29Si Chemical Shift Anisotropies in Hydrated Calcium Silicates: A Computational Study

2013 ◽  
Vol 117 (16) ◽  
pp. 8374-8380 ◽  
Author(s):  
Pawel Rejmak ◽  
Jorge S. Dolado ◽  
Malcolm J. Stott ◽  
Andrés Ayuela
Keyword(s):  
Chemical Shift ◽  
Computational Study ◽  
Calcium Silicates ◽  
Hydrated Calcium ◽  
29Si Chemical Shift

29Si Chemical Shift Anisotropies in Calcium Silicates from High-Field29Si MAS NMR Spectroscopy

2003 ◽  
Vol 42 (7) ◽  
pp. 2368-2377 ◽  
Author(s):  
Michael Ryan Hansen ◽  
Hans J. Jakobsen ◽  
Jørgen Skibsted
Keyword(s):  
Nmr Spectroscopy ◽  
Chemical Shift ◽  
Mas Nmr ◽  
Calcium Silicates ◽  
29Si Chemical Shift

scholarly journals Strength Performance and Microstructure of Calcium Sulfoaluminate Cement-Stabilized Soft Soil

2021 ◽  
Vol 13 (4) ◽  
pp. 2295
Author(s):  
Hailong Liu ◽  
Jiuye Zhao ◽  
Yu Wang ◽  
Nangai Yi ◽  
Chunyi Cui
Keyword(s):  
Soft Soil ◽  
Hydration Product ◽  
X Ray Diffraction ◽  
Calcium Sulfoaluminate Cement ◽  
Strength Performance ◽  
X Ray ◽  
Calcium Sulfoaluminate ◽  
Stabilized Soil ◽  
Calcium Silicates ◽  
Hydrated Calcium

Calcium sulfoaluminate cement (CSA) was used to stabilize a type of marine soft soil in Dalian China. Unconfined compressive strength (UCS) of CSA-stabilized soil was tested and compared to ordinary Portland cement (OPC); meanwhile the influence of amounts of gypsum in CSA and cement contents in stabilized soils on the strength of stabilized soils were investigated. X-ray diffraction (XRD) tests were employed to detect generated hydration products, and scanning electron microscopy (SEM) was conducted to analyze microstructures of CSA-stabilized soils. The results showed that UCS of CSA-stabilized soils at 1, 3, and 28 d firstly increased and then decreased with contents of gypsum increasing from 0 to 40 wt.%, and CSA-stabilized soils exhibited the highest UCS when the content of gypsum equaled 25 wt.%. When the mixing amounts of OPC and CSA were the same, CSA-stabilized soils had a significantly higher early strength (1 and 3 d) than OPC. For CSA-stabilized soil with 0 wt.% gypsum, monosulfate (AFm) was detected as a major hydration product. As for CSA-stabilized soil with certain amounts of gypsum, the intensity of ettringite (Aft) was significantly higher than that in the sample hydrating without gypsum, but a tiny peak of AFm also could be detected in the sample with 15 wt.% gypsum at 28 d. Additionally, the intensity of AFt increased with the contents of gypsum increasing from 0 to 25 wt.%. When contents of gypsum increased from 25 to 40 wt.%, the intensity of AFt tended to decrease slightly, and residual gypsum could be detected in the sample with 40 wt.% gypsum at 28 d. In the microstructure of OPC-stabilized soils, hexagonal plate-shaped calcium hydroxide (CH) constituted skeleton structures, and clusters of hydrated calcium silicates (C-S-H) gel adhered to particles of soils. In the microstructure of CSA-stabilized soils, AFt constituted skeleton structures, and the crystalline sizes of ettringite increased with contents of gypsum increasing; meanwhile, clusters of the aluminum hydroxide (AH3) phase could be observed to adhere to particles of soils and strengthen the interaction.

scholarly journals Use of thermodynamic chemical potential diagrams (µCaO, µCO2) to understand the weathering of cement by a slightly carbonated water

Cerâmica ◽  
2008 ◽  
Vol 54 (331) ◽  
pp. 356-360 ◽  
Author(s):  
A. Blandine ◽  
G. Bernard ◽  
B. Essaïd
Keyword(s):  
Chemical Weathering ◽  
Chemical Potential ◽  
Chemical Elements ◽  
Continuous Solid Solution ◽  
The Core ◽  
Chemical Potentials ◽  
Knowing That ◽  
Cement System ◽  
Calcium Silicates ◽  
Hydrated Calcium

Cement is a ubiquitous material that may suffer hazardous weathering. The chemical weathering of cement in natural environment is mostly characterized by the leaching of CaO and the addition of CO2. The different weathering zones that develop at the expense of the cement may be predicted by the help of chemical potential phase diagrams; these diagrams simulate the behaviour of systems open to some chemical elements. Some components have a so-called inert status, that is to say the system is closed for these components, their amount in the system remains constant; some other components have a mobile status, that is to say these components can be exchanged with the outside of the system, their amount can vary from one sample zone to another. The mobile components are represented in the model by their chemical potentials (linked to their concentrations) that are variable in the external environment. The main features of the weathering of a cement system open to CaO and CO2 are predicted in a phase diagram with µCaO et µCO2 as diagram axes. From core to rim, one observes the disappearance of portlandite, ettringite and calcium monosulfoaluminate, the precipitation of calcite and amorphous silica, the modification of the composition of the CSH minerals (hydrated calcium silicates) that see a decrease of their c/s ratio (CaO/SiO2) from the core to the rim of the sample. For the CSH minerals, we have separated their continuous solid solution into three compositions defined by different CaO/SiO2 ratios and called phases 1, 2 and 3: CaO = 0.8, 1.1, 1.8 respectively for one mole of SiO2 knowing that H2O varies in the three compositions.

Are the amide bonds in N-acyl imidazoles twisted? A combined solid-state 17O NMR, crystallographic, and computational study

2015 ◽  
Vol 93 (4) ◽  
pp. 451-458 ◽  
Author(s):  
Xianqi Kong ◽  
Aaron Tang ◽  
Ruiyao Wang ◽  
Eric Ye ◽  
Victor Terskikh ◽  
...  
Keyword(s):  
Solid State ◽  
Chemical Shift ◽  
Crystal Structures ◽  
Computational Study ◽  
Chemical Shifts ◽  
Amide Bond ◽  
Chemical Shift Tensors ◽  
Amide Bonds ◽  
Bond Rotation ◽  
Quadrupole Coupling

We report synthesis of 17O-labeling and solid-state 17O NMR measurements of three N-acyl imidazoles of the type R-C(17O)-Im: R = p-methoxycinnamoyl (MCA-Im), R = 4-(dimethylamino)benzoyl (DAB-Im), and R = 2,4,6-trimethylbenzoyl (TMB-Im). Solid-state 17O NMR experiments allowed us to determine for the first time the 17O quadrupole coupling and chemical shift tensors in this class of organic compounds. We also determined the crystal structures of these compounds using single-crystal X-ray diffraction. The crystal structures show that, while the C(O)–N amide bond in DAB-Im exhibits a small twist, those in MCA-Im and TMB-Im are essentially planar. We found that, in these N-acyl imidazoles, the 17O quadrupole coupling and chemical shift tensors depend critically on the torsion angle between the conjugated acyl group and the C(O)–N amide plane. The computational results from a plane-wave DFT approach, which takes into consideration the entire crystal lattice, are in excellent agreement with the experimental solid-state 17O NMR results. Quantum chemical computations also show that the dependence of 17O NMR parameters on the Ar–C(O) bond rotation is very similar to that previously observed for the C(O)–N bond rotation in twisted amides. We conclude that one should be cautious in linking the observed NMR chemical shifts only to the twist of the C(O)–N amide bond.

Pore structures of hydrated calcium silicates and portland cements by nitrogen adsorption

1970 ◽  
Vol 34 (4) ◽  
pp. 560-570 ◽  
Author(s):  
E.E Bodor ◽  
Jan Skalny ◽  
Stephen Brunauer ◽  
Julius Hagymassy ◽  
Marvin Yudenfreund
Keyword(s):  
Nitrogen Adsorption ◽  
Portland Cements ◽  
Pore Structures ◽  
Calcium Silicates ◽  
Hydrated Calcium

INVESTIGATION OF COLLOIDAL HYDRATED CALCIUM SILICATES. I. SOLUBILITY PRODUCTS

1960 ◽  
Vol 64 (9) ◽  
pp. 1151-1157 ◽  
Author(s):  
S. A. Greenberg ◽  
T. N. Chang ◽  
Elaine Anderson
Keyword(s):  
Calcium Silicates ◽  
Solubility Products ◽  
Hydrated Calcium

The hydrated calcium silicates

1937 ◽  
Vol 18 (1) ◽  
pp. 261
Author(s):  
E. P. Flint ◽  
Lansing S. Wells
Keyword(s):  
Calcium Silicates ◽  
Hydrated Calcium

A re-examination of tobermorite

1952 ◽  
Vol 29 (218) ◽  
pp. 960-962 ◽  
Author(s):  
G. F. Claringbull ◽  
M. H. Hey
Keyword(s):  
Chemical Composition ◽  
Current Interest ◽  
Hydrated Silicate ◽  
The Third ◽  
Calcium Silicates ◽  
Hydrated Calcium

Tobermorite, a hydrated silicate of calcium, was described by M. F. Heddle in 1880 from three Scottish localities: two near Tobermory in the island of Mull, and the third a quarry near the pier at Dunvegan in Skye. Further localities for the mineral are Sgfirr nam Boc, Loch Eynort in Skye, and Ardtornish Bay in Morven (Morvern), Argyllshire.Because of marked similarity in chemical composition it has been suggested that tobermorite might be identical with gyrolite. In view of this and of the current interest in hydrated calcium silicates in cement chemistry the species has been re-examined.

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