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Calcium silicate hydrate

Calcium silicate hydrates (CSH or C-S-H) are the main products of the hydration of Portland cement and are primarily responsible for the strength of cement-based materials.[1] They are the main binding phase (the "glue") in most concrete. Only well defined and rare natural crystalline minerals can be abbreviated as CSH while extremely variable and poorly ordered phases without well defined stoichiometry, as it is commonly observed in hardened cement paste (HCP), are denoted C-S-H.

Preparation

When water is added to cement, each of the compounds undergoes hydration and contributes to the final state of the concrete.[2] Only calcium silicates contribute to the strength. Tricalcium silicate is responsible for most of the early strength (first 7 days).[3] Dicalcium silicate, which reacts more slowly, only contributes to late strength. 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:

2 Ca3SiO5 + 7 H2O → 3 CaO · 2 SiO2 · 4 H2O + 3 Ca(OH)2 + 173.6 kJ

also written in cement chemist notation, (CCN) as:

2 C
3S + 7 H → C
3S
2H
4 + 3 CH + heat

or, tricalcium silicate + water → calcium silicate hydrate + calcium hydroxide + heat

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.[4]

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 (Ca/Si, or CaO/SiO2) ratios. The C-S-H from cement phases can also be treated with an ammonium nitrate solution in order to induce calcium leaching, and so to achieve a given C/S ratio.

Properties

C-S-H is a nano sized material[5][6] with some degree of crystallinity as observed by X-ray diffraction techniques.[7] The underlying atomic structure of C-S-H is similar to the naturally occurring mineral tobermorite.[8] 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 [9][10] (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 dynamic nuclear polarisation surface-enhanced nuclear magnetic resonance.[11] The exact nature of the interlayer remains unknown. One of the greatest difficulties in characterising C-S-H is due to its variable stoichiometry.[citation needed]

The scanning electron microscope 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.[12][13]

See also

Other C-S-H minerals:

  • Afwillite – Nesosilicate alteration mineral also sometimes found in hydrated cement paste
  • Gyrolite – Rare phyllosilicate mineral crystallizing in small spheres (a rare mineral from hydrothermal alteration, or an ageing product of alkali-silica reaction)
  • Jennite – Inosilicate alteration mineral in metamorphosed limestone and in skarn
  • Thaumasite – Complex calcium silicate hydrate mineral
  • Tobermorite – Inosilicate alteration mineral in metamorphosed limestone and in skarn
  • Xonotlite – Inosilicate mineral

Other calcium aluminium silicate hydrate, (C-A-S-H) minerals:

  • Hydrogarnet – Calcium aluminium garnet
  • Hydrotalcite – Hydrated Mg-Al layered double hydroxide (LDH) containing carbonate anions
  • Tacharanite – Calcium aluminium silicate hydrate mineral (Ca12Al2Si18O33(OH)36, and also Ca12Al2Si18O51(OH)2 · 18 H2O)

Mechanisms of formation of C-S-H phases:

References

  1. ^ Richardson, I.G. (February 2008). "The calcium silicate hydrates". Cement and Concrete Research. 38 (2): 137–158. doi:10.1016/j.cemconres.2007.11.005. ISSN 0008-8846.
  2. ^ "Hydration of Portland Cement". engr.psu.edu. Retrieved 2022-11-29.
  3. ^ "Building Materials". indiabix.com. Retrieved 2022-11-29.
  4. ^ "Portland Cement Hydration" (PDF). Archived from the original (PDF) on 2017-02-15. Retrieved 2013-02-21.
  5. ^ Allen, Andrew J.; Thomas, Jeffrey J.; Jennings, Hamlin M. (25 March 2007). "Composition and density of nanoscale calcium–silicate–hydrate in cement". Materials. 6 (4): 311–316. Bibcode:2007NatMa...6..311A. doi:10.1038/nmat1871. PMID 17384634.
  6. ^ Andalibi, M. Reza; Kumar, Abhishek; Srinivasan, Bhuvanesh; Bowen, Paul; Scrivener, Karen; Ludwig, Christian; Testino, Andrea (2018). "On the mesoscale mechanism of synthetic calcium–silicate–hydrate precipitation: a population balance modeling approach". Journal of Materials Chemistry A. 6 (2): 363–373. doi:10.1039/C7TA08784E. ISSN 2050-7488. S2CID 103781671.
  7. ^ 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. Bibcode:2009JSSCh.182.3312R. doi:10.1016/j.jssc.2009.09.026.
  8. ^ 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.
  9. ^ 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.
  10. ^ 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.
  11. ^ 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.
  12. ^ "Archived copy". Archived from the original on 2015-03-15. Retrieved 2013-06-01.{{cite web}}: CS1 maint: archived copy as title (link)
  13. ^ "Potential Application of Nanotechnology on Cement Based Materials" (PDF). Archived from the original (PDF) on 2012-02-17. Retrieved 2013-02-21.
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