Prediction of pore-water alkali concentrations in hydrating OPC

In this paper the release and binding of alkalis in a hydrating cement system is studied. First, the binding factors for sodium and potassiwn as determined by Taylor [5] and the corresponding distribution ratios as determined by Hong and Glasser [6, 7] are expressed in each other. It follows that the sorption of sodium is practically identical, whereas for potassium Taylor [5] predicts a substantial lower degree op sorption. The concept of alkali release, pore water decrease and sorption by formed C-S-H, is incorporated in the NIST hydration model (CEMHYD3D). Subsequently, the model is compared with OPC hydration experiments reported by Larbi et al. [12]. Good agreement is obtained when the distribution ratios of Hong and Glasser [6] are applied. The results suggest that C-S-H is the only binder of alkalis in hydrating OPC.