castables

Castables are refractory concretes that can be cast, pumped, or gunned into place to form monolithic linings for furnaces and reactors. Unlike brick lining, castables produce a continuous, crack-minimizing lining that can be repaired by removing damaged material and replacing it with fresh castable.

They consist of a refractory aggregate bound by hydraulic cement systems. Aggregates include high-alumina, silica, magnesia, or other corrosion-resistant materials, often with inert filler and additives to adjust porosity. Binders include calcium aluminate cement, Portland cement, or other hydraulic binders; products are supplied as dry mixes, plastic castables, or gun-ready formulations. Additives such as plasticizers, accelerators, air-entraining agents, and anti-strip agents tune workability and setting.

Installation involves mixing to a plastic or flowable consistency and placing by pouring, casting into molds, vibration, or cladding gunning. After placement, curing with moisture or steam, followed by drying and sometimes firing, develops strength. Care is taken to minimize cracks and ensure bonding to adjacent linings.

Performance depends on composition and temperature exposure. Dense castables offer high refractoriness and strength; insulating castables provide low thermal conductivity but lower strength. Low-cement and zero-cement variants reduce hydration heat but require careful installation. Typical tests include cold crushing strength, porosity, bulk density, and thermal conductivity.

Applications include steelmaking furnaces and ladles, cement kilns, glass furnaces, and petrochemical reactors. Castables suit complex geometries and rapid repairs, but require skilled mixing and curing to avoid cracks and dust. Safety concerns include precautions for cement and silica-containing materials.