In the simulation technique of evaluating the ionic mass transfer for the durability assessment of RC structures, the development of models for chemical reactions, such as binding of chloride ions, has recently become a significant issue. In this study, thermodynamic modeling was investigated to simulate the changes of hydrate phases caused by neutralization using PHREEQC - a computer program for aqueous geochemical calculations. The model has been applied successfully to describe the dissolution/precipitation behavior of calcium aluminate phases, especially the decomposition of Friedel's salt, and releasing chloride ion into pore solution. For the behavior of C-S-H gel, utilizing the proposed model assuming a binary non-ideal solid solution of Ca(OH)₂ and SiO₂, a continued reduction of CaO/SiO₂ can be reproduced. Accordingly, this model has allowed appropriate evaluation of chemical reactions of cementitious materials under any type of deterioration.