Interface fracture behavior of rehabilitated concrete infrastructures using engineered cementitious composites.

Abstract

This dissertation investigates Engineered Cementitious Composite (ECC) as a potential repair material for durable rehabilitation of concrete infrastructures. The ECC is designed to satisfy the requirement of the interfacial crack trapping mechanism first introduced and analyzed in this study. The trapping mechanism is effective in delaying the delamination and/or spalling failures commonly observed in concrete repaired systems. Interface fracture mechanics serves as the analytical tool to predict interface fracture behavior in rehabilitated structural systems. An interface appears when a repair material is applied to an aged infrastructure. The interface in a bimaterial system is relatively weaker than either side of materials. Thus, the failure of repaired structures is usually related to the failure of the interface. Better understanding of this interface fracture behavior can provide a longer life of the repaired structures. The bond strength concept accepted in the repair industry is not enough to predict interface fracture behavior. Therefore, interface fracture mechanics is adopted as a predictive analytical tool in this study. Also, interface fracture mechanics provides the theoretical foundation for the interface crack trapping mechanism uncovered in this research. To utilize interface fracture mechanics, interface toughness is an important system property. In this study, the interface toughness in concrete/cementitious composite interface systems is measured at varied phase angles. The interface toughness in concrete/cementitious composite systems is found to increase with increasing phase angle. The fracture parameters (interface fracture driving force and phase angle) at the interface crack tip are evaluated based on finite element method. This numerical method can provide solution for problems with various boundary and loading conditions that are intractable with available close-form solutions. The fracture parameters for pavement overlay systems subjected to various environmental loading conditions are evaluated. The trapping mechanism with ECC as a repair material confirmed in interface fracture toughness tests was further investigated in specimens which mimic an overlay on a concrete substrate with an existing joint. This trapping mechanism can enhance durability in practical repaired systems. As a potential repair material, the shrinkage behavior of ECC is also investigated. In addition, the influence of shrinkage on early age flexural properties is included in this thesis research.