Experimental Investigation on the Chloride Transport Characteristics from Soda Residue Foundation to Semiburied Concrete under Water Environmental Factors

Use of soda residue as engineering backfill is the most practical and economical method for reusing soda residue. In the existing research on soda residue soil as engineering backfill, most scholars focus on the bearing capacity of a soda residue foundation, while ignoring the failure of reinforced concrete (RC) built on soda residue foundation caused by the residue's high salinity and high water content. In this study, a semiburied concrete indoor natural exposure experiment in a soda residue soil environment was conducted to investigate chloride transport between the foundation and the concrete, considering the effects of water environmental factors, including groundwater level of the foundation, relative humidity (RH) above ground, saturation of the foundation, and precipitation. The results show that chloride concentration in the above-ground part of the concrete (enriched in a range from ground level to a height of 100 mm) is apparently higher than that in the below-ground part, while chloride concentration in the concrete below the groundwater level is slightly higher than that from groundwater level to ground level. In the above-ground part of the concrete, the chloride concentration decreases with RH above ground. In the below-ground part, the chloride concentration in the unsaturated soda residue soil environment is higher than that in the saturated soda residue soil environment. Precipitation can effectively reduce chloride in the concrete in a soda residue foundation, while the total invasion of chloride decreases from 9 to 3 g in 120 and 180 days compared with that in a nonprecipitation environment. The time-dependent prediction empirical model of concrete chloride concentration in a soda residue foundation environment was established by introducing water environmental parameters of groundwater level of the foundation, RH above ground, saturation of the foundation, and precipitation environment. The reference apparent chloride diffusion coefficient D0 is 33.6x10-12, 33.9x10-12, and 20.01x10-12 m2/s in groundwater, from groundwater level to ground level, and above-ground, respectively.