PhD Dissertation Final Oral Defense (June 2024)

Title of dissertation: Assessment of Bent and Straight GFRP Reinforcement Conditioned in Harsh Environments
Name of Candidate: Ahmed Mohsen Khalil
Name of Supervisor: Dr. Rami Hawileh; Co-Advisor: Dr. Mousa Attom
Program: PhD in Materials Science and Engineering (PhD MSE)

Abstract
This dissertation investigates the impact of durability on the strength of bent and straight glass fiber-reinforced polymer (GFRP) bars in challenging harsh environments. The typical tensile strength observed in bent rebars compared to the strength of straight rebars is on average lower by 40%, which is considered significant. In addition, there is a lack of studies in the literature that examined the durability of bent FRP bars in harsh environments, as encountered in the UAE and Gulf region. To address this gap, two sets of durability tests were conducted, one indoors and another outdoors, with a specific focus on performance in saline environment. A comparative analysis was conducted among the results of control unconditioned samples, those exposed to outdoor saline environment of the UAE, and those subjected to indoor accelerated durability setups in the laboratory. The aim is to identify any consistent patterns of strength deterioration in straight and bent GFRP rebars across these two testing setups (indoor and outdoor), as compared to control unconditioned specimens. The variables of the experimental program are GFRP rebar diameter, manufacturer, rebar shape, radius of curvature, durability setup and aging duration. The results covered failure modes, load-deflection responses, strain measurements, tensile strength retention, and microstructure analysis of the GFRP rebars. Test results showed that GFRP rebars, whether straight or bent, demonstrated similar initial stiffness. However, variations in load capacity and deflection were observed based on rebar size and exposure conditions. The microstructure analysis through SEM showed that the manufacturing bending process changed the cross-section of GFRP rebars from circular to approximately rectangular, which changed the load distribution and induced differential stresses along the rebar length. Additionally, environmental exposures caused notable fiber and fiber-matrix interface damages in the GFRP rebars. This study concludes that, there was a moderate retention of tensile strength, with an average of about 80% for outdoor setup and 75% for indoor accelerated setup over the exposure periods. Thus, nonmetallic GFRP reinforcement is a viable alternative to steel reinforcement in RC structures exposed to marine and harsh saline environments.

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