Chloride ion transport properties in microcracked ultra-high performance concrete in the marine environment

Abstract

Ultra-high performance concrete (UHPC) has excellent mechanical properties and durability. To determine the allowable tensile deformation range for good durability of these materials in the marine environment, the effects of tensile deformation and subsequent cracking upon the chloride ion permeability properties are investigated herein. The permeability law of chloride ions under tensile deformation is analyzed via marine exposure and indoor immersion testing, and the evolution process of tensile damage and the distribution of steel fibers are characterized by acoustic emission and X-ray computed tomography (X-ray CT) techniques, respectively. The results show that the permeability of chloride ions is larger in the marine environment than in a high chloride-concentration indoor environment. In addition, the permeability of chloride ions is found to increase with the increasing tensile deformation. The relationship between free and bound chloride ions conforms to the Freundlich isothermal equation. Finally, based on Fick's second law, the two-dimensional diffusion process of chloride ions in UHPC is fitted, and the relationship between the tensile deformation and the diffusion coefficient of chloride ions is established.