One of the most necessary and most important materials in construction is cement. It is used for the manufacture of asbestos-cement, reinforced concrete and concrete elements, mortars. Cement refers to a group of hydraulic binders, the basic part of which are aluminates and silicates, formed during processing of raw materials at high temperature and reduced to full or partial melting.
Features of the composition
Pure limestones and bauxites are used as raw materials. The latter are rock, which consists of impurities and hydrates. Bauxites have become widespread in the industrial field for the production of adsorbents, refractories, aluminum and other things.
Alumina cement is distinguished by the predominance of single-calcium aluminate in clinker, which determines the main characteristics of the binder. It also contains gelenite as a ballast impurity and dicalcium silicate, a characteristic feature of which is slow hardening.
When mixed with water, one-calcium aluminate begins to hydrate. Substances formed in this case act as an integral part of the hardened material. Expanding cement begins to set in 45-60 minutes, complete solidification occurs after 10 hours. It is possible to change the setting period by adding accelerators (gypsum, lime) or moderators (calcium chloride, boric acid).
Specifications
Alumina cement has a low ability to deform, since the forming stone has a coarse-grained structure. In addition, the presence of hydrated cubic monoaluminate leads to weight loss during formation.
Characteristic of this material is the transfer of a large amount of heat that occurs in the first few hours of solidification. This property is useful when carrying out concrete work in the winter, but at the same time reduces the range of applications for massive structures.
Expanding cement made from alumina is one of the flame retardant materials. It is used to form refractory hydraulically setting solutions in combination with refractory components such as fireclay, 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 capable of providing mortar and concrete with moisture resistance and significant density. But it is subject to rapid destruction under the influence of alkalis and ammonium salts.
Production
Alumina cement is made by two methods: roasting before sintering and melting the raw material charge. The latter method requires the preparation of the mixture, melting, followed by cooling, crushing and grinding. The baking method is characterized by drying the initial components, fine grinding and mixing until uniform homogenization is obtained, then the granular or powder mixture is fired in various types of furnaces. After the material is cooled and crushed.
Cement stone acquires less strength with an increase in pour point due to recrystallization of hydroaluminate. Therefore, manufactured products are not autoclaved and steamed.
Less intense hardening occurs when the temperature decreases. If the mass is cooled to negative values, hardening with water will become practically impossible, therefore, the provision of suitable temperature conditions is required.
Types of Alumina Cement
There are 2 types of material: high alumina and standard cement. The brand is determined on the third day after the production of samples. Given the high cost and lack of raw materials, cement is sold in a relatively small volume. The material is a fine powder of black, brown or dark green. Alumina cement, the price of which starts at 40 rubles per kg, is packaged in containers and bags of 50 kg. The possibility of rapid solidification in water is the most important characteristic.
Application
It is used for the formation of reinforced concrete and concrete structures, when concrete must reach its rated strength after 1, 2 or 7 days, as well as for the construction of underground and offshore facilities requiring 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 repair damage in maritime transport.
HZ 40 alumina cement has found its application in the creation of expanding compositions - it is a non-shrinking waterproof, expanding waterproof and expanding alumina cement.
Useful Features
Alumina cement is a strong astringent, used for heat-resistant and mortar, characterized by rapid hardening in air and water. It is formed using a raw material mixture of fine grinding with a high content of alumina and calcined before fusion or sintering. Firing is carried out today mainly in electric arc or blast furnaces to a melting state. At the same time, there is no need for strong grinding of the components of the raw material, and there is the possibility of removing silica and iron.
Types of alumina cement give products increased resistance to compounds of starch, hydrochloric acid, lactic acid, sulfur and increase the temperature resistance to 1700 degrees.
In addition, the effect of mineral waters is reduced due to the inability to form calcium hydrate when interacting with the 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, in a concentrated solution of magnesium sulfate and in active acidic media.