High alumina cement is composed of calcium aluminate, unlike Portland cement, which is composed of calcium silicate. It is manufactured from limestone or chalk and bauxite (especially clays with very high alumina content). High-alumina cement was originally developed by cement producer Lafarge and was launched in the UK in 1925. It is especially used in marine applications where it is considered chemically resistant. High-alumina cement became popular in the 1950s because the strength of high alumina refractory cement developed rapidly and was relatively fast to manufacture. High alumina cement is widely used in structural concrete such as precast beams.
Compared with the calcium sulfoaluminate cement, high alumina cement is an inorganic material that forms a dense texture when it reacts with water, and has excellent fire resistance, fast hardening and chemical resistance. This type of cement is produced by grinding clinker formed from calcined bauxite and lime. Bauxite is an aluminum ore. It is stipulated that the total alumina content should not be less than 32%, and the weight ratio of alumina to lime should be between 0.85 and 1.30. Extra care should be taken when using high alumina cement to ensure that the high alumina cement does not come into contact with any traces of lime or ordinary cement.
The characteristics of this high-alumina cement can be summarized as follows: high -alumina cement has a low pH value ; high-alumina cement has high refractoriness ; high- alumina cement has high durability in sulfuric acid ; high-alumina cement hardens rapidly ; high- alumina cement Less reactive than alumina or hydraulic lime ; when added to refractory castables, high- alumina cement can be used as a bonding material because it forms a ceramic bond at high temperatures ; high-alumina cement has high chemical resistance. Therefore, high alumina cement is also widely used in the construction of water pipes, sewage pipes, factory drain pipes, coastal buildings and factory chimneys.
This high alumina cement has an initial setting time of more than 3.5 hours and a final setting time of about 5 hours , so it allows more time for mixing and setting operations. High alumina cement can withstand high temperatures and release a lot of heat during the setting process. Therefore, it is not affected by frost. High alumina cement resists the action of acids in a better way , it sets quickly and reaches a higher ultimate strength in a short time. The strength is about 40 N/ ㎟ after 1 day , and about 50 N/㎟ after 3 days. The curing action of high alumina cement is mainly dependent on chemical reactions, so it is not necessary to grind it to a fine powder.