Studies on bonding properties between polypropylene waterproof plate and concrete segment in shield tunnels

Abstract

This paper studies the threaded polypropylene bar as the connecting piece to line the polypropylene waterproof plate inside concrete segment. The polypropylene bars are welded to the polypropylene waterproof plate so that the polypropylene waterproof plate and the concrete segment can be cast together to achieve high-efficient waterproofing. The bonding properties between polypropylene bar and concrete have been tested. A pullout test including 16 pull-out specimens composed of concrete cube block and polypropylene bar was conducted under pull-out loading. The parameters included surface type and diameter of polypropylene bar and concrete strength grade. Test results show that the maximum bond strength between polypropylene bar with threads on the surface and concrete reaches 3.14MPa, which is 12.8 times stronger than polypropylene bar with smooth surface. The bond strength between polypropylene bars with a diameter of 30mm has doubled strength than polypropylene bars with a diameter of 25mm. The concrete strength has no significant effect on the bond strength. 3D model of pull-out specimens was established in simulation software ABAQUS. The bonding connection was performed by utilizing the non-linear spring elements. The results display that the stress distributed on concrete starts to radiate from the bonding interface to the surroundings in a dumbbell shape and gradually decreases. The stress distribution on polypropylene bar gradually decreases from the loaded end to the free end. The deviation between calculated value and test value within anchoring range 14%. The finite element model can closely reflect bond-slip characteristics between polypropylene bar and concrete.