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What crushed stone is needed to prepare concrete. How to choose the right fraction of crushed stone for the manufacture of reinforced concrete structures? Types and characteristics

01.06.2018

Concrete is a modern building material that involves the use of a mixture of cement with water, sand and any other hard material. Most often, crushed stone is used from solid materials, due to its special properties and good opportunities For versatile application. But it can be different, and if you want to order crushed stone, you should decide what fraction of crushed stone is needed for concrete.

Why crushed stone is a good filler for concrete

Crushed stone is made from solid mountain deposits, the grain size of which is at the level of 0.05-0.7 cm according to European standards. This installation material is worth using due to the following advantages:

Crushed stone should be defined as a coarse aggregate, which makes it possible to eliminate all processes of instability and compaction of the structure. In this regard, its use helps to increase the quality of the entire mixture.

Adding rubble forms the skeleton concrete structure, in which the filler can be up to 90%.

The largest expenditure of financial resources is on cement. To save money, you need to strive to reduce costs while maintaining sufficient quality. The most important quality parameter and its indicator is strength, which depends on the total mass density. For this purpose, crushed stone of a special size is selected, which, when compacted, can be distributed into smaller ones. From this we can conclude that good concrete assumes the presence of different fractions of the material.

Fractional division of crushed stone

To talk about which crushed stone is best for concrete, it is worth understanding what the fraction is. A fraction is defined as nothing more than the division of particles into groups of the same size.

After crushing the material, we obtain the following fractional indicators:

• 0.05-0.1; 0.05-0.2 cm;
• 0.1-0.15; 0.1-0.2 cm;
• 0.15-0.2 cm;
• 0.2-0.4 and 0.4-0.8 cm;

However, according to individual order You can get crushed stone with a grain size of up to 1.5 cm.

A few words about the correct selection of fractions for the mixture

Most often, crushed stone is used for the mixture, the particles of which can be classified as the first fraction. Although this option is not economical from a financial point of view, it remains popular for the reason High Quality the resulting mixture. When using larger fractions, the concrete will not be evenly filled with solid material, which will significantly reduce the strength of the structure.

An important aspect when determining the fractional component is the subsequent area of ​​use of the concrete mixture. The following table will help you navigate:

As is clear from the table, the fraction is determined based on the scale of activity and the required durability of the hardened mixture.

The durability of the mixture is also affected by the hardness of the filling material, which must be selected as follows:

The data presented should not be taken as an unshakable truth. Deviations are more than possible and they are eliminated by changing the ratios of other components. For example, if high-quality concrete is needed, but only low-strength crushed stone is available, then more cement is added to the final mixture. The same works in the absence of filler of the required fractionation, but only by changing the amount of sand added.

From this we can conclude that the durability of concrete depends not so much on the materials chosen, but on how the proportions for the mixture were selected.

You can buy crushed stone or concrete in Rostov-on-Don from our company “Beton 61”. You can be confident in the timely and high-quality provision of services.

We all know that crushed stone is used in the production of concrete mortar, but not everyone understands its purpose and the characteristics that this important component of the mixture must meet. We will tell you what crushed stone is needed for concrete, and also dwell on its varieties, characteristics and show why crushed stone is needed in concrete.

Construction crushed stone

Purpose and properties

Crushed stone is a mineral inorganic product of crushing rocks, gravel, boulders, mining waste, processing ores, slag from metallurgical plants and thermal power plants, as well as recycling construction waste. The stone must be free-flowing and have a fraction from 3 – 5 mm to 150 mm and above. Particularly large screenings are called bute ().

The average density of crushed stone is 1.2 - 3 tons per cubic meter.

In addition, there is a set of important properties by which the quality and suitability of raw materials for certain purposes are assessed:

1. Factional composition– one of the main characteristics of the product. Determined by the largest size of the grains included in the composition, despite the fact that these grains are at least 30%. Separation into fractions is carried out during the process of mining and crushing stone in special separators and screenings;
2. Bean shape– no less important characteristic gravel, on which its quality and possibility of use in construction and production of reinforced concrete products depend. The grains should be as close as possible to a cubic shape, otherwise they speak of a high flakiness of the material, that is, the stones in it have a flat or needle-shaped shape when the thickness or width of the grain is more than three times its length;
3. Grain strength– the most important parameter that depends on the rock and origin of the stone. There are high strength - M 1200 - M 1400, strong - M 800 - M 1200, medium - M 600 - M 800, weak - M 300 - M 600 and very weak - M 200. Strength is determined by checking crushability in the cylinder, tensile strength at compression and wear in the shelf drum, simulating the wear of stone during road work;
4. Frost resistance– an important indicator of the quality of the stone, which is characterized by the number of freezing-thawing cycles or saturation-drying cycles in a solution of sodium sulfate. The following brands are distinguished by frost resistance: F15, F25, F50,<…>, F300, F Products of the F300 and F400 brands are used in construction;
5. Radioactivity– a mandatory characteristic that shows the safety and applicability of crushed stone for residential construction. For the construction of houses, high-strength crushed stone of class I radioactivity is used, that is, the effective activity of radionuclides in the composition of the stone (Aeff) does not exceed 370 Bq/kg. For the construction of roads within cities, raw materials of class II radioactivity are allowed, with Aeff not exceeding 740 Bq/kg;
6. Stone type or composition– also an important indicator of quality. Granite is considered the most durable and high quality crushed gravel, limestone material is also quoted, sometimes slag and recycled gravel are used. Recycled concrete crushed stone is a product of crushing and screening out construction waste.

Important! Crushed stone for concrete according to GOST 8267-93 must have a fraction of 3 - 8 or 5 - 20 for the production of commercial mortar and reinforced concrete products; for laying foundations and cushions, a fraction of 20 - 40 is used, and sizes 25 - 60 and 40 - 70 are used in road construction according to GOST R 54748-2011.

Also, the named construction standard suggests the use of other fractions, but this practice is limited and rare. The extra-large fraction can be used in very large volumes of filling during the construction of large objects, such as dams, piers, bridges, and foundation bases.

Crushed stone is used to produce concrete mortar, including commercial concrete, reinforced concrete products, screeds, foundations, floor slabs and columns, load-bearing elements and in monolithic construction.

This material is also used in road work, when preparing crushed stone-mastic asphalt concrete, making cushions and drainage bedding under rails, as well as for other construction activities within the above areas.

Types and characteristics

There are different types of crushed stone ().

The following are used in construction and manufacturing:

• Granite. It is mined by mining and crushing granite rock and solidified magma, obtaining durable and high-strength (M 800 - M 1600) screenings with low flakiness, high frost resistance and class I radioactivity. It is considered the best aggregate for high grade concrete;
• Gravel. It is mined by sifting quarry rocks and crushing stone rocks, obtaining screening with a fraction of 5 - 40 mm. It is inferior in strength to granite, but has a low radioactive background and is cheaper. Widely used in construction, reinforced concrete production and road work;
• Limestone. They are mined by crushing sedimentary rocks consisting of limestone and calcite, obtaining high-quality stone, which is also used in construction and production along with granite and gravel raw materials, as well as for the construction of drainage bedding;
• Slag. Produced by crushing slag dumps and melts, as well as porous slags with high gas saturation (aerated concrete crushed stone). Used in construction and production of reinforced concrete products, road works and landscaping work as bedding for asphalt and concrete as a cheaper product;
• Secondary. The price of granite and gravel raises the question: “How to replace crushed stone in concrete?”, and the answer was the processing of concrete into crushed stone, as well as crushing construction waste - bricks, reinforced concrete products, asphalt, etc. The material makes it possible to reduce the cost of producing the solution by about a quarter.

Important! In private construction, raw materials from granite and gravel are most often used, but sometimes they produce secondary material with their own hands by crushing substandard bricks, construction waste and products from the dismantling of screeds or walls with hammer drills and sledgehammers.

In some cases, the instructions do not suggest the use of granite and gravel, since their excessive strength makes it difficult to process the products. This is relevant for floors with subsequent grinding of the screed, when cutting reinforced concrete is required diamond wheels or diamond drilling holes in concrete. Crushed limestone is more suitable for these procedures.

Conclusion

Crushed stone – important and widely used construction material, indispensable in the production of concrete mortar, reinforced concrete products, road work, construction of cushions, drainage bedding and landscaping ().

The video in this article will help you learn more about this material.

Concrete is modern building materials, for the preparation of which the following components are required: sand, cement and solid filler (gravel or crushed stone). Crushed stone is a bulk building material obtained by crushing rocks (gravel, granite or limestone). After this, the crushed stone is divided into fractions depending on the size of the grains. Sometimes crushed stone is mined using a quarry method, using the sifting method.

This material reduces shrinkage and creep of concrete, increases its strength and durability. The shape of the crushed stone influences the convenience of pouring concrete. For example, spiny and flat material will reduce the strength of the concrete mortar, increase cement costs, and reduce frost resistance.

There are the following types of crushed stone:

• granite;
• gravel;
• limestone.

There is also secondary and slag crushed stone. The secondary type is made from construction waste, fragments of concrete, reinforced concrete, brick, etc. Slag crushed stone is made from slag generated in metallurgical production. But its scope of application is limited due to the content of harmful components.

Permissible content of harmful components in the filler

There is an acceptable percentage for the content of harmful rocks and minerals in the additive material:

• sulfates (gypsum, anhydrite), sulfides and sulfur no more than 1.0% for fine aggregate and up to 1.5% for coarse additive material;
• layered silicates (hydromica, mica, chlorite) - no more than 15% of the volume of coarse aggregate and up to 2% for fine aggregate;
• amorphous types of silicon dioxide, soluble in alkalis (chalcedony, opal, flint) - up to 50 mmol/l;
• halides (halite, sylvite, etc.), including water-soluble chlorides - up to 0.1%;
• pyrite – no more than 4% by weight;
• iron hydroxides, apatite, magnetite, nepheline, phosphorite - up to 10% of each mineral;
• coal – no more than 1% by weight;
• asbestos fiber – up to 0.25% by weight.

Crushed stone should not contain more than 35% flakie-shaped grains. The composition of dust and clay particles in material from igneous and metamorphic rocks should not exceed 1% by weight for any concrete solutions.

Features of granite crushed stone

Granite crushed stone can be used as a filler for high-grade concrete solutions intended for pouring airfield, bridge and road surfaces. In this case, much attention is paid to the transfer of significant dynamic loads.
Concrete on granite crushed stone is also used in critical areas (floor slabs, columns, walls). The material must guarantee resistance to dynamic and static pressure.

The following quality indicators of crushed granite stone are distinguished:

• compression density;
• fraction;
• density;
• flakiness.

The bulk density of a material is the ratio of the volume of crushed stone to the area it occupies. All natural voids and distances between grains are taken into account. This is an important indicator for construction and transportation. Bulk density must be distinguished from simple density, which is an indicator of the building material from which crushed stone is made.

Crushed granite should have fractions from 5 to 150 mm. A fraction of less than 5 mm is granite screenings with small grains. Screening is used in decorative design lawns, flower beds, flowerpots, etc. Such crushed stone is rarely used as an additional component in concrete mortar. The use of such a fraction is permitted when used as a fine sand aggregate having a particle size modulus of no more than 2.5.

A material fraction of 5-20 mm is considered fine. It ensures high reliability and durability of foundations, reinforced concrete and road structures. The cost of such an additive is low.
The average fraction of granite crushed stone has grain sizes of 20-40 mm. It is used as an additive to concrete mortar when constructing foundations in large industrial facilities.
Large aggregate with grain sizes of 40-70 mm is intended for the construction of foundations for massive objects. Larger sizes of material can be used when constructing a rubble concrete foundation. But such crushed stone is rarely used as a concrete filler.

By technical specifications, crushed granite is a fairly durable material. Its brand is in the range of 1200-1400, the level of frost resistance is up to 400 cycles.
The flakiness of the material (an indicator of grain shape) is low and equal to 15-18%. Flakiness is expressed as the percentage composition of lamellar and needle-shaped grains from the total volume of granite crushed stone.

When using selected material without flaws, all characteristics can be improved. The absence of deformation allows you to improve the structure and create a more durable monolithic structure.

Features of crushed gravel

Adding gravel to concrete mortar is common in the construction of roads, foundations and the production of reinforced concrete products.
In terms of strength, gravel is inferior to granite filler. Compared to granite crushed stone, gravel is a more affordable material.

Distinguish the following types crushed gravel:

• gravel with rounded grains. The shape of the grains is obtained from exposure to river or sea water;
• crushed, crushed or natural crushed stone.
  
  Crushed gravel is also divided depending on the size of the fractions into the following types:
• fine with grain sizes up to 10 mm;
• medium with grains 10-20 mm in size;
• large – grain size is no more than 40 mm.

Features of crushed limestone

The level of frost resistance of crushed limestone is about 50-100 cycles, which does not allow the use of this building material in capital construction in high latitudes.
The material is the most accessible aggregate used in construction work. It contains calcium, so the material looks like white stones. The shade of crushed limestone depends on the impurities contained (clay, iron or quartz).

Limestone crushed stone can be divided into the following groups according to strength class:

• M 300-600 – mainly made from limestone.
• M 600-800 is the result of processing limestone and dolomite. It has high performance and large-sized fractions.
• M 200 is practically not used in concrete production due to the high cost of crushed stone.

Limestone crushed stone is environmentally friendly and highly resistant to impacts and temperature changes.

Features of secondary crushed stone

Secondary crushed stone is obtained by crushing construction waste (asphalt, brick, concrete) in accordance with GOST 25137-82. The same equipment is used for the work that is used in the production of other types of crushed stone. At the beginning construction garbage a loader is placed in the feeder hopper, then large pieces are broken into crushed stone with a crusher and metal inclusions are sorted.

The main advantage of recycled crushed stone is its low cost (about 2 times less than granite). Compared to other types of crushed stone, energy costs for its production can be 8 times lower.

In terms of frost resistance, strength and some parameters, recycled crushed stone is inferior to material made from natural raw materials. But such crushed stone is widely used in the form of coarse aggregate for concrete, the strength of which is 5-20 MPa; in landscaping; in road construction; when strengthening weak soils.

Features of slag crushed stone

Slag crushed stone is obtained by crushing metallurgical waste slag or by special processing of fiery liquid slag melts. Nowadays, different types of concrete have been developed and used in construction work, where aggregates and binders made from metallurgical slag are used. The price of products made from slag concrete is 20-30% lower compared to traditional types. Based on the grain size, crushed stone is divided into fractions: 5-10 mm, 10-20 mm, 20-40 mm, 40-70 mm and 70-120 mm. The composition of crushed slag stone grains is selected to obtain minimal voids. The lowest bulk density of each fraction is about 1000 kg/m3. The content of flaky (plate-shaped) and needle-shaped grains for cube-shaped crushed stone should not exceed 15%, improved - up to 25%, ordinary crushed stone - 35%. The length of the grains is several times greater than their width or thickness.

Together with dense dump slag, porous slag is used to make crushed stone. They are formed from melts with increased gas saturation, swelling of the released gases in the form of bubbles. The strength of such material is 2.5-40 MPa, average density lump form is 400-1600 kg/m3, which allows the use of porous slags for making a lung concrete.

Dependence of the brand of concrete mortar on the brand of crushed stone

Any hard rock (limestone, granite, expanded clay, gravel, crushed brick or asphalt) can be used as the main filler. However, each filler has its own strength, which may lead to limitations in use. For example, when constructing critical structures, you cannot use broken bricks.

The durability of the solid drive corresponds to its brand. The approximate ratio of crushed stone and concrete grades is as follows:

• crushed stone grade M1200 is suitable for concrete M400 and M500;
• crushed stone M1000 is intended for concrete mortar of grade M300;
• M800 filler is used in M200 concrete;
• M600 crushed stone is suitable for M100 concrete.

But deviations are possible, which may vary from the ratio of sand and cement in concrete.

Basically, concrete of grade M250 and below is produced using gravel, and grade M300 and above is produced using granite. The strength of concrete cannot be higher than the strength of fillers. To obtain the required brand you need to do right choice proportions of all components of the solution.

Why do you need to add crushed stone to concrete?

Crushed stone makes up 80-85% of the total volume of concrete. The use of such filler reduces the processes of shrinkage and creep, increases the density, strength, crack resistance and water resistance of the structure.

The main factor for obtaining high strength concrete mortar is the reduction of intergranular space. To do this, you need to select the parameters of the crushed stone and sand particles in such a way that when the concrete is compacted, the space between the large crushed stone particles is filled with large sand particles. For high-quality concrete, you need to use several fractions of coarse aggregate. This ensures savings in cement when producing concrete. It is known that large particles have a smaller specific surface area (compared to small particles), therefore, when using fine sand and crushed stone, a larger volume of cement will be required to envelop the surfaces. But this leads to a decrease in the strength of concrete.

Before purchasing crushed stone for addition to concrete mortar, you should check the availability of special documents. Based on the documentation, it is possible to determine the compliance of the expected and required indicators with the type of crushed stone that will be used in construction work.

Crushed stone is a bulk building material on an inorganic basis with different sizes fractions (grains). It is most often used as a non-binding filler in concrete, which allows future structures and their foundations to withstand operational stresses. Crushed stone is added to the solution both to reduce its cost and to give it strength and elasticity after hardening, reducing shrinkage and the risk of deformation.

The material is obtained by crushing rocks or industrial waste, as a result - the stones have various shapes and remain rough, which increases their adhesion to cement and sand. The size of crushed concrete fractions is influenced by the maximum size of individual elements; it is marked accordingly, which makes selection and purchase easier. Depending on this, the solution acquires certain properties, in particular - the addition of large rock increases the strength during setting, and small stones - density (promotes better filling of voids).

Varieties

This material is classified according to several criteria: the type of raw materials used, the size and shape of crushed particles, frost resistance and strength. Crushed stone is made from hard granite, metallurgical and construction slag, gravel and limestone rocks. The stronger the raw material, the stronger the load it can withstand future design. For example, the best option for pouring a foundation would be granite, and the best option in terms of price and quality would be gravel. Depending on the shape of the crushed stone fractions and their percentage in the total mass, three types of mixtures are distinguished:

1. Cuboid (from 12 to 15%), the densest.
2. Regular (18–35%), with an average distance between particles.
3. Flaky (from 25%), with a high content of grains with a lamellar or needle shape (width and thickness less than 3 times the length).

But the main indicator that determines the properties of crushed stone for concrete remains the size of the fractions. The standard ones include: from 3 to 8 mm (eurocrushed stone), 5–20, 10–20, 20–40, 25–60, 20–70, 40–70. Crushed stone with fractions from 5 to 10, 10–15, 15–20, 70–120, 100–300 is considered non-standard. The smaller the size, the more expensive the building material, this is due to the complexity technological process when crushing it and more thoroughly sifting. In some cases, it is possible to mix a coarse fraction of crushed stone and small stone chips, the latter being used as an accompanying filler.

The most popular sizes are 20–40 mm, this is due to the low cost of this brand, but for pouring a foundation or with high requirements for concrete strength, it is better to buy backfill with grains from 5 to 10 mm or 5–20.

Markings

Depending on the frost resistance of the material, they are distinguished: F15, F25, F50, F100, F150, F200, F300, F400. The grade is not related to the size of the crushed stone fraction and is determined by the number of cycles of thawing or defrosting or saturation and drying in a solution of sodium sulfate. For mixing concrete, the optimal frost resistance is 300 or more (this is sufficient for pouring foundations and frequently used external structures). This indicator must be written down in the crushed stone passport, as well as the size of the fractions.

The main marking implies the strength of the source material under compression, crushability when crushing rock and the degree of wear during grinding in a drum. The indicator indicates the resistance of concrete external influences like the weight of a vehicle or the load on a foundation. High-strength crushed stone grades include M1200–1400, very weak grades include M200; the norm is considered to be the percentage of grains obtained from weak rocks (when compressed in a water-saturated state of up to 20 MPa). For comparison, in the M300 this figure exceeds 15%, in the M1400 - no more than 5.

The ratio of crushed stone and concrete grades

The strength of the solution is determined by its fillers, the characteristics of which are indicated in the attached instructions or on the packaging. In practice, this means that M400 cement will not produce M500 or higher concrete; the corresponding ratio of grades is presented in the table:

Determining the strength of concrete depending on the fraction of crushed stone is approximate, but deviations are allowed. The latter are regulated by changing the ratio of sand or cement, adding granite chips. But in general, to obtain the required grade, it is important to observe strict proportions of the solution. Before choosing what crushed stone is needed for concrete, it is recommended to determine intended purpose structures and calculate future loads. For a solution up to M250, gravel is sufficient; the use of non-standard sizes grains High-strength grades (M300 and more) require the addition of granite screenings, preferably with square fractions up to 20.

According to building regulations, the content of crushed stone with increased coarseness in the mixture varies from 1 to 20%, and undersized crushed stone should be within 20% of the total mass. If crushed stone with a fraction of up to 20 mm is used for concrete, problems with the distribution of voids do not arise. When this indicator increases to 40 mm, another type of filler (with different, smaller grain sizes) should be added to the solution. Accordingly, choosing a filler with a grain size of up to 70 mm implies adding at least three different options crushed stone fractions. The size cannot be less than 2/3 of the distance between the longitudinal reinforcement, but also no more than 30% of the smallest element of the building structure.

Examples of using

Fine-grained mixtures are needed in the manufacture decorative items made of concrete, artificial stone, paving slabs, it is also added to the composition for asphalt or other road surfaces. The use of too fine filler for pouring foundations and structures load-bearing walls not economically feasible, plus the risk of shrinkage and deformation increases. The medium and most popular crushed stone fraction (20–40 and 10–20) is better suited for creating large and small concrete structures. This perfect option for pouring the foundation. For cooking quality solution A concrete mixer should be used, it is difficult to achieve uniformity when mixing crushed stone, sand and binder cement manually.

Material with a fraction from 40 to 70 is classified as coarse-grain, and is needed when constructing massive buildings and mixing concrete in large volumes. It is better not to add it to solutions when pouring the foundation without adding auxiliary fillers of other sizes. Such material is difficult to obtain, the required quantity is calculated in advance, and its delivery is ordered separately. Crushed stone with a coarse fraction of 100 mm or more is called rubble or building stone; it is used mainly for decorative purposes, and not for preparing concrete. The same applies to small granite chips, but the latter is indispensable when creating self-leveling floors and as an auxiliary additive.

Particular attention is paid to the choice of filler when making mortar for pouring the foundation. The base can withstand maximum loads, so this type of work requires concrete with a strength of at least M300. Accordingly, a granite filler of at least M1200 is needed, although gravel can be added for country houses. Recommended fractions of crushed stone for the foundation: 5–10, 10–20, 20–40, it is advisable to buy grades with a square grain shape.

When mixing the ingredients of concrete solutions - water, cement, sand, chemical additives - you need to decide what crushed stone is needed for concrete. He plays an important role in its composition.

Characteristics and significance of the material

Why is crushed stone needed in concrete? This component of the solution is bulk material in the form of irregularly shaped stones - it is a large filler; it creates a frame that absorbs all the loads of the solution. Thanks to it, the finished solution shrinks less, becomes more elastic, durable, creep is much reduced, and the deformation of the product under load is reduced. The composition of concrete is cheaper with fillers, since cement is more expensive than crushed stone.

According to the standards, the content of high-fineness filler should be from 1 to 20% of the mass of the solution, and low-fineness filler - no more than 20%. The solution must contain crushed stone of at least two fractions with a maximum grain size of up to 40 mm or three - with 40–70 mm.

The maximum grain size should be less than 2/3 of the shortest distance between the reinforcement bars, and also no more than 1/3 of the smallest product size (for example, the width of the tape). This material has sharp edges and a rough surface, so it adheres well to the components of the solution.

Classification

It is customary to classify crushed stone for concrete by density, size, flakiness (flatness, needle-like particles in the body of the stone), compressive strength, and frost resistance.

Kinds

Crushed stone is often called granite material, and gravel is crushed stone made from natural stone, but common name both are rubble. It is created from different breeds and it happens:

• granite;
• gravel;
• dolomite (limestone);
• slag;
• secondary.

The first two are used for medium and heavy concrete, the rest - for light, cellular solutions, foam, aerated concrete. Granite material is more durable and is created by crushing blocks of natural granite. The stone is sorted by size through a special vibrating sieve.

Granite crushed stone is used for road and airfield pavements, critical areas under heavy loads, columns, walls, slabs, bridges. This is the most durable filler, it is available in durable concrete high brands. Its grade is 1200-1400, and its frost resistance level is up to 400 cycles.

Is it better to use crushed stone or gravel? The second is formed by crushing ordinary natural stone rock and sifting it. It is less durable than crushed granite. If you need especially durable frost-resistant concrete, the latter is recommended. On the other hand, crushed gravel has advantages: low radioactive background, low price. It is most often used for private construction, foundations of mansions, and road construction.

Two types of gravel are produced:

• crushed;
• natural.

Limestone (dolomite) filler is obtained from sedimentary rocks - limestone. Its components are mainly carbonate, calcium and similar compounds. He becomes limp from the water. It is undesirable for serious structures, and some experts do not recommend this crushed stone for concrete at all.

Slag, recycled materials are used for very lightweight concrete that serves as thermal insulation.

Form

There are four types of crushed stone according to their geometric appearance. The determining factor is the level of content of the forms of individual grains as a percentage of the volume. According to this criterion, there is the following crushed stone:

• cuboid, wedge-shaped – 12–15%;
• regular (acute-angled) – 18–25%;
• flakier – 25%. There are different degrees of flakiness (flatness) of the grains. In turn, the material comes with needle-like or lamellar grains.

Cuboidal or low-face concrete crushed stone is most often produced in quarries; it is the most durable. The mixture of its grains has the densest packing of all types of crushed stone. Concrete with it is much stronger than with needle or plate stones, since the latter increase the distance between particles in the solution - accordingly, they require more cement.

Factions

By fraction there is large, medium, small crushed stone. Small material is always more expensive and requires more effort when processing stone blocks. For construction concrete, a grain range of 5-70 mm is used. Faction is maximum size individual grain. The lower its number, the finer the crushed stone grains.

Categories

The following fractions of granite crushed stone can be distinguished.

One category is fine (5–10; 5–20; 10–20 mm), very fine (2–5) and gravel chips (1–3). The first is the most popular, used for reinforced concrete products, bridges, road surfaces, in private construction, and for foundations. The second is for artificial concrete stone, concrete decorative details, thin paving slabs, small structures. Crushed gravel is also used for paving slabs, self-leveling floors, products that do not require special strength and play a decorative role.

The second category - medium (20–40 mm) is also popular for private construction and industrial facilities. First of all, it is used for foundations, road structures, in the construction of houses, floors, load-bearing structures, in the production of concrete slabs, beams, for ordinary work in private construction.

The third category - large (40–70 mm) - is used for rubble concrete foundations, when preparing a large amount of mortar, for massive structures. It is usually ordered in large quantities and in advance, since it is not very popular and is not always in stock.

Gravel fractions:

• small (up to 10 mm);
• medium (10–20 mm);
• large (40 mm).

The areas of application are the same as for granite material, but take into account that gravel is much weaker (but much cheaper). It is used for low grades of concrete.

For structures that require frost resistance and special strength, granite is recommended, although crushed gravel is a standard component of concrete for the foundations of private houses.

Frost resistance

Using this parameter, the grade of material is determined by the number of freezing/thawing cycles. Frost resistance can also be assessed by cycles of lowering it into sodium sulfate and drying. For this filler, there are frost resistance grades from F300 and higher.

Contrary to popular belief - the larger the concrete crushed stone, the stronger the solution, this is not always the case, for example, for structures that work in bending or are reinforced with a better fraction of a smaller fraction. To withstand vertical loads, coarse crushed stone is better.
The material must be clean without adhering dirt, clay, dust, soil, ores. It is sometimes washed at the construction site. The concrete must cover the grains completely on all sides.

Crushed stone is always taken two or three grades higher than the design grade of the mortar, since concrete gains strength and density over the course of six months, a year or more, but crushed stone does not have this property. Thus, these two indicators are balanced.

Grain size selection

Large grains make the solution stronger, fine grains make it denser. Large pebbles contribute to the formation of porosity, which is undesirable, while small pebbles fill voids better. Therefore, it is recommended to combine them. For example, good faction 5–20, it contains large grains of 20 mm and smaller grains of 5 mm. It is this kind of concrete – ready-mixed – that fills well monolithic structures. This kind of stone is recommended for reinforced foundations.

Concrete with large crushed stone is more difficult to compact, reinforce and pull apart on the formwork. For densely reinforced and complex structures It’s better to take a smaller stone and add more cement. To increase the strength of the mixture, if there is no coarse crushed stone, it is recommended to add more cement.

Application

For concrete floors and similar products, a solution with fine crushed stone is used, since the thickness of the floor is small. A flatter (flakier) stone increases the consumption of binder material and cement; such a solution is less compacted. It is better not to use such crushed stone for foundations; it is well suited for blind areas.

For foundations, it is better to use granite crushed stone of medium-sized fractions (5–20, 5–10) - the concrete will be dense and frost-resistant. Granite filler has high frost resistance, so it is the best for our climate. For low temperatures A value of at least F150 is recommended.

For concrete grades below M250, it is more appropriate, more economical and more profitable to use gravel. From M300 – granite crushed stone. Good choice there will be granite crushed stone 5–20. This size is more universal and can be used for foundations, blind areas, and floors.

When increasing the density, a finer fraction is used, but here you need to take into account that this will cost more, since more cement is needed and it itself is more expensive. To reduce the cost of the solution, you can mix granite and gravel concrete crushed stone. When using coarse crushed stone, you need more sand to fill the voids or combine it with finer sand.

Here is an approximate table of brand correspondences:

Concrete	Crushed stone
100	600
200	800
300	1000
400-500	1200