shear test.The peak load,shear-slip relationship,shear-concrete strain,shear-steel strain and failure mode of specimens were analyzed.The results show that 12 specimens are completely destroyed along the interface between old and new concrete.The stress state of the interface can be divided into three stages: elastic stage,crack development stage and failure stage.The specimens without shear reinforcement are divided into two parts along the interface.When the specimen is damaged,the coarse surface concrete are peeled off,and the key groove are separated into two parts along the root of the key groove.The failure is sudden,and the failure types are brittle failure characteristics.With the increase of reinforcement ratio,the shear bearing capacity increases.Due to the effect of shear reinforcement,the vertical crack width can be restricted,and the failure mode is ductile.The shear reinforcement can effectively increase the shear bearing capacity of interface between the new and old concrete.The shear bearing capacity of interface treatment with shear key is more stronger than that of rough interface.Based on the bonding mechanism and shear friction theory,the failure mechanism of the specimen was studied of interface between the old and new concrete.The influence of concrete strength,interface treatment method and interface shear reinforcement ratio on the bearing capacity of the specimen was analyzed.The results show that the shear strength of specimens treated with rough surface is transferred by the bonding force,and the shear bearing capacity increases slightly with the increase of the ordinary concrete strength.The failure of specimens treated with keyway is shear failure at the root of self-compacting HPC keyway,and the bearing capacity depends on the smaller value of shear strength at the root of precast concrete and post-cast concrete keyway.The tensile force of the shear reinforcement makes the interface clamping produce compressive stress,which improves the friction force of the rough surface and the shear capacity of the key groove.The shear bearing capacity of specimens increases with the increase of the reinforcement strength,and it is approximately linear relationship between shear capacity and strength of shear reinforcement.The bearing capacity of specimens with keyway treatment is higher than that of the specimens with rough surface treatment.Through the comparative analysis of the test and theoretical results,and referring to the relevant norms and literature at home and abroad,suggestions are put forward for the shear design of interfaces between the new and old concrete.