clinker

Clinker is a nodular material produced in the kilns during the manufacture of cement. After cooling, it is ground together with a small amount of gypsum to produce cement powder. The term most commonly refers to Portland cement clinker, the main intermediate product of cement production.

In ordinary Portland cement, clinker consists predominantly of calcium silicate minerals, primarily alite (C3S) and belite (C2S), along with smaller amounts of calcium aluminate (C3A) and calcium ferrite (C4AF). The nodules form at high temperatures in rotary kilns, typically around 1400–1450°C, where raw materials calcine and fuse before cooling into spherical or irregular clinker particles.

Clinker nodules are usually a few millimeters to a couple of centimeters in diameter. Their exact mineral makeup and size distribution influence the hydration characteristics and final strength of the cement. After cooling, the clinker is ground to a fine powder and commonly blended with gypsum to regulate the setting time of the cement. Different cement types use clinker with varying compositions, and supplementary cementitious materials may be added to achieve desired properties.

A related but distinct use of the term clinker appears in brickmaking. Clinker bricks are produced by firing clay to the point of vitrification, creating a dense, glass-like surface. These bricks, known for their dark, glossy appearance and durability, have been used in various architectural styles, particularly in the United Kingdom.

Clinker production is energy-intensive and contributes substantially to CO2 emissions. Industry measures seek to improve energy efficiency, optimize raw mixes, and substitute alternative fuels to reduce environmental impact.