Investigation on the Interfacial Deterioration in Fiber Reinforced Polymer (FRP) Bonded System
Student thesis: Doctoral Thesis
Related Research Unit(s)
The demand on repairing and strengthening existing civil infrastructures has been greatly increasing in recent years, due to the unavoidable deterioration by the environment, defects and failures in the completion of structures, unsuitable design, quality of materials, bad execution and failure caused by inappropriate utilization, etc. Among different materials, fiber reinforced polymer (FRP) has been proven as a promising material to be used as both internal, near-surface, and external reinforcement for the propose of repairing or strengthening the structure components. A lot of buildings, bridges and other concrete structures have been rehabilitated to date, providing an effective service life extension to deficient systems and a huge saving to the economy. Although the FRP materials show great tolerance towards different environmental attacks, the interface in the FRP bonded system is sensitive to the different service conditions such as moisture attack, chloride ion attack or elevated temperature exposure. Such interfacial deterioration and interfacial defects are the most vulnerable region in the FRP bonded system, and it can lead to the global failure of the structure. In order to address the effect of interfacial deterioration on the structural behavior of FRP repairing or strengthening structural components, and to explore deterioration mechanism of the interface and near interfacial region in the FRP bonded system under different environmental condition, including moisture, high chloride ion content and high temperature environments, using FRP bonded concrete system and FRP bonded wood system as examples. The interfacial fracture toughness and interfacial energy were used as indicators to evaluate the localized interfacial deterioration using fracture-based approach, and the corresponding information can be further adapted in the development of bond-slip models for the numerical modeling using finite element methods (FEM) for the prediction of global structural behavior due to the interfacial deterioration. The microstructure characterization has been conducted to understand the change of material morphology at interface region due to environmental attack. Furthermore, in order to understand the effect of localized interfacial defects on the structural performance, experimental and numerical studies have been conducted for the interfacial criticality in FRP reinforced beam and FRP confined columns. The predictive models and assessment schemes have been proposed to provide practical recommendations on quantifying the deteriorated structural performance when interfacial defects are detected. It is envisioned that the findings in this thesis provide not only a direct effect on the application and design of FRP reinforced structures, but also the scientific understandings on the deterioration mechanism of FRP bonded materials system, which serve as the fundamental information on the further development of a more durable FRP strengthening and retrofitting of civil structures.