Bond behavior between normal concrete and UHPC and PUC layers subjected to different loading conditions coupled with fracture analysis technique

Construction materials such as ultra-high-performance concrete (UHPC) and polyurethane-based polymer concrete (PUC) are efficient repair materials for normal concrete (NC) structures. However, the effectiveness of the repair depends on adequate interface bond characteristics under various loading circumstances. This study examined the bond characteristics between the NC substrate, UHPC, and PUC layers under various tests, including splitting tensile, compression, flexural, and U-shaped repeated drop-weight impact tests. The study compares the bond strength efficacy of composite NC-UHPC and NC-PUC and their corresponding failure patterns under different surface treatments including natural fracture surface (NB), smooth surface (SM), and grooves surface (GB). In addition, the fracture behavior in the interfacial zone of the composite specimen was analyzed using digital image correlation (DIC) and scanning electron microscopy (SEM) coupled with energy dispersive spectroscopy (EDS). The results showed that the bond strength between the composite NC-PUC interface is superior to that of the NC-UHPC, leading to enhanced performance across all testing situations. The bond strength of the NC-UHPC and NC-PUC with groove surface and natural fracture surface is classified as excellent. The splitting tensile bond strength of NC-PUC is 10.2%, 15.7%, and 48.5% greater than that of NC-UHPC for NB, GB, and SM surface interfaces, respectively. The flexural strength of the NC-UHPC-NB increased by 63.1%, whereas the flexural strength of the NC-PUC-NB increased by 18.9%. The impact strength results demonstrate that NC-PUC-NB had the largest average number of drops at both the initial crack and failure stages, with N1 = 134 blows and N2 = 147 blows. The specimens examined under static load conditions are characterized by three main failure modes: pure interface failure (B), partial interface failure (B/C), and N/C failure. The predominant failure pattern of U-shaped specimens is an interfacial vertical separation of concrete substrates, confirmed in DIC analysis. The PUC concrete shows the potential of repairing concrete structures.