Abstract
The microstructural study was conducted on cement and cement-slag pastes immersed in different concentrations of Mg(NO3)2 solutions utilizing 29Si, 27Al NMR spectroscopy and XRD techniques. The results show that the hydration of both the cement and cement-slag pastes is delayed when the pastes are cured in Mg(NO3)2 solutions as compared to the pastes cured in water. Moreover, Mg2+ ions also exhibit an decalcifying and dealuminizing effect on the C-A-S-H in cement and cement-slag pastes, and thereby decrease Ca/Si and Al[4]/Si ratios of the C-A-S-H. The dealuminization of C-A-S-H is mitigated for cement-slag paste as compared to pure cement paste. The depolymerized calcium and aluminum ions from C-A-S-H gel mainly enter the pore solution to maintain the pH value and form Al[6] in TAH, respectively. On the other hand, Mg2+ ions exert an impact on the intra-transition between Al[6] species, from AFm and hydrogarnet to hydrotalcite-like phase. NO3- ions are interstratified in the layered Mg-Al structure and formed nitrated hydrotalcite-like phase (Mg1-xAl x (OH)2(NO3) x •nH2O). Results from both 27Al NMR and XRD data show that ettringite seems not to react with Mg2+ ions.
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Funded by National Natural Science Foundation of China (Nos. 51778513, 51402003, 51578004) and China Ministry of Science and Technology (No. 2015CB655101)
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Ding, Q., Yang, J., Zhang, G. et al. Effect of magnesium on the C-S-H nanostructure evolution and aluminate phases transition in cement-slag blend. J. Wuhan Univ. Technol.-Mat. Sci. Edit. 33, 108–116 (2018). https://doi.org/10.1007/s11595-018-1794-z
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DOI: https://doi.org/10.1007/s11595-018-1794-z