Effect of Curing Regime on Degree of Al3＋ Substituting for Si4＋ in C-S-H Gels of Hardened Portland Cement Pastes

• Published in: Journal of Wuhan University of Technology. Materials science edition Vol. 29; no. 3; pp. 546 - 552
• Main Authors: Hu, Chenguang, Hu, Shuguang, Ding, Qingjun, Feng, Xiaoxin, Huang, Xiulin
• Format: Journal Article
• Language: English
• Published: Heidelberg Wuhan University of Technology 01.06.2014
• Subjects: Chemistry and Materials Science; CSH凝胶; Materials Science; 内部温度; 固化; 恒定温度; 核磁共振; 温度制度; 硬化水泥浆体; 非线性关系; substituting for Si; C-S-H; variable temperature; constant temperature; hardened cement pastes; degree of Al
• ISSN: 1000-2413; 1993-0437
• DOI: 10.1007/s11595-014-0955-y

The effect of curing regime on degree ofAl3＋ substituting for Si^4＋ （Al/Si ratio） in C-S-H gels of hardened Portland cement pastes was investigated by 29Si magic angel spinning （MAS） nuclear magnetic resonance （NMR） with deconvolution technique. The curing regimes included the constant temperature （20, 40, 60 and 80 ℃） and variable temperature （simulated internal temperature of mass concrete with 60 ℃ peak）. The results indicate that constant temperature of 20 ℃ is beneficial to substitution ofAl3＋ for Si4＋, and AI/Si ratio changes to be steady after 180 d. The increase of Al/Si ratio at 40 ℃is less than that at 20℃ for 28 d. The other three regimes of high temperature increase Al/Si ratio only before 3 d, on the contrary to that from 3 to 28 d. However, the 20 ℃ curing stage from 28 to 180 d at variable temperature regime, is beneficial to the increase of AI/Si ratio which is still lower than that at constant temperature regime of 20 ℃ for the same age. A nonlinear relation exists between the Al/Si ratio and temperature variation or mean chain length （MCL） of C-S-H gels, furthermore, the amount ofAl3＋ which can occupy the bridging tetrahedra sites in C-S-H structure is insufficient in hardened Portland cement pastes.