Ca3SiO5

Ca3SiO5, commonly known as tricalcium silicate (C3S) or alite, is a calcium silicate mineral that is a principal phase in ordinary Portland cement clinker. Its chemical formula is Ca3SiO5. In cement chemistry, C3S is responsible for rapid strength development during the early hours after mixing with water.

Production and occurrence: Ca3SiO5 is produced industrially by high-temperature calcination of limestone (CaCO3) with silica (SiO2) in cement kilns, forming clinker minerals that are ground to produce cement. In nature, the mineral can occur only in trace amounts; its primary significance is industrial rather than geological.

Structure and properties: C3S crystallizes in a calcium silicate framework and exists in several polymorphs, with beta-C3S typically cited as the form stable at room temperature. The phase is a white to gray powder and is highly reactive with water, contributing to the early hydration processes of cement.

Hydration and cement chemistry: When Ca3SiO5 hydrates, it reacts with water to form calcium silicate hydrate (C-S-H) and calcium hydroxide, releasing a considerable amount of heat. The C-S-H phase gradually hardens, providing early strength and setting for cement-based systems. The rate and extent of hydration depend on factors such as fineness, temperature, moisture, and the presence of other clinker phases.

Industrial significance: The proportion of C3S in clinker strongly influences setting time and early strength development of cement. It is typically balanced with other phases like C2S, C3A, and C4AF to achieve desired performance characteristics.