The Crystal Structure of Tobermorite 14 Å (Plombierite), a C–S–H Phase

Abstract

The crystal structure of tobermorite 14 Å (plombierite) was solved by means of the application of the order-disorder (OD) theory and was refined through synchrotron radiation diffraction data. Two polytypes were detected within one very small crystal from Crestmore, together with possibly disordered sequences of layers, giving diffuse streaks along c à . Only one of the two polytypes could be refined: it has B11b space group symmetry and cell parameters a 5 6.735(2) Å , b 5 7.425(2) Å , c 5 27.987(5) Å , c 5 123.25(1)1. The refinement converged to R 5 0.152 for 1291 reflections with F o 44s(F o ). The characteristic reflections of the other polytype, F2dd space group, a % 11.2 Å , b % 7.3 Å , c % 56 Å , were recognized but they were too weak and diffuse to be used in a structure refinement. The structure of tobermorite 14 Å is built up of complex layers, formed by sheets of sevenfold coordinated calcium cations, flanked on both sides by wollastonite-like chains. The space between two complex layers contains additional calcium cations and H 2 O molecules; their distribution, as well as the system of hydrogen bonds, are presented and discussed. The crystal chemical formula indicated by the structural results is Ca 5 Si 6 O 16 (OH) 2 Á 7H 2 O. J ournal

Coupling thermodynamics and digital image models to simulate hydration and microstructure development of portland cement pastes

“…From these kinds of experiments, it is observed that C-S-H exhibits a diffuse peak at 0.304 nm (hereafter called the "ordered" C-S-H peak) amid a broad amorphous hump in the background. Although a number of structure models for C-S-H analogs have been published, [37][38][39] we have not been able to find one that readily fits the ordered C-S-H peak and the broad background. Therefore, rather than using what is most likely an improper structure model, we elected to include the contribution of C-S-H in the amorphous category along with water and other amorphous components that may be present.…”

Effect of temperature and aluminium on calcium (alumino)silicate hydrate chemistry under equilibrium conditions

“…These products are structurally similar to the tobermorite group of minerals, which contain aluminosilicate chains in 'dreierketten'-type arrangements that are flanked on either side by an 'interlayer' region and a calcium oxide sheet ( Figure 1) [13,14]. Al substitutes into bridging sites with strong preference over paired sites in these chains [15,16].…”

“…11Å tobermorite [18] ( Figure 1A). and B) non-cross-linked C-(A-)S-H products as structural analogues of double chain 11 Å tobermorite [18] and 14 Å tobermorite [13] respectively. The grey diamonds are Ca species in the Ca-O sheet, and red and blue triangles are aluminosilicate units in paired and bridging sites respectively.…”

Calcium-aluminum-silicate-hydrate “cement” phases and rare Ca-zeolite association at Colle Fabbri, Central Italy

“…Tobermorite occurs at CF in two varieties: a 14 Å-tobermorite and an 11 Å-tobermorite, with compositions that differ in their water content and periodicities along the silicate chains. For more details see [24]. Jennite, Ca 9 Si 6 O 18 (OH) 6 ·8H 2 O, appears in acicular crystals up to 0.5 mm along the b axis, usually grouped together to form tight bundles or radial aggregates.…”

“…It often occurs in the innermost part of concentrically layered amygdales, which contain a core of amorphous silica, microcrystalline calcite, aragonite and ettringite ( Figure 3F). Very recent structural studies have clarified the structural arrangements of both jennite and an alteration product of jennite with lower H 2 O content [23,24]. Jennite is a rare mineral usually found in association with thaumasite in vugs of the famous Kalyango carbonatite lava at Fort Portal, Uganda [17].…”