Fracture propagation of concrete and ultra-high-performance concrete (UHPC) interface affected by repaired layer thickness

An integrated experimental and numerical study was conducted to understand the behavior of reinforced concrete (RC) wide beams with top UHPC overlay under a four-point bending load.An experimental study was carried out to assess the influence of different overlay thicknesses.It showed improvement in the structural performance compared with the beam without repair.In the numerical simulation, a three-dimensional finite element modeling was carried out, and its results were matched with the experimental results.This paper focuses on crack growth and stress around cracks at the interface between normal concrete and UHPC overlay.The FEM results showed that the locations of debonding occur at the pure moment zone, and delamination at the interface is caused by different stresses acting at the same location.At the interface surface where compression stress from the RC acts, tension stress from the UHPC overlay is also applied at the same location.Additionally, with a thinner overlay, partial delamination occurred at the interface because of the bending experienced throughout the repaired beam.Conversely, a 50 mm UHPC overlay provides sufficient stiffness to resist bending, which can lead to faster delamination over a larger area of the beam's surface.