Durability of GFRP Reinforcing Bars Embedded in Moist Concrete Mathieu Robert 1 ; Patrice Cousin 2 ; and Brahim Benmokrane 3 Abstract: 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. DOI: 10.1061/ASCE1090-0268200913:266 CE Database subject headings: Durability; Fiber reinforced polymers; Moisture; Aging; Alkalinity; Predictions; Mechanical properties; Microstructures. Introduction Fiber-reinforced polymers FRP have been widely used in aero- nautical and chemical engineering for decades. FRP materials are also increasingly being used for engineering applications. How- ever, the low cost-to-performance advantage of glass fiber re- inforced polymers GFRP is the driving force behind its worldwide use and acceptance. GFRP materials are attributed to being of high strength, light weight, noncorrosive, and noncon- ductive. Unfortunately, in some special conditions, such as in a high alkalinity environment, the long-term performance of the GFRP is still an unresolved question. Strength of the glass fibers and resin matrix, the two constituents of the GFRP materials, can decrease when subjected to a wet alkaline environment. Several research works were carried out to investigate the durability of GFRP materials under different environmental conditions that are anticipated under actual service conditions. Sen et al. 1999 investigated the durability of S-2 glass/epoxy prestressed beams exposed to wet/dry cycles in a 15% salt solution and found that GFRP bars lost their effectiveness within 3–9 months of exposure. S-2 glass has many of the features of glass fiber with increased strength and temperature resistance. Porter et al. 1997 exposed three different types of E-glass FRP bars manufactured using an isophthalic polyester resin to high alkaline solution and a maximum temperature of 60° C for a pe- riod of 2 – 3 months. Their test results indicated that the acceler- ated aging severely reduced the ultimate tensile strength and the maximum strain capacity of the GFRP bars. Dejke 1999 re- ported that glass fibers are known to degrade in the presence of water, and that moisture can decrease the glass transition tempera- ture T g  of the resin and act as a plasticizer, potentially having significant effect on flexural strength. The reaction of FRP composite with alkali of concrete is one of the major durability concerns for design engineers. Typically, concrete environment has high alkalinity, which depends on the design mixture of the concrete, and the type of cement used Diamond 1981; Taylor 1987. This alkaline environment damages glass fibers through loss in toughness, strength, and embrittlement. Recently, Chen et al. 2007 studied the durability of bare FRP bars and bars em- bedded in concrete immersed in different solutions at different temperatures and time of exposure. The writers found that GFRP bare bars and embedded in concrete bars showed a significant strength loss when exposed to simulated environments, especially for solutions at high temperature of 60° C Chen et al. 2007. Glass fibers are damaged due to the combination of two pro- cesses: 1 chemical attack on the glass fibers by the alkaline cement environment; and 2 concentration and growth of hydra- tion products between individual filaments Murphy et al. 1999. The embrittlement of fibers is due to the nucleation of calcium hydroxide on the fiber surface. The hydroxylation can cause fiber surface pitting and roughness, which act as flaws severely re- ducing fiber properties in the presence of moisture. In addition, calcium, sodium, and potassium hydroxides found in the concrete pore solution are aggressive toward glass fibers Benmokrane et al. 2002, Nkurunziza 2004. Therefore, the degradation of glass 1 Ph.D. Candidate, Dept. of Civil Engineering, Univ. of Sherbrooke, Sherbrooke PQ, Canada J1K 2R1. E-mail: mathieu.robert2@usher brooke.ca 2 Research Associate, Dept. of Civil Engineering, Univ. of Sherbrooke, Sherbrooke PQ, Canada J1K 2R1. E-mail: patrice.cousin@usher brooke.ca 3 NSERC Research Chair Professor in Innovative FRP Composite Materials for Infrastructures, Dept. of Civil Engineering, Univ. of Sherbrooke, Sherbrooke PQ, Canada J1K 2R1 corresponding author. E-mail: Brahim.Benmokrane@USherbrooke.ca Note. Discussion open until September 1, 2009. Separate discussions must be submitted for individual papers. The manuscript for this paper was submitted for review and possible publication on October 4, 2007; approved on November 25, 2008. This paper is part of the Journal of Composites for Construction, Vol. 13, No. 2, April 1, 2009. ©ASCE, ISSN 1090-0268/2009/2-66–73/$25.00. 66 / JOURNAL OF COMPOSITES FOR CONSTRUCTION © ASCE / MARCH/APRIL 2009 Downloaded 10 Jun 2009 to 132.210.80.41. Redistribution subject to ASCE license or copyright; see http://pubs.asce.org/copyright