Hydration of clinker phases

The reaction of cement with water is a very eomplex process for a long time it has been the subject of numerous discussions and controversies. The contradictoiy opinions derived from the crystallization theory proposed by Le Chatelier and the colloidal concept announced by Michaehs retinn again and a in in the renewed theories and reaction schemes. There are some serious questions as the mechanism of reaction, particularly at early age, is concerned the factors leading to an apparent hindering of reaction in the so-called induction period are not completely understood. 

These discussions and doubts result first of all from the complexity of reaction of unhydrous cement phases with water. This can be illustrated taking into account a simple, on a first appearance, example of gypsum hemihydrate hydration. This reaction served as a basis of Le Chatelier s crystallization theory. The uncompUcated, at first sight, reaction  

The studies of hydration proeess reveal that the mechanism at early age is more sophisticated [1]. It is not only the break down of the bonds in crystal stracture by water molecirles (an endothermic process with thermal effect corresponding to lattice energy) and the transport of ions (or molecules) into the solution with their simirltaneous hydration (an exothermic process). 

Just after the contact of water with the hemihydrate grains water molecules are absorbed by the sohd and a type of solid solution in the sulphate hemihydrate 

The three endothermic peaks at temperatures 80, 110 and 120 °C respectively are attributed to the aforementioned three types of water (Fig. 3.2). In the loosely bound layer of water the dissolution of hemihydrate is facilitated and when the 

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Hydration of Clinker Phases (J/g) for some types of cements, measured according to PN-EN... 

Lukas, W., The Influence of Melment on the Hydration of Clinker Phases in Cement, 5th Int. Melment Symp., Munich, pp. 17-21 (1979)... 

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