Classification of refractory lightweight castables

Classification of lightweight castables

1. Low temperature lightweight castable

The use temperature of low-temperature lightweight castables is below 900°C, and expanded vermiculite, expanded perlite, ceramsite, etc. are often used as aggregates. Use ordinary Portland cement, alumina cement or water glass as binding agent. For example, the properties of the castable obtained by preparing expanded perlite with a particle size of 8~1mm and alumina cement at a ratio of perlite:cement of 35~50, :50~65, after being burned at 900°C, have a bulk density of 0.3 ~0.7g/cm. Compressive strength is 0.5~0.9MPa, thermal conductivity is 700℃, 0.06~0.18W/(m·K).

2. Lightweight thermal insulation castable

Medium temperature lightweight castable. The service temperature of medium-temperature lightweight castable is 900~1200℃. Porous clay particles, clayey ceramsite, shale ceramsite, etc. are usually used as aggregates. Use alumina cement, calcium aluminate cement or aluminum dihydrogen phosphate as binding agent. A small amount of silica powder and floating beads can be added to the fine powder to reduce its volume density. The amount of cement and other binding agents can be determined according to the strength requirements. The higher the strength requirement, the greater the amount of binder added.

3. Porous clinker lightweight castable

High temperature lightweight castable. The use temperature of high-temperature lightweight castables is higher than 1200℃. They use light particles or hollow balls such as corundum, high alumina, mullite, clay, magnesia, and magnesia-aluminum spinel as aggregate. It is a combination system of calcium aluminate cement, aluminum dihydrogen phosphate, silica sol, aluminum sol, and silica micropowder. Fire-resistant fibers can be added to them to increase their strength. The most common are clay and mullite lightweight castables.

2. Precautions for construction of lightweight castable materials

1. Formwork: The formwork for lightweight castable construction can be made of steel plate or hardwood plywood, and the formwork must have sufficient strength. It has good rigidity, does not lose shape, does not shift, and does not leak slurry. The rigid template must be coated with release agent. Wooden formwork should be coated with waterproofing agent, and reused formwork should be cleaned first and then painted before use. Inspection holes and cleaning holes should be made of regular wood moldings.

2. Water-cement ratio: The amount of water added when mixing lightweight castables must be strictly controlled in accordance with the instructions and must not exceed the limit. On the premise of ensuring construction performance, the amount of water added should be less but not too much.

3. Stirring: The mixing time of lightweight castables should be no less than 5 minutes, subject to the requirements of the instruction manual, and a forced mixer must be used during operation. When mixing, it is advisable to mix dry first, then add 80% of the water and mix. Then, depending on how wet or dry it is, slowly add the remaining water and continue stirring. until a suitable level of work is obtained. When mixing lightweight castables, the mixer must be cleaned.

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