Full metadata record
| DC Field | Value | Language |
|---|---|---|
| dc.contributor | Department of Civil and Environmental Engineering | en_US |
| dc.contributor.advisor | Yu, Tao (CEE) | en_US |
| dc.creator | Cui, Chuying | - |
| dc.identifier.uri | https://theses.lib.polyu.edu.hk/handle/200/14586 | - |
| dc.language | English | en_US |
| dc.publisher | Hong Kong Polytechnic University | en_US |
| dc.rights | All rights reserved | en_US |
| dc.title | Performance of FRP bars in ultra-high strength sea-sand concrete in coastal environments under natural and accelerated aging conditions | en_US |
| dcterms.abstract | To address the challenge of the shortage of river sand, non-desalted sea-sand has emerged as a promising alternative aggregate in ultra-high strength concrete (UHSC), leading to the development of sustainable sea-sand UHSC (UHSSC). However, the use of steel reinforcement in sea-sand concrete is limited by severe corrosion risks. High-strength, corrosion-resistant fiber-reinforced polymer (FRP) offers a viable reinforcement solution for UHSSC, particularly in coastal and marine construction. To ensure the effective and safe use of FRP-reinforced UHSSC structural members, this thesis presents a comprehensive investigation into the short-term and durability performance of FRP bars in UHSSC under coastal environmental conditions. | en_US |
| dcterms.abstract | The thesis is structured into two main parts. The first part presents an experimental investigation into the short-term bond behavior between FRP bars and UHSSC, followed by the development of a widely applicable bond strength model for FRP bars in concrete. The second part focuses on the durability of FRP bars in UHSSC under both accelerated aging and natural coastal exposure conditions. Furthermore, a bond degradation model was developed, and long-term predictions of the tensile performance of FRP bars embedded in concrete were conducted. | en_US |
| dcterms.abstract | The first part begins with a systematic experimental study on the bond performance of FRP bars in UHSSC. Direct pullout tests were performed on 107 pullout specimens, covering four concrete strength grades and five types of FRP bars from three manufacturers. In addition to concrete strength, bar diameter, and fiber type, this study examined the effects of horizontal shear properties and surface topography of FRP bars on their bond performance in UHSSC, factors that have not been quantitatively evaluated in previous research. To this end, two series of companion tests were performed: topographical measurements of bar surface and short-beam shear tests to assess the physical surface geometries and shear properties of FRP bars. The experimental results reveal that the surface topographical regularity, fiber type, and horizontal shear performance of FRP bars are the three key factors influencing their bond performance in UHSSC, which are not adequately addressed in current design guidelines. In general, in UHSC, carbon FRP (CFRP) bars exhibit substantially higher bond strength than glass FRP (GFRP) bars produced using the same fabrication technology, and the bond strength increases with the horizontal shear strength of FRP bars. Surface imperfections, however, are detrimental to the bond strength. It is therefore recommended to incorporate a fiber factor, a surficial reduction factor, and an upper limit based on the horizontal shear strength of FRP bars when predicting their bond strength with UHSC. Based on these findings, design recommendations for the bond of FRP bars in UHSC were provided, laying the foundation for the reliable bond strength model developed in the subsequent part of this thesis. | en_US |
| dcterms.abstract | Following the experimental study, this thesis then presents the development of a new bond strength model for commercially available FRP bars through a large test database assembled by the author. The database comprises 687 pullout test results, sourced from 29 published papers as well as the test data generated in this PhD study. Statistical analyses, including analysis of variance (ANOVA) and corresponding post hoc tests, were performed on the assembled database. The results highlight the significant effects of bar type, bar diameter, concrete strength, and fiber type, as well as their two-way interactions. Existing bond strength models were first evaluated against the assembled database. Subsequently, a new model was developed based on the general size effect law, incorporating the effects of these four key parameters and their statistically significant coupling effects. The proposed bond strength model demonstrates broader applicability than existing models, as it is valid for a wide range of concrete grades, from normal concrete to UHSC. Importantly, the new bond strength model accurately captures both the size effect and the two-way interaction effects of key parameters, which are overlooked in existing models. Comparative assessments confirm that the proposed model offers superior accuracy in predicting bond strength. | en_US |
| dcterms.abstract | The second part of this thesis presents a comprehensive investigation into the durability performance of FRP bars embedded in UHSSC in coastal environments, using both accelerated aging and field exposure tests over a period of around one year. In the accelerated aging study, two batches of UHSSC mixtures and four types of FRP bars were tested. In total, 554 specimens, including 117 for pullout tests, 199 for tensile tests, and 238 for short-beam shear tests, were immersed in artificial seawater at room temperature (about 23°C), 40°C, and 60°C. The results show that the saline-alkalinity environment within UHSSC does not adversely affect the tensile and shear properties of FRP bars and may even slow their degradation. Furthermore, the FRP bar-UHSSC system demonstrates reliable bond durability under seawater immersion, with no significant changes observed in failure mode or key bond characteristics, such as bond strength, bond stiffness, and relative post-peak strength. However, in UHSSC with a low compressive strength of around 120 MPa, FRP bars exhibited an increase of around 10% in bond strength but a notable 30% decrease in bond stiffness. This is attributed to the increased compressive strength of the UHSSC mixture and a subsequent change in failure mode from debonding at the bar-concrete interface to shear failure within the FRP bars after one year of seawater immersion. | en_US |
| dcterms.abstract | In the field exposure tests, four types of FRP bars were conditioned at a wharf in Zhanjiang, China, across four distinct coastal environments: atmospheric, splash, tidal, and underwater zones. Comparative tests, including 148 specimens, were performed on both bare FRP bars and bars embedded in UHSSC to evaluate their tensile, horizontal shear, and bond properties before and after exposure. The results show that the tidal and underwater zones were identified as the most critical conditions, causing significant degradation in the tensile strength and horizontal shear strength of bare FRP bars. In contrast, the FRP bars embedded in UHSSC exhibited minimal degradation in tensile, shear, and bond performance after one year of natural coastal exposure. | en_US |
| dcterms.abstract | Finally, based on these experimental observations, a new bond degradation model was developed that accounts for the changes in the material properties of both the FRP bars and the surrounding concrete. The model demonstrates reasonable agreement with experimental results. In addition, this thesis synthesized durability data from 430 accelerated aging tests on FRP bars. Based on this comprehensive database, long-term predictions were carried out using the Arrhenius relation, considering the effects of bar type, concrete wrap, alkalinity level, relative humidity (RH), and mean annual temperature (MAT) of exposure. The field durability of internal FRP reinforcement was further estimated based on short-term accelerated aging test results reported in the literature. | en_US |
| dcterms.abstract | In summary, the investigation into the short-term and bond durability performance of FRP bars establishes a reliable foundation for ensuring adequate bonding of FRP bars in concrete, particularly in UHSSC, thereby enabling effective control of cracking and deflection in FRP bar-reinforced UHSSC members throughout their service life. Furthermore, durability studies and long-term predictions of the tensile properties of FRP bars help quantify the effect of environmental exposure on FRP-reinforced UHSSC structures. | en_US |
| dcterms.extent | xxi, 237 pages : color illustrations | en_US |
| dcterms.isPartOf | PolyU Electronic Theses | en_US |
| dcterms.issued | 2026 | en_US |
| dcterms.educationalLevel | Ph.D. | en_US |
| dcterms.educationalLevel | All Doctorate | en_US |
| dcterms.accessRights | open access | en_US |
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