Behavior of FRP-confined concrete after high temperature exposure Yousef A. Al-Salloum a , Hussein M. Elsanadedy b, * ,1 , Aref A. Abadel a a Department of Civil Engineering, King Saud University, Riyadh, Saudi Arabia b Specialty Units for Safety & Preservation of Structures at King Saud University, Riyadh, Saudi Arabia article info Article history: Received 8 July 2009 Received in revised form 20 June 2010 Accepted 29 June 2010 Available online 23 July 2010 Keywords: Fiber reinforced polymers Concrete columns High temperature Rehabilitation Strengthening abstract This paper presents the results of an experimental program to investigate the effect of high temperature on the performance of concrete externally confined with FRP sheets. For this purpose, a two-phase exper- imental program was conducted. In the first phase, 42 standard 100  200 mm concrete cylinders were prepared. Out of these specimens, 14 cylinders were left unwrapped; 14 specimens were wrapped with one layer of CFRP sheet; and the remaining 14 specimens were wrapped with one layer of GFRP sheet. Some of the unconfined and FRP-confined specimens were exposed to room temperature; whereas, other cylinders were exposed to heating regime of 100 °C and 200 °C for a period of 1, 2 or 3 h. After high tem- perature exposure, specimens were tested under uniaxial compression till failure. The test results dem- onstrated that at a temperature of 100 °C (a little more than the glass transition temperature (T g ) of the epoxy resin), both CFRP- and GFRP-wrapped specimens experienced small loss in strength resulting from melting of epoxy. This loss of strength was more pronounced when the temperature reached 200 °C. In the second phase of the experimental program, three 100  100  650 mm concrete prisms were pre- pared and then overlaid by one layer of CFRP and GFRP laminates for conducting pull-off strength tests as per ASTM D4541 – 09. The objective of this testing was to evaluate the degradation in bond strength between FRP and concrete substrate when exposed to elevated temperature environments. One prism was exposed to room temperature whereas the other two specimens were exposed to heating regime of 100 °C and 200 °C for a period of 3 h. It was concluded that a significant degradation in the bond strength occurred at a temperature of 200 °C especially for CFRP-overlaid specimens. Ó 2010 Elsevier Ltd. All rights reserved. 1. Introduction Research initiatives around the world during the past two dec- ades have documented the behavior of externally bonded fiber reinforced polymers (FRPs) for strengthening reinforced concrete (RC) structures. In these applications, FRPs are bonded to the exte- rior of RC structures, typically using an epoxy resin saturant/adhe- sive, to provide additional tensile or confining reinforcement, which supplements that provided by the internal reinforcing steel. Sufficient research and implementation has now been conducted for the development of various design codes and guidelines for the application of FRPs in conjunction with concrete structures [1–4]. Numerous studies have shown that circumferential wraps of FRP on the exterior of reinforced concrete columns can signifi- cantly increase the strength and ductility of these members [5– 7]. Hence, FRP applications have been widespread in repair and restoration of reinforced concrete columns in existing bridges. The application of FRP wraps in buildings, however, has been hin- dered due to uncertainties regarding their behavior in fire. Most FRPs are susceptible to combustion of their polymer matrix, potentially resulting in increased flame spread and toxic smoke evolution. In addition, commonly used polymer matrices and adhe- sives rapidly lose strength and stiffness above their glass transition temperature (T g ). The critical T g threshold, which depends on the specific polymer matrix constituents, among other factors, typi- cally varies from 65 to 82 °C for externally bonded systems [1]. Thus, if left unprotected in fire, FRPs may ignite, supporting flame spread and toxic smoke evolution [8], and may rapidly lose mechanical and/or bond properties [9]. This may raise concerns as to the fire performance of FRP-strengthened reinforced concrete columns in buildings, where fire is one of the primary design con- siderations. To date, information in this area is extremely scarce, and a great deal of further work is required to fill all the gaps in knowledge. The purpose of this paper is to fill some of the gaps in understanding the performance of the fire endurance of struc- tures strengthened with FRPs. A limited number of studies exist on the behavior of FRP- strengthened concrete members under fire conditions. Deuring [10] conducted a fire test program which demonstrated that rect- angular RC beams strengthened in flexure with externally bonded 0950-0618/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.conbuildmat.2010.06.103 * Corresponding author. Tel.: +966 505428970. E-mail address: elsanadedy@yahoo.com (H.M. Elsanadedy). 1 On leave from the Department of Civil Engineering, Helwan University, Cairo, Egypt. Construction and Building Materials 25 (2011) 838–850 Contents lists available at ScienceDirect Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat