Fatigue Behavior of Steel Fiber Reinforced Concrete in Uniaxial and Biaxial Compression

The fatigue strength and behavior of plain and fiber concrete are investigated. Seventy-two steel reinforced concrete specimens, with 1 volume percent of 25-mm (1-in)-long fibers, were tested under compression fatigue loading. The S-N curves were obtained under four stress ratios of 0 (uniaxial), 0.2, 0.5, and 1.0, resulting in a series of fatigue stress envelopes for fiber concrete. Deformations in all three principal directions were measured. The S-N curves, strength envelopes, failure modes, and cyclic deformations of fiber concrete are compared to those of plain concrete. It is found that addition of fibers does not increase the endurance limit but is beneficial above the endurance limit in the low-cycle region. Furthermore, adding fibers to concrete increases its ductility, and changes failure modes from splitting-type to faulting-type. All these phenomena can be explained by the development of microcracks in the cement-sand matrix and at the bond surfaces between the matrix and aggregates.