Transport behaviors of concrete under complex coupled effects of freeze-thaw, high-frequency load, and chloride attack: An experimental and numerical study

Transport behavior of chloride ions fundamentally affects the service life of ballastless tracks, of which the wide applications expose the reinforced concrete to extremely complex coupled conditions, including freeze-thaw cycles and high-frequency fatigue load in addition to chloride ion transport. Previous studies mainly focused on either factor affecting diffusion of chloride ions, based on which the predicting model could not accurately describe the depth and concentration of chloride ion transport. Herein, the coupling effect on the chloride permeability of concrete was experimentally investigated by sequentially and repeatedly applying high-frequency (20 Hz) bending fatigue loading and freeze-thaw treatment in presence of chloride ions. A predictive model for concrete transport performance under the coupled actions of freeze-thaw cycles-fatigue load-chloride attack was established to describe the transport behavior of chloride ions in concrete with predicting accuracy higher than -90%. The influence of important factors including water-binder ratio, external chloride concentration, freeze-thaw cycles, and fatigue load on the chloride transport performance of concrete has been systematically determined. Compared with only considering the coupling of freeze-thaw action, the established model accurately predicted the distribution of chloride ion concentration in concrete, i.e., advancing the predicting time required to reach chloride concentration of 40 mol/m3 by -12.80%. Our proposed model presents more timely pre-warning of chloride penetration, and provide useful information in describing the deteriorating rule of concrete under complex multi-field actions, contributing to the efficient, safe and stable long-term operation of ballastless track.