Calcium aluminate cement is a hydraulic cement obtained by crushing a solidified melt or clinker consisting mainly of calcium aluminate, which is formed from a proportional mixture of aluminium and calcareous materials. They are generally divided into three groups (low-purity, medium-purity, and high-purity) based on their alumina and iron oxide content. Calcium aluminate clinker is mainly used for high temperature refractories. Other uses include moderate acid resistance applications, high early strength and fast setting mixtures, and as part of the expansion component in certain shrinkage compensating cements. These cements are generally designed to gain strength faster than regular Portland cement and are mainly composed of calcium aluminate, which generates a lot of heat during the first 24 hours.
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 calcium aluminate cement is made by reacting lime-containing materials with aluminum-based materials to form calcium aluminate.
Second, 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, calcium aluminate cement is rarely used for cast-in-place structural work. Some of the uses for which calcium aluminate cement concrete can be identified include: cold weather work; high temperature resistance; mild acid and alkali resistance; sulfate, seawater, and purified water resistance; rapid hardening. It is important to distinguish between rapid setting and rapid hardening. Aluminate cement concrete is not fast setting. However, they are hardening rapidly. That is, they will be as strong at 24 hours as Portland cement concrete after 28 days.
Calcium aluminate cement concrete should be cured for at least 24 hours using water spray or mist, standing water, wet burlap or cured film . When working with 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 generate heat much faster than Portland cement concrete and must be well cured within 24 hours of placing for satisfactory strength gains.
