Interfacial properties between ultra-high performance concrete (UHPC) and steel: From static performance to fatigue behavior

Interfacial properties between UHPC and steel play a vital role in the application of UHPC as overlay in flexural members in bridges, and the shortcomings aroused by welded shear connectors could be eliminated by utilization of steel-UHPC interfaces without mechanical connectors. However, few researchers concerned about the influences of bending conditions and fatigue loading. This paper investigates properties of steel-UHPC interfaces, considering the affecting factors of interface treatments, boundary conditions, and loading patterns. In phase Ⅰ, the static interfacial properties under tension, shear, and bending were investigated by pull-off tests, push-out tests, and bending tests, respectively. In phase Ⅱ, fatigue bending tests were conducted to study the fatigue interfacial properties. The results indicate that the bond connection between the UHPC and the smooth plate was weak. Certain surface roughness is beneficial to the bond strength, and the degree of influence varies with the boundary and loading conditions. For the interface between UHPC and sandblasted steel plate, the nominal bond strength reached 4.84 MPa under bending with superior fatigue performance. Though the nominal bond strength of the steel-UHPC interface with an epoxy layer could reach 4.24 MPa under bending, the fatigue performance is very poor that the interface would slide and fail after about ten to twenty thousand loading cycles.