Aluminous cement: composition, characteristics, application
One of the most necessary and most important materialsin construction is cement. It is used for manufacturing asbestos-cement, reinforced concrete and concrete elements, mortar. 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 resulted in complete or partial melting.
Features of composition
Used as raw materials are pure limestones andbauxites. 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 differs predominanceodnokaltsievogo aluminate in the composition of clinker, which determines the main characteristics of the binder. Also contains gehlenite in the role of ballast admixture and dicalcium silicate, the characteristic feature of which is the slow hardening.
When water starts to hydratesingle-calcined aluminate. 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).
Aluminous cement is lowthe ability to deform, since the forming stone has a coarse-crystal structure. In addition, the presence of hydrated cubic monoaluminate results in loss of mass during formation.
Characteristic for this material is thethe amount of heat that occurs 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 fromaluminous, belongs to the number of fire-resistant materials. It is used to form refractory hydraulically settable solutions in combination with refractory components such as chamotte, ore, magnesite.
In addition, a distinctive feature is a cement stone with high strength, which determines a significant resistance against vegetable oils, acids, sea water.
This material is able to provide a solution and concrete with moisture-proofness and considerable density. But it is prone to rapid destruction under the influence of alkalis and ammonium salts.
Aluminous cement is produced by twomethods: firing to sintering and melting the raw material charge. The latter method requires preparation of the charge, melting followed by cooling, crushing and grinding. The method of baking by drying of the original components, fine grinding and mixing until the uniform homogenization is obtained is characterized, then the granular or powder mixture is fired in different types of furnaces. After the material is cooled and crushed.
Cement stone acquires less strength withincrease in the pour point due to recrystallization of the hydroaluminate. Therefore, the products produced are not subjected to autoclaving and steaming.
Less intensive hardening occurs whenlowering of temperature. If the mass is cooled to negative values, hardening with water becomes practically impossible, therefore, it is necessary 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.
It is used to form ferro-concrete andconcrete structures, when concrete should reach the 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 damages 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.
Aluminous cement is an astringenta 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 grinding 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 components of the raw material, 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 reduceddue to the impossibility of forming calcium hydrate when interacting with an aqueous medium. Resistance to sulfate corrosion was 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.