Moutzouri, Pinelopi, and Lyndon Emsley. “The Atomic-Level Structure of Cementitious Calcium Aluminate Silicate Hydrate Determined by NMR.” CHIMIA 75, no. 4 (April 28, 2021): 272.
https://doi.org/10.2533/chimia.2021.272.
We review our recent paper which resolves the long-standing dilemma of the location and nature of the six-fold coordinated aluminum in calcium aluminate silicate hydrate (C-A-S-H) samples. First principles calculations predict that at high Ca:Si and H2O ratios, aluminum is incorporated into the bridging sites of the linear silicate chains and that the stable coordination number is six. We confirm this hypothesis experimentally by one- and two-dimensional dynamic nuclear polarization enhanced 27Al and 29Si solid-state NMR experiments in which we correlate the distinctive six-fold coordinated aluminum NMR signal at 5 ppm to 29Si NMR signals from silicates in C-A-S-H.