Flexural Behavior of Concrete Beams Strengthened with New Prestressed Carbon-Basalt Hybrid Fiber Sheets

Abstract

The prestressed fiber-reinforced polymer (FRP) strengthening technique has been demonstrated to be an effective method to improve the effectiveness of FRP materials and the performance of the strengthened members under normal service conditions. Resin-impregnated FRP plates have been the primary form of prestressed strengthening material in many applications. However, FRP plates are somewhat inflexible, which makes it difficult to control the bond quality between the FRP plates and imperfect concrete surfaces in field applications. Using dry fiber sheets instead of FRP plates is an effective solution to this problem. However, the prestressing control stress of dry fibers is much lower than that of the corresponding FRP laminates with impregnated resin. A method using partially impregnated carbon-basalt hybrid fiber sheets (CBHFS) is proposed in this paper to improve the tensile capacity of dry fiber sheets. The following parameters of the fiber sheets were tested: fiber hybridization ratio, partial impregnation, and specimen length. The test results show that the tensile capacity of dry fiber sheets can be enhanced effectively and that it is not influenced by the specimen length when fiber hybridization and partial impregnation are applied together. Furthermore, the strengthening effects of prestressed CBHFS were verified by externally bonded RC and prestressed concrete (PC) T-beams. Vacuum-assisted resin transfer molding (VARTM) technique was applied in the tests to improve the impregnation and bond quality of the fiber sheets. Test results indicate that the prestressed strengthening of externally bonded CBHFS can significantly improve the flexural performance of RC beams under normal service conditions compared with traditional FRP strengthening techniques.