The use of by-product gypsum is an important alternative in concrete design. In present experiment, conduction calorimetry
was applied to investigate the early hydration of calcium aluminate cement (CAC)/flue gas desulfurization (FGD) gypsum paste,
supplemented with the determination of setting times and analysis of hydrates by X-ray diffraction (XRD). It was found that
different profiles of heat evolution rate were presented depending on the CAC/FGD gypsum ratio. Two distinct exothermic peaks,
associating with CAC hydration and ettringite formation respectively, appeared when the FGD gypsum content was less than 20%.
Hydrate barrier mechanism was introduced to explain the difference in induction periods of the pastes with or without FGD
gypsum. It is concluded that the blending of FGD gypsum accelerates the hydration of CAC for the quick formation of ettringite
and generates greater hydration heat from per gram of pure CAC for the high exothermic effect of ettringite formation. The
dissolution and diffusion of gypsum plays an important role of reacting controller during the hydrations of the pastes with
FGD gypsum. The modified hydration process and mechanism in this case is well visualized by means of calorimetry.