Durability of Hybrid Composite Beam Bridges Subjected to Various Environmental Conditioning

AbstractThe hybrid composite beam (HCB) is a novel idea that combines conventional construction materials (i.e., steel and concrete) with fiber-reinforced polymer (FRP) composites in a new configuration. This hybridization aims to optimize the beam’s structural performance and produce a structural element that is more durable than conventional members. This study examined the durability of a commercial glass FRP (GFRP) laminate that was used to encase the HCB elements in a recently constructed HCB bridge. The E-glass/vinyl ester laminate was subjected to five aging regimes. These conditioning regimes simulated an alkaline attack, a salt attack, a salt attack that was preceded by ultraviolet (UV) irradiation exposure, and sustained stresses that were accompanied by controlled thermal cycles and natural weathering. The durability of the E-glass/vinyl ester laminate was examined in terms of changes that occurred in the ultimate tensile strength. A microstructural analysis was performed on both unconditioned and conditioned specimens via optical microscopy (OM), scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) analysis, and Fourier transform infrared (FTIR) spectroscopy. The microstructural analysis revealed that the hydroxide and chloride ions penetrated the laminate through the existing voids and cracks without causing hydrolysis to the vinyl ester resin. Both the alkaline and the salt solutions caused fiber-matrix debonding and reduced the glass fibers load-bearing through physico-chemical processes (leaching and the dissolution of fibers). The tensile strength was reduced greatly under the alkali attack. The mechanical testing and the microstructural analysis provided fundamental insight into the durability and stress corrosion mechanisms of the examined GFRP shell under different environmental effects. This information is valuable to enhance the GFRP shell’s durability.