Durability Of Glass Fiber Reinforced Polymer Bars Research Articles

Study on the durability of GFRP bars and carbon/glass hybrid fiber reinforced polymer (HFRP) bars aged in alkaline solution

Using glass fiber reinforced polymer (GFRP) bars as the reinforcement of concrete structures is becoming more and more popular. Carbon/glass hybrid-fiber reinforced polymer bars (HFRP bars), formed by wrapping a thin layer of carbon fiber reinforced polymer (CFRP) on GFRP bars, is expected to have better durability than GFRP bars. In order to evaluate the effects of CFRP layer on the durability of GFRP bars, the water absorption behaviors of both GFRP and HFRP bars were characterized, and the interlaminar shear strength degradation of GFRP and HFRP bars aged in alkaline solution was investigated with short beam shear test. The results indicate that after being aged in alkaline solution, the remaining interlaminar shear strengths of HFRP bars were larger than that of GFRP bars. And, the deterioration of HFRP bars aged in alkaline solution was found occurring at the CFRP/CFRP interface. The long-term interlaminar shear strength of GFRP and HFRP bars aged in alkaline solution was predicted using the Arrhenius theory. The present study shows that the CFRP layer enhances the durability of GFRP bars in alkaline environment, due to the delayed water and OH– diffusion in CFRP and the better alkaline resistance of CFRP.

Prediction of the Long-Term Performance and Durability of GFRP Bars under the Combined Effect of a Sustained Load and Severe Environments.

With the continuous development of production technology, the performance of glass-fiber-reinforced polymer (GFRP) bars is also changing, and some design codes are no longer applicable to new materials based on previous research results. In this study, a series of durability tests were carried out on a new generation of GFRP bars in laboratory-simulated seawater and a concrete environment under different temperatures and sustained loads. The durability performance of GFRP bars was investigated by analysing the residual tensile properties. The degradation mechanism of GFRP bars was also analysed by scanning electronic microscopy (SEM). Furthermore, the long-term performance of GFRP bars exposed to concrete pore solution under different stress levels was predicted using Arrhenius theory. The research results show that the degradation rate of GFRP bars was increased significantly at a 40% stress level. By comparing the test results, design limits, and other scholars’ research results, it is demonstrated that the GFRP bars used in this test have a good durability performance. It is found that the main degradation mechanism of the GFRP bars is the debonding at the fiber-matrix interface. In the range test, the effects of a 20% stress level on the degradation of GFRP bars were not obvious. However, the long-term performance prediction results show that when the exposure time was long enough, the degradation processes were accelerated by a 20% stress level.

Durability of GFRP bars in the simulated marine environment and concrete environment under sustained compressive stress

The accelerated aging test results of the study on the compressive performance of glass fiber reinforced polymer (GFRP) bars under sustained compressive stress in the marine environment simulated by a salt solution and the concrete environment simulated by an alkaline solution were presented in this paper. The test parameters were sustained stress levels (0%, 20%, 40% of the ultimate compressive strength), exposure temperature (40 °C, 60 °C, 80 °C) and exposure time (16 d, 60 d, 90 d). The test results indicated that high temperature led to postcure of the resin matrix which was beneficial to the compressive performance of the GFRP bars. The conditioned GFRP bars failed due to the longitudinal splitting of the resin matrix or the fracture of the fibers and the debonding of the fiber/matrix interface. After immersing in the salt solution at 80 °C for 90 d, the strength retentions of the specimens with stress levels of 0%, 20% and 40% were 67%, 62% and 55% respectively. After immersing in the alkaline solution at 80 °C for 90 d, the strength retentions of the specimens with stress levels of 0%, 20% and 40% were 44%, 36% and 24% respectively. The compressive strength retention of the conditioned GFPR bars decreased with the increase of the sustained stress level, exposure temperature or exposure time. Increasing the exposure temperature or the sustained stress level could increase the degradation rate of the compressive strength of the GFRP bars. The compressive strength retention of the GFRP bars conditioned in the alkaline solution was lower than that in the salt solution. And the higher the temperature, the more obvious the detrimental effect of the stress level on the compressive strength of the GFRP bars was. Based on the test results, a degradation model for the compressive strength of the GFRP bars under sustained compressive stress in the simulated marine and the simulated concrete environments was proposed.

FE Evaluation of Reinforced Concrete Bridge Decks with Glass-FRP Composite Bars

In order to resolve the steel corrosion problem in bridge decks, glass fiber reinforced polymer (GFRP) has been recommended as a substitute to the conventional steel reinforcement in bridge decks. However, the use of GFRP bars in bridge decks is still limited by several concerns, including the long-term durability of GFRP bars in the concrete under sustained loadings. Literature review showed that the tensile strength reduction of the GFRP bar should be governed by the sustained stress level in the GFRP bar. In this regard, a GFRP reinforced concrete deck was simulated in this paper, aiming to investigate the sustained stress levels in the GFRP bars through three dimensional finite element (FE) modeling. Per AASHTO LRFD specifications, one lane loaded and two lane loaded cases were examined to identify the maximum tensile strains in the internal GFRP bars subjected to dead loads and HL-93 design loadings. The FE results showed that the maximum tensile stresses in GFRP bars under service loads were less than 1% of the GFRP design strength, which implied that the GFRP bars could have excellent long-term performance in real concrete bridge decks.

Microstructural investigation of glass fiber reinforced polymer bars

Abstract Microstructural characteristics are crucial in understanding and predicting the behavior of glass fiber reinforced polymer (GFRP) bars used for concrete reinforcement. Considering the lack of extensive GFRP microstructural knowledge, the main purpose of this study is to provide a documentation of GFRP microstructure and demonstrate its contribution in the durability of GFRP bars. Scanning electron microscopy (SEM) imaging was performed at different magnification levels on the cross-section of four different commercially available pristine GFRP bars. As a result of differences in the production method by pultrusion, each pristine bar presented a unique microstructural pattern including voids, defects, and fiber distribution. Two of the bars which demonstrated the most different patterns were exposed to accelerated conditioning in alkaline solution. The horizontal shear test was performed and the results were compared with the pristine bars. The difference in microstructural patterns was found to significantly contribute to GFRP durability. These results can be used as a benchmark for the microstructure of commercially available pristine GFRP bars and serve as a base for monitoring possible changes after any conditioning or testing.

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.