The adsorption and diffusion behavior of chloride in recycled aggregate concrete incorporated with calcined LDHs

Recycled concrete aggregate (RCA) is an important form for reusing of waste concrete. However, the presence of corrosive ions, specifically chloride ions, which are absorbed on the surface of RCA or infiltrated from the external environment, significantly affects the mechanical performance and durability of recycled aggregate concrete (RAC). This paper aims to suppress the erosion and diffusion of chloride ions in RAC by adding calcined layered double hydroxides (LDOs), utilizing the restructuring and anions exchange properties of LDOs. The dissolution ratio of chloride ions carried by RCA and the adsorption efficiency of LDOs on the leaching ions were analyzed using the silver nitrate titration method. The maximum chloride adsorption capacity of the LDOs is 31.052 mg/g. Additionally, the inhibitory effect and mechanism of LDOs on chloride ion attack were detailed evaluated by the techniques combining mercury intrusion porosimetry (MIP), scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM and EDS), rapid chloride migration coefficient method (RCM), and electrochemical impedance spectrum. The results indicate that LDOs exhibit a good adsorption effect on chloride ions leaching from RCA, and the adsorption efficiency is negative correlation with the pH value. Furthermore, the small size effect of LDOs plays a filling role in the pores of concrete, increasing the compactness and penetration resistance of chloride ions of RAC. This work provides a promising approach to enhance the mechanical and durability properties of RAC by incorporating with LDOs utilizing its chloride ion capture feature and nano-filling effect. And the findings of this research can also be extended to the use of LDOs for treatment of other corrosive anions, such as SO42- and CO32- in RAC, demonstrating its applicability in a broader context.