Validating Concrete-to-Concrete Interfacial Modeling through a Multiparametric Experimental Campaign

Abstract

The aging and deterioration of existing RC structures are often addressed with jacketing of weak structural members. This study proposes a blend of numerical methods to precisely simulate the interfacial bond performance in composite sections consisting of fresh and hardened concrete layers. A comprehensive experimental campaign of 75 direct shear tests was conducted, focusing on three key contributors to bonding strength: (1) surface roughness, (2) application of a bonding agent, and (3) the impact of interfacial compressive normal stresses due to confinement or external forces. The results indicated, as anticipated, that roughening benefits bonding capacity, and the bonding agent’s contribution was evident only on smooth surfaces. Regarding the effect of normal stresses, bonding performance was enhanced only up to a certain load. To further and more accurately analyze contact behavior, a novel numerical simulation integrates cohesion, friction, and plastic damage models in computer simulation and employs contact elements under explicit dynamic analysis. The proposed modeling technique efficiently accounts for various parameters, including roughness, concrete properties, and pressure on the interface, offering a versatile tool for analysis. Furthermore, a generalized optimized model has been proposed to complement the analytical simulations and categorize surfaces as either smooth or rough, with acceptable convergence, providing a practical, and robust approach for concrete-to-concrete contact modeling. The deterioration of existing infrastructure, combined with economic and sustainability concerns, have stimulated significant efforts to strengthen it. A key retrofitting technique known as jacketing involves adding a new stronger reinforced concrete layer externally to weak structural elements. A strong connection between the old and new concrete layers is crucial for transferring stresses effectively, although this is not always guaranteed. To enhance the connection credibility various techniques have been developed: (1) applying bonding agents, (2) roughening the old surface before adding the new layer, and (3) applying pressure to the interface to increase frictional forces. Experimental results showed that surface roughness improves bonding. Bonding agents are essential primarily on smooth surfaces, and their effectiveness diminishes as roughness increases. The impact of compressive normal stresses on bonding is noticeable up to a certain load level, beyond which this effect can diminish or even reverse. The most accurate, albeit quite complex, method to assess the behavior of these bonded sections is through numerical modeling. The proposed modeling approach provides researchers and designers with a flexible, highly analytical, and reliable tool for bond analysis. It also introduces a simplified version of this model based on the same principles, encouraging broader practical applications.