Calcium aluminate (CA) cements are similar to the more familiar Portland cements in that they both require water for hydration, they both form concretes that set in about the same time, and they both require similar mix designs and placing techniques. There are, however, important differences between the two cements. First, Portland cements are made by reacting limestone and clay to produce calcium silicates, while calcium aluminate cements (also called high-alumina cements) are made by reacting a lime-containing material with an aluminous material to produce calcium aluminates.
Second, calcium aluminate cements, when mixed with suitable aggregates, are generally used for special applications where advantage can be taken of their unique properties. Calcium aluminate cements are rarely used for cast-in-place structural work, except for emergency repairs and foundation construction. Some of the purposes for which CA cement concretes may be specified include: cold weather work; resistance to high temperatures; resistance to mild acids and alkalies; resistance to sulfates, sea water, and pure water; and rapid hardening. It is important to differentiate between rapid setting and rapid hardening. Calcium aluminate cement concretes are not rapid setting. They are, however, rapid hardening; that is, they will develop as much strength in 24 hours as Portland cement concrete will achieve in 28 days.
Calcium aluminate cement concretes should be cured for at least 24 hours, using a water spray or fog, ponding, wet burlap or a curing membrane. When working with calcium aluminate cement concrete for the first time, one must remember that is should be handled much the same way as Portland concrete. For satisfactory results, however, two points should be emphasized. First, keep the water-cement ratio below 0.4 and use mechanical vibration to place the concrete. Second, these concretes develop heat much more rapidly than Portland cement concrete does, and good curing for 24 hours after placement is mandatory for satisfactory strength gain.