Alkali concentrations of pore solution in hydrating OPC

In order to study the pore solution, the release and binding of alkalis in a hydrating cement system have been studied. First, the binding factors for sodium and potassium as determined by Taylor [Adv. Cem. Res. 1 (1987) 5] and the corresponding distribution ratios as determined by Hong and Glasser [Cem. Concr. Res. 29 (1999) 1893; Cem. Concr. Res. in press] are related to each other. It follows that the sorption of sodium is practically identical, whereas for potassium Taylor [Adv. Cem. Res. 1 (1987) 5] predicts a substantial lower degree of sorption. The concept of alkali release, pore solution decrease and sorption by formed calcium-silicate hydrate (C-S-H), is incorporated in the NIST hydration model (CEMHYD3D). Subsequently, the model is compared with ordinary Portland cement (OPC) hydration experiments reported by Larbi et al. [Cem. Concr. Res. 20 (1990) 506]. Good agreement is obtained when the distribution ratios of Hong and Glasser [Cem. Concr. Res. 29 (1999) 1893] are applied. The results suggest that C-S-H is the only binder of alkalis in hydrating OPC.