Flexural Performance of Reinforced Concrete Beams Externally Strengthened with Carbon and Basalt FRP Sheets

Abstract

Different strengthening systems have been widely used for many years to retrofit and repair deficient structural members. Reinforced concrete (RC) slabs and beams are commonly strengthened in flexure by externally bonding Carbon Fiber Reinforced Polymer (CFRP) sheets to the bottom side of the member. The CFRP sheets used in strengthening applications have high strength; however, they are brittle materials with low ductility. Basalt Fiber Reinforced Polymer (BFRP) sheets on the other hand have relatively lower strength compared to CFRP, however they have higher ductility. As a result, there is growing interest among researchers and practitioners in combining different types of FRP sheets to produce an enhanced strengthening system in terms of strength and ductility. This study investigates the flexural behavior of RC beams externally strengthened with CFRP sheets, BFRP sheets, and their hybrid combination (CFRP-BFRP). This hybrid system is designed to enhance the properties of composites, where it combines the high strength of CFRP and high ductility of BFRP sheets, respectively. To investigate the behavior of the different strengthening systems, an experimental program was conducted on ten RC beams that were tested under four-point bending. The load versus mid-span deflection data were recorded and used to compare the performance of the strengthened specimens. The test results indicated that all strengthened specimens yielded higher flexural capacity and lower ductility values compared to the unstrengthened control beam. The increase in the flexural capacity of the strengthened beams ranged from 23% to 68% of the control beam. Moreover, the beams strengthened with BFRP and hybrid CFRP-BFRP sheets achieved higher ductility compared with the beams strengthened with CFRP sheets. Thus, it was concluded that the use of a hybrid combination of CFRP-BFRP sheets could achieve the desired increase in the flexural capacity of RC beams with an improved ductility compared to that with CFRP sheets only. Finite element (FE) models were also developed and were able to capture the behavior of the tested beams with a good level of accuracy. The predicted flexural capacity along with the associated mid-span deflection differed by 1% to 10% from the experimental values.