Flexural Tensile Behavior of Interface between Precast and Cast-in-Place UHPC Members Based on Four-Point Bending Test

This paper proposed a new method of exposing fibers using expandable polyethylene (EPE) foam to improve the interface performance. The flexural tensile behavior of the interface between precast steam-cured and cast-in-place non-steam-cured ultra-high performance concrete (UHPC) members was examined under four-point bending. The improvement effects of four non-destructive interface treatments-e.g., coating with epoxy glue and coating with a cement-based interface agent-were experimentally studied for comparison. The load-deflection curves of the specimens were measured, and the flexural tensile behavior of the interfaces was analyzed, including the failure mode, flexural tensile strength, ductility, fracture energy, and residual strength. The results indicate that the flexural tensile strength of an interface without any treatment is low and that coating with the cement epoxy glue or the cement-based interface agent has a limited effect on improving the flexural tensile strength. As a result of the bridging effect, the exposed steel fibers can transfer the tensile force across the interface. Therefore, exposing fibers using EPE foam can significantly improve the bond behavior of an interface. This enhancement effect depends on the number of exposed steel fibers and can be simulated based on the pullout load-slip relationship of the steel fiber embedded in the UHPC matrix. The proposed numerical model can be used to predict the bond behavior of an interface with the fiber-exposing treatment.