Flexural fatigue analysis of hybrid fibre-reinforced concrete

This paper presents the results of an investigation conducted to examine the probability distributions and flexural fatigue performance of hybrid fibre-reinforced concrete (HyFRC) containing different proportions of steel and polypropylene fibre. An experimental programme was planned to obtain the fatigue lives of HyFRC, in which approximately 435 beam specimens of size 100 x 100 x 500 mm were tested under four-point flexural loading. Approximately 225 static flexural strength tests were also conducted to facilitate fatigue testing. The specimens incorporated different proportions of steel and polypropylene fibres in the ratio of 25:75%, 50:50% and 75:25% by volume at each fibre volume fraction of 0.5%, 1.0% and 1.5%. The fatigue test data were used to establish probability distributions of HyFRC at different stress levels. The gradual replacement of steel fibres by polypropylene fibres in the HyFRC mix was found to significantly reduce the variability in the distribution of fatigue life of HyFRC compared with steel fibre-reinforced concrete containing comparable mono steel fibres in terms of size and shape. To examine the flexural fatigue performance of HyFRC, the test results are presented in the form of S-N diagrams; two million cycles of fatigue strengths/endurance limits were determined for different fibre mix combinations corresponding to each fibre volume fraction. The test results indicate that a combination of 50% steel fibres and 50% polypropylene fibres is the most appropriate for both reduction in variability and flexural fatigue performance in terms of the two-million cycle fatigue strength/endurance limit of HyFRC.