Influence of specimen size and fiber content on fatigue flexural strength of high-performance fiber-reinforced concrete

This paper studies the impact of specimen size and fiber content on the flexural fatigue response of high-performance fiber-reinforced concrete (HPFRC). For this purpose, six series of prismatic specimens were fabricated, considering two sizes (75 × 75 × 300 mm and 150 × 150 × 600 mm) and three fiber contents (0.3%, 0.6% and 1%). Twelve specimens from each series were tested in flexural fatigue under the same relative stress levels. It was sought to explain the variations in fatigue response through the observation of the mesostructure. In particular, correlations were established between the fiber distribution and the fatigue strength of all series. The results reveal that the parameter that most influences the ultimate static bending strength (σ ult ) is the fiber volume in the central region of the specimens (V fib ), with the orientation having a much lower weight. In contrast, the opposite is true for cyclic tests. Since the fatigue stress levels were calculated in relation to σ ult of each series, the influence of V fib is negligible. In this case, a clear correlation between fiber orientation with the longitudinal axis and fatigue strength is observed. Specifically, the orientation factor η X accurately predicts both the characteristic fatigue life and the rate at which damage progresses in the main macrocrack. • The fiber volume in the central region of the specimens is higher in the small specimens than in the large ones. • Specimen size has much more impact on fiber orientation than fiber content. • A strong correlation is found between the fiber volume in the central region and the static flexural strength. • The orientation factor in the longitudinal axis accurately predicts both the fatigue life and the fatigue damage rate in the main macrocrack.