Abstract
Glass fiber reinforced polymer (GFRP) is considered as an alternative to steel materials in civil engineering applications to avoid steel corrosion issues. Specifically, GFRP rebars have been employed to replace steel reinforcements in concrete structures. In this case, concrete can also be made with seawater and sea-sand to preserve fresh water and eliminate the extraction of river sand which is harmful to the environment. However, the durability of GFRP composite is threatened by moist/alkaline conditions, and the corresponding inherent degradation mechanism is still not fully understood. To overcome this research gap, both multi-scale experimental studies and numerical simulations are conducted in this thesis to investigate the effects of moisture and exposure pH on GFRP durability.Bench-scale acceleration tests were carried out to study the mechanical behavior of GFRP rebars after subjecting to various exposure conditions. The results demonstrated that the durability of GFRP rebars could be enhanced with the adoption of low-pH CSA concrete (pH = 11) in comparison to that embedded in the normal concrete (pH = 13.6). Moreover, the tensile strength degradation of GFRP rebar was uncovered to be mainly determined by the concrete alkalinity rather than the w/c ratio or saline content.
Then GFRP rebars were directly exposed to simulated solutions with varying pH levels (7 ~ 13.6) and temperatures (23, 40 and 60 ℃) for up to 12 months, building up a comprehensive database incorporating the synergetic influence factors of exposure pH, temperature and aging time. An empirical degradation law based on the exponential degradation tendency, Arrhenius equation and chemical reaction kinetics were proposed. Furthermore, the degradation of glass fibers, matrix and fiber/matrix interface were studied at the microscopic level to provide explanations for the change in macroscopic mechanical performance of conditioned GFRP rebars.
In addition, a diffusion-reaction-degradation framework was established to simulate the time-dependent degradation process of GFRP composite, relating the physical diffusion of H2O/OH- in the matrix and the chemical reaction of glass fibers to the tensile strength degradation of GFRP composites. Simulation results were found to be in good agreement with test data on GFRP rebars.
The outcome of this thesis yields useful information to engineers regarding the microscopic mechanisms behind degradation in macroscopic mechanical properties and the main factors governing the degradation. Specifically, reducing the exposure pH is identified to be the most promising approach to enhance GFRP durability. Moreover, the developed theoretical framework for degradation modeling enables the estimation of lifetime for GFRP components of different geometries under various exposure conditions.
| Date of Award | 2022 |
|---|---|
| Original language | English |
| Awarding Institution |
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| Supervisor | Christopher Kin Ying LEUNG (Supervisor) |
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