Experimental investigations on layered functionally graded fiber-reinforced concrete

A spatial gradation of fiber dosage has the potential to yield a cost-effective and efficient solution to fiberreinforced concrete (FRC). The aim of this study is to comprehensively evaluate the flexural and fracture response of functionally graded fiber-reinforced concrete (FGFRC) and FRC reinforced with hooked-end steel fibers. For this, forty-eight beam specimens comprising plain concrete, FRC, and FGFRC were fabricated and tested. The workability, compressive strength, and split-tensile strength of all the mixes are reported. The volume fractions of fibers used for FRCs are 0.14 %, 0.28 %, 0.42 %, 0.8 %, 1 %, 1.2 %, and 1.6 %. The gradation of fiber dosage in layers was employed for two FRC beams, each consisting of optimal and low volume fractions of fibers (1.2 % and 0.42 %), respectively, to fabricate FGFRC beams with 0.14 %, 0.21 %, 0.28 %, 0.4 %, 0.6 %, 0.8 %, 0.9 %, and 1.05 % as effective volume fractions of fibers. The flexural behavior was evaluated from load vs. crack mouth opening displacement curves of notched beams subjected to a three-point bending test. The post-peak response was analyzed using the fracture energy obtained from the work-of-fracture method and residual flexural tensile strengths, following the recommendations of RILEM. The FGFRC beam with 0.9 % fibers showed flexural strength similar to the optimal beam (1.2 % fibers), albeit with a 20 % lesser fracture energy in comparison to the optimal beam. The gradation of the FRC beam with 0.42 % fibers has shown improvement in both the flexural strength and fracture energy by employing only 0.21 % fibers. Furthermore, a comparison of FGFRC properties against the predictions of fitted models for FRCs advocates the superior performance of FGFRCs. Advances in 3D concrete printing to control the extrusion of fiber dosages could extend this concept to continuously graded FGFRCs.