The Effects of Elevated Temperatures on Fibre Reinforced Polymers for Strengthening Concrete Structures
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The use of fibre reinforced polymer (FRP) composites for strengthening reinforced concrete structures has become increasingly popular in recent years. However, before FRPs can be implemented in interior building applications their performance during fire must be assessed and understood. There currently remains a paucity of information in this area for most currently available FRP strengthening systems. This thesis presents a study of the mechanical and bond properties of selected currently available FRP strengthening systems for concrete structures at elevated temperatures such as might be experienced during a fire. Testing has been performed and is reported to study the continuous unidirectional coupon tensile strength, lap-splice FRP-to- FRP shear bond strength and tensile elastic modulus at elevated temperatures. Results of thermal characterization tests are also completed in an attempt to relate properties of the polymer matrix, such as the glass transition temperature, and thermal decomposition temperature to the losses of strength and stiffness observed for FRP coupons during steady-state and transient exposure to elevated temperatures up to 200oC. A simple analytical model is presented, for which the input parameters can be determined using dynamic mechanical thermal analysis and thermogravimetric analysis, to describe the reduction in mechanical and bond properties of the FRP systems at elevated temperatures. Based on this testing and subsequent analysis it is recommended that a conservative limit on the allowable temperature exposure for FRP systems during fire be set as the glass transition temperature measured using dynamic mechanical thermal analysis. Furthermore it is suggested that differential scanning calorimetry may not be an appropriate method of determining the glass transition temperature for available FRP systems used in concrete strengthening applications.