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![[Figure 9]](po5053fig9mag.jpg)
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Figure 9
Proposed evolution of C–S–H structure as a function of its Ca/Si ratio. At low Ca/Si ratio, the structure is a nanocrystalline turbostratic tobermorite having corrugated layers. When the Ca/Si ratio increases, Si bridging tetrahedra are progressively removed. A first step of structural evolution consists in an increase of the layer-to-layer distance, because layer-to-layer connectivity weakens. In a second step, layer-to-layer distance decreases, because interlayer Ca is progressively incorporated and holds the layers together. In a final step, Ca coordination spheres connect to form interlayer Ca(OH)2 resembling portlandite. The structure of samples having a Ca/Si of ∼1.5 shares a number of similarities with the Richardson (2014  ) model, except that that model is three-dimensionally ordered, whereas the present one assumes turbostratism, but these two models can straightforwardly be reconciled (see text). The final step of structural evolution could not be observed here, as all samples contained some Si bridging tetrahedra. Note that the structure of the samples of lowest Ca/Si ratio may vary depending on the synthesis procedure, as some other studies have observed the absence of connectivity between adjacent layers (see text for details). |
![[Figure 9]](po5053fig9.jpg)
 | JOURNAL OF APPLIED CRYSTALLOGRAPHY |
ISSN: 1600-5767
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