Crushed stone type and group by origin. What is natural gravel and its characteristics

Crushed stone is one of the huge number of types of building materials, which in the modern world is one of the most popular, as it has found its application in various branches of modern construction. Due to its characteristics, crushed stone is very common in construction and is used as a filler in the production of large concrete structures. For example, concrete columns and panels used in the construction of bridges for housing construction are made using crushed stone. The construction of the railway and paved roads is also not complete without concrete. The final price of crushed stone is set on the basis of its existing characteristics - rock hardness, density, processing technology. Many do not know that crushed stone is produced from a variety of rocks.

All crushed stone used in the construction of buildings or roads was once a solid stone massif. In order to extract crushed stone, it is necessary to produce artificial destruction of rocks. For this, the most modern technologies and powerful special equipment are used. In order to open the rock mass at the very beginning, the so-called overburden works are carried out, which include the removal of all vegetation and the fertile layer, as well as the sandy-clay layer and the stone affected by erosion from the place of the intended extraction. After that, drilling is carried out. An explosion is carried out and clearing is carried out with the help of heavy equipment. The shock wave destroys the rock, which breaks up into blocks of various sizes.

Further, the loading is carried out on equipment and delivered to the place of subsequent processing, where, with the help of crushing machines, the blocks are crushed into smaller stones. As a result, a mass is obtained from the whole array, consisting of stone grains (fractions) of various sizes. To obtain high-quality building material, the crushed stone fractions are further separated, since each grain size is used in a specific area. This is done with the help of screens that sort the stone grains by size and then place them in separate containers.

Sorting of crushed stone occurs in three stages:

• First, the smallest parts are eliminated. This is a preparatory process that will further facilitate the processing of crushed stone.
• Then large stones and stones of needle shape and with high flakiness are sifted out. These stones will eventually be re-crushed to improve the quality of the product.
• And only at the third, final stage, the crushed stone is sorted into fractions.

Crushed stone becomes suitable for use in the construction industry only after passing through all stages of processing.

Granite crushed stone

This is the most popular type of crushed stone, which has high strength and durability. These characteristics noticeably distinguish it from other varieties of crushed stone, and allow the preparation of expensive high-strength concrete from it. The fact that crushed stone from granite is very difficult to prepare is its only big drawback, which significantly affects the cost of the finished material. Indeed, in order to crush such a strong stone, much more energy is expended than in order to crush rocks that have a softer composition. Granite crushed stone belongs to the highest class of building materials, as it has frost resistance, energy activity and flakiness.

gravel crushed stone

This type of crushed stone is much cheaper for buyers. To obtain it, the spent rock is first sifted, and then it is crushed. Slightly inferior in quality, such crushed stone is perfect for road construction. Pebble shores are considered to be a natural source for gravel crushed stone. Rounded pebbles are the best suited for filling the resulting voids and filling the concrete mass.

Slag crushed stone

It has been in increasing demand in recent years. For its production, waste obtained from the metallurgical industry is used. It should be noted that two methods are used for the manufacture of this material:

1. Ebb in the required form;
2. Crushing of frozen slag mass.

Using the technology of casting slag crushed stone in production, it is possible to obtain the highest quality of the material and the cubic shape of crushed stone, which is more preferable. Slag is significantly inferior to granite in strength, but, nevertheless, buildings made of concrete with its use have almost the same durability. Slag crushed stone, used as a filler, makes concrete cheaper than its initial cost by almost a third. This is an important point when conducting large-scale construction with an insufficient budget.

The existing market of secondary raw materials significantly reduces the cost of the material, since the use of unsuitable building materials for the production of crushed stone (most often scrap bricks and concrete) allows this to be done. Parking lots, sidewalks, trash bins and paved areas are most often made from such material.

Dolomite crushed stone

Limestone is used to produce this type of crushed stone. The same technology is used for its crushing. When mixed with crushed gravel, it is widely used in the road industry, and it is also used in the production of reinforced concrete structures. The use of limestone with a lower specific gravity and density as a filler for reinforced concrete structures can significantly reduce their weight, with virtually no effect on the strength and quality of future structures. It is possible to obtain the best result and high durability of structures built using crushed stone only with the correct selection of the brand of crushed stone and its composition.

The construction of all the latest highways, bridges and overpasses, as well as modern buildings and structures, is currently carried out only through the use of crushed stone.

The word "gravel" can mean both natural material and artificial (expanded clay), produced industrially. Both natural and expanded clay gravel are popular with builders, concrete makers, designers, and other professionals.

Description

Natural gravel is a natural material that is formed under the influence of wind and the destruction of rocks. Depending on the type of occurrence, it can be mountainous (or ravine), river, lake, sea or even glacial.

Mountain gravel has a slightly rough surface. It contains clay, dust, sand, organic matter and other impurities. If the percentage of sand exceeds 25-40%, it is a sand and gravel mixture.

A little cleaner in composition, sea and river gravel. But at the same time, it is smoother, therefore it is characterized by poor adhesion with a bonding agent.

Typically, builders choose mountain gravel because its technical qualities are somewhat better than other types. It is used for the construction of tracks, foundations, backfilling of various sites, and for obtaining roofing materials.

Gravel has various shades: black, yellow, white, gray-blue, brown, pink. Its color may change somewhat under the influence of lighting or humidity. That is why it is popular in landscape design: when decorating summer cottages, paving garden paths, laying out flower beds, etc.

GOST for natural gravel

Whether it is permissible to use gravel for one purpose or another depends on its physical and technical qualities, which are approved at the level of GOSTs and technical instructions.

For gravel and crushed stone, which has an average granule density of 2-3 g / cm3 and is used to produce heavy concrete, road and other construction work, GOST 8267-93 “Crushed stone and gravel from dense rocks for construction work. Specifications".

In this standard, mountain weather gravel is a granular material having an inorganic base, with a granule size of more than 5 mm, which is formed during the sieving of a gravel-sand mixture.

The standard specifies the requirements for the size of fractions, the shape of the granules, strength properties, the percentage of granules of weak rocks and harmful components, frost resistance, acceptance nuances, control methods, requirements for transportation and storage, etc.

There is also GOST 8269.0-97, which describes in detail the methods for determining the main physical and mechanical properties of the material.

Most often, the determination of future properties and their compliance with GOST occurs, which includes mining in quarries, washing and sorting.

Factions

During the purchase process, special attention should be paid to the fractions of gravel. They are determined both by the size of the granules and by the density. The grains can have a size from 5 up to 70 mm.

Main fractions of gravel (mm):

1. 5(3)-10;
2. 10-15;
3. 10-20;
4. 15-20;
5. 20-40;
6. 40-80(70);
7. combination of fractions 5(3)-20.

Material in the form of other combinations of different fractions and larger grains can be produced by agreement between the manufacturer and the buyer.

Gravel with a size of 3-10 mm is used in the arrangement of playgrounds and sports grounds, private beaches, for filtering wells or springs, in floristry. Gravel 10-20 mm in size is used to obtain lightweight concrete. In 1 m3 of concrete, there is approximately 1 ton of gravel in the form of a filler.

Large fractions of the order of 20-40 mm are used for the construction of roads, bridges, airfield pavements, etc. Gravel of 40-70 mm and above is used mainly as a decorative material. They finish aquariums, pools, animal cages, pave the streets, and are used in the construction of dams.

Due to its versatility, combined with ease of use and low cost, gravel has gained wide popularity.

Specifications and properties

Gravel acquires some parameters already in the process of its preparation and processing (sieving, cleaning, mixing, etc.). Such preparation helps to obtain a material that is quite homogeneous in composition and to achieve compliance with official standards.

The main properties of natural gravel:

• The density of the material may vary depending on its type. The average gravel density is 2.6-2.7 t/m3. Bulk density can have a value from 1.43 to 1.61 t/m3;
• volumetric weight is 1600 kg/m3, and specific weight is 1400 kg/m3;
• the shape of the grains can be round, rounded-angular, angular. According to GOST 8267-93, gravel can contain no more than 35% (by weight) of grains that have a needle or lamellar shape;
• the strength of the material is expressed in crushability grades during crushing (or compression) in the cylinder. There are such grades for strength: DR8, DR12, DR16, DR24. The ultimate compressive strength is 1.5 t/cm2;
• for gravel, which is used in road construction, an additional measure of abrasion is established, which is determined as a result of tests in a shelf drum. At the same time, brands I-I, I-II, I-III and I-IV are distinguished;
• based on the degree of frost resistance, grades of gravel are distinguished from F15 to F400.

For comparison, here is a table comparing the characteristics of natural gravel with artificial (expanded clay):

How to distinguish gravel from pebbles and rubble

The word "gravel" usually refers to mountain gravel mined in quarries. Pebbles are the same river or sea gravel formed as a result of grinding small flat stones with sand and water. Thus, pebble is a subtype of gravel.

Pebbles can have different colors. The most common are multi-colored pebbles or pebbles of pink, yellow, gray, brown or marbled hue. Sea pebbles have a flatter shape than river pebbles.

Gravel can be distinguished from crushed stone by its shape and texture. Crushed stone has a rough surface and an acute-angled shape, while gravel is smoother and more rounded.

Crushed stone is formed in the process of crushing rocks in a quarry or during the processing of industrial waste. Thus, gravel is a material formed naturally, and crushed stone is industrial. Sometimes, in order to improve the quality of the adhesion of gravel to the solution, it is crushed into smaller fractions, obtaining crushed stone.

What is gravel, how it looks and how it visually differs from crushed stone can be seen in the photo picture below:

Which is better and cheaper: gravel or crushed stone

Due to its irregular shape, crushed stone forms a more reliable adhesion to the mortar than gravel. Thus, in terms of performance, crushed stone is significantly better than gravel.

The main advantage of gravel can be considered a lower price. It is about 20% cheaper than crushed stone, which is why it is often chosen as an aggregate in the production of heavy concrete. Gravel is often used to build low houses in summer cottages and even to form a foundation.

What to choose - crushed stone or gravel - also depends on the properties of concrete. When the concrete is very strong, it is advisable to use crushed stone. For concrete with a moderate level of strength, inexpensive gravel is suitable.

It is difficult to name the sphere of construction, wherever crushed stone is used. This is an indispensable bulk material, which is distinguished by a huge variety of types, and in each case, one should use a material of one or another fraction, strength, flakiness, color and frost resistance. Let's try to understand the volumetric classification and understand what types of crushed stone exist, what fractions and grades it comes in, and how to choose crushed stone so that it optimally matches the scope.

No. 1. How is crushed stone obtained and where is it used?

Crushed stone is called bulk material, which can differ significantly in color, size of fractions, strength and other parameters. The main reason for such a wide discrepancy in characteristics lies in the origin.

By origin, crushed stone is divided into:

The second two types of gravel, although less popular, still find application, since scope of crushed stone wide enough. It is used for the manufacture, construction and, in the production of block building material, for drainage, the creation of various types of road surfaces, incl. bulk and highway. In addition, crushed stone cannot be dispensed with when arranging runways and railways, and designers have fallen in love with this material for the possibility of flower beds, ponds, embankments and indoor surfaces.

No. 2. Fractions of rubble

As a result of crushing of raw materials, particles of different sizes are formed, or, in other words, different fractions of crushed stone. To separate one fraction from another, crushed stone is sieved through a special sieve called a roar. There are particles of crushed stone from 3 mm to 300 mm and more.

There are even more classifications of crushed stone by fractions than the fractions themselves. The simplest is division into five fractions:

There is another, more detailed classification of crushed stone by size, which implies separation of standard and non-standard fractions. The standard ones include fractions such as 3-8 mm, 5-10 mm, 10-20 mm, 20-40 mm, 25-60 mm, 20-70 mm, 40-70 mm. By agreement with the consumer, non-standard fractions of 10-15 mm, 15-20 mm, 80-120 mm and 120-150 mm can be produced.

No. 3. The flakiness of rubble, or the geometry of form

In the mass of crushed stone there are elements of different forms. There are stones that are distinguished by the presence of flat, even edges, they have lamellar or needle-shaped. Stones with conditionally equal faces are called cuboid. The greater the content of lamellar and needle-shaped elements in crushed stone, the higher flakiness index. The performance characteristics of crushed stone and the scope of its use depend on it.

By flakiness, crushed stone is divided into the following types:

• ordinary crushed stone with a flakiness of 25-35%;
• improved crushed stone, where part of the needle-shaped grains is 15-25%;
• cube-shaped crushed stone with a flakiness of not more than 15%.

Crushed stone with a low flakiness index is used where it is important to compact the concrete mix tightly. Needle grains create unnecessary voids in concrete, so more crushed stone has to be added, but even so, the compressive strength and finished material will be lower. Crushed stone with a high flakiness is used in drainage works, used in the construction of roads.

No. 4. Density and strength of crushed stone

The density of crushed stone varies from 1.2 to 3 g/cm 3 and strongly depends on the type of origin of the material. The higher the density index, the more versatile the material is. The density and strength of crushed stone are directly proportional.

Strength is the ability of a material to withstand various types of mechanical stress. Research and determination of the strength grade is carried out by a series of tests, checking the crushed stone in the cylinder, shelf drum and compressing it. Such experiments make it possible to simulate the real conditions of future operation. According to the strength grade, crushed stone is from M200 to M1600(the numerical indicator means the maximum withstand load in kg / cm 2) and is divided into the following classes:

In rubble they ration the amount of impurities of weak rocks, because the strength of the material directly depends on this. To determine this parameter, tests are carried out and pressure is applied to crushed stone of 20 MPa. According to GOST 8267-93, some impurities of low-strength rocks are normalized as follows:

• for crushed stone M1600 - no more than 1%;
• for crushed stone M1000-M1400 - no more than 5%;
• for crushed stone M400-M800 - no more than 10%;
• for crushed stone M200-M300 - no more than 15%.

No. 5. Frost resistance of crushed stone

Frost resistance shows how many cycles of freezing and thawing crushed stone can withstand without losing its main strength qualities. In laboratory conditions, this indicator is determined by drying and saturating the material in a solution of sodium sulfate. Strength is indicated in the marking by the letter F, followed by a number - an indicator of the number of freeze-thaw cycles. Frost resistance of crushed stone fluctuates fromF15 toF400, and in the construction of buildings it is best to use crushed stone frost resistance not less thanF300.

According to the level of frost resistance, the following types of crushed stone are distinguished:

• unstable,F15-F It is used as bedding, for drainage and for interior work in constantly heated rooms;
• stable,F50-F150. Can be used for low-rise residential construction in the southern regions;
• highly resistantF200-F This is the most versatile type of crushed stone, which can be used for the construction of critical structures, in high-rise construction, when creating various kinds of reinforced concrete products.

No. 6. Level of radioactivity

Radioactivity is just as important an indicator of the quality of crushed stone as strength or frost resistance. In many ways, the natural radioactive background depends on what rock the crushed stone is made of. Granite is characterized by increased radioactivity, while quartzite and limestone have a low natural background.

According to the level of radioactivity, crushed stone is divided into such classes:

• I class- this is a material with low radioactivity, not exceeding 370 Bq / kg. A versatile material that is suitable for the construction of any kind of objects. This crushed stone is ideal for residential construction;
• II class– crushed stone with radioactivity up to 740 Bq/kg. It is only suitable for road construction.

The radioactivity of crushed stone must be documented, therefore, when choosing and purchasing material, it does not hurt to make sure that there are appropriate certificates and sanitary and epidemiological conclusions.

No. 7. A shade of rubble

The color of crushed stone depends on the origin of the material. When it comes to the construction of foundations, drainage and the production of precast concrete, the shade of crushed stone does not play any role. If the material is used for decorative work (for example, for interior wall decoration, decorating flower beds and ponds), then color is of great importance, fortunately, there are a lot of different options. Crushed stone has a huge variety of colors, from gray to reddish, brownish, pink and yellowish.

No. 8. The most popular types of crushed stone (by origin)

We have already mentioned that crushed stone can have a different origin, on which its performance depends. Today, the most popular types of gravel are:

• crushed granite- the most durable and versatile. It is obtained from rocks of igneous origin, which may include crystals of feldspar, mica and quartz. Depending on the predominance of certain minerals, the color of such rubble can be gray, pink or even reddish. Granite crushed stone is very durable (M1400-M1600), frost-resistant (F300-F400), has a low flakiness, but may have an increased radioactive background, so you should definitely look at certificates when buying it. Granite crushed stone is the best in all respects, therefore its price is appropriate, but still it is most often used in construction. It is used in the production of reinforced concrete, concrete, foundations, the construction of roads of all types, the construction of critical facilities, bridges, airfields, etc. Allocate fractions from 5-10 mm to 150-300 mm;
  
• gravel crushed stone obtained by the explosive development of stone rocks and sifting of quarry rock. The shape of the particles can be streamlined and cornerstone, the color is predominantly gray, but there may be elements with a greenish, white and beige tint. According to the main indicators, crushed gravel is inferior to granite, but still its properties allow the material to be used in the construction of critical objects. Maximum strength - M1200, it has good frost resistance and low radioactive background. Since there are many quarries for its extraction, and the process itself is not as laborious as in the case of granite, the price of crushed gravel is significantly lower. A fraction of 5-20 mm is used in the production of paving slabs, 5-40 mm - for the production of some reinforced concrete products, 20-40 mm - for the production of concrete and road filling;
  
• crushed quartzite obtained from rocks, the basis of which is the mineral quartz. In terms of strength, such crushed stone is practically not inferior to granite, has a slight radioactive background and boasts an excellent appearance, so it is often used in decorative work;
  
• limestone rubble obtained from sedimentary rocks. It has the lowest strength among all types of crushed stone of mountain origin. The color is white, may have shades of yellow, brown and gray. The main advantage is the low price. Due to the low operational qualities, crushed limestone can only be used in the construction of non-critical structures, for example, low-rise buildings and roads with a small load, as well as in the production of the simplest reinforced concrete products. It is also used for the manufacture of mineral fertilizers, etc.;
  
• secondary crushed stone obtained by processing construction waste, incl. brick, concrete, asphalt, etc. The production process remains the same as for the production of primary crushed stone, with the exception of raw materials. The main advantage of such crushed stone is the price, but in terms of basic indicators it is inferior to the granite counterpart, however, there are areas where the most durable and frost-resistant crushed stone is not required. Maximum strength corresponds to about M800, frost resistance - F Secondary crushed stone is used in the construction of roads with a small load, as a large aggregate for concrete, and also to strengthen weak soils;
  
• slag rubble obtained by processing metallurgical slags. As a result, a material with particles of 5-120 mm in size comes out. It is used in the production of cement concrete and for strengthening foundations in road construction.
  

As you can see, for any purpose of use, you can find crushed stone with suitable properties and the most favorable price. The main thing is to read the documentation when buying.

Crushed stone is a loose building material of a granular structure, obtained from inorganic rocks by crushing them. Depending on the nature of the natural material, crushed granite (crushing hard rock), gravel (sifting quarry rock or crushing stone rock) and limestone crushed stone (crushing sedimentary rock) are mined in industry. As a result of the processing of waste from mining and metallurgical enterprises, secondary and slag crushed stone are also obtained. All listed types of crushed stone are widely used in construction.

Fractions of rubble

Crushed stone is usually evaluated by fractional composition. The fraction of crushed stone means a given range of sizes of its individual grains. The fractionation process consists in sieving crushed stone through a special fractional sieve - a screen.
Fractions of crushed stone are usually divided into standard and non-standard.

To standard fractions include the following (dimensions are in millimeters):

• from 3 to 8 (European standard)
• from 5 to 10
• 10 to 20
• from 5 to 20
• from 20 to 40
• from 25 to 60
• from 20 to 70
• from 40 to 70

To non-standard factions(manufactured in agreement with the consumer) include (dimensions in millimeters):

• 10 to 15
• 15 to 20
• from 80 to 120
• from 120 to 150

In construction, mixtures and screenings of crushed stone with a fractional composition of 0-20 mm and 0-40 mm have also been used. Within individual types of crushed stone, its own breakdown into fractions is possible.

Main characteristics

The general characteristics of crushed stone include the following indicators:

• Flakiness - the degree of flatness and elongation of the grain.
• Strength - the ultimate strength of the rock.
• The level of radioactivity.
• Frost resistance.

All these characteristics are indicated in the passport for crushed stone.

Granite crushed stone It is high-strength and frost-resistant, characterized by low flakiness and a relatively low level of radioactivity, which does not exceed permissible norms.
gravel crushed stone inferior to crushed stone from granite in terms of strength, but is characterized by a minimal radioactive background and low cost.
limestone rubble is a low-strength, but environmentally friendly and cheap material.

Flakiness is the most important indicator of the quality of crushed stone. A low percentage of flakiness allows you to get a dense compaction of the concrete mixture and ensure its high strength. At the same time, the increased flakiness of crushed stone provides high drainage properties, which is necessary in the construction of railways and roads.

Scope of the main types of crushed stone

Granite crushed stone is characterized by the highest strength indicators among other types of crushed stone, increased frost resistance and low flakiness. Available in grey, red or pink. The level of radioactivity of crushed granite does not exceed the established norms. All these characteristics make this material the most popular in construction. Granite crushed stone is considered the best filler for high-strength concrete. It serves as the main material in the construction of highways, the manufacture of high-strength concrete, and the construction of foundations for massive structures.

Depending on the fraction, crushed granite finds application in the following areas:

• Small fraction of crushed stone - 5-20(mixture of fractions 5-10 and 10-20). The most demanded, widely used in the production of concrete and building structures from this material, in foundation work, for pouring bridge decks, airfield and road surfaces.
• Medium fraction 20-40. It finds application in the production of concrete and the construction of reinforced concrete structures, in the laying of railways and roads, tram lines, laying the foundation and construction of industrial buildings.
• Large fraction 20-70, 40-70. It is used in the production of concrete and large-sized structures from it, as well as when working with large volumes of concrete. It can also be used in the construction of roads located within settlements, in the construction of industrial facilities.
• 70-120, 120-150, 150-300 (BUT)- building stone, rarely used, mainly for decorative purposes - for finishing fences, pools, reservoirs, for the construction of retaining walls, fences, in the construction of foundations. Waste from its preparation after crushing can be used as aggregate for concrete.
• Screenings and mixtures from 0 to 5 (granite chips), from 0 to 20, from 0 to 40- are used for the construction of bases and coatings of roads, as well as when laying crushed stone using the wedge method, laying footpaths.

The standard methods of using crushed stone fractions from granite are listed. However, for each of them, other applications are possible. For example, granite chips in addition to the specified scope, it can be used in the manufacture of paving slabs, concrete floors, as a decoration for interiors and facades, for filling children's and sports grounds, paths, as an anti-icing agent, as well as in landscape gardening.

gravel crushed stone also characterized by sufficiently high rates of strength and frost resistance. It can be used in various qualities - concrete and reinforced concrete aggregate, for the construction of bases and coverings of platforms and paths, as a ballast layer of a railway track. Gravel crushed stone is divided into fractions as follows: 5-20 mm, 20-40 mm, 40-70 mm.

limestone rubble is the most common. Its main advantage is its low cost. This material is composed of calcium carbonate. It can be white, yellow, reddish, brown and other colors, depending on the impurities it contains. In most cases, it is used in the national economy, for example, in the production of mineral fertilizers, soda, as a flux in the manufacture of Portland cement, for the purification of beet juice, in order to make glass heat-resistant, in the printing industry. Standard fractions of crushed limestone: 5-20mm; 20-40mm; 40-70 mm.

For construction work it is very beneficial to use crushed stone of secondary production. This material has a low cost, but it is not inferior in quality to primary crushed stone. It is necessary that it be of a medium fraction with a sufficiently low flakiness index (grains should be similar to a cube). This will ensure high-quality adhesion to the concrete solution. The use of secondary crushed stone will reduce the cost of work performed by one and a half times and solve the issue of disposal of construction waste. In construction, both individual fractions of secondary crushed stone and non-fractional material with individual grain sizes from 0 to 70 mm can be used.

Slag gravel can be used as a cement concrete filler, for strengthening foundations in road construction and for asphalt concrete pavement. This building material comes in the following fractions: 5-10mm, 10-20mm, 20-40mm, 40-70mm, 70-120mm.

How to choose crushed stone for concrete?

Concrete is a building material, which in a given proportion includes cement, crushed stone, sand and water. The well-coordinated interaction of the listed components makes it possible to obtain high-strength concrete. Crushed stone and sand play the role of natural fillers, the specific gravity of which in the total volume of the mixture can reach 80% , which allows you to save the consumption of more expensive building material - cement.

The filler is used to stiffen the concrete and control its degree of density. The smaller the size of the filler used, the lower the porosity and, as a result, the higher the strength. Particularly heavy aggregates make concrete impervious to radiation.

Crushed stone significantly extends the service life of concrete structures and ensures their strength. To obtain the optimal characteristics of a concrete solution for traditional purposes, it is recommended to use fine crushed stone with grain sizes in the range of 2-20 mm. This will reduce porosity and guarantee strength. If for some reason it is important to use crushed stone of larger fractions, then the requirements of the current building codes and regulations should be followed, according to which the size of the crushed stone fraction should not exceed one third of the size of the smallest element of the structure being erected.

In the manufacture of concrete products of small thickness, it is recommended to use crushed stone fractions up to 10 mm. In the case of the manufacture of concrete products of large thickness, fractions of 10-20 or more can be used. In any case, the use of a fraction larger than 150 mm is not recommended.

Three types of crushed stone are used for the manufacture of concrete: granite, gravel and limestone.

Granite crushed stone used to obtain the most durable concrete grades. This material is most suitable for the manufacture of concrete, which will be used for laying the foundation of high-rise buildings and in the construction of roads. In addition to high strength characteristics, concrete obtained using crushed granite will be characterized by high frost resistance due to low water absorption.

gravel crushed stone also widely used in construction. It is somewhat inferior to granite in terms of strength properties, however, it allows you to significantly win in price. This material is very popular on construction sites, since it is not so often required to obtain concrete with increased strength characteristics. Gravel crushed stone is the best choice in terms of price-quality ratio.

limestone rubble used in the process of manufacturing low-strength concrete grades. In addition to low strength indicators, limestone is characterized by relatively low frost resistance.

Can be used for concrete production secondary crushed stone resulting from the processing of construction waste. The cost of concrete obtained using secondary crushed stone is reduced by 25%.

How to choose crushed stone for the foundation?

To make a foundation in most cases, crushed gravel is used. It is characterized by satisfactory strength characteristics and is quite inexpensive in comparison with granite. but in the case of laying the foundation for a massive building object, for example, a residential building, it is necessary to give preference to granite rubble. For light and non-responsible buildings such as a garage, barn or gazebo you can use cheap limestone rubble. An important advantage of crushed limestone is the low radiation background of this material in comparison with other aggregates.
So the most acceptable material for the foundation are crushed stone fractions from 5 to 20 mm and from 20 to 40 mm.

Crushed stone for filling

Sometimes during the construction process it is required to perform artificial raising of the soil - dumping. Crushed stone of various fractions is also used as a material for backfilling.

rubble stone is the most suitable material for these purposes, since it is characterized by natural resistance to destructive external influences (heat, cold, soil acidity), is characterized by various sizes, irregular shapes and alternating sharp and obtuse angles. These characteristics help to prevent possible sagging of the cushion even in harsh climatic conditions.

In the case of using crushed stone of standard fractions preference should be given to the largest of them, despite the high cost, since it is such a material that can provide the necessary strength of the backfill. Crushed stone to create a pillow is used, as a rule, in the case of an average level of groundwater.

screening, consisting of dust and fragments, is not a reliable material, although it compares favorably in price. It can be used for summer cottage construction in the presence of stable soil to protect against melt water. The screening pillow can sag unevenly over time due to washing out of dust with water, which in turn will cause cracks.

The term "gravel crushed stone" refers to non-metallic bulk building materials obtained by sifting rock or ASG, or by crushing rocks and boulders. In terms of strength and frost resistance, this variety is inferior to granite gravel, but outperforms dolomite and slag. The same applies to cost, gravel screenings and fractions occupy an intermediate position, they are often used as a budget alternative to high-strength grades. The main scope of application includes the manufacture of concrete and reinforced concrete products, foundation and road works, some types are suitable for decorating and landscaping.

Depending on the method of obtaining, there are two main varieties:

1. Gravel - obtained by sifting ASG (a mixture of sand and loose sedimentary rocks). Its strength grade varies within M800-1000, the shape of the fractions is round (pebbles belong to the same species). Due to its smooth walls and inevitable impurities, it is poorly suited for concreting monolithic load-bearing structures and is more often used as a decorative material.

2. Actually, crushed stone obtained by crushing and sifting the same rocks, but larger fractions. Its strength rarely exceeds M1000, but due to the presence of rough walls, it is better suited for the preparation of concrete. There are two subgroups: seeded and washed, the second has a minimum content of impurities.

The characteristics of crushed stone for construction work are regulated by GOST 8267-93. The following indicators and properties are distinguished:

• Strength - within M800-M100. This means that gravel screenings and fractions contain from 5 to 10% of grains of weaker rocks (for quality grades, this value does not exceed 1.5%), the rest of the mass has the same limit as that of the original rock.
• Frost resistance - from 150 cycles, the value of this characteristic allows the use of such crushed stone for concreting foundations. In this regard, gravel outperforms limestone by at least twice, but is slightly inferior to granite.
• The content of dust and clay impurities - the less, the better, the upper limit is 0.6%.
• Flakiness - from 7 to 17%. The proportion of needle-shaped grains is rare. Due to the low flakiness, shrinkage and tamping in building mixtures during its use is good; in this regard, the material is many times better than stratified limestone rocks.
• Radioactivity class - 1, which implies not only cleanliness and safety, but the ability of gravel to absorb radiation.
• Density: average - 2400 kg / m3, bulk - 1300-1600 kg in one cube in a dry state. The specific gravity of crushed stone largely depends on the size of the fractions and the method of production.

The quality of adhesion with the rest of the mortar components is affected by the roughness of the walls and the shape of the gravel grains; in crushed varieties it is higher than that of sea or river pebbles. But at the same time, crushed rocks have a higher percentage of foreign impurities, dry sieving is not enough to achieve the desired purity. Regardless of the place and method of extraction, the material has low porosity (and, as a result, good water transmission capacity), it practically does not absorb moisture and dries quickly. All characteristics declared by the manufacturer must be confirmed by the appropriate certificate, verification of its availability is mandatory.

Scope of application

The functional purpose depends on the variety, gravel allows you to quickly and inexpensively equip a garden path, flower bed or playground. In this case, the smoothness of the walls is not a disadvantage, but an advantage; people can safely walk on round pebbles. Rocks from different quarries differ in color, this property is positively evaluated by landscape designers. But the main area of ​​\u200b\u200buse of this material is still construction:

1. Gravel screenings (0-5 mm), in addition to landscaping, are used for the manufacture of certain grades of concrete and sprinkling of roads; they are rarely found on sale. For more information on the use of crushed stone screenings - c.

2. A small fraction (3-10 mm) is advised to buy for preparing a solution for self-leveling floors and pouring the foundation.

3. 5-10 mm - a popular brand, used in the manufacture of concrete for foundations, load-bearing structures and other types of reinforced concrete products.

4. Crushed stone fraction 20-40 mm (medium) - the same, plus drainage work. The disadvantage is the possible content of quarry sand, this brand is most often seeded.

5. Large fraction (40-70 mm) - repair, road and drainage works, concreting and strengthening of massive structures. Rarely found on the open market.

In addition to a slight concession in strength, the differences between gravel and granite rubble include a reduced background of radioactivity, as a result, this variety is indispensable in the construction of civil structures, it is recommended that developers of private houses choose it. Due to its more affordable price, it is often considered as an alternative to high-strength grades, but the admissibility of such a replacement is trusted exclusively by specialists.

An important role is played by the purity of crushed stone: washed is used almost without restrictions, dry-cleaned is not suitable for all concretes, its use lengthens the time of work due to the need for additional preparation.

Material cost

The average price per cube depends on the size of the fractions (the demand for the brand), the method of obtaining (chopped gravel is more expensive due to better adhesion to cement) and strength. Approximate prices are shown in the table:

The cost and distance of delivery is negotiated separately, when buying large quantities (from 20 cubic meters and more), this service can be provided free of charge. Prices are seasonal, in the period from May to October, crushed stone is more expensive, especially popular brands. In order to reduce costs, it is recommended to buy it in bulk; savings when ordering lots of more than 100 cubic meters reach 10-20%.