Alite

Alite is a name for tricalcium silicate, Ca₃SiO₅, sometimes formulated as 3CaO·SiO₂ (C₃S in cement chemist notation, CCN). It is the major, and characteristic, mineral phase in Portland cement. The name was given by Törneborn in 1897 to a crystal identified in microscopic investigation of Portland cement. Alite is a name in common use in the cement industry, although it is not a recognised mineral name.

Composition and structure

The alite found in Portland cement differs in composition from simple tricalcium silicate. It is a solid solution and contains minor amounts of other oxides besides CaO and SiO₂. A typical composition is:

Based on this, the formula can be expressed as Ca_2.90Mg_0.06Na_0.01Fe_0.03Al_0.04Si_0.95P_0.01O₅. In practice, the composition varies with the bulk composition of the clinker, subject to certain limits. Substitution of calcium ions or orthosilicate ions requires that electric charges be kept in balance. For instance, a limited number of orthosilicate (SiO₄⁴⁻) ions can be replaced with sulfate (SO₄²⁻) ions, provided that for each sulfate ion, two aluminate (AlO₄⁵⁻) ions are also substituted.