Recently, there have been concerns regarding the long-term behaviour of FRP reinforced concrete members. Freeze/thaw degradation is among the most important factors affecting cracked concrete members taking into account the fact that concrete is a permeable material. Thus, water could potentially accumulate at the FRP-concrete interface. As temperatures drop below freezing, the water will expand and as it crystallizes it could potentially induce forces that will damage the bond between the FRP and concrete. In addition, the behaviour of concrete members under sustained loading changes with time due to creep and shrinkage of the concrete. The gradual development of creep strain in a beam causes an increase in curvature and beam deflection. As in service conditions, the concrete members can be subjected to freeze/thaw and sustained load (dead load plus portion of live loads) simultaneously. The coupled effects of both conditions are also of great concern. Very limited experimental and analytical data is available on the effects of cold temperature or freeze-thaw action on concrete members reinforced with FRP bars. Virtually no work has been done on the combined effects of freeze/thaw cycles and sustained load action on concrete members reinforced with FRP bars.
An extensive research program investigating the individual and coupled long-term effect of sustained loads and freeze/thaw cycles on the flexural behaviour of concrete beams reinforced with different types of glass and carbon FRP bars is currently in progress. The research program is carried out on 50 concrete beams reinforced with FRP bars (Glass and Carbon) and subjected to different numbers of freeze/thaw cycles (100, 200, and 300 cycles - between -20 ° C and + 20 ° C) and sustained loads (1.4 times the cracking moment of the beams, which is equivalent to 23% to 27% of the ultimate strain of the FRP bars under consideration). The beams are 1800 mm long with a rectangular cross-section of 130-mm width and 180-mm depth. Furthermore, a new loading system to apply constant sustained loads to beams has been developed and 50 systems were fabricated at the machine shop of the Faculty of Engineering of Université de Sherbrooke. To date, 15 GFRP reinforced concrete beams were exposed to 200 freeze/thaw cycles either in an unstressed state or loaded in bending and tested up to failure in four-point bending. 35 beams are in conditioning to be tested on August 2002. The preliminary results show that the change in the overall behaviour in terms of deflection, cracking, ultimate capacity, and mode of failure, for the tested beams after conditioning compared to unconditioned control beams can be considered insignificant.
Laoubi, K., (2004). "Durability Studies on Concrete Beams Reinforced with FRP Bars". Ph.D. Thesis (in French), Department of Civil Engineering, Université de Sherbrooke, Sherbrooke, Québec, November, 205 p.
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