External sulfate attack on concrete under combined effects of flexural fatigue loading and drying-wetting cycles
he concrete transportation infrastructures will undergo both fatigue traffic loading and environmental impacts during the whole service life, including rigid pavements, bridges decks, airfield runways, railway bridges, even high-speed railways and concrete structures in the ocean. This study aims to investigate the effects of external sulfate attack on concrete under flexural fatigue loading and drying-wetting cycles. The changes of mass loss rate and relative dynamic elastic modulus were measured to indicate the influence of the coupled effects on the integrity and mechanical performance of concrete, also the sulfate content inside concrete was determined to indicate the permeability of sulfate ion under different experimental conditions. Moreover, the phase composition of samples was analyzed using X-ray diffraction (XRD). In addition, the effect of fly ash on sulfate attack was duly studied. Fatigue loading causes cracking in the interfaces of various phases and forms cracks in the concrete. Within the influence depth of drying-wetting cycles, concrete is subjected to both water convection due to capillary action and diffusion due to concentration gradients. The results indicate the fatigue loading and drying-wetting cycles can accelerate the transportation of sulfate ion inside concrete and the deterioration degree of concrete subjected to sulfate. The findings in this study can help to understand the influence of fatigue loading and drying-wetting cycles on the development of sulfate attack.