Chloride ion diffusion in recycled concrete containing slag under biaxial compression

Abstract

The presence of cracks and pores in recycled aggregates exacerbates the susceptibility of recycled concrete to chloride ion penetration, thereby diminishing its durability. The incorporation of slag has shown promise in enhancing the chloride ion resistance of recycled concrete, although its mechanism under biaxial loading conditions remains unclear. In this study, a self-made apparatus was employed to investigate chloride ion diffusion in recycled concrete with slag content ranging from 0 % to 30 %, subjected to biaxial loading with stress ratios of 1:0, 1:1, and 2:1. To validate the reliability of the self-made device, both natural diffusion tests and standard rapid chloride ion migration (RCM) tests were conducted. All three approaches provided consistent evidence of a decrease in the chloride ion diffusion coefficient as the slag content increased. This phenomenon was attributed to the slag's capacity to fill large pores and interrupt interconnected cracks, as observed through SEM analysis, even though porosity increased. Under biaxial loading, the chloride ion diffusion coefficient of slag-recycled concrete exhibited an initial decrease followed by an increase as the stress level escalated. The lowest chloride ion diffusion coefficient for recycled concrete was achieved at a stress ratio of 1:1, a stress level of 0.5, and a slag content of 30 %. Furthermore, a predictive model for the chloride ion diffusion coefficient in slag concrete under biaxial loading conditions was developed.