One of the most essential and essential building materials is cement. It is used for the manufacture of asbestos-cement, reinforced concrete and concrete elements, mortars. Cement is a group of hydraulic binders, the basic part of which are aluminates and silicates, formed during the processing of raw materials at high temperature and brought to complete or partial melting.
Features of the composition
Pure limestone and bauxite are used as raw materials. The latter are a rock, which consists of impurities and hydrates. Bauxites have become widespread in the industrial sector for the extraction of adsorbents, refractories, aluminum and other things.
Aluminous cement is distinguished by the predominance of one-calcium aluminate in the composition of clinker, which determines the main characteristics of the binder. It also contains gelena as a ballast impurity and dicalcium silicate, whose characteristic feature is slow hardening.
When mixing with watermonocalcium aluminate begins to hydrate. The substances formed in this case act as an integral part of the solidified material. Expanding cement begins to set after 45-60 minutes, complete solidification occurs after 10 hours. It is possible to change the setting period by adding accelerators (gypsum, lime) or retarders (calcium chloride, boric acid).
Features
Aluminous cement has a low ability to deform, as the forming stone has a coarse-grained structure. In addition, the presence of hydrated cubic monoaluminate leads to mass loss during formation.
Typical for this material is the release of a large amount of heat that occurs in the first few hours of solidification. This property is useful for concrete work in winter, but it reduces the range of applications for massive structures.
Expanding cement, made from aluminous, is one of the fire-resistant materials. It is used to form refractory hydraulically setting mortars in combination with refractory constituents such as chamotte, ore, magnesite.
Besides this, a high-strength cement stone is a distinctive feature, which determines significant resistance to vegetable oils, acids, sea water.
This material is able to provide mortar and concrete with moisture resistance and significant density. But it is subject to rapid destruction under the influencealkalis and ammonium s alts.
Production
Aluminous cement is produced by two methods: by firing before sintering and by melting the raw charge. The latter method requires charge preparation, 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 furnaces of various types. After the material is cooled and crushed.
Cement stone acquires less strength with increasing pour point due to recrystallization of hydroaluminate. Therefore, the manufactured products are not subjected to autoclaving and steaming.
Less hardening occurs with decreasing temperature. If the mass is cooled to negative values, hardening with water becomes almost 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 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 color. Aluminous cement, the price of which starts from 40 rubles per kg, is packaged in containers and bags of 50 kg. Possibility of fasthardening in water is the most important characteristic.
Application
It is used to form reinforced concrete and concrete structures where the concrete is expected to reach design strength in 1, 2 or 7 days, and for underground and offshore structures 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 repairing damage in maritime transport.
Aluminous cement HZ 40 has also found its application in the creation of expanding compositions - it is a non-shrinking waterproof, expanding waterproof and expanding aluminous cement.
Useful Features
Aluminous cement is a strong binder used for heat-resistant and building mortars, characterized by rapid hardening in air and in water. It is formed by using a finely ground mixture of raw materials with a high alumina content and fired to fusion or sintering. Roasting is carried out today mainly in electric arc or blast furnaces to the state of melting. At the same time, there is no need for strong grinding of raw materials components, and it is possible to remove silica and iron.
Types of aluminous cement give products increased resistance to starch, saline, lactic acid, sulfur compounds and increase temperature resistance up to 1700 degrees.
In addition, the impact of mineral waters is reduced due to the impossibilitythe formation of calcium hydrate when interacting with the aquatic environment. Resistance to sulfate corrosion is obtained due to the absence of tricalcium hydroaluminate. Cement is subject to corrosion in the alkaline sphere, a concentrated solution of magnesium sulfate and active acidic environments.
