Due to common heavy snowfall in winter, concrete structures in cold countries are regularly in contact with water. Hence, concrete undergoes abnormal leaching of ionic species present inside the liquid pores of the material. The leaching slowly degrades the structures and may have an influence on the diffusive properties of the chloride ions, coming from the de-icing salts and responsible for the corrosion of the steel reinforcements present in the reinforced concrete. In this work, an experimental and numerical study is propounded to better understand the influence of the leaching state of cementitious material on the diffusive behaviour of chloride ions. Natural and accelerated diffusion tests were performed on samples of hydrated cement paste and concrete samples with lower chloride concentrations (50 mol/m3). The materials were conserved at different leaching state with care not to degrade the microstructure: safe (S), partially leached (PL), and leached (L). The simulation of those various tests was carried out on the reactive transport software PhreeqC to quantify the chloride diffusion. This numerical model allows distinguishing the influence of the geometry of the material (porosity, tortuosity, constrictivity…) to the chemical reactions occurring between chloride ions and the cementitious phases. It then appeared that chloride ions do not diffuse in the same way depending on the leaching state of the cementitious material. Same observations are made on hydrated cement paste and concrete samples. In a safe material, the chloride ions diffuse slowly than in a leached material. It seems not to be due to the material geometry nor chemical reactions. The numerical model developed confirms this hypothesis as it allows to distinguish and quantify their both influence on the chloride diffusion. This study, therefore, highlights the importance of considering the leaching effects in the prediction model for concrete structure durability in cold countries.