Structural performances of PBO FRCM-strengthened RC beams

Innovative composites made by fibre meshes (glass, carbon or polypara-phenylene-benzo-bisthiazole (PBO) fibre meshes) embedded into an inorganic stabilised cementitious matrix called fibre-reinforced cementitious mortars (FRCM) represent a very effective solution for strengthening reinforced concrete beams. The FRCM strengthening system can be considered alternative to the well-known fibre-reinforced polymers (FRP) system made by unidirectional fibre sheets embedded into organic resins; the FRCM system, in fact, allows the reduction or elimination of some disadvantages related to the use of organic resin such as lack of fire resistance, degradation under ultraviolet light and low compatibility with the concrete substrate, without compromising the performance of strengthened members. Owing to the large slip at the fibre-cementitious matrix interface, a more ductile behaviour and different failure modes were experimentally observed in FRCM strengthened beams with respect to those strengthened with fibre-reinforced polymers. These structural aspects are analysed and discussed in the paper by means of the results of an experimental investigation carried out on reinforced concrete beams flexurally strengthened with PBO-FRCM. Obtained results indicate an improvement of the flexural capacity of PBO-FRCM-strengthened beams, the change of the failure modes with the increase of PBO reinforcement ratio and, in the presence of debonding, the occurrence of a gradual failure.