Types of crushed stone: description, characteristics, uses and origin

Building material, produced by crushing various hard rocks or processing industrial waste, is called rubble. This inorganic bulk material, outwardly resembling a small chipped stone, is widely used in many spheres of human activity. Different types of rubble, depending on its physical and technical characteristics, are used in the capital and reconstruction construction of buildings, roads, railways, the 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 worked out. Manufacturers always provide the necessary information. The origin of crushed stone characterizes its quality, and therefore, the scope of its application. The main types of crushed stone by origin are divided into:

• Granite . This is one of the most durable types of rubble. It is obtained from solid rock, one of the most common on Earth. A granite rock refers to igneous (primary) rocks and is a magma thrown 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 for construction and landscape planning, road and railway equipment, drainage, decorative design are used.
• Gravel . Crushed stone, produced by sifting or crushing rock. Has almost the same strength as granite, but has a smaller radiation background and is cheaper. Gravel types of crushed stone for concrete, concrete products, foundation works and road construction are used.
• Limestone . This crushed stone is a product of crushing of sedimentary (secondary) rock - limestone, the main component of which is calcite. Limestone and dolomite crushed stone is much inferior in strength to gravel and granite. It is used in road construction and concrete products.
• Slag . This product is the crushing of waste metallurgical production. The main advantage of such rubble is a relatively low cost. Most often used as binders for the preparation of concretes.
• Secondary crushed stone . A product of crushing construction debris - brick, concrete, asphalt. Such crushed stone in all characteristics is inferior to products made from natural materials, but it is still widely used as a filler for concrete, road facilities, strengthening of weak soils, improvement.

Crushed stone production

Crushed stone production consists of several stages:

• Mining of rock;
• 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 resulting grains depends on this operation. Crushing is carried out in 2-4 cycles on special equipment - crushing machines. Depending on the method of grinding, different types of crushers of crushed stone are distinguished:

• Jaws - are installed in the first stage of crushing. The principle of operation is the unstressed crushing of the rock between two plates.
• Centrifugal . These crushing machines are most often used to produce crushed stone of fine fraction of any hardness used in road construction.
• Cone crushers are one of the most expensive machines for crushed stone production. Their main advantage is universality. Such crushing machines can produce crushed stone of any fraction and even artificial sand.
• Rotary . In these machines the grinding of the rock is carried out by the impact energy. The buried rock with a high speed repeatedly strikes against the plate and is crushed until it falls into the calibrated output slots.

At the last stage, before shipment of products to consumers, crushed stone is divided into fractions. The operation is performed on equipment called a screen. These machines can be stationary or suspended. During sorting, the crushed rock passes through several vibrating sieves with holes of different diameters. On each of them the crushed stone of the established fraction is separated.

Fractions of rubble

At the outlet after crushing, grains of different sizes are obtained. For further implementation, the crushed stone is sorted based on the particle size. Fraction is the maximum permissible value of a separately taken grain (stone). Types of rubble by factions are divided into basic and accompanying. Basic - the size of 5 to 70 mm. The sizes of accompanying fractions and screenings are from 0 to 40 mm. For special applications, types of crushed stone of special fractions are produced: 70-120 mm and 120-150 mm.

Crushed stone is the main natural stone material. The greatest demand is a granite gravel 5-20 mm in size. Such material is used in the production of concrete, asphalt and concrete products. Granite rubble of large fractions (20-45, 20-65, 25-60, 40-70 mm) is also quite in demand on the market, it is used for railroad embankments, in construction with reinforcement of foundations and foundation laying, as cushion layer in the construction of highways .

Gravel and crushed stone

For the production of concrete such large aggregates are used: natural stone crushed stone, gravel and gravel crushed stone, aggregate from blast furnace slag. Gravel, used in construction, is mountain, river and sea. The latter two, because of their smooth polished surface, have the worst adhesion. Stone crushed stone for construction is produced by crushing natural rocks. Such types of rubble have a rough surface and an acute-angled shape, due to which they have better adhesion to astringents than gravel. The quality of gravel and crushed stone is characterized by:

• Strength;
• Size and shape of grains;
• Frost resistance;
• Content of harmful impurities.

Physical properties of crushed stone

The physical characteristics of the material are given much more attention than the 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 grains;
• Radioactivity.

Crushed stone crushed stone

The content of lamellar and acicular grains is normalized in crushed stone, whose thickness or width is three times larger than the length. This is an important characteristic, which is primarily paid attention when using crushed stone in construction and production of reinforced concrete products. In the presence of a large number of granular and needle-shaped grains in the total mass of crushed stone, the concrete mixture can turn out to be of poor quality and require additional compaction. A large number of grains of this form lead to the formation of numerous voids. By percentage of lamellar and acicular grains in the mass, broken stone is divided into groups:

• I - up to 15%, cuboid;
• II - 15-25%, improved;
• III and IV groups of common fl usiness - 25-35% and 35-50% respectively.

Cuboid crushed stone is most suitable for the preparation of concrete due to the absence of problems with voids.

Strength of rubble

This property of rubble is characterized by the limit of the strength of the original rock. Strength of this natural stone material is determined by imitation of mechanical effects on compression, crushing at crushing in the cylinder, abrasion in the shelf drum. The highest strength is in granite. The most demanded is granite rubble М1200 with the content of stones of weak rocks no more than 5%. Its main application is the construction of foundations, the production of high-strength concretes and 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.

Activity of radionuclides of crushed stone

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 works and must comply with sanitary and epidemiological standards, which is confirmed by appropriate conclusions and certificates. The first class of radioactivity of high-strength crushed stone corresponds to a value of less than 370 Bq / kg. For the second class - more than 370 Bq / kg.