Alumina cement

Also called fused cement. A hydraulic cement whose main components are CaO and Al ₂ O _3. It is roughly divided into two types: construction cement and heat-resistant cement. Construction cement is mainly composed of CaO･Al ₂ O ₃ , with small amounts of 12CaO･7Al ₂ O ₃ and others. Refractory cement has a higher amount of Al ₂ O ₃ to increase its fire resistance, and for high temperatures, there are ones that contain 70-80% Al ₂ O ₃ and low amounts of Fe ₂ O ₃ and SiO _2. The most common manufacturing method is the melting method, but recently the firing method has also been used. Alumina cement is expensive and expensive to manufacture, but it hardens much faster than high-early-strength Portland cement, so it is often used in urgent construction projects such as railways, roads, airports, gas, water, and sewage works. It also generates a lot of heat, making it suitable for work in cold weather, and is used in places such as the Antarctic. It hardens rather quickly at low temperatures, but at high temperatures (over 25°C), hardening is delayed and strength decreases. It has excellent chemical resistance, so it is often used in chemical plants. Although the hardened material loses strength when overheated, it is relatively stable and does not lose much fire resistance. It is also resistant to abrasion and thermal shock, so it is used together with aggregate as a shaped refractory material, helping to reduce the labor required for furnace construction and repair.

Source: Morikita Publishing "Chemical Dictionary (2nd Edition)" Information about the Chemical Dictionary 2nd Edition

溶融セメントともいう．CaO，Al₂O₃を主成分とした水硬性セメント．構築用と耐熱材用のほぼ2種類に分類される．構築用のセメントはCaO･Al₂O₃がおもな鉱物であり，少量の12CaO･7Al₂O₃その他を含む．耐火用セメントはAl₂O₃の量を増やし耐火度を上げ，高温用としてはAl₂O₃70～80％ でFe₂O₃，SiO₂含有量の少ないものがある．製造法としては溶融法が一般的であるが，最近は焼成法も行われている．アルミナセメントは製造コストが高く高価であるが，早強ポルトランドセメントよりはるかに早く硬化するため，急を要する鉄道，道路，空港，ガス，水道，下水などの工事に多く用いられ，また，発熱量が多いため寒中の作業に適し，南極などでも利用されている．低温度でむしろすみやかに硬化し，高温(25 ℃ 以上)では硬化が遅れ強度も低下する．化学抵抗性がすぐれているので化学工場などでしばしば用いられる．また，硬化体は過熱されると強度は低下するが比較的安定で，耐火度の低下も少なく，摩耗，熱衝撃に強いので骨材とともに造形耐火物としても用いられ，築炉と補修の省力化にも役立っている．

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