# Shear Properties of the Interface Between Polyurethane Concrete and Normal Concrete
## 1 Introduction  
Normal concrete (NC) is a traditional building material widely used in modern civil engineering. However, over time, concrete structures face long-term effects from loads and different, physical, chemical, and biological factors. These influences often result in varying degrees of damage and degradation, reducing the load-bearing capacity, and even structural collapse, which severely impacts safety and durability [1, 2, 3]. As a result, the development of new materials and technologies forefficient, durable, and low-cost concrete structure repair and reinforcement has become a key area of research. Polyurethane concrete (PUC) has gradually been integrated into the manufacturing process to meet higher requirements for mechanical strength and durability [4; 5; 6]. In particular, the combination of epoxy resins and polyurethane helps to improve the mechanical properties and durability of cement-based materials. Although epoxy resin enables precise control of concrete's physical-mechanical properties--including shrinkage deformation, density, strength, and hardness--its brittleness and high cost limit its large-scale application [7; 8; 9]. In contrast, PUC not only provides superior mechanical properties and durability but also features short curing times, non-toxicity, and environmental friendliness, all at a moderate cost, making it an essential material for concrete structure repair [10; 11; 12]. Recent studies suggest that PUC holds promising potential in the reinforcement and maintenance of reinforced concrete structures [13; 14]. [PERSON] et al. [15; 16] investigated the basic mechanical properties of PUC and evaluated its feasibility in bridge expansion joint repair. Similarly, [PERSON] et al. [17] developed an innovative type of PUC, whose mechanical performance was tested to provide theoretical support for its engineering applications. Research by [PERSON] et al. focused on the performance of modified PUC at varying temperatures, offering valuable mechanical analysis for its application in steel-structured bridges [18]. PUC's excellent mechanical properties, including high compressive strength, tensile strength, and elasticity, enable it to withstand heavy traffic loads and stress without cracking or degradation. Its corrosion resistance further makes it ideal for environments exposed to water, salts, and chemicals, such as road surfaces and industrial settings. These properties make it well suited for rapid pavement repairs, overcoming the limitations of traditional materials [19; 20; 21; 22]. However, performance differences between polymer concrete and conventional cement concrete can lead to a weak interface transition zone, often considered a critical vulnerability in structures [23]. The effectiveness of concrete pavement repair depends not only on the performance of the polymer concrete but also on the adhesive bond strength between it and the cement concrete. Insufficient bond strength between the two materials can result in interface damage or even delamination, under external loads and environmental factors. Such issues pose serious threats to the structural integrity and safety of repaired pavement [24; 25]. Research Significance  
A key issue in civil engineering is the repair and reinforcement of aging concrete structures. The bond strength at the PUC-NC interface is considered a critical factor in determining the success of these interventions. This study provides a comprehensive theoretical foundation by examining the factors influencing this bond strength and offers valuable insights for practical repair and reinforcement strategies. By optimizing interface treatment methods and selecting appropriate adhesives and steel fiber content, the safety and durability of the repaired structures can be significantly enhanced. This approach not only extends the lifespan of the structures but also reduces the economic costs associated with frequent maintenance and reconstruction.