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Open AccessArticle

Strontium Retention of Calcium Zirconium Aluminate Cement Paste Studied by NMR, XRD and SEM-EDS

Faculty of Materials Science and Ceramics, AGH University of Science and Technology, al. A. Mickiewicza 30, 30-059 Krakow, Poland
Materials 2020, 13(10), 2366; https://doi.org/10.3390/ma13102366
Received: 18 April 2020 / Revised: 17 May 2020 / Accepted: 19 May 2020 / Published: 21 May 2020
(This article belongs to the Special Issue Innovative Materials for Construction)
This work concerns the hydration mechanism of calcium zirconium aluminate as a ternary compound appearing in the CaO-Al2O3-ZrO2 diagram besides the calcium aluminates commonly used as the main constitutes of calcium aluminate cements (CACs). Moreover, a state-of-the-art approach towards significant changes in hydraulic properties was implemented for the first time in this work, where the effect of structural modification on the hydration behavior of calcium zirconium aluminate was proved by XRD, 27Al MAS NMR and SEM-EDS. The substitution of Sr2+ for Ca2+ in the Ca7ZrAl6O18 lattice decreases the reactivity of Sr-substituted Ca7ZrAl6O18 in the presence of water. Since the original cement grains remain unhydrated up to 3 h (Ca7ZrAl6O18) or 72 h (Sr1.25Ca5.75ZrAl6O18) of curing period in the hardened cement paste structures, strontium can be considered as an inhibition agent for cement hydration. The complete conversion from anhydrous 27AlIV to hydrated 27AlVI species was achieved during the first 24 h (Ca7ZrAl6O18) or 7 d(Sr1.25Ca5.75ZrAl6O18) of hydration. Simultaneously, the chemical shift in the range of octahedral aluminum from ca. 4 ppm to ca. 6 ppm was attributed to the transformation of the hexagonal calcium aluminate hydrates and Sr-rich (Sr,C)3AH6 hydrate into the cubic phase Ca-rich (Sr,C)3AH6 or pure C3AH6 in the hardened Sr-doped cement paste at the age of 7 d. The same 27Al NMR chemical shift was detected at the age of 24 h for the reference hardened undoped Ca7ZrAl6O18 cement paste. View Full-Text
Keywords: Ca7ZrAl6O18; 27Al MAS NMR; Sr-rich (Sr,C)3AH6; cement hydration; refractories; immobilization of radioactive Sr Ca7ZrAl6O18; 27Al MAS NMR; Sr-rich (Sr,C)3AH6; cement hydration; refractories; immobilization of radioactive Sr
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Madej, D. Strontium Retention of Calcium Zirconium Aluminate Cement Paste Studied by NMR, XRD and SEM-EDS. Materials 2020, 13, 2366.

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