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Carbon fiber-reinforced polymer (CFRP) has many advantages as a construction/structural-strengthening material. However, there are still concerns regarding the long-term performance of these materials when used with reinforced concrete (RC) structures. Environmental conditions have an adverse effect on the behavior of CFRP and the bond between these sheets and concrete. Therefore, the durability of CFRP used for strengthening RC beams was evaluated under different environmental scenarios, including subjection to immersion in deicing agents, tap water, and saltwater, freeze-and-thaw cycles, and outdoor environmental changes. Laboratory tests were performed to examine the influence of these environmental scenarios on the bonding behavior between CFRP sheets and concrete in terms of deformations and modes of failure. Two types of test setups were performed in this study, namely pull-off shearing and three-point bending. Forty-two concrete prisms with CFRP were prepared and tested by using the pull-off shearing setup. It was observed that as the period of exposure increased, noticeable effects on the CFRP sheet as well as the bond stiffness were observed. Exposure to tap water had a greater impact than saltwater on the CFRP–concrete bond strength as well as the CFRP. In addition, eighteen notched concrete beams strengthened with an external CFRP were tested under three-point bending. The tap water exposure showed a 3.6% increase in the bond strength compared to the control specimen. However, the saltwater exposure showed a 10% increase.

In this paper, experimental investigations for strengthening reinforced concrete (RC) continuous beams were performed. Eighteen T-beams were cast, twelve of which were inverted T-beams where the flange portion of the T-beam was subjected to positive flexure to represent the support region of a continuous beam. Six of the T-beams were non-inverted where the web is subjected to positive flexure. Carbon fiber reinforced polymer (CFRP) sheets with different widths were considered, and different strengthening configurations with the same area of CFRP were investigated. The use of one-layer, multiple layers, or multiple strips of CFRP were evaluated to investigate the effect of these configurations on the ultimate capacity and ductility of the strengthened beams. From the experimental observation of the non-inverted beams, it was found that the ultimate load capacities of the CFRP-strengthened beams were enhanced by 4% to 90% compared to the control beam. Using multiple layers of CFRP sheets enhanced the stiffness of the beams by 4% to 46%, depending on the CFRP area and configurations. The debonding of CFRP before the ultimate failure provided additional ductility to the tested beams. For the strengthening of the inverted beams, it was found that the addition of CFRP strips did not increase the strength of the beams when the width of CFRP to beam width ratio was less than 0.25, but the ductility of the beam was enhanced slightly. The use of multiple strips was found to be a more effective way for the strengthening of the negative moment region than using multiple layers. This can also provide more desirable modes of failure than when applying CFRP in multiple layers. Ductility was found to be lower if multiple layers were used compared to other configurations. Moreover, it was observed that as the compressive strength of concrete increased the addition of the CFRP improved the beams ductility.