Aluminous cement: composition, characteristics, application

One of the most necessary and most important materials in the construction is cement. It is used for manufacturing asbestos-cement, reinforced concrete and concrete elements, mortars. By cement is meant a group of astringent hydraulic substances, the basic part of which is aluminates and silicates formed during processing of raw materials at high temperature and reduced to complete or partial melting.

Features of composition

Clean limestones and bauxites are used as raw materials. The latter are a rock, which consists of impurities and hydrates. Bauxite has become widely spread in the industrial sphere for the production of adsorbents, refractories, aluminum and other.

Aluminous cement is characterized by the predominance of a single-calcined aluminate in the clinker composition, which determines the main characteristics of the binder. Also contains gehlenite in the role of ballast admixture and dicalcium silicate, a characteristic feature of which is the slow hardening.

When the water is immobilized, the single-calcined aluminate begins to hydrate. The substances formed in this case act as an integral part of the solidified material. Expanding cement begins to set in 45-60 minutes, complete hardening occurs after 10 hours. It is possible to change the setting period by the addition of accelerators (gypsum, lime) or retarders (calcium chloride, boric acid).

Characteristics

Aluminous cement has a low deformation ability, since the forming stone has a coarse-grained structure. In addition, the presence of hydrated cubic monoaluminate results in loss of mass during formation.

Typical for this material is the return of a large amount of heat, occurring in the first few hours of solidification. This property is useful in carrying out concrete work in the winter, but at the same time reduces the range of applications for massive structures.

Expanding cement, made of aluminous, belongs to the number of fire-resistant materials. It is used for the formation of refractory hydraulically settable solutions in combination with such refractory components as chamotte, ore, magnesite.

In addition, a distinctive feature is a cement stone with high strength, which determines significant resistance against vegetable oils, acids, sea water.

This material is able to provide a solution and concrete with a moisture-tightness and a significant density. But it is prone to rapid destruction under the influence of alkalis and ammonium salts.

Production

Aluminous cement is produced by two methods: firing to sintering and melting of raw batch. The latter method requires preparation of the charge, melting followed by cooling, crushing and grinding. The method of baking by drying the original components, fine grinding and mixing until the uniform homogenization is obtained is characterized, then the granulated or powder mixture is fired in different types of furnaces. After the material is cooled and crushed.

Cement stone acquires less strength with increasing pour point due to recrystallization of hydroaluminate. Therefore, the products produced are not subjected to autoclaving and steaming.

Less intense hardening occurs when the temperature decreases. If the mass is cooled to negative values, hardening with water becomes practically impossible, therefore, it is required to provide suitable temperature conditions.

Types of aluminous cement

There are 2 types of material: high-alumina and standard cement. The mark is determined on the third day after the production of the samples. Given the high cost and lack of raw materials, cement is sold in a relatively small amount. The material is a fine powder of black, brown or dark green color. Aluminous cement, whose price starts from 40 rubles per kg, is packed into containers and bags of 50 kg. The possibility of rapid hardening in water is the most important characteristic.

Application

It is used for the formation of concrete and concrete structures when concrete must reach design strength after 1, 2 or 7 days, as well as for the construction of underground and offshore facilities that require high sulfate resistance. It is worth noting the high efficiency in the restoration of bridges and buildings, the rapid formation of foundations for cars and sealing of damage in maritime transport.

Cement alumina GC 40 has found its application also in the creation of expanding compounds - it is a non-shrink waterproof, expanding waterproof and expanding cement alumina.

Useful Features

Aluminous cement is an astringent solid substance used for heat-resistant and mortar, characterized by rapid solidification in air and water. It is formed by means of a raw mixture of fine milling with a high content of alumina and fired to fusion or sintering. Today, firing is carried out mainly in electric arc furnaces or blast furnaces to the melting point. In this case, there is no need for a strong grinding of the raw material components, and there is the possibility of removal of silica and iron.

Types of alumina cement give the products increased resistance to starch, brine, lactic acid, sulfur compounds and increase the temperature resistance up to 1700 degrees.

In addition, the effect of mineral waters is reduced by the inability to form calcium hydrate when interacting with an aqueous medium. Resistance to sulphate corrosion is obtained due to the absence of tricalcium-type hydroaluminate. Cement is susceptible to corrosion in the alkaline sphere, a concentrated solution of magnesium sulfate and active acidic media.