Calcium silicate hydrate

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Calcium silicate hydrates (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.

Contents

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:

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

Mechanisms of formation of C-S-H phases:

Related Research Articles

<span class="mw-page-title-main">Silicate</span> Any polyatomic anion containing silicon and oxygen

In chemistry, a silicate is any member of a family of polyatomic anions consisting of silicon and oxygen, usually with the general formula [SiO(4-2x)−
4−x]
n, where 0 ≤ x < 2. The family includes orthosilicate SiO4−4, metasilicate SiO2−3, and pyrosilicate Si2O6−7. The name is also used for any salt of such anions, such as sodium metasilicate; or any ester containing the corresponding chemical group, such as tetramethyl orthosilicate. The name "silicate" is sometimes extended to any anions containing silicon, even if they do not fit the general formula or contain other atoms besides oxygen; such as hexafluorosilicate [SiF6]2−.Most commonly, silicates are encountered as silicate minerals.

<span class="mw-page-title-main">Pozzolana</span> Natural siliceous or siliceous-aluminous material

Pozzolana or pozzuolana, also known as pozzolanic ash, is a natural siliceous or siliceous-aluminous material which reacts with calcium hydroxide in the presence of water at room temperature. In this reaction insoluble calcium silicate hydrate and calcium aluminate hydrate compounds are formed possessing cementitious properties. The designation pozzolana is derived from one of the primary deposits of volcanic ash used by the Romans in Italy, at Pozzuoli. The modern definition of pozzolana encompasses any volcanic material, predominantly composed of fine volcanic glass, that is used as a pozzolan. Note the difference with the term pozzolan, which exerts no bearing on the specific origin of the material, as opposed to pozzolana, which can only be used for pozzolans of volcanic origin, primarily composed of volcanic glass.

<span class="mw-page-title-main">Hexafluorosilicic acid</span> Octahedric silicon compound

Hexafluorosilicic acid is an inorganic compound with the chemical formula H
2SiF
6. Aqueous solutions of hexafluorosilicic acid consist of salts of the cation and hexafluorosilicate anion. These salts and their aqueous solutions are colorless.

Alite is an impure form of tricalcium silicate, Ca3SiO5, sometimes formulated as 3CaO·SiO2, typically with 3-4% of substituent oxides. It is the major, and characteristic, phase in Portland cement. The name was given by Törnebohm in 1897 to a crystal identified in microscopic investigation of Portland cement. Hatrurite is the name of a mineral that is substituted C3S.

Belite is an industrial mineral important in Portland cement manufacture. Its main constituent is dicalcium silicate, Ca2SiO4, sometimes formulated as 2 CaO · SiO2 (C2S in cement chemist notation).

<span class="mw-page-title-main">Alkali–aggregate reaction</span> Expansive chemical reaction damaging concrete

Alkali–aggregate reaction is a term mainly referring to a reaction which occurs over time in concrete between the highly alkaline cement paste and non-crystalline silicon dioxide, which is found in many common aggregates. This reaction can cause the expansion of the altered aggregate, leading to spalling and loss of strength of concrete.

<span class="mw-page-title-main">Thaumasite</span> Complex calcium silicate hydrate mineral

Thaumasite is a calcium silicate mineral, containing Si atoms in unusual octahedral configuration, with chemical formula Ca3Si(OH)6(CO3)(SO4)·12H2O, also sometimes more simply written as CaSiO3·CaCO3·CaSO4·15H2O.

Geopolymers are inorganic, typically ceramic, alumino-silicate forming long-range, covalently bonded, non-crystalline (amorphous) networks. Obsidian fragments are a component of some geopolymer blends. Commercially produced geopolymers may be used for fire- and heat-resistant coatings and adhesives, medicinal applications, high-temperature ceramics, new binders for fire-resistant fiber composites, toxic and radioactive waste encapsulation and new cements for concrete. The properties and uses of geopolymers are being explored in many scientific and industrial disciplines: modern inorganic chemistry, physical chemistry, colloid chemistry, mineralogy, geology, and in other types of engineering process technologies. The field of geopolymers is a part of polymer science, chemistry and technology that forms one of the major areas of materials science.

<span class="mw-page-title-main">Alkali–silica reaction</span> Chemical reaction damaging concrete

The alkali–silica reaction (ASR), also commonly known as concrete cancer, is a deleterious swelling reaction that occurs over time in concrete between the highly alkaline cement paste and the reactive amorphous silica found in many common aggregates, given sufficient moisture.

Friedel's salt is an anion exchanger mineral belonging to the family of the layered double hydroxides (LDHs). It has affinity for anions as chloride and iodide and is capable of retaining them to a certain extent in its crystallographical structure.

Mineral trioxide aggregate (MTA) was developed for use as a dental root repair material by Mahmoud Torabinejad. It is formulated from commercial Portland cement, combined with bismuth oxide powder for radio-opacity. MTA is used for creating apical plugs during apexification, repairing root perforations during root canal therapy, and treating internal root resorption. This can be used for root-end filling material and as pulp capping material. Originally, MTA was dark gray in color, but white versions have been on the market since 2002.

<span class="mw-page-title-main">Jennite</span> Inosilicate alteration mineral in metamorphosed limestone and in skarn

Jennite is a calcium silicate hydrate mineral of general chemical formula: Ca9Si6O18(OH)6·8H2O.

<span class="mw-page-title-main">Tobermorite</span> Inosilicate alteration mineral in metamorphosed limestone and in skarn

Tobermorite is a calcium silicate hydrate mineral with chemical formula: Ca5Si6O16(OH)2·4H2O or Ca5Si6(O,OH)18·5H2O.

<span class="mw-page-title-main">Concrete degradation</span> Damage to concrete affecting its mechanical strength and its durability

Concrete degradation may have many different causes. Concrete is mostly damaged by the corrosion of reinforcement bars due to the carbonatation of hardened cement paste or chloride attack under wet conditions. Chemical damages are caused by the formation of expansive products produced by various chemical reactions, by aggressive chemical species present in groundwater and seawater, or by microorganisms. Other damaging processes can also involve calcium leaching by water infiltration and different physical phenomena initiating cracks formation and propagation. All these detrimental processes and damaging agents adversely affects the concrete mechanical strength and its durability.

<span class="mw-page-title-main">Geopolymer cement</span> Aluminosilicate-based cement with a low-carbon footprint

Geopolymer cement is a binding system that hardens at room temperature.

The pozzolanic activity is a measure for the degree of reaction over time or the reaction rate between a pozzolan and Ca2+ or calcium hydroxide (Ca(OH)2) in the presence of water. The rate of the pozzolanic reaction is dependent on the intrinsic characteristics of the pozzolan such as the specific surface area, the chemical composition and the active phase content.

<span class="mw-page-title-main">Energetically modified cement</span> Class of cements, mechanically processed to transform reactivity

Energetically modified cements (EMCs) are a class of cements made from pozzolans, silica sand, blast furnace slag, or Portland cement. The term "energetically modified" arises by virtue of the mechanochemistry process applied to the raw material, more accurately classified as "high energy ball milling" (HEBM). This causes, amongst others, a thermodynamic transformation in the material to increase its chemical reactivity. For EMCs, the HEBM process used is a unique form of specialised vibratory milling discovered in Sweden and applied only to cementitious materials, here called "EMC Activation".

<span class="mw-page-title-main">Gyrolite</span> Rare phyllosilicate mineral crystallizing in spherules

Gyrolite, NaCa16(Si23Al)O60(OH)8·14H2O, is a rare silicate mineral (basic sodium calcium silicate hydrate: N-C-S-H, in cement chemist notation) belonging to the class of phyllosilicates. Gyrolite is also often associated with zeolites. It is most commonly found as spherical or radial formations in hydrothermally altered basalt and basaltic tuffs. These formations can be glassy, dull or fibrous in appearance.

<span class="mw-page-title-main">Tacharanite</span> Calcium aluminium silicate hydrate mineral

Tacharanite is a calcium aluminium silicate hydrate (C-A-S-H) mineral of general chemical formula Ca12Al2Si18O33(OH)36 with some resemblance to the calcium silicate hydrate (C-S-H) mineral tobermorite. It is often found in mineral assemblage with zeolites and other hydrated calcium silicates.

AFt Phases refer to the calcium Aluminate Ferrite trisubstituted, or calcium aluminate trisubstituted, phases present in hydrated cement paste (HCP) in concrete.

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". Nature 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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