Fiber-reinforced concrete (FRC), its behavior, and the effects of cyclic loading on its internal microstructure are studied in this paper. Particular attention is given to the evolution of the residual tensile strength of the fiber-reinforced concretes and damage following cyclic flexural loading. A numerical equation is also proposed to estimate the residual tensile strength, depending on crack width, damage, fiber content, and fiber orientation. A total of 65 prismatic specimens, in two different series, were tested: one designed with 1% of fibers by volume and the other with 2% of fibers. The specimens were not notched, but had previously been subjected to pre-cracking, which has a similar effect to notching, although the specimens become more vulnerable to fatigue. Both fiber content and fiber orientation were measured using computed tomography (CT) scans. The results showed that the damage provoked a progressive reduction in the residual tensile strength. The differences in the behavior of both series were mainly related to their fiber content and, to a lesser extent, to their fiber orientation.
