ESTIMATION OF SILANOL SITE DENSITY OF SYNTHESIZED C-S-H

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  • 合成C-S-HにおけるSiOH基密度の推定

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Chloride induced steel corrosion is the greatest durability problem in the reinforced concrete structures exposed to marine environment. Therefore, it is important to elucidate the mechanism of chloride transport into cementitious materials. Both ion-ion and ion-solid interactions are influencing on the chloride transport into cementitious materials. Chloride can interact with cement hydrates chemically as well as physically. The electrostatic interaction of chloride on the surface of calcium silicate hydrate（C-S-H）, the main hydration product of cementitious materials, can be considered as the physical adsorption. It has been proved that the physical adsorption of chloride on C-S-H dominates its transport into matured cement paste. However, the surface electrical properties of C-S-H have not properly determined yet. Thus, the main purpose of this study is to determine the amount of surface site on C-S-H and its associated equilibrium constants. The objectives are achieved through experimental and modeling techniques. A two-layer surface complexation model was used to determine the surface site density of C-S-H（with Ca/Si of 0.6, 0.83 and 1.0）and the equilibrium constant values for dissociation of silanol sites and adsorption of calcium on silanol sites. The parameters are derived by fitting the titration and calcium adsorption experimental data to the model results. It can be inferred that the estimated parameters in this study will provide insight into the prediction of adsorption and diffusion of not only chloride but also other ions in cementitious materials.

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