Mechanical behavior of multiscale hybrid fiber reinforced recycled aggregate concrete subject to uniaxial compression

Abstract

This paper presents a multiscale hybrid fiber reinforcing strategy that can remarkably compensate for the adverse effects of recycled coarse aggregate (RA) on the performance of concrete. The hybrid fibers including macro steel fiber (SF), micro polypropylene fiber (PPF), and cellulose nanofiber (CNF) were utilized for crack arresting at multi-levels and improving the mechanical properties of RA concrete (RAC). This work aims to investigate the mechanical performance of multiscale hybrid fiber reinforced RAC (MFRRAC) under uniaxial compression and unveil the multiscale hybrid fiber reinforcement mechanism. A total of 34 groups of prismatic specimens were tested, with an emphasis on the effects of RA replacement rate and fiber parameters on the failure mode, compressive strength, deformation ability, and stress-strain curve. The results showed that the incorporation of multiscale hybrid fibers has a marked impact on the compressive properties of RAC. Specifically, the addition of multiscale hybrid fibers could significantly alter the failure pattern of RAC. In addition, compared with RAC without fibers, the axial compressive strength and peak strain of MFRRAC could be increased by up to 39.34% and 24.85%, respectively. Furthermore, the hybrid fiber reinforcement mechanism on the mechanical enhancement in a physical-chemical manner was revealed, in particular, multiscale crack resistance and hybrid fiber synergetic effect. Finally, a stress-strain model was developed with RA replacement rates and fiber parameters taken into account, and the predictions can correlate well with available experimental results with wide applicability. This research work lays a foundation for the accurate design and analysis of MFRRAC structures.