Cyclic tensile behavior of ultra-high performance concrete with hybrid steel-polypropylene fiber: Experimental study and analytical model

Abstract

The present study deals with the effect of steel-polypropylene hybrid fiber on the tensile stress–strain behavior of ultra-high performance concrete (UHPC) subjected to monotonic and cyclic loading. Eight batches of UHPC samples with hybrid fibers were tested, with the failure process monitored by acoustic emission (AE) technique synchronously. The failure mechanism of UHPC and reinforcing mechanism of hybrid fibers were analyzed based on the combination of AE source location and scanning election microscope (SEM) observation results. The results indicated that the inclusion of hybrid steel-polypropylene fibers in UHPC matrix contributes to the enhancement of tensile mechanical performance with respect to the tensile strength, peak strain and especially the tensile toughness. Moreover, the relationship between plastic strain accumulation and envelope unloading strain during cyclic tension presents a linear pattern and appears insensitive to the variation of fiber parameters. However, the hybrid fibers significantly contribute to alleviation of the elastic stiffness degradation of UHPC during the cyclic tension. Based on the stiffness degradation process, a damage evolution law characterized by an exponential equation associated with fiber reinforcement indexes is proposed. Notably, the failure of UHPC specimen stems from concurrent macro-crack propagation and multiple cracking behavior throughout the whole loading process, which is improved due to the multi-scale reinforcement effect of hybrid fibers. Finally, in consideration of the effect of hybrid fibers, an analytical constitutive model is developed to generalize the tensile behavior of UHPC, and the comparisons yield a close estimation with test results in current research and literature.