Calcium Silicate Hydrate Information
Calcium Silicate Hydrate is the main product of the hydration of Portland cement and is primarily responsible for the strength in cement based materials.
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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:
2 Ca3SiO5 + 7 H2O —> 3 CaO · 2 SiO2 · 4 H2O + 3 Ca(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.
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
The crystal structure of C-S-H in cement paste has not been fully resolved yet and there is still ongoing debate over its nanostructure.
The SEM micrographs of C-S-H does not show any specific crystalline form. They usually manifest as flakes or dendrites/fibrils.
Synthetic C-S-H can be divided in two categories separated at the C/S 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.
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:
References
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Categories: Calcium compounds | Cement | Concrete | Hydrates | Inorganic compounds | Silicates
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