Calcium silicate hydrate

Calcium silicate hydrate (or C-S-H) is the main product of the hydration of Portland cement and is primarily responsible for the strength in cement based materials.

Preparation

Calcium silicate hydrate (also shown as C-S-H) is a result of the reaction between the silicate phases of Portland cement and water. This reaction typically is expressed as:

2Ca
3SiO
5 + 7H
2O → 3CaO · SiO
2 · 4H
2O + 3Ca(OH)
2 + 173.6 kJ

The stoichiometry of C-S-H in cement paste is variable and the state of chemically and physically bound water in its structure is not transparent, which is why "-" is used between C, S, and H.[1]

Synthetic C-S-H can be prepared from the reaction of CaO and SiO2 in water or through the double precipitation method using various salts. These methods provide the flexibility of producing C-S-H at specific C/S ratios. The C-S-H from cement phases can also be treated with ammonium nitrate in order to achieve desired C/S ratio.

Properties

C-S-H is a nano sized material[2] with some degree of crystallinity as observed by X-ray diffraction techniques.[3] The underlying atomic structure of C-S-H is similar to the naturally occurring mineral Tobermorite.[4] It has a layered geometry with calcium silicate sheet structure separated by an interlayer space. The silicates in C-S-H exist as dimers, pentamers and 3n-1 chain units [5][6] (where n is an integer greater than 0) and calcium ions are found to connect these chains making the three dimensional nano structure as observed by DNP surface enhanced NMR.[7] The exact nature of the interlayer remains unknown. One of the greatest difficulties in characterising C-S-H is due to its variable stoichiometry.

The SEM micrographs of C-S-H does not show any specific crystalline form. They usually manifest as foils or needle/oriented foils.

Synthetic C-S-H can be divided in two categories separated at the Ca/Si ratio of about 1.1. There are several indications that the chemical, physical and mechanical characteristics of C-S-H varies noticeably between these two categories.[8][9]

See also

References

  1. ↑ Portland Cement Hydration
  2. ↑ Allen, Andrew J.; Thomas, Jeffrey J.; Jennings, Hamlin M. (25 March 2007). "Composition and density of nanoscale calcium–silicate–hydrate in cement". Nature Materials. 6 (4): 311–316. doi:10.1038/nmat1871.
  3. ↑ Renaudin, Guillaume; Russias, Julie; Leroux, Fabrice; Frizon, Fabien; Cau-dit-Coumes, Céline (December 2009). "Structural characterization of C–S–H and C–A–S–H samples—Part I: Long-range order investigated by Rietveld analyses". Journal of Solid State Chemistry. 182 (12): 3312–3319. doi:10.1016/j.jssc.2009.09.026.
  4. ↑ TAYLOR, HARRY F.W. (June 1986). "Proposed Structure for Calcium Silicate Hydrate Gel". Journal of the American Ceramic Society. 69 (6): 464–467. doi:10.1111/j.1151-2916.1986.tb07446.x.
  5. ↑ Cong, Xiandong; Kirkpatrick, R.James (April 1996). "29Si and 17O NMR investigation of the structure of some crystalline calcium silicate hydrates". Advanced Cement Based Materials. 3 (3–4): 133–143. doi:10.1016/S1065-7355(96)90045-0.
  6. ↑ Brunet, F.; Bertani, Ph.; Charpentier, Th.; Nonat, A.; Virlet, J. (October 2004). "Application of Si Homonuclear and H− Si Heteronuclear NMR Correlation to Structural Studies of Calcium Silicate Hydrates". The Journal of Physical Chemistry B. 108 (40): 15494–15502. doi:10.1021/jp031174g.
  7. ↑ Kumar, Abhishek; Walder, Brennan J.; Kunhi Mohamed, Aslam; Hofstetter, Albert; Srinivasan, Bhuvanesh; Rossini, Aaron J.; Scrivener, Karen; Emsley, Lyndon; Bowen, Paul (7 July 2017). "The Atomic-Level Structure of Cementitious Calcium Silicate Hydrate". The Journal of Physical Chemistry C. 121 (32): 17188–17196. doi:10.1021/acs.jpcc.7b02439.
  8. ↑ http://www.mdpi.com/1996-1944/3/2/918/pdf
  9. ↑ Potential Application of Nanotechnology on Cement Based Materials
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