When water is added to cement, each of the compounds undergoes hydration and contributes to the final state of the concrete. Only calcium silicates contribute to the strength. Tricalcium silicate is responsible for most of the early strength (first 7 days). 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  + 7 H →  + 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.
Synthetic C-S-H can be prepared from the reaction of CaO and SiO 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/SiO) 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.