An Experimental and Computational Investigation on Durability of Fiber Reinforced Polymer (FRP) Bonded Material Systems
Student thesis: Doctoral Thesis
Related Research Unit(s)
Many of the world’s civil structures are deteriorating. Strengthening and retrofitting existing structures is economical and practical, and it can save resources and energy. Fiber-reinforced polymer (FRP) is one prevalent and efficient material for strengthening or retrofitting civil structures. The effectiveness of strengthening or retrofitting schemes has been found to be highly dependent on the properties of the constituent materials, and the bond performance at the interfaces. In particular, bonding at interfaces has been found to be the most vulnerable component and it governs structural integrity. In this study, a comprehensive investigation of the durability of FRP-bonded material systems was conducted through an experimental approach. Wood and concrete were chosen as representative natural and synthetic construction materials. The service conditions of FRP-bonded material systems, including loading and environmental conditions, play an important role in their long-term performance. A durability assessment of FRP-bonded material systems was studied through an experimental fracture-based approach. The debonding resistance at the local interfacial regions can be quantified by interfacial fracture toughness. Moisture can weaken both the epoxy–wood and concrete–epoxy interfaces significantly, resulting in a big drop in the mechanical performance of the entire FRP-bonded system. Furthermore, the experimental results show that a drastic deterioration in interfacial fracture toughness, up to 77%, can be observed under coupled sustained load and moisture exposure. Based on the experimental results, a predictive model can be developed to describe the bond property variations in interfaces with long-term sustained load and moisture exposure. Given that the interface has a significant effect on structural integrity, and interfacial defects can easily form during service life, an understanding of the criticality of interfacial defects from the perspective of defect size and position is necessary to ensure the safety and reliability of FRP-bonded structures. The experimental results indicate that an interfacial defect located near the quarter position is the most critical as it may induce shear stress concentration and initiate local bond failure, with further adverse effects on global performance. Although the mechanical properties of structures can be improved through FRP-bonding, it may decrease the energy efficiency of buildings and cause sustainability concern due to the high absorbance of FRP material. To improve the energy efficiency and sustainability of buildings, a sandwich wall design and reflective coating design are proposed. The thermal performance of these two design schemes was evaluated through experimental and numerical approaches. The results show that the proposed schemes can retard unwanted heat transfer effectively, improving energy efficiency and promoting the sustainability of buildings. It is envisioned that the findings and proposed design schemes can serve as a basis for more reliable structural designs and maintenance planning for the improved durability and sustainability of FRP-bonded structures.