Hugo Biscaia
Assistant Professor
in
Behaviour and Modeling of GFRP‐to‐Concrete Interfaces of Reinforced Concrete Elements Exposed to Aggressive Environments (PhD Thesis)
The present work focus in the degradation of the GFRP‐to‐concrete interface due to environmental exposure. The motivation of the studys lies on the fact that several structures have been retrofitted or reinforced with FRP composites and, due to the short period of their application, the long‐term performance of the FRP‐to‐concrete interfaces is still unkwon. In particular, the knowledge of the performance of those interfaces is very deficient when submitted to environmental severe conditions like the presence of salt, wet and dry conditions, freeze and thaw cycles, high temperatures (close to Tg), etc..
In addition, the motivation of the study lies on the fact that many regions of the portuguese territory have high temperature range and/or salted environment.
The application of FRP composites in reinforced concrete (RC) beams provides a substantial increase in their ductility and ultimate strength. However, the strength of FRP composites in RC beams is not reached and a lot of material is not mobilized when FRPs debond from concrete. The analysis and understanding of the performance of the FRP composites and the FRP‐to‐concrete interfaces is important and lead to the necessity of defining rupture criteria that can estimate the premature debonding of the FRP composite from concrete. Some of these criteria have been implemented in commercial codes helping engineers to estimate the ultimate strengths of RC structures reinforced with FRP composites.
In the present study, 79 double shear tests were perfomed with GFRP composites bonded to concrete cubes. The same bonded length of 150mm was used in all tests and different parameters like normal stress (perpendicular to the bonded surface), exposure to salt fog cycles, wet/dry cycles, temperature cycles between +7,5°C and +47,5°C and betweem ‐10°C and +30°C were analised. The results allowed to verify that the interface behaves according to the Mohr‐Coulomb rupture criterion and therefore, values for internal friction angle and cohesion were quantified for all environmental conditions herein studied.
The present work, 47 tests with RC beams being 3 of them T‐beams with realistic dimensions were also tested and analysed. With the objective of analysing the degradation of the bond between GFRP composites and concrete, the other 44 beams have rectangular section and small dimensions. Several aspects were studied for the environmental conditions and were compared with the control specimens. Essentially, the parameters studied were maximum bond stress, maximum load transmitted to GFRP, maximum strain, relative displacements between materials (slip) and fracture energy.
A commercial code was used and allowed the modelling of the GFRP‐to‐concrete interface. The results were compared with those obtained from the experiments. Some proposals were also made in order to determine the condition for the GFRP debonding from the concrete surface and the results were compared with some international rules or codes.