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Concrete is one of the most widespread and major building materials. It represents a mix of a knitting material (cement) with a fine filler (sand), a large filler (gravel, rubble, a fragmentary stone and т. Item) and water. The filler at hardening concrete forms the original skeleton which is not allowing concrete to settle. At construction the preference is given natural fillers, such, as rubble, gravel, a fragmentary stone and т. The item are made To them following demands: they should be firm, durable and should not contain a plenty of clay, loam, silt, mica, slate, alkalis and organic substances. However use of an artificial filler as which acts, for example, slag of blast furnaces is not excluded also.
Fillers are classified and on grains. So, the preference is given large sand before fine. But there is also more successful variant: use смешенного sand where the size of grains varies from large up to moderately fine. Thus defining criterion there is a kind that kind of works where concrete will be used. If it is thin walls it is necessary to use a filler with the small size of grains (the same at use of cement close арматурных cores), and here in massive concrete use of a filler with grains up to 15 - 20 mm is admissible.
Water does a mix plastic and convenient in application and as it takes up with портландцементом which gives to concrete greater durability. For manufacturing concrete it is used unsalted (that there was no threat of corrosion of steel in ferro-concrete) and necessarily pure. Besides water, to be exact its quantity, defines durability and many other things qualities of concrete. So, on a bag of cement which weight makes 43 kg, goes from 15 up to 23 л waters (the exact quantity will depend on humidity of used sand, from demanded durability and stability). And than less waters it will be used, concrete will be especially strong.
There are some kinds of concrete: not reinforced concrete, ferro-concrete, concrete with a fibrous filler (фибробетон) and preliminary intense concrete. Any of these kinds of concrete can be made of one of five types of cement: I type - usual портландцемент (cement of a general purpose); II type - modified портландцемент, it is moderate сульфатостойкий (it is used for constructions in a ground); III type - быстротвердеющий; IV type - with low экзотермией; V type - сульфатостойкий (it is used for adverse soil conditions).
For erection of especially responsible designs use so-called torket - concrete. Owing to the raised density and water resistance it becomes a necessary element at repair and strengthening of any designs, erection of thin-walled ferro-concrete designs, the device of coverings and water-proof обделок. Manufacture of торкрет-concrete occurs as follows: by means of so-called cement-gun a solution and a concrete mix spray under pressure of compressed air upon a surface of designs in the form of торкрет-concrete (range of submission of a solution across reaches 70). Loading of a dry mix of sand and cement in cement-gun occurs continuously, that allows to optimize all process as much as possible.
Owing to the тестообразному to a condition (before hardening) concrete can be used in designs of different type, for this purpose the special form (timbering) which do not delete up to full схватывания a concrete mix should be used. If in a design stretching or bending pressure concrete reinforce steel are stipulated.
Concrete is a fire-resistant material and possesses low heat conductivity. On factor of thermal expansion it is similar to steel. It guarantees its reliability and safety.
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