Uniaxial compressive behavior of hook-end steel and macro-polypropylene hybrid fibers reinforced recycled aggregate concrete

Abstract

The incorporation of hybrid fibers in recycled aggregate concrete (RAC) is an effective method to enhance the performance of RAC. This study aims to study the fresh properties and the uniaxial compressive behavior of hooked-end steel (HES) and macro-polypropylene (MPP) hybrid fibers reinforced recycled aggregate concrete (HFRRAC). For this purpose, three series of HFRRAC were designed with different recycled coarse aggregate (RCA) replacement ratios and hybrid fibers with different combinations at the total volume fraction of 1.5%. The results indicated that the effect of HES fibers on the workability of fresh concrete was much greater than that of MPP fibers. For natural aggregate concrete and recycled aggregate concrete with partial RCA, the hybrid combination of 1.0% HES fibers and 0.5% MPP fibers were observed as an optimum synergy effect in compression characteristics and damage evolution. However, the positive effect of single hook-end steel fibers on toughness and damage evolution was superior to that of hybrid fibers when RCA entirely replaced the natural coarse aggregate. The empirical formulas for predicting the characteristic indices and shape parameter of the piecewise constitutive model were proposed, taking the reinforcing index of hybrid fiber and RCA replacement ratio into account. Besides, the redefined damage parameter well described the damage evolution process of HFRRAC. It is concluded that the proposed model can be applied to predict the uniaxial compressive behavior of HFRRAC effectively.