Gypsum formation from cement

Gypsum, 4 582-601 5 467, 785t 23 576 forms and composition, 4 583t hardness in various scales, 7 3t in Portland cement, 5 467 in Portland cement hydration, 5 477t thermal reduction of, 23 577 thermodynamics and kinetics of formation- decomposition, 4 586-588 Gypsum board, 4 600-601 Gypsum processes, obtaining sulfur from, 23 576-577... 

Figure 19. Cement hydration process. Calcium silicate hydrates to form C-S-H, a quasi-amorphous gel of composition close to C3S2H3. The excessive rate of hydration of the aluminate phase is controlled by gypsum through the formation of a calcium trisidfoaluminate hydrate, ettringite. (Reproduced with permission from reference 5. Copyright 1991 Elsevier.)...

Heat liberation in the hydration of sulfobelite cements is characterized by two peaks within the first few hours, attributed to the formation of gypsum from anhydrite and the precipitation of ettringite (Sudoh et al, 1980 Sahu et al, 1993). In spite of rapid heat liberation at the beginning of hydration, due mainly to the formation of ettringite, the total amount of heat liberated in the hydration of sulfobelite cements is lower than that of Portland cement, and amounts to about 200 kJ/kg (Su et al, 1997). This is due to the absence of C3S and C3A in this cement, which are phases whose hydration is highly exothermic. The overall heat of hydration of sulfobelite cement will decline with increasing belite content. 

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