Hydration behavior of C2S and C2AS nanomaterials, synthetized by sol-gel method

Hydration behavior of dicalcium silicate (C2S) (Cement chemistry nomenclature is used where C=CaO, S=SiO2, A=Al2O3, S=SO3) and gehlenite (C(2)AS), synthesized by sol-gel method was investigated by means of isothermal heat flow calorimeter at different temperatures. These phases were obtained by crystallization processing at different temperatures from their xerogels (nano-crystalline) prepared by the sol-gel method at ambient temperature. The crystallization of C2S begins below 600 degrees C and it is well crystallized at 900 degrees C. X-ray diffraction patterns reveal that beta-C2S is formed and it remains stable since after slow cooling. The crystallization of C(2)AS xerogels starts with the formation of C2S, then it reacts with alumina to form mineral C(2)AS at 1100 degrees C. The effect of hydration temperature upon the hydration reaction of C2S obtained at 600 and 900 degrees degrees C and C(2)AS annealed at 600 and 1100 degrees C was investigated by means of isothermal calorimeter. An increase in the temperature of hydration brought about initial acceleration of all samples, as indicated by the increased magnitude of peak of calorimetric curves. The microstructure of the samples cured at hydrothermal condition after 1 and 7 days has been examined by means of scanning electron microscopy (SEM). Fine crystals of calcium silicate hydrate (C-S-H) were developed in C2S samples, while C(2)AS has been hydrated to form gehlenite hydrate supplemented by C-S-H.