Shear Properties of the Interface Between Polyurethane Concrete and Normal Concrete

Polyurethane concrete (PUC) is a promising candidate for structural repair materials due to its excellent mechanical properties and durability. However, the bonding performance between PUC and concrete interfaces may limit its broader application. This study examined the factors affecting the shear strength at the PUC–NC interface. A total of 16 oblique shear tests, varying by interface treatment methods (smooth—GH, roughened—ZM, and grooved—KC), adhesive application rates—NJJ (0, 0.2, and 0.3 kg/m2), and steel fiber contents—GXW (0%, 0.5%, 1%, and 1.5%), to evaluate their impact on the mechanical properties of the PUC–NC interface. The results demonstrated that roughening the interface significantly improved the shear strength, resulting in a 32% increase compared to a smooth interface and 15% compared to a grooved interface. A moderate adhesive application rate (0.2 kg/m2) enhanced the interface strength, while excessive adhesive did not further increase the shear strength. The optimal steel fiber content (1%) resulted in the highest shear strength, improving it by 22%, whereas excess steel fibers (1.5%) reduced the interface strength. This is due to fiber agglomeration, which weakens mechanical interlocking and introduces defects that impair interfacial bonding. Load–slip curve analysis revealed that roughened interfaces combined with the appropriate amount of steel fibers improved the interface toughness, delaying the failure process. This study presents a model for calculating the shear strength of steel fiber-reinforced PUC–NC interfaces, incorporating shear slip. Compared to existing models, it more accurately reflects the experimental data.