Hydration of tricalcium silicate

The results of following the quantities of free Ca(OH)2 in tricalcium silicate (3CaO.SiO2) of portland cement during the hydration and the influence of the presence of free CaO on the reaction are in agreement with the hypothesis of Stein and Stevels with regard to the hydration of 3CaO.SiO2 (CA 61: 9280g). The hydration process was studied by ir spectra and the electron microscope. When 3CaO.SiO2 comes in contact with the water, the hydrate (I) which is not distinguished from the 3CaO.SiO2 by an electron microscope is formed close to the 3CaO.SiO2 surface. Hydrate I has a very high CaO/SiO2 ratio (.apprx.3:1 moles) and strongly retards further hydration. Hydrate I is converted to a 2nd hydrate (II) which retards the hydration reaction less and has a lower CaO/SiO2 ratio. Once nuclei of hydrate II are formed the conversion takes place with a higher velocity and hydrate II converts to hydrate (III), the poorly crystd. hydrate with a CaO/SiO2 mole ratio >1.5 (tobermorite gel). The transition from hydrate I to hydrate II is accelerated by a decrease in the Ca2+ and OH- concn. in the water phase under which the formation of hydrate II nuclei is accelerated. [on SciFinder (R)]