Experimental investigation on fractal characterization of roughness and bond‐shear behavior at concrete interface treated by prefabricated rubber formwork

Abstract This study compared the interfacial performance and failure modes of prefabricated rubber formwork and traditional chiseling technique through slant shear test and splitting tensile test to reveal the governing mechanism of interface roughness on new and old concrete bond shear behavior. The fractal dimension value obtained via 3D laser scanning technology was used to quantitatively characterize interface roughness. This study conducted an in‐depth analysis of fractal dimension correlation with cohesion and friction coefficient, and established the fractal dimension‐interface shear strength quantitative model. The results demonstrate that the fractal dimension can effectively quantify interface roughness and exhibit the quadratic polynomial positive correlation with sand‐filling depth ( R 2 = 0.969); compared to the traditional chiseling technique, the prefabricated rubber formwork significantly enhances interface shear strength, splitting tensile strength, and ductility due to its uniform texturing while inducing negligible substrate damage; the fractal dimension exhibits the linear positive correlation with cohesion and friction coefficient ( R 2 = 0.887, 0.908). It is suggested that the rough surface with the sand‐filling depth H s > 1.5 mm (the fractal dimension D > 2.1296) should be preferred in the engineering practice to ensure the interface mechanical properties meet the existing code requirements; within the theoretical framework of the Mohr‐Coulomb criterion, the quantitative relationship model between fractal dimension and interface shear strength was established, and the theoretical values demonstrated close agreement with experimental results (errors < 5%), thus providing the theoretical basis for calculating the shear capacity of new and old concrete interface. Consequently, the prefabricated rubber formwork demonstrates significant advantages in enhancing the mechanical performance of new and old concrete interfaces. Its characteristics, such as prefabrication capability, reusability, construction efficiency, and cost‐effectiveness, endow it with broad application prospects in prefabricated structures.