Congruent reaction, defined

The results of experiments at high w/s ratios have been interpreted assuming superficial hydroxylation of the CjS followed by congruent dissolution and subsequent precipitation (B63,B57). Reaction in pastes must also occur at least partly by dissolution and precipitation, since much of the product is deposited at a distance from the starting material, and because both C<-jo and Csjoj pass through maxima. Topochemical mechanisms, defined as ones in which the material does not pass through a true solution phase, may also occur, especially in the late stage of reaction (T26). 

---