Residual mechanical properties of fire exposed GFRP reinforcement in concrete elements

Technologies developed over the last two decades have facilitated the use of glass fiber reinforced polymer (GFRP) composites as internal reinforcement bars (rebars) for concrete structures; providing an alternative to steel reinforcement due to significant advantages such as magnetic transparency and most importantly, corrosion resistance leading to a sustainable and durable solution for the built infrastructure. Composites reduce the long-term maintenance costs over the lifetime of a structure, especially in reinforced concrete (RC) elements in corrosive environments such as coastal constructions. However, this technology has not been embraced in buildings due to concerns regarding fire resistance of RC-GFRP elements, where bond-to-concrete concerns are raised due to different available surface enhancement solutions in GFRP rebars. In order to accelerate the integration of sustainable construction materials in RC buildings, the residual strength of fire exposed RC-GFRP slabs is studied. To this end, RC-GFRP slabs with two significantly different surface features, namely deformed lugs comparable to steel rebar and sand coated, were exposed to a combined fire and sustained three-point bending service load for two hours. Upon completion of the test, the residual slab strength was tested by conducting a static test. GFRP bars were then extracted from the concrete evaluate the residual mechanical properties including shear strength, glass transition temperature, and visual analysis using Scanning Electron Microscopy (SEM). Overall the results for both types of rebars showed that the GFRP-RC slabs did not lose structural integrity after the fire. Additionally, fire exposed GFRP rebars showed equivalent properties to unexposed rebars. The results may provide necessary information to accelerate the integration of this sustainable technology into the built infrastructure.