Abstract: Using PYTHON algorithm and COMSOL software , we have developed a three-dimensional spherical mesoscopic model for recycled aggregate concrete (RAC) based on the Monte-Carlo principle and Fuller gradation theory. The model encompasses natural aggregate, old interface transition zones (OITZ), old mortar, new interface transition zones (NITZ), and new mortar. By simulating and calculating the chloride diffusion process in RAC with varying aggregate volume fractions, old mortar diffusion coefficients, and old mortar thickness, we have examined and compared the chloride resistance of RAC. Our research demonstrates that the three-dimensional spherical random aggregate model of RAC, established through random theory, closely resembles the actual mesostructure of RAC and fulfills the requirements of general engineering. Moreover, the mesoscopic numerical simulation results for chloride diffusion based on this model are consistent with experimental findings. Specifically, when the recycled aggregate content increases from 10% to 30% and 50%, the apparent diffusion coefficients of the recycled concrete increase by 6.56% and 19.43% respectively. Additionally, the diffusion coefficient of the old mortar is quadrupled, resulting in a 19.28% increase in the apparent chloride diffusion coefficient. Furthermore, the old mortar thickness doubles, leading to an 8.1% increase in the apparent chloride diffusion coefficient. Overall, the chloride resistance of RAC weakens as the thickness and diffusion coefficient of the old mortar increase.

Key words: recycled aggregate concrete, random spherical aggregate, chloride diffusion, mesoscopic performance, numerical simulation