Hysteretic deteriorating behaviors of fiber-reinforced recycled aggregate concrete composites subjected to cyclic compressive loadings

An intensive test is designed to investigate the reinforcing mechanism of fibers, stress-strain relationship, and damage evolution of fiber-reinforced recycled aggregate concrete (FRAC). Hooked-end steel fiber (SF) and polypropylene fiber (PPF) are used, and four volume fractions of 0, 0.968%, 1.653%, and 2.338% are considered. The hysteretic deteriorating properties of FRAC under cyclic loadings are revealed, and the fracture interface inclination model is suggested accounting for the fiber content. The stress process and fiber reinforcing mechanism under cyclic loadings are explored. The toughness of FRAC depends strongly on the fiber reinforcing parameter. When the steel/PP fiber volume ratio reaches 1.653%, the toughness indexes of SFreinforced RAC and PPF-reinforced RAC are increased by 88% and 80%, respectively. The function model for the toughness index of FRAC accounting for the fiber content is proposed. In the pre-peak load stage, the damage modulus decreases slowly because the residual strain is very small. However, in the post-peak loading stage, the damage modulus decreases continuously with the increase of residual strain. The residual strain is related closely to the degradation of the damaged modulus. A new degradation model represented by residual strain is suggested accounting for the fiber content.