Flexural fatigue performance of recycled sand concrete for high-speed railway track bed

To investigate the applicability of recycled sand concrete in high-speed railway ballastless track bed, in this study, the fatigue life, strain evolution curve and calculated stiffness of C40 concrete incorporating 0, 50 % and 100 % recycled sand were explored. Digital image correlation (DIC) and the nanoindentation test were used to explore the influence of recycled sand on the performance of concrete. The results show that the flexural fatigue life of recycled sand concrete conforms to a two-parameter Weibull distribution. The fatigue strain progression and calculated stiffness demonstrate a distinct three-stage trend. Compared to natural aggregate concrete, the first-stage strain contribution of recycled sand concrete decreases by approximately 10 %. With the increase of fatigue cycles, the calculated stiffness decreased significantly, the dissipated energy increases gradually. Compared with recycled sand-free concrete and full recycled sand concrete, the concrete containing 50 % recycled sand possesses the highest elastic modulus and lowest thickness of the interfacial transition zone (ITZ), thus the average fatigue life of recycled sand concrete increased by 4.9 and 10.2 times.