Durability and degradation mechanisms of GFRP reinforcement subjected to severe environments and sustained stress

Abstract

Despite the large amount of research that has been carried out to date on the use of glass fibre reinforced polymer (GFRP) bars in concrete, one factor still hindering their widespread use in civil engineering applications is the lack of comprehensive data on their long-term in-service performance. This paper presents the test results of an experimental study investigating the physical and mechanical properties of GFRP bars exposed to severe environments and subjected to different levels of sustained load. The test environments included moist concrete, alkaline solution and tap water, with temperatures varying from 20°C to 60°C. The mechanical properties of the bars were characterized through direct tension, flexural and inter-laminar shear tests, while the physical and chemical properties were determined through the implementation of a series of complementary techniques, including moisture absorption measurements, scanning electron microscope (SEM), Fourier Transform Infrared Spectroscopy (FTIR) and Energy dispersive x-ray analyses (EDX). The test results showed that the elevated temperatures play a key role in triggering and accelerating the development of critical degradation mechanisms. The reduction in the tensile strength of all conditioned samples subjected to a sustained stress equivalent to 3000 µε was always within the limits recommended in existing codes for high durability bars, while a lower average strength retention was observed for higher levels of sustained stress (equivalent to 5000 µε). Finally, it can be conclude that the long-term mechanical properties of the tested GFRP bars appeared to be mainly affected by moisture diffusion through the resin rich layer and debonding at the fibre/matrix interfaces due to the dissolution of the silane coupling agents.

Bond Behavior of GFRP-Concrete Under Long-term Exposure to Aggressive Environments

“…Since the alkaline solution contains more hydroxide ions, this effect is considered more serious. In addition, between the resin matrix and the fiber, there is a thin layer of coupling agent, which is composed of salt-based materials that are impressionable to water and alkaline environments (Fergani et al 2018). Therefore, water and alkaline solution can dissolve the coupling agent and cause local adhesion loss such as interface cracks and peeling.…”

Mechanical and durability properties of GFRP bars exposed to aggressive solution environments

“…By comparison with the results given in some literatures [13][14][15], it could be indicated that the impact of resin matrix on the deterioration of GFRP bars would be changed as pH value and temperature increase. Under the room temperature, GFRP bars with E-CR glass fibers [9] showed higher resistance to strength degradation than the ones with Eglass fibers [7,8] exposed to the same solution conditions with the same exposure period, however, this phenomenon would exist until the environmental temperature reached up to 60 ∘ C.…”

“…It has been proved in existing studies that the direct immersion of GFRP bars in conditioned solutions is believed to be more aggressive than any practical civil engineering application [9]. However, it is an effective way to obtain the valuable results within a relatively short period of testing time and some solution conditions have been included and recommended in some test guidelines [18,19].…”

“…As a result, the investigation on the properties of both ingredients and fiber-resin interface has to be made with respect to the influence of environmental conditions [6]. It is significant to find that the glass fibers themselves are exceedingly sensitive to deterioration in the water and moist environments and in the alkaline (hydroxyl ions) environment due to leaching and etching actions [7][8][9], as shown in Eqs. (1) and (2).…”

“…Several experimental works [7][8][9][11][12][13][14][15] have been carried out to explore the long-term mechanical properties of GFRP bars under various aggressive solution conditions. Furthermore, in order to shorten the exposure period, the solution temperature was usually evaluated up to 60~80 ∘ C in these studies.…”