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Chloride induced steel corrosion is the greatest problem in durability of the reinforced concrete structures exposed to marine environments.Addition of the blast furnace slag to cement suppresses the transportation of chloride ion into the concrete, especially the hardened cement paste.The transportation of chloride is influenced by the physical and chemical adsorption to the cement hydrate such as CSH and Friedels salt as well as the ionic diffusion.In particular, chloride ions adsorbs dominantly on the C-S-H, which in the mainly hydration of cement.It is well known that an aluminum substituted calcium silicate hydrate gel (C-A-S-H) is produced when added blast furnace slag.However, the effect of Al substitution on the physical adsorption of chloride ions of C-S-H has not been understood enough.In this study, C-S-H and two types of C-A-S-H substituted 4 and 8 mole % of Si by Al, of which Ca/(Si+Al) molar ratio equal to 1.0 were synthesized.The physical adsorption of calcium and chloride ions for synthesized C-S-H and C-A-S-H were experimentally quantified by ion chromatography.The enhanced surface complexation model was proposed by considering silanol and aluminol groups in silicate tetrahedral of C-A-S-H as adsorption sites.Parameters of the model were obtained by fitting the model to the experimental data for adsorption and zeta potential.We obtained a good fit between the model results and experimental data on chloride adsorption.