What crushed stone is needed for concrete. Faction selection

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 strength concrete mortar, increases cement costs, reduces 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

Eat permissible percentage to contain harmful rocks and minerals in the additive material:

• sulfates (gypsum, anhydrite), sulfides and sulfur not 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 airfields, bridges 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 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 screening having 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, granite crushed stone is enough 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

Frost resistance level crushed limestone is equal to 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 because of high cost 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. First, construction waste is placed in the feeder hopper by a loader, 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 treatment fiery liquid slag melts. Now developed and used in construction work different types concrete, where aggregates and binders 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 a material is 2.5-40 MPa, the average density of the lump form is 400-1600 kg/m3, which allows the use of porous slag for the production of lightweight 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 aggregate 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 will require a larger volume of cement 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.

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, ore processing, 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 ().

Average density crushed stone is 1.2 - 3 tons per cubic meter.

In addition, there is a set 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, which depends on the breed 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. Crushed granite and gravel are considered the most durable and high-quality, limestone material is also quoted, and 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 a screening 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, granite and gravel raw materials are most often used, but sometimes they produce recycled material with your own hands by crushing substandard bricks, construction waste and products from dismantling 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 with diamond wheels or diamond drilling of holes in concrete is needed. Crushed limestone is more suitable for these procedures.

Conclusion

Crushed stone is an important and widely used building 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.

Most of us know that concrete is made from a mixture of cement, sand and water. Depending on the required strength of the future solution, the proportions for creating this mixture may be different, but the ingredients do not change. Sometimes, for special type concrete, other components are added to the cement mixture in small quantities, but in general the principle of creating concrete does not change. Here many people have a question: in what cases is crushed stone added to concrete and what is it for?

Crushed stone is also a building material. It is obtained by crushing rock stones into small fractions ranging in size from 5 to 70 or more millimeters. As you know, crushed stone has an uneven surface.

There are several types of crushed stone, each of which is used in in a certain form construction work:

• granite;
• gravel;
• limestone;
• slag or artificial.

Granite crushed stone is considered the most optimal for use in construction. However, it is worth considering that it is also the most expensive in price.

Crushed stone is added to concrete for several reasons, one of which is that crushed stone, as a more cheap material Compared to cement, but with a high degree of density and hardness, it perfectly replaces it when creating a concrete mixture. In addition, crushed stone has other advantages over cement. It reduces creep and shrinkage of the mixture. Concrete using crushed stone is much less likely to crack than conventional concrete cement mixture, and its density and water resistance are much higher.

When adding crushed stone to concrete, some nuances should be taken into account. Despite the fact that crushed stone, in construction terminology, is a large filler and significantly increases the density of the finished concrete mixture, it should be added to a mixture of sand and cement with caution. To prevent air pockets from appearing near individual fractions of crushed stone, it is best to mix large particles of crushed stone with small particles of crushed stone and sand. That is, if you want to make strong concrete, it is not enough to add only large crushed granite stone, which has increased hardness, to it - it will be much more effective to mix large, medium and small crushed stone with a mixture of sand and cement. This will allow you to make a truly durable and reliable concrete, minimizing the amount of cement in the overall mixture.

Adding only small crushed stone is not a very effective idea. In order to receive durable concrete, you will need not so little cement, so the effect will not be as significant as from using crushed stone of different sizes.

Most often, concrete using crushed stone is made when creating hydraulic reinforced concrete structures, tunnels, bridge elements, stone supports, fences and various foundations. Gravel is widely used in decorative architecture and landscape design. Not a single construction of railways and highways can be done without coarse crushed stone.

If you are going to add crushed stone to concrete, you should consider that great value The strength of the concrete mixture is determined by the absence of dust and other impurities in the crushed stone. According to GOST, their content should not exceed 1-2% of the total mass of crushed stone. In order to ensure the cleanliness of the crushed stone, it can be washed with water pressure from a hose.

Despite the fact that in many cases crushed stone is added to concrete in order to reduce its cost by reducing the amount of cement, it is highly discouraged to use recycled crushed stone in construction work, especially in laying the foundation. Despite its relative cheapness, its density is noticeably lower than that of new crushed stone.

To make a concrete mixture, you need to use several basic components. This list includes sand, cement, water and aggregate. Crushed stone is most often used as the latter. This building material comes in several varieties, each of which has its own characteristics.

Why do you need crushed stone in concrete?

Crushed stone is bulk material, which is obtained by crushing rocks, including boulders and gravel. In other words, crushed stone is usually understood as irregularly shaped stones that can belong to different rocks.

When dealing with the question of why crushed stone is added to concrete, it is necessary to emphasize several features. This building material is not always used when preparing a concrete mixture, but its inclusion in the composition allows you to solve a number of problems:

1. Strengthening. Crushed stone particles have irregular shape, due to which the adhesion of materials is enhanced and creep is reduced.
2. Increased water resistance. Concrete mixtures with the addition of coarse filler is used if the finished coating will often come into contact with moisture.
3. High strength. If such a filler is present in the mixture, it will take on the role of a frame. Concrete on crushed stone can be subject to increased loads. For this reason, this technology is used in the construction of tunnels, bridges, hydraulic structures, and foundations for buildings that are subject to increased requirements.
4. Reducing construction costs. When making a solution, the filler partially replaces cement, which is characterized by a higher price.

If you decide to use a filler, you should consider the following nuances:

1. Presence of several fractions of crushed stone. If the mixture contains only large stones, then air pockets may appear during the laying process, and therefore the strength will decrease.
2. The maximum size of stones depends on the design features. The fraction should be less than ⅔ than shortest distance between adjacent reinforcing bars. Another calculation option is based on width finished product— stones should not exceed ⅓ of this figure.

Main characteristics of crushed stone

Having figured out why crushed stone is in concrete, it is necessary to indicate several basic characteristics on which the technical indicators of ready-made mixtures depend:

1. Density. Affects the strength of the finished product. The optimal density can be called density, which varies between 1.4-3 g/cm3.
2. Flakiness. This term refers to the plane of the stones. Based on this indicator, several types of crushed stone are distinguished: cuboid, acute-angled, lamellar. Cuboid grains have maximum strength.
3. Compressive strength. This indicator is determined during the process of compression and crushing of rock.
4. Fraction. The characteristic is one of the main ones. It is usually understood as the size of stones (grains). There are 3 main categories: large, medium and small. Knowing the main characteristics and features, you can choose the optimal crushed stone fraction for, M100 and any other.
5. Radioactivity. Indicated on the packaging. It means what natural radioactive background the building material has. Class I can be used in any construction work, including the construction of buildings. II - for the construction of highways.
6. Frost resistance. Using this characteristic, they indicate at what temperature conditions the strength of the finished concrete is maintained. This indicator is written using a letter. A number is indicated next to it - this means how many freezing and thawing the crushed concrete can withstand. For the climate of Moscow and most other regions of Russia, it is better to choose material with an F300 index.

Classification

Bulk filler is usually divided into several categories, taking into account the rocks from which this material was produced:

• granite;
• gravel;
• limestone;
• slag;
• secondary.

Granite

This type of crushed stone is obtained by crushing nonmetallic rocks, most often it is a monolithic rock. Granite quality building material regulates GOST 8267-93. This material is superior in strength to other types of filler.

Several categories can be distinguished depending on what fraction the crushed stone is:

• fine-grained (fraction 0-5 mm and 5-10 mm);
• medium-grained (5-20 mm and 20-40 mm);
• coarse-grained (the stones here reach 40-70 mm or 70-120 mm).

In construction work, the middle fraction (5-20 mm) is most often used. This option is considered optimal for laying highways, building foundations, and erecting reinforced concrete structures.

Gravel

Such bulk material is produced from rocks. Often, rock dispersion technology is used for mining after extraction from the quarry. Product quality must meet the requirements of GOST 8267-93.

The strength of these stones is lower than granite, but this variety has several advantages:

• low price (relative to other types of crushed stone);
• minimal radioactivity.

Depending on the extraction method, building materials are of the following types:

• gravel for concrete - these stones are of river and sea origin;
• crushed - it can be obtained by crushing rocks.

Fractions of crushed stone of this variety can be as follows:

• small - the size of the stone varies between 3-10 mm;
• medium - 2 options are presented here (5-20 mm and 5-40 mm);
• large - grains reach 20-40 mm.

Gravel material has found application in the construction of pedestrian paths, filling reinforced concrete products, and construction of platforms.

Limestone

Sedimentary rocks are used to produce crushed limestone. Stones in in this case are calcium carbonate. The advantage is the minimum cost.

There can be several grain sizes:

• 5-20 mm (the smallest fraction);
• 20-40 mm (most popular);
• 40-70 mm.

Due to its low strength, limestone material has limited use. It is suitable for the construction of paths with light loads, work in the printing and glass industries, and the preparation of cement mortar.

Slag

Slag rubble is usually understood as stones different sizes, which are obtained from the slag used in production.

Depending on the size of crushed stone there are:

• large;
• average;
• small;
• elimination

You can use this filler for cooking. The most common application is thermal insulation.

Secondary

Recycled crushed stone is called secondary because this material is obtained from construction waste, including old asphalt, bricks, and concrete. These products must meet the criteria of GOST 25137-82. The main advantage is low cost.

Disadvantages include low strength and frost resistance. Despite this, recycled materials are often used to strengthen weak soils and build roads.

Criterias of choice

To achieve maximum strength and durability of concrete, crushed stone must be selected carefully. There is no universal option, so when selecting it is necessary to take into account why the concrete is being prepared.

First of all, you need to check compliance with GOST. To do this, the seller is asked to provide accompanying documents for the shipment of goods. Another requirement is the minimum content of dust, sand and other impurities. The maximum figure is considered to be 2% of the total mass.

Fraction

When choosing what kind of crushed stone is needed for concrete, you should be extremely careful in selecting the grain sizes. Large stones should be used in structures that must withstand vertical loads. Such crushed stone takes on the main load and acts as a frame.

Smaller fractions are chosen for reinforced products and those elements that must withstand a large deflection load.

The ratio of concrete grade and crushed stone grade

Before you purchase all the ingredients to create the mixture, you need to select the appropriate crushed stone for concrete. The technical and operational characteristics of the finished products will depend on this.

The table below shows the use cases recommended by the manufacturers.

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