Mechanical performance of steel-polypropylene hybrid fiber reinforced concrete subject to uniaxial constant-amplitude cyclic compression: Fatigue behavior and unified fatigue equation

Abstract

In the natural environment, concrete-built structures are frequently undergoing repetitive loadings, e.g., earthquake, automobile traffic, or wind during their entire service life. Those repetitive cyclic loadings trigger gradual initiation, expansion and coalesce of inner cracks, resulting in progressive deterioration of mechanical performance until eventual fatigue failure. This paper presents a hybrid fiber reinforcing strategy that could significantly increase the service life of concrete. In this work, the compressive fatigue performance of steel-polypropylene hybrid fiber reinforced concrete (HFRC) under fatigue compression was investigated. A total of 36 groups of prismatic specimens were tested for various stress levels (0.7, 0.8, and 0.9). With respect to the fatigue deformation, fatigue life, and fatigue strength, the effects of fiber parameters were analyzed, including steel fiber volume fractions (1%, 1.5%, and 2%) and aspect ratios (30, 60, and 80), as well as polypropylene fiber volume fractions (0.1%, 0.15%, and 0.2%) and aspect ratios (167, 280, and 396). The results showed that the incorporation of hybrid fiber exerts a pronounced impact on the fatigue performance of concrete. Specifically, in contrast to plain concrete, the ultimate fatigue deformation and fatigue strength of HFRC could be increased by up to 63.29% and 37.18%, respectively. In addition, owing to a positive synergetic effect generated in the hybrid system, HFRC is more superior to polypropylene fiber reinforced concrete (PFRC) or steel fiber reinforced concrete (SFRC) in fatigue performance. Furthermore, a unified fatigue model was proposed to estimate the fatigue strength of HFRC with consideration of fiber parameters. The predictions were found to correlate well with available experimental results, demonstrating a wide applicability of the model in prediction of fatigue life of concrete with reasonable accuracy.