Building material produced by crushing various hard rocks or processing industrial waste is called crushed stone. This inorganic bulk material, resembling a small chopped stone, is widely used in many areas of human activity. Various types of crushed stone, depending on its physical and technical characteristics, are used in the capital and restoration construction of buildings, roads, railways, production of concrete products, landscape planning.
Varieties of rubble and where each species is used
Crushed stone is classified by origin. This is, first of all, the type of rock from which it is developed. Manufacturers always provide the necessary information. The origin of crushed stone characterizes its qualities, and, therefore, the scope of its application. The main types of rubble by origin are divided into:
- Granite . This is one of the most durable types of rubble. It is obtained from hard rock, one of the most common on Earth. Granite rock belongs to igneous (primary) rocks and is a magma cast to the surface and solidified. Granite is formed from a number of crystals: quartz, spar, mica, etc. It has a red, pink, and gray color. Gravel types of crushed stone are used for construction and landscape planning, road and railway construction, drainage, and decoration.
- Gravel . Crushed stone produced by screening or crushing rock. It has almost the same strength as granite, but has a lower radiation background and cheaper. Gravel types of crushed stone are used for concrete, concrete products, foundation works and in road construction.
- Limestone . This crushed stone is a product of crushing of sedimentary (secondary) rock - limestone, the main component of which is calcite. Limestone and dolomite gravel is significantly inferior in strength to gravel and granite. It is applied in road construction and production of concrete goods.
- Slag . This is a product of crushing waste from metallurgical production. The main advantage of such crushed stone is its relatively low cost. Most often used as binders for concrete.
- Secondary crushed stone . The product of crushing building waste - brick, concrete, asphalt. Such crushed stone is inferior in all characteristics to products made from natural materials, but is still widely used as aggregate for concrete, road construction, strengthening of soft soils, and improvement.
Crushed stone production
Crushed stone production consists of several stages:
- rock mining;
- transportation (if necessary);
- several stages of crushing;
- sorting by fractions.
The main stage of crushed stone production is crushing. The shape and size of the obtained grains depends on this operation. Crushing is carried out in 2-4 cycles on special equipment - crushing machines. Depending on the grinding method, different types of crushed stone crushers are distinguished:
- Jaw - are installed at the first stage of crushing. The principle of action is shockless crushing of rock between two plates.
- Centrifugal . These crushing machines are most often used for the production of crushed stone of a fine fraction of any hardness used in road construction.
- Cone crushers are one of the most expensive crushed stone machines. Their main advantage is versatility. Such crushing machines can produce crushed stone of any fraction and even artificial sand.
- Rotary . In these machines, rock grinding is carried out by impact energy. Fillable rock with high speed repeatedly hits the baffle plates and crushes until it falls into the calibrated output slots.
At the last stage, before the products are shipped to consumers, crushed stone is divided into fractions. The operation is carried out on equipment called roar. These cars can be stationary or suspended. In the sorting process, crushed rock passes through several vibrating screens with holes of various diameters. On each of them the crushed stone of the established fraction is separated.
Crushed stone fractions
At the output after crushing, grains of various sizes are obtained. For further implementation, crushed stone is sorted based on particle size. Fraction - the maximum allowable value of a single grain (stone). Types of gravel by fractions are divided into main and related. The main ones are from 5 to 70 mm in size. The sizes of the accompanying fractions and screenings are from 0 to 40 mm. For special applications, grades of crushed stone of special fractions are produced: 70-120 mm and 120-150 mm.
Crushed stone is the main natural stone material. Granite crushed stone with a size of 5-20 mm is in greatest demand. Such material is used in the production of concrete, asphalt and concrete products. Granite crushed stone of large fractions (20-45, 20-65, 25-60, 40-70 mm) is also quite demanded in the market, it is used for railway embankments, in construction for strengthening foundations and laying the foundation, as a pillow layer for the construction of roads .
Gravel and crushed stone
For the production of concrete, such large aggregates are used: natural stone gravel, gravel and gravel gravel, blast-furnace slag aggregate . Gravel used in construction is mountain, river and sea. The last two, due to their smooth polished surface, have worse adhesion. Crushed stone for construction is produced by crushing natural rock. Such types of crushed stone have a rough surface and an acute-angled shape, due to which they have better adhesion to binders than gravel. The quality of gravel and gravel is characterized by:
- strength;
- grain size and shape;
- frost resistance;
- content of harmful impurities.
Physical properties of crushed stone
The physical characteristics of the material are given much more attention than origin. It is on the basis of these properties of crushed stone that the scope of its use is determined. All types of crushed stone are characterized by the following main indicators:
- strength;
- flattery;
- frost resistance;
- water absorption;
- the shape of the grains;
- radioactivity.
Crushed stone flare
In gravel, the content of lamellar and needle grains is normalized, whose thickness or width is three times greater than length. This is an important characteristic that is primarily paid attention to when using crushed stone in the construction and production of reinforced concrete products. In the presence of a large number of grains of lamellar and needle shape in the total mass of crushed stone, the concrete mixture may turn out to be of low quality and require additional compaction. A large number of grains of this shape leads to the formation of numerous voids. The percentage of lamellar and needle grains in the mass of crushed stone is divided into groups:
- I - up to 15%, cuboid;
- II - 15-25%, improved;
- III and IV groups of ordinary flakiness - 25-35% and 35-50%, respectively.
Cube-shaped crushed stone is most suitable for concrete preparation due to the absence of problems with voids.
Crushed stone strength
This property of crushed stone is characterized by the strength limit of the original rock. The strength of this natural stone material is determined by simulating mechanical effects on compression, crushability when crushed in a cylinder, and abrasion in a shelf drum. Granite has the highest strength. The most popular is the M1200 granite crushed stone with the content of stones of weak rocks not more than 5%. Its main application is the construction of foundations, the production of high-strength concrete and load-bearing structures.
Frost resistance of the material
The property of the material to maintain integrity, strength and mass after repeated freezing and thawing is called frost resistance. This characteristic is especially important for crushed stone used in the construction of foundations in regions with low temperatures. High frost resistance is possessed by materials with high density and low porosity.
The activity of crushed stone radionuclides
One of the most important characteristics of any material used in construction is the radioactivity of crushed stone. It determines its suitability for all types of construction work and must comply with sanitary and epidemiological standards, which is confirmed by the relevant conclusions and certificates. A value of less than 370 Bq / kg corresponds to the first class of radioactivity of high-strength crushed stone. For the second class - more than 370 Bq / kg.