Estudo sobre a substituição de armadura metálica por barras de GFRP em vigas de concreto armadas à flexão quando submetidas ao ataque acelerado de íons cloreto

Abstract

The use of reinforced concrete structures with steel bars is recurrent in the construction industry in Brazil. However, alternative materials are studied due to the existence of problems related to the use of this traditional constructive system, such as the corrosion of metallic reinforcements, the exposure of structures to aggressive environments and to environments in which magnetic neutrality is necessary. Among these materials, huge attention is given to Fiber Reinforced Polymer (FRP), which have high mechanical strength and good resistance to environmental aggressiveness agents, nonmetallic materials capable of replacing steel reinforcement in reinforced concrete structures. In this sense, this work aims to study the replacement of steel bars by GFRP bars in reinforced concrete beams, analyzing, over time, the mechanical behavior and durability against the chloride attack. For this purpose, concrete beams reinforced with steel bars and GFRP bars were molded, of which four were used as a reference, four were kept for 1000h in a laboratory environment and four were exposed to the chloride attack, for 1000h, through their immersion in NaCl solution with 3,5% concentration maintained at the temperature of (50±3) °C, according to the recommendations of ACI 440.9R (2015). These beams were subsequently subjected to three-point bending tests, in order to obtain and compare the resistant capacity, the vertical displacement and the rupture mode presented by the beams. The entrance of chlorine ions to the concrete was evaluated by means of a colorimetric test to determine the chloride penetration depth, in order to detect the possible corrosion of the reinforcement. The results obtained by the three-point bending tests were compared to the theoretical results obtained by using the provisions of ACI 440.1R (2015) for the design of beams reinforced with GFRP and ACI 318 (2019) and ABNT NBR 6118 (2014) for the design of beams reinforced with steel bars. The results showed a reduction in the stiffness of the beams by replacing steel reinforcement with GFRP bars by about 66 %, 72 % and 70 % for the reference beams and maintained in the laboratory environment and exposed to chlorides, respectively. The beams reinforced with GFRP bars resisted a maximum force about 27 % greater than that the beams with steel bars. No major changes were observed in the stiffness and maximum strength resisted by beams reinforced with steel bars and GFRP bars exposed to chloride attack, however, there was an increase in deformability, since the deformations in concrete and reinforcement of beams exposed to chlorides were higher than for beams maintained in a laboratory environment, considering the same applied force. It was concluded that an accelerated exposure of 1000h to the chlorine ions attack has not yet been sufficient to cause changes in the behavior of reinforced concrete beams with steel bars and GFRP bars, being necessary to evaluate the results to be obtained after 3000h and 10000h of exposure, which are the continuation of the current research program. Regarding the use of the calculation models of ACI 318 (2019) and ABNT NBR 6118 (2014) for beams reinforced with steel bars and ACI 440.1R (2015) for beams reinforced with GFRP bars, it is concluded that these standards provide safe values of capacity and conducted to the experimental observed failure modes.