Bond durability and degradation mechanism of GFRP bars in seawater sea-sand concrete under the coupling effect of seawater immersion and sustained load
Introduction
Fiber-reinforced polymer (FRP) bar is a suitable alternative of steel bar in corrosive environment due to its good corrosion resistance, high strength-to-weight ratio, et al. [1], [2], [3], [4], [5], [6], [7]. In recent years, the investigations on the short-term and long-term properties of FRP bars [8], [9] and their resin matrix [10], [11] have gained some achievements, which speed up the extension and utilization of the bars in civil engineering. The seawater sea-sand concrete (SWSSC) structure reinforced with FRP bars has a promising prospect for development [12], [13], [14]. The bond performance of FRP bars in SWSSC is the foundation of their joint work. It determines the stress transfer between FRP bars and SWSSC. Moreover, the bond durability significantly affects the long-term behavior of the structure. Therefore, it’s important to investigate the bond durability of FRP bars in SWSSC.
The influences of the seawater and sea sand on the concrete have been studied for years. Notably, opposite conclusions were reported according to the existing studies. For example, Dhondy et al. [15] found that the compressive strength of SWSSC at 28 days was 16% higher than that of the normal concrete, while Guo et al. [16] observed a lower compressive strength of SWSSC by comparing the two types of concrete. The various chemical and physical properties of seawater and sea sand from different regions may be one of the reasons for the difference in the research results [15]. However, it is generally accepted that the chemical ions in seawater and sea sand could increase the early compressive strength of concrete slightly [17], [18], [19]. The concrete incorporated with seawater and/or sea sand has a shorter setting time compared with the normal concrete [20], [21]. Shells in the sea sand harm the workability of concrete [22] and a small seashell content has a minor effect on the compressive strength [23]. Research on the durability of concrete with seawater and/or sea sand is insufficient. Some studies have concluded that the sea sand concrete suffers a lower freeze–thaw resistance than normal concrete, and the sea sand has little effect on carbonation [24].
Very few researchers have focused on the bond durability of FRP bars embedded in SWSSC or seawater concrete. Dong et al. [25] studied the bond properties of basalt FRP (BFRP) bars embedded in SWSSC under wet-dry cycles (a cycle included 6 h for seawater immersion at 40 °C and 6 h for drying) and seawater immersion at 50 °C. After 90 days of exposure, the bond strengths under the two conditions decreased by 8% and 22%, respectively. The studies have shown that SWSSC has similar mechanical properties to normal concrete [24]. Khatibmasjedi et al. [26] observed that the GFRP bars in seawater concrete had an 11% reduction in the bond strength after exposure to seawater for one year. Although researches on the bond durability of FRP bars in SWSSC are very limited, the bond durability of FRP bars in normal concrete had received much attention. Robert and Benmokrane [27] investigated the bond behavior of glass FRP (GFRP) bars embedded in concrete. The specimens were exposed to tap water for 180 days at 23, 40, and 50 °C, respectively. The test results showed that the bond strength decreased with the increase of duration and temperature. Chen et al. [28] reported that the bond strength of GFRP bars embedded in concrete achieved a 12% reduction after alkaline solution (pH = 12.7) immersion for 60 days at 60 °C. Zhou et al. [29] studied the influence of acidic solutions with different pH on the bond performance of GFRP bars in concrete. They found that the bond strength decreased with the increase of pH. Dong et al. [30] studied the long-term bond performance of different types of FRP bars immersed in seawater. The results indicated that the bond durability of fiber-reinforced epoxy bars was better than that of fiber-reinforced vinyl ester bars. Yan and Lin [31] studied the bond behavior of GFRP bars in concrete immersed in sodium chloride solution. The study concluded that the bond strength decreased with the increase of exposure time. The degradation rate at 70 °C was higher than that at 50 °C. Bazli et al. [32] reported that compared with alkaline solution and seawater, the acidic solution caused a more significant reduction in the compressive strength of concrete, and the bond performance between GFRP bars and concrete degraded more seriously. Altalmas et al. [33] and El Refai et al. [34] showed that at the initial stage of solution immersion, the adhesion between FRP bars and concrete increased due to the water swelling of the bar. Based on the acceleration test results, Hassan et al. [35] predicted the bond durability of BFRP bars in concrete for 50 years of service life at different temperatures and humidities. The bond strength retentions were not <71%. Through a microstructural analysis, Davalos et al. [36] proposed that the degradation of the bond between FRP bars and concrete was mainly caused by the bar degradation, while the effect of concrete was minor. A similar theory of bond degradation mechanism was also put forward by Dong et al [37]. Belarbi et al. [38] carried out an experimental investigation and proved that the bond durability of carbon FRP (CFRP) bars was better than that of GFRP bars in concrete under aggressive environments. Al-Tamimi et al [39] reported that the bond strength of GFRP bars showed little difference after exposure to sun and cyclic splash for 60 and 90 days.
The literature mentioned above worked on the effect of aggressive environments on the bond durability of FRP bars embedded in concrete. But during the service period, besides exposure to the surrounding environment, the concrete structures are inevitably subjected to sustained load at the same time. Only considering the influence of the environment on the bond durability may lead to a large deviation between research results and actual situations. Recently, several scholars have carried out investigations on the bond durability between FRP bars and normal concrete (not SWSSC) under the coupling effect of aggressive environments and sustained load. Alves et al. [40] and Bakis et al. [41] reported the bond behavior of FRP bars subjected to sustained load under different environments including indoor, outdoor, freeze–thaw cycles, and alkali solution. But they did not take the sustained load as an independent variable in their studies. Benmokrane et al. [42] studied the coupling effect of alkali solution and sustained load on the bond durability of an innovative GFRP bar (a head made of a thermoplastic matrix is cast at the end of the bar) in normal concrete. Compared with the individual effect of alkaline solution, the bond performance under the coupling effect was markedly degraded. Significantly, the test bar wasn’t the conventional deformational bar, which could induce different bond performance.
Few studies pay attention to the bond durability between FRP bars and SWSSC under the coupling effect of aggressive environment and sustained load. Moreover, the degradation mechanism of bond performance is not clear, which hinders the wide use of SWSSC structures reinforced with FRP bars. Therefore, it is necessary to make up for the research insufficiency. Seawater immersion is one of the most common corrosions for concrete structures in the marine environment. Among the commonly used FRP bars, GFRP bars have the highest performance-price ratio. Therefore, the research focuses on SWSSC structures reinforced with GFRP bars subjected to sustained load under seawater immersion.
Overall, the research objective in this paper was to explore the bond durability behavior of GFRP bars in SWSSC under the coupling effect of seawater immersion and sustained load and clarify the corresponding degradation mechanism. 42 pullout specimens were tested after conditioning. The effects of bar diameter, immersion time, and sustained load on the bond performance were investigated. Based on the microstructural analysis, the degradation mechanism of bond performance was also proposed. Furthermore, the long-term bond strength under the coupling effect of the marine environment and sustained load was predicted according to fib Bulletin 40 [43]. These results are expected to help people better understand the bond durability of GFRP bars in SWSSC, and provide a reference for the design and application of the SWSSC structures reinforced with GFRP bars.
Section snippets
Material properties
GFRP bars used in this study were provided by Huyu Glass Fiber-reinforced Polymer Products Co., Ltd., Nantong, China. The bars were made of E-glass fibers and vinyl ester resin. The nominal diameters are 12 and 16 mm, respectively. There are ribs made by spiral winding of a nylon laminate on the surface of the bar. Details can be seen in Fig. 1. The mechanical properties of GFRP bars are presented in Table 1.
The seawater and sea sand were taken from Bohai Strait and the chloride ion contents
Results and discussions
Table 4 shows the bond test results. The specimens are named as followed. The letter G represents the GFRP bar. The first number represents the bar diameter. The second number indicates whether the specimen was subjected to sustained load or not. Moreover, 0 represents no sustained load, and 25 represents a sustained load which was 25% of the ultimate pullout force of the unconditioned control specimen. The third number represents the immersion time. The fourth number represents the specimen
Prediction of long-term bond strength under the coupling effect of the marine environment and sustained load
To evaluate the bond degradation of GFRP bars in SWSSC subjected to sustained load in seawater, the long-term bond strength was predicted. Compared with the effect of seawater immersion, the coupling effect of seawater immersion and sustained load could accelerate the degradation rate of bond performance. Furthermore, the degradation mechanism of bond performance didn’t change. Therefore, the prediction methods for the bond strength under aggressive environments could be used to predict the
Conclusions
This paper presents a systematic research about the bond performance of glass fiber-reinforced polymer (GFRP) bars embedded in seawater sea-sand concrete (SWSSC) under the coupling effect of seawater immersion and sustained load. A better understanding of bond durability and degradation mechanism was achieved by analyzing the influences of immersion time and sustained load on the failure mode, bond stress vs. slip relationship, and bond strength. According to the results and discussions, the
CRediT authorship contribution statement
Yufei Chang: Investigation, Conceptualization, Formal analysis, Writing – original draft, Data curation. Yanlei Wang: Conceptualization, Funding acquisition, Methodology, Supervision. Mifeng Wang: Investigation, Writing - review & editing. Zhi Zhou: Methodology, Investigation, Supervision. Jinping Ou: Methodology, Supervision.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments
The authors wish to acknowledge the financial support provided by the National Natural Science Foundation of China (Nos. 51778102 and 51978126).
References (72)
- et al.
Enhancement of bond characteristics of ribbed-surface GFRP bars with concrete by using carbon fiber mat anchorage
Constr. Build. Mater.
(2017) - et al.
Effect of applied stress and bar characteristics on the short-term creep behavior of FRP bars
Constr. Build. Mater.
(2018) - et al.
Monotonic axial compressive behaviour and confinement mechanism of square CFRP-steel tube confined concrete
Eng. Struct.
(2020) - et al.
Axial compressive behavior and confinement mechanism of circular FRP-steel tubed concrete stub columns
Compos. Struct.
(2021) - et al.
Comparative durability of GFRP composite reinforcing bars in concrete and in simulated concrete environments
Cem. Concr. Compos.
(2020) - et al.
Ageing of particulate-filled epoxy resin under hygrothermal conditions
Constr. Build. Mater.
(2020) - et al.
Effects of ultraviolet solar radiation on the properties of particulate-filled epoxy based polymer coating
Polym. Degrad. Stab.
(2020) - et al.
A novel seawater and sea sand concrete filled FRP-carbon steel composite tube column: Concept and behavior
Compos. Struct.
(2020) - et al.
Characterization of the mechanical properties of eco-friendly concrete made with untreated sea sand and seawater based on statistical analysis
Constr. Build. Mater.
(2020) - et al.
Sorptivity and mechanical properties of fiber-reinforced concrete made with seawater and dredged sea-sand
Constr. Build. Mater.
(2021)
Secondary aggregates and seawater employment for sustainable concrete dyke blocks production: Case study
Constr. Build. Mater.
Fresh and hardened properties of seawater-mixed concrete
Constr. Build. Mater.
Effect of oyster shell substituted for fine aggregate on concrete characteristics: Part I. Fundamental properties
Cem. Concr. Res.
Effect of partial replacement of sand with dry oyster shell on the long-term performance of concrete
Constr. Build. Mater.
Use of sea-sand and seawater in concrete construction: Current status and future opportunities
Constr. Build. Mater.
Effect of aging on bond of GFRP bars embedded in concrete
Cem. Concr. Compos.
Accelerated aging tests for evaluations of durability performance of FRP reinforcing bars for concrete structures
Compos. Struct.
Durability and service life prediction of GFRP bars embedded in concrete under acid environment
Nucl. Eng. Des.
Bond durability of BFRP bars embedded in concrete under seawater conditions and the long-term bond strength prediction
Mater. Des.
Bond durability assessment and long-term degradation prediction for GFRP bars to fiber-reinforced concrete under saline solutions
Compos. Struct.
Experiments and probabilistic models of bond strength between GFRP bar and different types of concrete under aggressive environments
Constr. Build. Mater.
Bond degradation of basalt fiber-reinforced polymer (BFRP) bars exposed to accelerated aging conditions
Constr. Build. Mater.
Bond durability of basalt-fiber-reinforced-polymer (BFRP) bars embedded in concrete in aggressive environments
Compos. Part B Eng.
Effect of FRP bar degradation on interface bond with high strength concrete
Cem. Concr. Compos.
Effect of sustained load and seawater and sea sand concrete environment on durability of basalt- and glass-fibre reinforced polymer (B/GFRP) bars
Corros. Sci.
Durability of flexurally strengthened RC beams with prestressed CFRP sheet under wet-dry cycling in a chloride-containing environment
Compos. Struct.
A comprehensive review on mechanical properties of pultruded FRP composites subjected to long-term environmental effects
Compos. Part B Eng.
The effect of exposure to alkaline solution and water on the strength-porosity relationship of GFRP rebar
Compos. Part B Eng.
Long term durability of pultruded polymer composite rebar in concrete environment
Mater. Des.
Interfacial microstructure and bond strength of nano-SiO2-coated steel fibers in cement matrix
Cem. Concr. Compos.
Improved interfacial strength of SiO2 coated carbon fiber in cement matrix
Cem. Concr. Compos.
Experimental study of bond behaviour between concrete and FRP bars using a pull-out test
Compos. Part B Eng.
Combined effects of saline solution and moist concrete on long-term durability of GFRP reinforcing bars
Constr. Build. Mater.
Long-term durability of basalt- and glass-fibre reinforced polymer (BFRP/GFRP) bars in seawater and sea sand concrete environment
Constr. Build. Mater.
Investigation of bond in concrete member with fibre reinforced polymer (FRP) bars
Constr. Build. Mater.
Behavior of circular ice-filled self-luminous FRP tubular stub columns under axial compression
Constr. Build. Mater.
Cited by (23)
Bond strength prediction of FRP bars to seawater sea sand concrete based on ensemble learning models
2024, Engineering StructuresInvestigation on bond durability of GFRP bar/engineered cementitious composite under alkaline-saline environments
2023, Journal of Building EngineeringBond durability of FRP bars and seawater–sea sand–geopolymer concrete: Coupled effects of seawater immersion and sustained load
2023, Construction and Building MaterialsDurability and microstructure degradation mechanism of FRP-seawater seasand concrete structures: A review
2023, Construction and Building Materials