Effect of magnesium on the C-S-H nanostructure evolution and aluminate phases transition in cement-slag blend |
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| Authors: | Qingjun Ding Jun Yang Gaozhan Zhang Dongshuai Hou |
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| Affiliation: | 1.School of Materials Science and Engineering,Wuhan University of Technology,Wuhan,China;2.Advanced Building Materials Key Laboratory of Anhui Province,Anhui Jianzhu University,Hefei,China;3.Department of Civil Engineering,Qingdao Technological University,Qingdao,China |
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| 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 Al4]/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 Al6] in TAH, respectively. On the other hand, Mg2+ ions exert an impact on the intra-transition between Al6] 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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