Flexural performance of layered macro fiber reinforced concrete beams

• The incorporation of macro fibers enhances the flexural strength and flexural toughness of concrete. • The application of layered structure effectively enhances the utilization of macro fibers in concrete. • The effects of the macro fiber content in the bottom layer as well as the height of the bottom layer were examined. Fiber-reinforced polymer (FRP) composites have been increasingly used in various sectors, which inevitably results in an increasing amount of FRP waste to be dealt with. A recent study conducted by the authors’ group explored a novel mechanical recycling method to process glass fiber-reinforced polymer (GFRP) waste into small slender elements (referred to as “macro fibers”) for reinforcing concrete, leading to so called “macro fibre reinforced concrete” (i.e., MFRC). The macro fibres recycled from waste FRP composites shows to effectively enhance the tensile performance of the resulting concrete (e.g., tensile strength, tensile toughness), while have a negligible effect on the compressive properties of MFRC. The concept of the layered beams has been therefore adopted with the bottom layer fabricated with MFRC and the top layer with plain concrete (PC) to improve the utilization and added values of the macro fibers from the structural level. A series of tests were conducted to justify the proposed technique. Test results indicate that an increase of 4.6%, 27.6%, and 44.3% in splitting tensile strength was observed for concrete with a macro fiber content of 1%, 1.5%, and 2%, respectively. Some of other mechanical properties of the resulting concrete (e.g., the compressive toughness, flexural strength and flexural toughness) were apparently enhanced as well by the incorporation of macro fibers. In addition, the flexural performance of concrete beams shows to be superior if the macro fibers mainly concentrated in the bottom layer (i.e., a layered beam), demonstrating a higher utilization and added values of macro fibers achieved by the application of layered beams.