Glass Fiber-Reinforced Polymer Reinforcing Bars Research Articles

Accelerated Aging Behavior in Alkaline Environments of GFRP Reinforcing Bars and Their Bond with Concrete.

This study investigates the durability of glass fiber-reinforced polymer (GFRP) reinforcing bars (rebars) and their bond in concrete. Accelerated aging tests were first conducted on bare rebars that were either subjected to direct immersion in an alkaline solution or previously embedded in concrete before immersion in the solution (indirect immersion). Accelerated aging was conducted at different temperatures of the solution (20 °C, 40 °C and 60 °C) and for various periods up to 240 days. Residual tensile properties were determined for rebars subjected to direct immersion and served as input data of a predictive Arrhenius model. A large decrease in the residual tensile strength assigned to the alkali-attack of glass fibers was extrapolated in the long term, suggesting that direct immersion is very severe compared to actual service conditions. Short-beam tests were also performed on rebars conditioned under direct/indirect immersion conditions, but did not reveal any significant evolution of the interlaminar shear strength (ILSS). In a second part, bond tests were performed on pull-out specimens after immersion in the alkaline solution at different temperatures, in order to assess possible changes in the concrete/GFRP bond properties over aging. Results showed antagonistic effects, with an initial increase in bond strength assigned to a confinement effect of the rebar resulting from changes in the concrete properties over aging, followed by a decreasing trend possibly resulting from interfacial degradation. Complementary characterizations by scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and Fourier transform infrared (FTIR) spectroscopy were also carried out to evaluate the effects of aging on the physical/microstructural properties of GFRPs.

Performance of Innovative Precast Concrete Sleepers Prestressed with Glass Fiber-Reinforced Polymer Reinforcing Bars

Performance of Innovative Precast Concrete Sleepers Prestressed with Glass Fiber-Reinforced Polymer Reinforcing Bars

Deformability and Stiffness Characteristics of Concrete Shear Walls Reinforced with Glass Fiber-Reinforced Polymer Reinforcing Bars

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Splice Strength of Staggered and Non-Staggered Bundled Glass Fiber-Reinforced Polymer Reinforcing Bars in Concrete

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Experimental Study on Splice Strength of Glass Fiber-Reinforced Polymer Reinforcing Bars in Normal and Self-Consolidating Concrete

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Relation between Tensile Strength and Modulus of Rupture for GFRP Reinforcing Bars

AbstractThis paper presents an investigation correlating tensile properties of glass fiber–reinforced polymer (GFRP) bars with the results obtained from flexural testing. Composite bars, in contras...

Shear Transfer Mechanisms for Glass Fiber-Reinforced Polymer Reinforcing Bars

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Fatigue Behavior of GFRP Reinforcing Bars in Air and in Concrete

Although the use of glass fiber-reinforced polymer (GFRP) reinforcing bars is gaining acceptance as an alternative to conventional steel reinforcement in concrete structures, little empirical data exist on the long-term fatigue performance of GFRP bars in concrete. Abrasion at the bar-concrete interface is known to have an adverse effect on bonds and on the overall member response under cyclic loading, although this effect was not adequately quantified until now. This paper presents the results of an experimental study comparing the fatigue performance of GFRP bars in air with the behavior of similar bars embedded in concrete. The experimental findings showed that the GFRP bars tested in air survived fatigue lives that were approximately a full order of magnitude longer than similar bars in concrete beams. The results were used to calibrate a statistical fatigue life model and a residual stiffness model for GFRP bars in reinforced concrete flexural members.

Time-Variant Strength Capacity Model for GFRP Bars Embedded in Concrete

Glass fiber-reinforced polymer (GFRP) concrete reinforcement exhibits high strength, is lightweight, can decrease time of construction, and is corrosion resistant. However, research has shown that chemical reactions deteriorate the GFRP reinforcing bars over time, resulting in a reduced tensile capacity. This paper develops a time-variant probabilistic model to predict the tensile capacity of GFRP bars embedded in concrete. The developed model is probabilistic to properly account for the relevant sources of uncertainties, including the statistical uncertainty in the estimation of the unknown model parameters (because of the finite sample size), the model error associated with the inexact model form (e.g., a linear expression is used when the actual and unknown relations are nonlinear), and missing variables (i.e., the model only includes a subset of the variables that influence the quantity of interest.) The proposed model is based on a general diffusion model, in which water or ions penetrate the GFRP bar matrix and degrade the glass fiber-resin interface. The model indicates that GFRP reinforcement bars with larger diameters exhibit lower rates of capacity loss. The proposed probabilistic model is used to assess the probability of not meeting the tensile strength requirement based on specifications over time and can be used to assess the safety and performance of GFRP reinforced systems. Sensitivity and importance analyses are carried out to explore the effect of the parameters and random variables on the probability estimates.

Behavior of GFRP Reinforcing Bars Subjected to Extreme Temperatures

Corrosion of steel reinforced concrete members has stimulated the research on fiber-reinforced polymers (FRP) to be used as an internal reinforcement for concrete structures. The behavior of glass fiber-reinforced polymer (GFRP) reinforcing bars subjected to extreme temperatures is very critical for applications in North America, especially in Canada. There is a high demand for experimental studies to investigate the thermal stability of strength, along with the ultimate elongation, and modulus of GFRP bars. This paper evaluates the variation of mechanical properties of sand-coated GFRP reinforcing bars subjected to low temperatures (ranging from 0 to −100°C ) and elevated temperatures (ranging from 23 to 315°C ). Tensile, shear and flexural properties are investigated to get an overview of the thermal stability of mechanical properties of GFRP bars subjected to large variations of temperatures. Microstructural analyzes using scanning electronic microscopy (SEM), physical measurements by thermogravimetric...

Durability of GFRP Reinforcing Bars Embedded in Moist Concrete

This paper presents mechanical, microstructural, and physical characterization of glass fiber-reinforced polymer (GFRP) bars exposed to concrete environment. GFRP bars were embedded in concrete and exposed to tap water at 23, 40, and 50°C to accelerate the effect of the concrete environment. The measured tensile strengths of the bars before and after exposure were considered as a measure of the durability performance of the specimens and were used for long-term properties prediction based on the Arrhenius theory. In addition, Fourier transform infrared spectroscopy, differential scanning calorimetry, and scanning electron microscopy were used to characterize the aging effect on the GFRP reinforcing bars. The results showed that the durability of mortar-wrapped GFRP bars and exposed to tap water was less affected by accelerated aging than the bars exposed to simulated pore-water solution. These results confirmed that the concerns about the durability of GFRP bars in concrete, based on simulated laboratory studies in alkaline solutions, do not properly correspond to the actual service life in concrete environments.

Residual Tensile Properties of GFRP Reinforcing Bars after Loading in Severe Environments

The long-term behavior of glass fiber-reinforced polymer (GFRP) reinforcing bars is one of the most critical issues for the acceptance of these materials as reinforcement for concrete structures. There is a high demand for experimental studies to investigate the stability of the tensile strength, ultimate elongation, and elasticity modulus. GFRP reinforcing bars inherently have a low elasticity modulus, which must not significantly decrease over time under loading or the serviceability behavior of the concrete element containing them will be jeopardized. This paper evaluates the residual tensile properties of three sizes of sand-coated GFRP reinforcing bars in alkaline and water environments combined with sustained loading and elevated temperature. Bar diameters of 15.9 (No. 5), 12.7 (No. 4), and 9.5 mm (No. 3) were loaded for different durations, then tested in axial tension for residual tensile properties. The test periods varied from 1 to 4 months under elevated temperature to hasten degradation and si...

Durability Prediction for GFRP Reinforcing Bars Using Short-Term Data of Accelerated Aging Tests

This paper presents a procedure based on the Arrhenius relation to predict the long-term behavior of glass fiber-reinforced polymer (GFRP) bars in concrete structures, based on short-term data from accelerated aging tests. GFRP reinforcing bars were exposed to simulated concrete pore solutions at 20, 40, and 60°C. The tensile strengths of the bars determined before and after exposure were considered a measure of the durability performance of the specimens. Based on the short-term data, a detailed procedure is developed and verified to predict the long-term durability performance of GFRP bars. A modified Arrhenius analysis is included in the procedure to evaluate the validity of accelerated aging tests before the prediction is made. The accelerated test and prediction procedure used in this study can be a reliable method to evaluate the durability performance of FRP composites exposed to solutions or in contact with concrete.

Effect of Sustained Load and Environment on Long-Term Tensile Properties of Glass Fiber-Reinforced Polymer Reinforcing Bars

Glass fiber-reinforced polymer (GFRP) bars are gaining popularity as reinforcement for concrete bridge deck slabs and other concrete structures. This article reports on a study of the creep behavior of GFRP bars in different environments under sustained load. Twenty GFRP bars (E-glass in vinylester matrix) 9.5 mm in diameter in four series were tested for over 417 days (10,000 h) under combinations of different sustained load levels and surrounding mediums in ambient temperature. The bars were subjected to two levels of sustained tensile stress at 25% and 38% of guaranteed tensile strength while being surrounded by either alkaline solution (pH 12.8) or de-ionized water (pH 7.0). Axial strain in the central conditioned part of the bars was monitored with time to evaluate the creep behavior. Following the extended creep test, the GFRP bars were tested in axial tension until failure for residual tensile strength, elastic modulus, and axial strain. Results showed that the tested GFRP bar performed very well under these extreme loading and environmental conditions. Creep strain in the GFRP bars is less than 5% of the initial value after 10,000 h of sustained tensile loading. The average residual tensile strength was found to be 139% and 144% of the design tensile strength for bars conditioned in de-ionized water at 25% and 38% stress level, respectively. Alkaline solution tends to have more harmful effects on the bars than de-ionized water at higher stress levels. In alkaline solution, this range was 126% and 97% at 25% and 38% stress level, respectively. More importantly, the modulus of elasticity of the bars is very stable and almost unaffected by the conditions and sustained stress levels used. The authors note that this finding is critical in the design of concrete elements reinforced with FRP bars because the modulus is directly related to the crack width, deflection, and other serviceability concerns.

Performance of Glass Fiber-Reinforced Polymer Reinforcing Bars in Tropical Environments - Part I: Structural Scale Tests

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Performance of Glass Fiber-Reinforced Polymer Reinforcing Bars in Tropical Environments- Part II: Microstructural Tests

In this part of a two-part paper, the authors pursue microstructural studies of glass fiber reinforced polymer (GFRP) reinforcing bars in concrete, including the nature, quantum, and mechanism of deterioration. A scanning electron microscope was used to show the changes in the microstructure. Energy-dispersive x-ray analysis (EDX) and inductively coupled plasma mass spectrometry (ICP-MS) were used to determine the chemical changes in the composite.

Durability of Glass Fiber-Reinforced Polymer Reinforcing Bars in Concrete Environment

Accelerated aging tests are being conducted on more than 20 types of glass fiber-reinforced polymer (GFRP) reinforcing bars, which are produced from different combinations of constituent materials, manufacturing parameters, sizes and shapes, and surface coatings. The specimens are being subjected to various sustained tensile loading (22 to 68% of ultimate strength) in three types of alkaline environments: NaOH, simulated pore-water solution, and embedded in concrete. Time to rupture or residual strength, as applicable, have been determined. Additionally, stress corrosion mechanisms were evaluated by various microstructural analyses. The results showed clearly that alkaline ions and moisture could penetrate or diffuse through the resin (or through cracks and voids) to the interphases and the fibers. For GFRP bars embedded in moist concrete under various sustained stress levels, three types of stress corrosion mechanisms have been identified: stress dominated, crack propagation dominated, and diffusion dominated.