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

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.

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

Cerâmica ◽

10.1590/s0366-69132008000300014 ◽

2008 ◽

Vol 54 (331) ◽

pp. 356-360 ◽

Cited By ~ 2

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.

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Formation of hydrated calcium silicates at elevated temperatures and pressures

Journal of Research of the National Bureau of Standards ◽

10.6028/jres.021.034 ◽

1938 ◽

Vol 21 (5) ◽

pp. 617 ◽

Cited By ~ 36

Author(s):

Einar P. Flint ◽

Howard F. McMurdie ◽

Lansing S. Wells

Keyword(s):

Elevated Temperatures ◽

Calcium Silicates ◽

Hydrated Calcium

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17 The Determination of Pore Structures from Nitrogen Adsorption Isotherms

Advances in Catalysis - Proceedings of the International Congress on Catalysis ◽

10.1016/s0360-0564(08)60163-7 ◽

1957 ◽

pp. 143-154 ◽

Cited By ~ 234

Author(s):

R.W. Cranston ◽

F.A. Inkley

Keyword(s):

Adsorption Isotherms ◽

Nitrogen Adsorption ◽

Pore Structures ◽

Nitrogen Adsorption Isotherms

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Surface and pore structures of CMK-5 ordered mesoporous carbons studied by nitrogen adsorption and surface spectroscopic methods

Nanotechnology in Mesostructured Materials, Proceedings of the 3rd International Materials Symposium - Studies in Surface Science and Catalysis ◽

10.1016/s0167-2991(03)80393-2 ◽

2003 ◽

pp. 335-338

Author(s):

Hans Darmstadt ◽

Christian Roy ◽

Serge Kaliaguine ◽

Tae-Wan Kim ◽

Ryong Ryoo

Keyword(s):

Nitrogen Adsorption ◽

Spectroscopic Methods ◽

Mesoporous Carbons ◽

Ordered Mesoporous Carbons ◽

Pore Structures ◽

Ordered Mesoporous

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INVESTIGATION OF COLLOIDAL HYDRATED CALCIUM SILICATES. I. SOLUBILITY PRODUCTS

The Journal of Physical Chemistry ◽

10.1021/j100838a012 ◽

1960 ◽

Vol 64 (9) ◽

pp. 1151-1157 ◽

Cited By ~ 53

Author(s):

S. A. Greenberg ◽

T. N. Chang ◽

Elaine Anderson

Keyword(s):

Calcium Silicates ◽

Solubility Products ◽

Hydrated Calcium

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Facile Synthesis and Photocatalytic Property of Titania/Carbon Composite Hollow Microspheres with Bimodal Mesoporous Shells

International Journal of Photoenergy ◽

10.1155/2012/976389 ◽

2012 ◽

Vol 2012 ◽

pp. 1-9 ◽

Cited By ~ 4

Author(s):

Guohong Wang ◽

Bei Cheng ◽

Jun Zhang ◽

Lin Xu ◽

Tingting Yin

Keyword(s):

Aqueous Solution ◽

Photocatalytic Activity ◽

Hollow Spheres ◽

Photocatalytic Property ◽

Nitrogen Adsorption ◽

Carbon Composite ◽

Hollow Microspheres ◽

Calcination Time ◽

One Pot ◽

Pore Structures

Titania/carbon composite hollow microspheres with bimodal mesoporous shells are one-pot fabricated by hydrothermal treatment of the acidic (NH4)2TiF6aqueous solution in the presence of glucose at180∘C for 24 h and then calcined at450∘C. The as-prepared samples were characterized by XRD, SEM, TEM, HRTEM, UV-visible spectroscopy, and nitrogen adsorption-desorption isotherms. The photocatalytic activity of the as-prepared samples was evaluated by daylight-induced photocatalytic decolorization of methyl orange aqueous solution at ambient temperature. The effects of calcination time on the morphology, phase structure, crystallite size, specific surface area, pore structures, and photocatalytic activity of the microspheres were investigated. The results indicated that the as-obtained TiO2/C composite hollow spheres generally exhibit bimodal mesopore size distribution with their peak intra-aggregated mesopore size in the range of 2.3–4.5 nm and peak interaggregated mesopore size in the range of 5.7–12.7 nm, depending on specific calcination time. The daylight-induced photoactivity of as-obtained hollow TiO2/C microspheres generally exceeds that of Degussa P25. The influences of calcination time on the photoactivity are discussed in terms of carbon content, phase structures, and pore structures.

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