Abstract
Calcium silicate, which is main compound of cement takes place the reaction with water topochemically；that is, hydration of calcium silicate proceeds the hydration products such as amorphous calcium silicate hydrate gel（C-S-H gel）and Ca（OH）2 to form “shells” around the cement grains. Thus it expected that the amount and properties of produced C-S-H gel, e.g. chemical composition and silicate anion structure, strongly influences the hydration kinetics of calcium silicate. However it has not been clearly understood the relationship between the hydration kinetics and the amount and properties of produced C-S-H gel.
In this paper aims to elucidate the influence of the amount and properties of produced C-S-H gel on the hydration kinetics of calcium silicate, the kinetics of hydration of tricalcium silicate（C3S）and CaCl2-accelerated C3S pastes were investigated by performing X-ray diffraction （XRD）, 29Si MAS NMR, and thermogravimetric analysis（TG/DTA）on parallel specimens during the first few days of hydration under the same curing conditions（water/C3S ratio of 0.5, 20℃）. CaCl2 were added by 2.5, 5 and 10％ for mass of C3S as a solution. CaCl2-accelerated paste showed that CaCl2 accelerated significantly the dissolution of C3S in the process of nucleation and growth of C-S-H. However, after deposition of initial C-S-H, higher concentration of CaCl2 in pore solution strongly prevented hydration of C3S by the repression of water diffusion due to formation of the C-S-H gel shells around the unhydrated C3S. 29Si MAS NMR spctra analysis indicated that the influence of CaCl2 on the kinetics of C3S hydration closely related to the change in the nano-scale crystalline structure of C-S-H gel, tobermorite-like one and jennite-like one, and corresponding change of diffusion of water through C-S-H gel around the unhydrated C3S.
