Failure characterization of the interface between concrete substrates and fiber reinforced concrete repairs

Concrete structures are severely susceptible to degradation as a result of mechanical or environmental processes. In most cases, retrofit is the only available option because reconstruction of the deteriorated structure is neither a feasible nor financially practical option. The overall performance of a repaired structure is highly dependent on the properties of its interface, which is the weakest part of the system. Fiber reinforced concrete (FRC) is a recognized repair material, however, there are still some knowledge gaps including lack of comprehensive understanding of the synergistic effects of fiber addition and surface preparation on composite structure, long-term behavior and durability of interfaces, and lack of standard design equations for concrete-FRC interfaces. In this study, synergistic effects of different fibers at various volume ratios and surface preparation on failure mechanism, bond strength, and crack growth resistance of concrete-FRC interfaces is investigated under Mode-I loading regime. Based on experimental data, design equations are proposed for concrete-FRC interfaces under Mode-I. These models address tensile strength and crack growth resistance of concrete-FRC interfaces encompassing various variables including surface preparation, type of repair material, and ductility of substrate and repair layers. Furthermore, the micromechanical properties of concrete-FRC interfaces are studied and the impact of fiber addition and curing condition on microhardness, porosity, durability, and water absorption of composite structures is assessed using micro-indentation, scanning electron microscopy (SEM), and micro-computed x-ray tomography (CT-scanning) techniques. Results indicate that there is a strong relationship between surface treatment, fiber content, and composite mechanical behavior. Fiber addition and improved surface treatment enhance response of composite systems in Mode-I. Semi-empirical models exhibit saturating trend between mechanical response improvement and surface preparation/fiber content. Moreover, micromechanical results indicate effectiveness of fibers in mitigating pre-loading and shrinkage damages. In conclusion, FRC can be considered as a promising repair material for repair of deteriorated concrete structures. It can effectively mitigate pre-loading damages as well as mitigating failure under tensile stresses leading to improved mechanical performance and durability of repaired systems. Suggestive models can be employed for numerical simulations and can be used by practitioners for design purposes and to predict composite response of repaired structures.Applied Science, Faculty ofCivil Engineering, Department ofGraduat