Estudio del fallo por delaminación de la fibra en refuerzos exteriores a base de polímeros reforzados con fibra de vidrio

Resumo

Behavior of bond between Fiber Reinforced Polymers (FRP) and concrete is a key controlling factor for the behavior of any structure externally reinforced with the help of FRP-based composite materials. In general, the adhesive is designed to achieve failure through concrete cover delamination or reinforcement failure. In the framing problem of this study, an additional constraint is introduced: the adhesive is approved for contact with potable water destined to human consumption, and its mechanical performance is less efficient than usual compared to adhesives specifically designed for structural reinforcement. A study to determine the behavior of this particular external reinforcement is thus proposed. To analyze this phenomenon, a test rig which satisfies the nessary conditions for bond studies and which is also adapted to an universal testing machine is developed. The test rig consists of two cylindrical concrete specimens, 15 cm diameter and 25 cm long. Each of the cylinders has an axially embedded steel reinforcement bar. Clamps pull on the steel bars which in turn transfer the load to concrete. A GFRP reinforcement band (three in total) is placed longitudinally on the rig every 120 ˚. Four setups combining different widths and bonded length values have been tested, plus a fifth setup with additional bonded transverse reinforcement. With the help of automatic monitoring, different data sets have been analyzed for identification of debonding areas, ultimate bond strength, and mechanical behavior of the reinforcment. Delamination mode is also studied, together with the influence of reinforcement width and bonded length on the obtained results. Finally, a comparison is made between results obtained and the ones predicted by the reference Bond Strength Model (Chen et al 2001), adjusting its coefficients to adapt its basic formulation to the particular features of the adhesive used in the test. It can be concluded that an increase in reinforcement width leads to an increase in ultimate resistance of the system, while an increase in reinforcement length beyond the critical development length increases the ductility of the delamination process without an increase in strength.