Equilibria and preparative methods

The solubility of gypsum is only slightly decreased in the presence of CH, and vice versa (Table 6.6). The effect, which could scarcely be explained if the only dissolved species were Ca , OH and occurs because 

Gartner el al. (G58) discussed equilibria governing precipitation of gypsum, CH and syngenite with reference to the early stage of cement hydration. They concluded that the equilibrium activity products at 25°C were (2.547 + 2.258/) x lO moH 1 for gypsum, 8.25 x 10 moF P  

Data have also been obtained at other temperatures from 1 C to 50 C (J19) some are considered in Section 10.1.5. At 50 C or above, the other ternary phases are rapidly replaced by CjAH.  

No detailed studies on the CaO-AljOj-SiOj-HjO system at ordinary temperatures have been reported, but, based largely on considerations of solubility products, Dron (D23) suggested the main features of a probable metastable equilibrium diagram, a modified form of which is shown in Fig. 6.7. The diagram indicates the metastable coexistence of CH, C-S-H and C4AH19, and that stratlingite cannot coexist with CH. In cement pastes, the AFm and AFt phases appear to accommodate some silicon the extents of these substitutions, and the related question of the scale on which the hydrated phases are mixed, are considered in Sections 7.2 and 7.3. 

Equilibria in the CaO-AljOj-SOj-HjO system were studied at 25 C by Jones (J20) and at 20°C by d Ans and Eick (D24). Eollowing Brown (B91), the latters results are shown on a three-dimensional diagram in which the 

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