Hydration topochemical reaction

The expansion mechanism has been the subject of numerous studies for mai r years. It is caused by the known contradiction consisting in the lowering of absolute volume of the system, due to ettringite or other hydrates formation this problem is discussed in Chap. 5. The oldest hypothesis was presented by Lafuma [60], which already in 1929 suggested that the formation of ettringite as a result of reaction in the solid state (topochemical reaction) will cause expansion, while occurring... 

Topochemical reaction—a chemical reaction, such as a hydration, taking place in a suspension in which the product of reaction occupies the space originally occupied by one of the reactants, rather than being precipitated randomly from the liquid phase. 

However, Fierens [9] has shown, that the hydroxylation of the slag glass surface layer, as a result of water molecules chemisorption, which is enhanced by the surface electron defects (trapped electrons), can be considered as a topochemical process. The topochemical processes became important also at later hydration stage, when the pozzolanic reaction of slag glass network, impoverishes of the majority of alkaline elements, with calcium ions is occtrrring, and calcium ions are chemisorbed on the active sites of solid phase. 

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