EFFECTS OF CALCIUM CHLORIDE ON THE HYDRATION KINETICS OF ALITE
| Autor: | Toyoharu Nawa, Tomotaka Awamura |
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| Rok vydání: | 2013 |
| Předmět: | |
| Zdroj: | Cement Science and Concrete Technology. 67:71-78 |
| ISSN: | 2187-3313 0916-3182 |
| DOI: | 10.14250/cement.67.71 |
| Popis: | 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.セメントと水はトポ化学的に反応するため、その反応速度と反応生成物であるC-S-Hの性状とは密接な関係にある。しかしマクロな水和現象とミクロなC-S-Hの化学組成や平均鎖長の変化との関連性は不明な点が多い。そこで本研究では、純水で水和させたエーライト（C₃S）と水和促進剤であるCaCl₂を添加したC₃Sの水和挙動の変化をXRD、²⁹Si MAS NMR、TG/DTAを用いて検証した。その結果、CaCl₂はごく初期のC₃Sの溶解を促進するが、CaCl₂濃度が大きい程、早期に水の拡散律速段階へと移行し、溶解速度が減少することが確認された。また、CaCl₂の影響はジェナイト型C-S-Hの生成などのC-S-Hのナノサイズの構造変化に伴うC-S-Hゲルの空隙構造の変化と密接に関連していることが示唆された。 |
| Databáze: | OpenAIRE |
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