Calcium silicate hydrate
Calcium silicate hydrates (or C-S-H) are the main products of the hydration of
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:
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
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 spherules (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:
- Alkali–silica reaction – Chemical reaction damaging concrete
- Alkali–aggregate reaction – Expansive chemical reaction damaging concrete
- Energetically modified cement – Class of cements, mechanically processed to transform reactivity
- Pozzolanic reaction– Capacity of silica-rich materials to react with calcium hydroxyde to form calcium silicate hydrates
References
- ISSN 0008-8846.
- ^ "Hydration of Portland Cement". engr.psu.edu. Retrieved 2022-11-29.
- ^ "Building Materials". indiabix.com. Retrieved 2022-11-29.
- ^ "Portland Cement Hydration" (PDF). Archived from the original (PDF) on 2017-02-15. Retrieved 2013-02-21.
- PMID 17384634.
- S2CID 103781671.
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- ^ "Archived copy". Archived from the original on 2015-03-15. Retrieved 2013-06-01.
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: CS1 maint: archived copy as title (link) - ^ "Potential Application of Nanotechnology on Cement Based Materials" (PDF). Archived from the original (PDF) on 2012-02-17. Retrieved 2013-02-21.