Abstract: Shear experiments were conducted on 18 Z-shape specimens from 6 different groups to investigate the shear properties of the interface of new and old concrete. The effects of different interfacial techniques,i. e., smearing cement paste, directly casting new concrete, and smearing commercial interfacial agents, on the shearpropertieswere investigated. The experimental results show that the interfacial techniques have a great effect on the shear properties of a new-to-old concrete interface. The shear strength of specimens is greatestwhen the technique of smearing cementpaste is used in the three interfacial techniques. Furthermore, reinforcing steel bar planting can improve the shear properties of the interface remarkably. The experiments show that the depth of reinforcing steel barplanting should be greater than ten times the diameter of a reinforcing steel bar in the repair and strengthening of structures.