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The calcium aluminate cements are similar to the more familiar Portland cements in that they both require water for hydration, they both form concrete that sets at about the same time, and they both require similar mixing designs and placement techniques. However, there are important differences between the two cements. First, Portland cement is made by reacting limestone and clay to form calcium silicate, while the calcium aluminate cement is made by reacting lime-containing materials with aluminum materials to form calcium aluminate.
Second, the calcium aluminate cement, when mixed with suitable aggregates, is often used for special applications where its unique properties can be exploited. Except for emergency repairs and foundation construction, the calcium aluminate cement is rarely used for cast-in-place structural works. Some of the uses for which the calcium aluminate cement concrete may be specified include: cold weather work; high temperature resistance; weak acid and weak base resistance; sulfate, seawater, and pure water resistance; rapid hardening. It is important to distinguish between rapid setting and rapid hardening. The calcium aluminate cement concrete does not set rapidly. However, they are hardening rapidly; that is, they will be as strong in 24 hours as Portland cement concrete in 28 days.
The calcium aluminate cement concrete should be cured for at least 24 hours using water spray or atomization, standing water, wet burlap or cured film. When working with the calcium aluminate cement concrete for the first time, it must be remembered that it handles in much the same way as Portland concrete. However, in order to obtain satisfactory results, two points should be emphasized. First, keep the water-cement ratio below 0.4, and pour the concrete with mechanical vibration. Second, these concretes heat up much faster than Portland cement concrete, and good curing 24 hours after pouring is essential to obtain satisfactory strength.
In most cases, the calcium aluminate cement and high-purity calcium aluminate cement contain more than 35% and 70% alumina, respectively. But cements with 80% alumina and more are made of 70% alumina grade material mixed with fine alumina and dispersion bales. This is because if a material is produced directly from the reagent mixture in that ratio.
There are two main methods that can be used to produce the calcium aluminate cement on an industrial level. The first method is fusion, which involves liquefying the raw materials of bauxite and limestone together in a reverberatory furnace. In the second method, high-purity limestone and high-purity alumina are sintered together in a rotary kiln, which produces a relatively pure cement, that is HAC.
