Avaliação da degradação de vigas reforçadas com FRP quando expostas ao intemperismo

Abstract

Considering structures natural aging process and also considering externally strengthened elements exposure to aggressive environments (freeze-thaw cycles, temperature, carbonation, ultraviolet radiation, wet-dry cycles, among others), little is known about the behavior and durability of the strengthening system bonding to the concrete substrate and the possible performance loss due to degradation of the intervening materials. In this context, the present work is based on the experimental analysis of the long term mechanical behaviorof the constituent materials of the reinforced concrete beams with carbon fiber sheets strengthening system (CFRP, Carbon Fiber Reinforced Polymer) applied according to the EBR (Externally Bonded Reinforcement) technique kept in laboratory environment (internal and protected) and exposed to weather (external exposure). Eight reinforced concrete beams with rectangular section, longitudinal reinforcement rate of 0.75% and concrete with compressive strength of 20 MPa, were tested. Among the set of beams, four were used as reference and two were strengthened with carbon fiber sheets, and the others were divided into two groups and exposed to six-months laboratory environment and six-months weather environment. These beams, with a distance between the supports of 230 cm, were submitted to three-points flexural testing with a midspan concentrated load. The beams were designed behave in strain limits with tension controlled rupture. Beams behavior analysis was performed based on the results of the loads and modes of rupture, deformation of the intervening materials and cracks propagation. The experimental results were also compared with the estimates limits specific at ABNT NBR 6118 (2014), ACI 318 (2014) and ACI 440.2R (2017). In addition, specimens of the strengthening system materials constituents were also created and exposed to the same environmental conditions as the beams. The mechanical properties of these materials were investigated from uniaxial tensile testing. The results showed that lamination epoxy adhesives present reductions of up to 70% in their mechanical properties when exposed to the weather, while the CFRP composite showed similar properties before and after exposure. In the case of the strengthened reinforced concrete beams, it was verified that the strengthening system provides increases of 50% and 28% in the load capacity and stiffness, respectively, when compared to non-strengthened specimens. However, the tests performed after exposure to the elements showed a reduction in the increase of the load capacity. In relation to the comparison between the theoretical and experimental results, taking into account the specifications at ABNT NBR 6118 (2014), ACI 318 (2014) and ACI 440.2R (2017), it was observed that the values of ultimate load and service load are close when property reductions are not applied.