Effect of PET waste fiber addition on flexural behavior of concrete beams reinforced with GFRP bars

This paper aims to experimentally investigate the flexural behavior of concrete beams reinforced with glass fiber reinforced polymer (GFRP) bars made of concrete with and without polyethylene terephthalate (PET) waste fiber addition. The test variable covers the structural application of different PET fiber lengths (20 mm and 40 mm). Firstly, several tests were done on ten concrete mixes containing 1-2% PET waste fiber with a 0.25% increment by volume. The mixture's concrete properties, including stress-strain curves, were studied to obtain the optimum percent-age of PET fiber. Furthermore, four GFRP reinforced concrete (RC) beams were cast from concrete containing 0% PET fiber (the control beam), 1% PET fiber volumes of 20 mm and 40 mm, and an equal mixture of both lengths. The beams were designed using ACI 440.1R to fail in GFRP rupture. The results showed that compressive strength increased by 8% and 6% using 1% fiber volume of 20 and 40 mm PET fiber, respectively. It was found that PET fiber addition had a negligible effect on changing the ductility, cracking pattern, or failure mode of under reinforced GFRP RC beams. The cracking and ultimate loads are slightly reduced, however, and the corre-sponding deflections are well reduced, especially when using 40 mm PET fiber. With the use of PET waste fiber, serviceability increased by up to 12% based on deflection limit control (L/240). The addition of 40 mm of PET fiber was found to enhance the beam stiffness by 25%. An analysis method has been proposed to predict the flexural strength of GFRP RC beams made with PET fiber. Moreover, it is recommended to treat the PET fiber surface to improve the fiber-concrete bond when used in non-ductile RC beams.