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.

This paper presents an experimental study aimed at investigating the long-term tension stiffening and flexural behaviour of concrete elements reinforced with glass fibre reinforced polymer (GFRP) bars subjected to accelerated aging conditions. Six tension stiffening specimens and eight small-scale GFRP RC beams were exposed to different environments and sustained stress levels for 120 and 270 days, respectively. Subsequently, the specimens were tested to failure and their behaviour was compared to that of reference specimens. The test results revealed that stressed specimens conditioned in a wet environment experienced a reduction in tension stiffening response as a result of bond degradation and a reduced stress transfer from the bar to the surrounding concrete. The results also indicate that the accelerated aging conditions affected the overall flexural behaviour and led to higher deflections and larger crack widths. The long-term deformation of elements subjected to a stress level representing typical in-service conditions, however, always complied with the design limits suggested by current guidelines. Higher imposed loads (inducing maximum strain level in the reinforcement of about 5000) led to both deflections and crack widths in excess of the values recommended at serviceability limit state. Finally, the response of the tested specimens is compared to that predicted according to fib Model Code 2010 and Eurocode 2 and it is shown that both models fail to capture adequately the long-term structural behaviour of stressed GFRP RC specimens conditioned in wet environment.