Role of local fiber content and orientation on the scatter of flexural fatigue behavior in steel fiber-reinforced concrete

This study investigates the scatter in fatigue life (N) of fiber-reinforced concrete (FRC) as a function of variability in local fiber orientation and content. To this end, three FRC series were produced with fiber contents of 0.3 %, 0.6 %, and 1.0 %. All specimens were scanned using micro-computed tomography (microCT) and subsequently tested under flexural fatigue. The results show a clear correlation between fiber orientation and fatigue strength: within each series, specimens with a higher orientation factor η X (which quantifies the degree of fiber alignment along the longitudinal axis) withstood a greater number of cycles to failure. A strong relationship was also identified between the number of fibers crossing the central section (N fib,c ) and fatigue life. Moreover, η X and N fib,c were found not to be independent variables, as a higher number of fibers is associated with better orientation. Finally, a model is proposed to estimate fatigue life as a function of η X and fiber dosage, which shows adequate accuracy in predicting the scatter in N for sets of identical specimens. • Fiber alignment along the prism axis increases flexural fatigue life in concrete. • More fibers crossing the fracture plane lead to improved fatigue strength. • Fiber content and orientation are interdependent due to fiber interaction effects. • A model that predicts fatigue life using fiber orientation and dosage is proposed. • An optimal fiber volume fraction of 0.66 % maximizes fatigue performance.