Calcium silicate hydrate
Encyclopedia
Calcium Silicate Hydrate is the main product of the hydration of Portland cement
Portland cement
Portland cement is the most common type of cement in general use around the world because it is a basic ingredient of concrete, mortar, stucco and most non-specialty grout...

 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
Portland cement
Portland cement is the most common type of cement in general use around the world because it is a basic ingredient of concrete, mortar, stucco and most non-specialty grout...

 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
Stoichiometry
Stoichiometry is a branch of chemistry that deals with the relative quantities of reactants and products in chemical reactions. In a balanced chemical reaction, the relations among quantities of reactants and products typically form a ratio of whole numbers...

 of C-S-H in cement
Cement
In the most general sense of the word, a cement is a binder, a substance that sets and hardens independently, and can bind other materials together. The word "cement" traces to the Romans, who used the term opus caementicium to describe masonry resembling modern concrete that was made from crushed...

 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:
    • Afwillite
      Afwillite
      Afwillite is a calcium hydroxide nesosilicate mineral with formula Ca32.2H2O. It occurs as glassy, colorless to white prismatic monoclinic crystals. Its Mohs scale hardness is between 3 and 4...

    • Jennite
      Jennite
      Jennite is a calcium silicate hydrate of general chemical formula: Ca9Si6O186·8.Jennite occurs in hydrated cement paste and can be found in nature in particular conditions, e.g., as alteration mineral in metamorphosed limestone and skarn....

    • Thaumasite
      Thaumasite
      -External links:*...

    • Tobermorite
      Tobermorite
      Tobermorite is a calcium silicate hydrate mineral with chemical formula:orTwo structural varieties are distinguished: tobermorite-11 Å and tobermorite-14 Å....

  • Other Calcium aluminium silicate hydrate, C-A-S-H minerals:
    • Hydrogarnet
    • Hydrotalcite
      Hydrotalcite
      Hydrotalcite is a layered double hydroxide of general formula Hydrotalcite is a layered double hydroxide of general formula Hydrotalcite is a layered double hydroxide of general formula (Mg6Al2(CO3)(OH)16·4(H2O) whose name is derived from its resemblance with talc and its high water content. It is...

  • Mechanisms of formation of C-S-H phases:
    • Alkali Silica Reaction
      Alkali Silica Reaction
      The alkali–silica reaction is a reaction which occurs over time in concrete between the highly alkaline cement paste and reactive non-crystalline silica, which is found in many common aggregates....

    • Alkali-aggregate reaction
      Alkali-aggregate reaction
      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...

    • Pozzolanic reaction
      Pozzolanic reaction
      The Pozzolanic reaction is the chemical reaction that occurs in hydraulic cement, a mixture of slaked lime with amorphous siliceous materials , forming non-water-soluble calcium silicate hydrates...

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