Durability of Composite Reinforcement for Timber Bridges

Fiber-reinforced polymeric (FRP) composites are materials that are increasing in use in civil engineering applications. Despite the excellent mechanical properties and corrosion resistance offered by these organic matrix materials, their susceptibility to the synergistic effects of stress and environmental weathering hinders their widespread acceptance in civil engineering. The durability of a specific formulation of wood-compatible, pultruded, E-glass–phenolic composite is characterized. This composite is unique because its layered structure and void content make it compatible with standard structural wood adhesives. The durability of this wood-compatible FRP reinforcement cannot be directly determined from published work on the durability of E-glass composites because of its unique design. A durability test matrix was generated according to specifications and test standards from the International Conference of Building Officials Evaluation Service, Inc., and from the California Department of Transportation. Physical and mechanical properties that were used as indicators of degradation mechanisms and that applied to the bridge environment included tensile behavior, interlaminar shear strength, void content, and glass-transition temperature. Environmental testing involved exposure to various storage media, such as moisture, saline solutions, and calcium carbonate, followed by mechanical testing. Other exposure treatments included dry heat, cyclic freeze-thaw, accelerated weathering, and natural weathering. In addition to the strength-retention determination after environmental conditioning, control and exposed specimens were examined visually with optical and scanning electron microscopy to determine surface changes and their effect on failure and fracture modes.