Effect of Load-Temperature-Osmotic Coupling on Chloride Ion Transport in Ultrahigh-Performance Concrete: Experiments and Models

Abstract

Under complex geological circumstances, the deep part of ultrahigh-performance concrete (UHPC) experiences high stress, high temperature, and high permeability, resulting in the rapid corrosion and damage of concrete structures. This paper evaluates the chloride ion transport performance of UHPC under the simultaneous impact of load, temperature, and osmotic pressure by measuring the chloride ion concentration distribution and employing X-ray diffraction. The results show that the chloride concentration and penetration depth increase with load, temperature, osmotic pressure, and water-binder ratio. The factors with the most significant influence on the chloride ion transport performance of UHPC in descending order are osmotic pressure, load, temperature, water–cement ratio, and fiber content. As the load, temperature, osmotic pressure, and water-binder ratio increase, the content of Ca(OH)2 decreases, while the content of the generated Friedel’s salt increases. Moreover, the content of Ca(OH)2 in pure UHPC is lower than UHPC mixed with fiber, and the content of generated Friedel’s salt is markedly higher than in UHPC mixed with fiber. A chloride ion transport diffusion-convection theoretical model is established and proven to be valid.