highalumina

High-alumina refers to materials that have a high content of aluminum oxide (Al2O3). In construction and materials science, the term most often denotes calcium aluminate cement (CAC) and related high-alumina refractories. CAC is a hydraulic cement produced by calcining bauxite with lime to form reactive calcium aluminates; when mixed with water it hydrates to form durable hydrates that impart early strength.

The favored phases in CAC systems are monocalcium aluminate (CA) and dicalcium aluminate (CA2), with minor CA6. Hydration yields calcium aluminate hydrates such as CAH10, C2AH8, and C3AH6, which confer rapid strength gain and high-temperature stability. The cement generally offers stronger early strength than ordinary Portland cement and enhanced performance in high-heat environments, along with improved resistance to certain chemical exposures.

Durability and limitations: CAC can undergo long-term conversion, where hydrates transform and may lead to changes in volume and potential loss of strength in some settings. Its resistance to sulfates is variable and depends on composition and service conditions. CAC is also more sensitive to prolonged moisture exposure and improper curing; storage and handling can affect performance, and formulations vary in durability.

Applications: CAC and high-alumina materials are used in refractory castables, kiln and furnace linings, and burner bricks. They are also employed in concrete and repair mortars designed for rapid strength gain or high-temperature service, and in chemical plant linings where heat resistance and chemical compatibility are required.

Production: CAC is produced by calcining bauxite and lime at high temperatures to form reactive calcium aluminates, then grinding the material to a fine powder for use as a hydraulic cement under various national standards.