calciumsilicatehydrate

Calcium silicate hydrate, or calcium silicate hydrates (C-S-H), is a family of hydrous calcium silicate phases that form as a primary product of the hydration of hydraulic cements, especially Portland cement. It is the principal binding phase in hydrated cement paste and largely determines the material’s strength and microstructure.

C-S-H does not have a single fixed formula. Its composition can vary, typically described by a general formula involving calcium oxide, silicon dioxide, and water with a calcium-to-silicon (Ca/Si) ratio that commonly ranges from about 0.6 to 2.0, depending on hydration conditions. The phase is predominantly amorphous or nanocrystalline and is often modeled as a disordered calcium silicate gel containing silicate sheets or chains intercalated with calcium ions and water. In some structural models, the silicate component resembles tobermorite- or jennite-like motifs, but with substantial disorder.

Formation occurs during the hydration of tricalcium silicate (C3S) and dicalcium silicate (C2S) when they react with water, releasing heat and producing C-S-H along with calcium hydroxide (portlandite). C-S-H nucleates throughout the pore solution, forming a continuous, interlocking network that binds grains together and reduces porosity.

In practical terms, C-S-H is the dominant phase responsible for concrete strength development. Its properties are influenced by the chemical environment and curing conditions, and its stability can be affected by processes such as carbonation or long-term aging, which can alter its structure and performance.