# Shear Properties of the Interface Between Polyurethane Concrete and Normal Concrete
## 5 Conclusions  
This study systematically analyzes the factors influencing the shear strength at the interface between PUC and NC through inclined shear testing. The effects of interface  
Figure 13: Proposed prediction model in this study. treatment methods, adhesive application rates, and steel fiber content on the mechanical properties of the interface are specifically examined. A total of 16 specimen groups were tested, featuring different combinations of variables, including three interface treatment methods (smooth, roughened, and grooved), varying adhesive application rates, and steel fiber contents (0%, 0.5%, 1%, and 1.5%). The results demonstrate that interface treatment methods, adhesive use, and steel fiber addition significantly affect the shear strength at the interface. 1. Effect of Surface Roughness on Shear Performance: The surface roughness of the interface has a significant impact on the shear strength of the PUC-NC interface. The roughened interface exhibited the highest shear strength, approximately 32% higher than the smooth interface and 15% higher than the grooved interface. Roughening significantly increased the surface roughness, enhancing the bonding strength between polyurethane and concrete, thus improving the shear performance. In contrast, the smooth interface showed the lowest shear strength (3.5 MPa), indicating insufficient mechanical bonding. 2. Effect of Adhesive Application Rate: The application rate of the adhesive had a notable effect on enhancing shear strength. An appropriate adhesive application rate (approximately 0.2 kg/m\({}^{2}\)) resulted in an 18% increase in shear strength, reaching 4.6 MPa, compared to the interface without adhesive. Excessive adhesive (application rate greater than 0.3 kg/m\({}^{2}\)) did not further improve the shear strength. The brittle layered structure formed by excess adhesive could even reduce the interface toughness. 3. Effect of Steel Fiber Content: The addition of steel fibers had a complex impact on the shear performance of the interface. At low fiber contents (e.g., 0.5% and 1%), steel fibers effectively improved the shear strength, with the highest shear strength of 5.3 MPa observed at 1% steel fiber content, which was a 22% increase compared to the interface without steel fibers. 4. Load-Displacement Behavior: The load-displacement curves of all specimens exhibited typical brittle failure characteristics, with the curves approximately linear up to the ultimate load. The interface treatment group (ZM) and adhesive application group (NJJ) showed a superior bonding performance, with significantly higher maximum displacement and shear strength compared to the other treatments. This confirms the importance of interface design in enhancing structural repair effectiveness. 5. Prediction Model for Shear Strength: Based on the adhesive test data, a predictive model for the shear strength of the PUC-NC interface is proposed. Through nonlinear regression analysis, the model can accurately predict shear strength under various interface treatment conditions, providing a theoretical basis for future interface design in engineering applications. This study demonstrates that the shear strength and shear stiffness between PUC and NC can be effectively improved by designing appropriate interface treatments, selecting the optimal steel fiber content, and controlling the adhesive application rate. These improvements can, in turn, enhance the effectiveness of concrete structure repair and reinforcement. Future research should focus on the mechanical behavior of interfaces under more complex interface conditions as well as the evolution of interface performance under long-term loading and environmental effects. Y.Z. : Writing--original draft, visualization, software, data curation. X.Y. : Methodology, formal analysis, data curation. Z.L. : Writing--review and editing, supervision, project administration. B.M. : Validation, resources. L.W. : Writing, data curation. Q.S.