Numerical modelling of old-to-new concrete interface with surface indentation

The treatment of the interface in concrete to concrete strengthening and structural reinforcement plays a vital role in structural performance, influencing shear transfer, flexural behavior, and overall integrity. However, limited studies have explored the shear behavior of old-to-new concrete interfaces with varying surface indentation geometries and substrate roughness. To address this gap, this study developed a 3D finite element (FE) model to investigate the shear behavior of an old-new concrete interface with surface indentations, considering factors such as tooth angle, depth, and distribution. The model was validated by comparing its results with experimental results. The old-to-new concrete interface was modeled using a combined traction-separation and friction-coupled cohesive interface model approach. The numerical results, including load-slip relationship, interface shear capacity, cracking pattern, and failure mode, closely matched the experimental data, especially the interface shear capacity. Parametric studies were then conducted to examine the effects of varying surface indentation geometries and confining pressure on the interface's shear capacity. The findings revealed that surface indentations significantly affected the interface's stiffness, shear capacity, and slip behavior at maximum shear. A linear relationship between confining pressure and shear capacity was observed, with increasing confining pressure enhancing the shear capacity of the interface. The traction-separation model with friction penalty demonstrated high accuracy, with a maximum error of about 6 % across all test specimens. Based on these results, a shear stress-slip constitutive model was proposed for the mechanical behavior of old-to-new concrete interfaces with surface indentations under combined normal pressure and shear stress.