The Influence of Fiber-Form Waste Tire Aggregates on the Flexural Strength, Ductility, and Energy Dissipation of Pultruded GFRP–Rubberized Concrete Hybrid Beams

Abstract

This study investigates the effects of different proportions of waste rubber fiber aggregates on the flexural behavior of reinforced concrete beams. Beam specimens were prepared with different proportions (5%, 10%, and 15%) of waste rubber fiber aggregates, and composite beams formed with pultruded GFRP profiles were tested under vertical load. According to the results of this study, cube compressive strength, cylinder tensile strength, and beam flexural strength decreased by 27.5%, 50%, and 47.6%, respectively, with the use of a 15% waste rubber aggregate. As a result of the four-point bending tests performed on reinforced concrete beams, the maximum load-carrying capacity of the beams decreased significantly after increasing the waste rubber aggregate ratio to 10% and 15%. However, a general improvement in the ductility of the beams was observed. One of the main results of this study is that when the waste rubber aggregate content is 5%, the best balance between strength and ductility is achieved, and the performance closest to the reference beams is obtained. The tests also revealed that the Ø10-5% specimen exhibited higher performance in terms of both load-carrying capacity and yield stiffness. On the other hand, although the 15% waste rubber aggregate ratio caused a decrease in the maximum load-carrying capacity. along with an increase in the diameter of the tensile reinforcement, this decrease was quite low. Finally, an overall decrease in energy consumption capacity was observed with increasing waste rubber aggregate content in all test beams. This can be attributed to the acceleration of shear damage in the beam and the shrinkage of the area under the load–displacement curve as the amount of waste increases. Additionally, SEM analyses were conducted in order to investigate the microstructural behavior of the rubberized concrete. This study has shown that the use of waste rubber aggregates can be environmentally and economically beneficial, especially at the 5% level. © 2025 by the authors.