We all know that during production concrete mortar crushed stone is used, 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:
- 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;
- Bean shape– no less important characteristic gravel, on which its quality and possibility of use in construction and production depend reinforced concrete products. 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;
- 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;
- 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;
- 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;
- 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 of 25 - 60 and 40 - 70 are used in road construction according to GOST R 54748-2011.
Also called building standard involves the use of other factions, 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, 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 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.
Before you decide what fraction of crushed stone is needed when performing concrete works for the production of reinforced concrete products and structures, it is necessary to consider such concepts as crushed stone and its fraction.
What fraction of crushed stone should be used in the manufacture of reinforced concrete structures?
Crushed stone– a building material obtained by crushing dense rocks into fractions of 5÷70 mm or more. It has a non-rounded, rough surface. After crushing the crushed stone, it is sieved into fractions.
Depending on the rock from which crushed stone is produced, there are the following types of crushed stone:
- limestone;
- gravel, or just gravel;
- granite;
- artificial (from industrial waste, for example, slag).
Granite aggregate is considered one of the best - it has high strength, but at the same time it is the most expensive.
Crushed stone fraction is a collection of particles of the same size or spacing.
So, next you need to figure out why crushed stone is added to the concrete mixture? Briefly, we will consider the reasons why it is necessary to use crushed stone, and then we will consider which fractions need to be added to the concrete mixture in order to obtain a strong and durable structure.
Why is it necessary to add crushed stone to prepare concrete?
- Crushed stone makes up the skeleton of concrete, which is approximately 80...85% of the total volume. Crushed stone in concrete is called coarse aggregate.
- The use of coarse aggregate in concrete allows to minimize the processes of shrinkage and creep, increases the strength, density, water resistance and crack resistance of the structure.
- Since the most expensive component of concrete is cement, it means that it is necessary to strive to reduce its consumption without deteriorating the properties of the concrete being produced. One of the factors in obtaining high strength concrete is density - the denser the concrete, the stronger it is. To reduce the intergranular space (voids) in concrete, it is necessary to select such sizes of sand and crushed stone particles so that when the concrete mixture is compacted, the space between large particles of crushed stone is occupied by smaller particles of coarse aggregate, and the voids between small particles of crushed stone are occupied by large particles of sand, etc. . So for good concrete it is necessary to have coarse aggregate particles of several fractions. This approach to calculating the composition of concrete saves a significant amount of cement during construction. The saving of cement is explained by the following: small particles of cement are like glue, which should cover and “glue” together all the surfaces of sand and crushed stone. As is known, large-sized particles have a smaller specific surface area than small-sized particles, therefore, if the crushed stone and sand are very fine, the amount of cement needed to “glue” it together will be greater, or the amount of cement will not be enough to envelop the surfaces (the strength will be significantly reduced) . To verify the correctness of the above justification, it is necessary to calculate the composition of concrete (using the NIIZhB method) using first a large fraction, and then several fractions, and then compare the cement consumption.
In quarries for the extraction of granite or other crushed stone, according to GOST 8267-93, the following main fractions of crushed stone are produced after crushing:
- 5 (3) ÷ 20 mm;
- 5 (3) ÷ 10 mm;
- 10 ÷ 15 mm;
- 10 ÷ 20 mm;
- 15 ÷ 20 mm;
- 20 ÷ 40 mm;
- 40 ÷ 80 (70) mm.
- Can also be produced according to individual order fractions 70 (80) ÷ 120 mm, 120 ÷ 150 mm.
What fractions are used to prepare concrete? How to choose the right crushed stone fractions?
However, to obtain high-quality concrete, not one, but two or three fractions of crushed stone are often used, or there is crushed stone different sizes. At enterprises producing concrete and reinforced concrete structures according to GOST 8267-93, quality control laboratories (technical control department) determine the grain composition, the smallest d and the largest D nominal sizes of crushed stone. These characteristics of crushed stone are determined by sifting crushed stone through standard sieves and weighing the residues on each sieve. Next, the total residues on each sieve are determined. The results obtained are compared with the values in table 1 from GOST 8267-93.
Table 1
Note:
- For crushed stone fractions 5(3)÷10 mm and a mixture of fractions 5(3)÷20 mm, an additional condition is applied under which the total residue on the lower sieve 2.5 (1.25) mm should be 95÷100%.
- It is allowed, at the request of the consumer, that the total residue on the 0.5 sieve (D min + D max) be 30-80% by weight.
After sifting, a graph of grain sifting of crushed stone is built and if the curve of this crushed stone falls into the shaded area of the graph ( rice. 1), which means that such crushed stone can be used in the manufacture of concrete and reinforced concrete. If the curve does not fall within the specified area, add another fraction and repeat the sifting.
Rice. 1. Grain composition of gravel (crushed stone)
According to GOST 26633-91* “Heavy and fine-grained concrete. Technical conditions" the largest crushed stone size for a given reinforced concrete structure should be established in the standards, in standard projects, technical conditions or working drawings of reinforced concrete structures. Knowing what the largest crushed stone grain size is provided in our case according to the table from the same GOST (clause 1.6.4.), we determine which fractions can be used, table 2.
table 2
Note. It is permissible to use a fraction of 3÷10 mm if sand is used as a fine aggregate with a particle size modulus of no more than 2.5.
In order not to plot the grain composition of crushed stone, you can use the table from GOST 8267-93 (clause 1.6.5., table 5) and check the content of individual fractions, table 3.
Table 3
| Largest aggregate size, mm | Content of fractions in coarse aggregate (crushed stone, gravel), % | ||||
| 5(3)÷10 mm | 10÷20 mm | 20÷40 mm | 40÷80 mm | 80÷120 mm | |
| 10 | 100 | – | – | – | – |
| 20 | 25 – 40 | 60 – 75 | – | – | – |
| 40 | 15 – 25 | 20 – 35 | 40 – 65 | – | – |
| 80 | 10 – 20 | 15 – 25 | 20 – 35 | 35 – 55 | – |
| 120 | 5 – 10 | 10 – 20 | 15 – 25 | 20 – 30 | 30 – 40 |
A simplified option for selecting the required crushed stone fraction
The process of selecting the correct fraction of crushed stone, which is briefly given above, mainly concerns enterprises that produce concrete and reinforced concrete products. But in most cases it is enough to know the following information given in table 4(based on SNiP 3.03.01-87 Load-bearing and enclosing structures).
Table 4
| Parameter | Parameter value |
| 1. Number of fractions of coarse aggregate with grain size: up to 40 mm more than 40 mm | At least two At least three |
| 2. Largest aggregate size for reinforced concrete products | No more than 2/3 of the smallest distance between reinforcement bars |
| 3. Largest aggregate size for reinforced concrete slabs | No more than 1/2 the thickness of the slab |
| 4. Largest aggregate size for reinforced concrete thin-walled products | No more than 1/3 – 1/2 of the thickness of the product |
| 5. When pumping with a concrete pump, the largest aggregate size | No more than 0.33 internal diameter of the pipeline |
| 6. When pumping with a concrete pump, the largest aggregate size, including grains largest size flakie and needle-shaped | No more than 15% by weight |
| 7. When concreting underground structures using injection and vibration injection methods (clause 2.7) | No more than 10÷20 |
According to SNiP 3.03.01-87 (clause 3.1), when constructing massive hydraulic structures, it is allowed to use crushed stone and gravel of the following fractions:
- 120÷150 mm;
- more than 150 mm should be laid directly into the form (formwork) before laying the concrete mixture.
For clarity, we present in tabular form the predominant use of crushed stone, depending on the fraction, table 5
Table 5
| Crushed stone fraction | Application area |
| 5 (3) ÷ 20 mm;5 (3) ÷ 10 mm;10 ÷ 15 mm;10 ÷ 20 mm;15 ÷ 20 mm; | Production of concrete, concrete and reinforced concrete structures, bridge elements, floor slabs, etc. |
| 20 ÷ 40 mm; 40 ÷ 80 (70) mm. | Laying the foundation, production of industrial buildings and structures, concrete, concrete and reinforced concrete structures, construction of roads and railways |
| Sharing of several fractions with particles from 20 to 70 mm | Construction of massive industrial buildings and structures, bridges, tunnels, etc. |
| 70 (80) ÷ 120 mm, 120 ÷ 150 mm, more than 150 mm | Construction of massive foundations, industrial buildings and structures, used in landscape design: decor, finishing of pools, pond banks |
A few more important notes you need to know in order to make the correct concrete mixture:
- Quality (cleanliness, absence of organic impurities) aggregate (crushed stone). According to GOST 26633-91* (clause 1.6.5), the content of dusty, clayey and organic impurities in coarse aggregate (crushed stone) should not exceed 1-3% by weight. If the crushed stone is still contaminated, you can wash it with water under pressure from a hose.
- The strength of the aggregate also has a significant influence on the strength of concrete. Depending on the class of concrete, the grade of crushed stone from natural stone must be no lower (GOST 26633-91*, clause 1.6.7). - see table below, table 6.
- It is not recommended to use recycled crushed stone to make the foundation.
Table 6
If you have any questions, write in the comments below.
You were advised by an expert
Konev Alexander Anatolievich
The composition of concrete includes components different types, which provide its main properties. There are three main components, each of which gives the material certain properties. These include, in particular, water as a filler and cement. Additives should also be mentioned here. They are not always used, which must be taken into account. Why is additional material needed? This procedure provides greater strength to the concrete. If there is a need to introduce such a component, you need to carefully read state standards on the brand and a substance to enhance the parameters.
Crushed stone as an additional component provides greater strength to concrete.
Handling crushed stone quickly and affordably! Crushed stone is one of the types of concrete aggregates that are used quite often.
The reason for this is the fairly high performance characteristics, which crushed stone has. For example, the strength of a material of this type can reach 1000 MPa or even higher. Everything depends on the specific breed and its characteristics. It is necessary to consider this type of material in more detail, since it requires a special approach.
For foundations and structures made of heavy concrete, gravel and crushed stone are used as coarse aggregates for concrete from dense rocks in accordance with GOST 8267, from ferroalloy and blast furnace slags of ferrous metallurgy and copper smelting and nickel slags of non-ferrous metallurgy in accordance with GOST 5578 and, finally, from thermal power plant slags, GOST 26644.
Mining Features
Crushed stone is mined in the following way: hard rocks are crushed, after which a separation is made depending on the size of the grains and a fraction is established.
Crushed stone is mined in the following way: hard rocks are crushed, after which a separation is made depending on the size of the grains and a fraction is established. Sometimes it is mined in a quarry, using the sifting method. On the territory of the Russian Federation, crushed stone is mined in the largest quantities in the quarries of the Urals, here are some of them:
- Syrostankinsky quarry;
- Medvedevsky quarry;
- Satka field;
- Mednogorskoye field;
- Maly Kubais mine;
- Novosmolinsky quarry;
- Mochischensky plant;
- Rezhevsky plant;
- Kazantsevsky quarry;
- Timofeevsky quarry, etc.
The shape of individual stones is very important for the production of concrete: the more cube-shaped the stone, the more of them will fit into a given volume. On the contrary, the presence of needle-shaped elements reduces the quality of the fill. Standard size, which one fraction has, is equal to 5 to 20 mm. Crushed stone for concrete, the fraction of which falls within these limits, makes it possible to significantly increase operational properties concrete, and in addition, also provides a large number of other benefits. For the production of high-grade compositions, crushed stone of larger sizes is used. This makes it possible to increase the strength indicator, but at the same time, the cost of such material also increases.
Limit of harmful substances content
There is an acceptable percentage of minerals and rocks that are considered harmful impurities in the additive material for concrete:
- sulfur, sulfides (except for pyrite) and sulfates (anhydrite, gypsum, etc.) in terms of SO3 no more than 1.5% for coarse aggregate by weight and up to 1.0% for fine aggregate by weight;
- amorphous types of silicon dioxide, which dissolves in alkalis (opal, chalcedony, flint) - no more than 50 mmol/l;
- layered silicates (chlorite, mica, hydromica, etc., which are rock-forming minerals) - no more than 15% for coarse aggregate by volume and for fine aggregate - no more than 2% by weight;
- pyrite in terms of SO3 – not higher than 4% by weight;
- halogens (sylvine, halite, etc.), which also includes water-soluble chlorides, when converted to chlorine ion: not more than 0.1% for coarse aggregate by weight and not more than 0.15% for fine aggregate by weight;
- magnetite, apatite, iron hydroxides (goethite, etc.), phosphorite, nepheline, which are the minerals that form the rock - no more than 10% each individually and no more than 15% in total by volume;
- coal – not higher than 1% by weight;
- free asbestos fiber – not higher than 0.25 by weight.
The content of clay and dust particles from metamorphic and igneous rocks should not exceed 1% by weight - for concrete of all classes. The content of clay and dust particles in crushed stone from sedimentary rock should not be more than 2% by weight for concrete of class B22 and above, no more than 3% by weight for concrete of class B20 and below. The content of flaky grains in crushed stone should not exceed 35% by weight.
The following types are distinguished:
- granite;
- gravel;
- the most common type is limestone.
Granite
Granite is best used as a filler for high-quality concrete mixtures that are used when pouring road, bridge and airfield pavements.
- Which nonmetallic material is the strongest and best ensures the strength of concrete? Granite. It is obtained by crushing natural granite, whose fragments, after a directed explosion, are ground in a special unit. Granite crushed stone It is better to use it as a filler for high-quality concrete mixtures that are used when pouring:
- road and airfield pavement and a number of other types of work. In this case, great attention is paid to the ability to withstand serious dynamic loads;
- bridge deck and other bridge structures. It should be noted that crushed stone for concrete in this case will be additionally affected by variable water levels, which is a serious problem;
- critical areas such as walls, columns and floor slabs that carry heavy loads. In such cases, crushed stone must guarantee the ability to withstand not only static pressure, but also dynamic pressure, which is important during operation.
Quality parameters:
- density;
- fraction;
- compressive strength;
- flakiness.
Material fractions
The fraction in the range of 5-20 mm is the smallest fraction; it provides high durability and reliability of the foundation.
Granite should have fractions ranging from 5 to 150 mm:
- the fraction less than 5 mm is called granite screening. It has small grains and is used as decorative design flowerpots, flower beds, lawns, etc. This is used quite rarely as an additional component in concrete. The use of this fraction is permitted when used as a fine sand aggregate with a particle size modulus of no more than 2.5;
- the fraction in the range of 5-20 mm is the smallest fraction that is best used. It is used in the construction of reinforced concrete products, bridges and road surfaces. This fraction provides high durability and reliability of the foundation. At the same time, such an additive has a low cost;
- medium fraction, which is characterized by grain sizes from 20 to 40 mm and is used as an additive to concrete in the construction of the foundations of large industrial buildings;
- large aggregate, 40-70 mm, which is used for the construction of the foundation of massive structures.
It is permissible to use crushed stone in the form of a mixture of a pair of adjacent fractions.
Larger stones can be used in the construction of a rubble concrete foundation. It must be taken into account that this type is used quite rarely for concrete.
Granite crushed stone is quite durable in its technical specifications, its grade ranges from 1200 to 1400, frost resistance up to 400 cycles. Its flakiness is low, equal to only 15-18%.
Flakiness is a characteristic of grain shape; it is expressed as the percentage of needle-shaped and plate-shaped grains from the total mass.
It is possible to increase all these characteristics if you use only selected stone that has no flaws. The absence of deformation makes it possible to improve the structure and make the monolithic mass more durable.
Application
The addition of gravel to concrete is widely used in foundation construction, road construction and the production of reinforced concrete products.
Crushed gravel is obtained by sifting quarry rock or crushing natural rocks. This material is inferior in strength to granite filler. Why use it in this case, you ask? Unlike granite, this one is more affordable. The addition of gravel to concrete is widely used in foundation construction, road construction and the production of reinforced concrete products. Gravel is divided into several types:
- gravel having rounded grains, which became such under the influence of sea or river water.
- crushed, crushed or natural.
It is also divided depending on the size of the fractions:
- fine – grains up to 10 mm.
- medium – grains from 10 to 20 mm.
- large – grain size does not exceed 40 mm.
Limestone
The frost resistance of crushed limestone is only 50-100 cycles, which makes it impossible to use this material in capital construction at high latitudes.
Limestone is one of the most readily available additive materials used in construction. It contains calcite, which is why the material has the appearance of white stones, the shade of which depends on impurities and can vary: from quartz, iron or clay.
Limestone can be divided into several groups depending on the strength class:
- M 300-600 – produced mainly from limestone.
- M 600-800 is the result of processing dolomite and limestone. He is characterized by high performance and large size fractions.
- M 200 is a group that is practically not used in concrete production due to the high cost of crushed stone for a material of this type. Breeds that are not so expensive are used.
Frost resistance has only 50-100 cycles, which does not make it possible to use this material in capital construction at high latitudes.
When you need to purchase crushed stone to add to the concrete foundation, you need to inquire about the availability of special documentation. From them you can understand the correspondence between the required and expected characteristics of the type you prefer to use in construction.
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:
- Strengthening. Crushed stone particles have irregular shape, due to which the adhesion of materials is enhanced and creep is reduced.
- Increased water resistance. Concrete mixtures with the addition of coarse filler are used if the finished coating will often come into contact with moisture.
- 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.
- 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:
- 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.
- Maximum size stones depends on the design features. The fraction should be less than ⅔ than the smallest 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 technical indicators ready mixtures:
- Density. Affects the strength of the finished product. The optimal density can be called density, which varies between 1.4-3 g/cm3.
- 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.
- Compressive strength. This indicator is determined during the process of compression and crushing of rock.
- 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.
- 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 in the construction of buildings. II - for the construction of highways.
- 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.
- gravel for concrete - these stones are of river and sea origin;
- crushed - it can be obtained by crushing rocks.
- 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, building sites.
Limestone
Sedimentary rocks are used to produce crushed limestone. The stones 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. Universal option does not exist, therefore, 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.
Any concrete mixture includes a number of components on which its main characteristics depend. Three of them are mandatory constituent elements: water, cement and filler. Crushed stone, which has excellent performance parameters, is usually used as a filler.
To obtain particularly high-strength concrete, high-quality crushed stone is used, the strength of which can reach 1000 MPa or more. This value is determined by what material is used to produce crushed stone and what its features are. Let's consider what kind of crushed stone can be used as the basis for producing a concrete mixture.
Types of crushed stone used to prepare concrete
By type, crushed stone can be:
- cube-shaped;
- having sharp corners;
- wedge-shaped;
- Flaky.
Crushed stone used for concrete can be of artificial or natural origin. Artificial is obtained by processing household slag and construction waste. It is a recycled material, so its cost is low. It is practically not used in construction work; it is used to strengthen weak soils during the construction of not very important roads. Natural crushed stone is obtained by crushing rocks. Right choice crushed stone can reduce soil shrinkage and creep, increase the durability and strength of concrete.
An important characteristic by which the choice of crushed stone suitable for specific work is made is the size of the fractions. This refers to the size of those particles that are most numerous in the material. How smaller size particles, the smaller the fraction number.
When forming a concrete mixture, crushed stone of large fractions is used where it is necessary to ensure high strength of concrete after it has set. Crushed stone of small fractions best fills cavities and voids.
Flat and needle-shaped crushed stone reduces the strength of the concrete mixture, and cement consumption also increases. The use of such crushed stone reduces the frost resistance of the finished concrete, so this form of crushed stone is practically not used in construction. Let's take a closer look at the types of crushed stone used in construction work.
Granite crushed stone - the best for concrete
This crushed stone is one of the most durable ore materials. It is obtained by crushing natural granite. For concrete, this type of crushed stone is the most best filler, it is used for those concretes that must have a high grade:
- pavement of roads and airfields;
- the most critical building elements experiencing maximum load (walls, slabs, columns);
- various bridge structures, including bridge deck.
Granite crushed stone is characterized by its quality by the following indicators: density, compressive strength, as well as fractionation, which can range from 5 to 150 mm. The most popular fraction ranges in size from 5 to 20 mm, which is used in the construction of reinforced concrete products, road surfaces and bridges. Its use guarantees a reliable mixture composition and high performance data.
Crushed stone of the medium fraction measuring 40 millimeters is used for the construction of industrial facilities. The large fraction used to create large concrete structures has dimensions of 40-70 mm. Crushed stone of larger forms is used to make rubble concrete foundations.
The operational parameters of granite material indicate its high strength. The grade of such crushed stone can be in the range of 1200-1400, and its frost resistance reaches 400 cycles.
Gravel and limestone material
Crushed stone of gravel type is obtained by sifting quarry rocks or crushing rocks of natural origin. The performance indicators of this material are inferior to granite, but its cost is lower. This filler is actively used in the manufacture of reinforced concrete products, in road works and in the creation of foundations. According to its fractionation, it can be divided into small, with sizes up to 10 mm, medium (from 10 to 20 mm) and large, with a fraction size up to 40 mm.
Limestone crushed stone is one of the cheapest types of filler. Depending on the accuracy class, this material can be divided into groups:
- M600-M800 - these grades are made from limestone or dolomite, their performance is high, and the fraction sizes are large;
- M300 - M600 - grades obtained from limestone;
- M200 is an expensive brand, so it is not used when producing concrete.
Relationship between concrete grade and crushed stone grade
The main filler can be any hard rock - granite, gravel, limestone, expanded clay, crushed brick and asphalt. But there are some peculiarities in the choice of filler. The strength of a particular filler may greatly limit its use. Yes, use broken brick completely impossible in the manufacture of critical concrete structures.
The grade of solid filler indicates its strength. The correspondence between concrete and filler grades is presented in the table:
| Brand of crushed stone | Concrete grade |
| M1200 | M400 - M500 |
| M 1000 | M 300 |
| M 800 | M 200 |
| M 600 | M 100 |
This table allows for some deviations, which are quite acceptable and are determined by the ratio of sand and cement. In practice, concrete of grade M250 and less is made using gravel, and above M300 granite is used.
Concrete cannot be stronger than its fillers, so it is impossible to obtain M500 concrete from M400 cement. Obtaining the correct concrete measurement depends on the selection of the proportions of its components.
What fraction of crushed stone is needed for concrete?
For the concrete mixture, crushed stone of a fraction of 5-70 mm is used. A finer division forms the subgroups 5-10 mm, 10-20 mm, 20-40 mm and 40-70 mm. For concreting, it is better to use larger crushed stone and gravel, since the used filler will have a smaller specific surface area and exert less pressure on cement mortar, which ensures the required mobility of the mixture.
There are standards according to which high-size filler should make up from one to twenty percent of the mass, and low-size filler should make up no more than 20% of the mixture.
In accordance with SNiP 3.03.01-87, the concrete mixture must contain crushed stone of at least two fractions with a maximum particle size of up to 40 mm, and at least three fractions if the largest particles are 40-70 mm. The maximum crushed stone size should be less than 3/3 minimum distance between longitudinal reinforcing bars. Also it should not exceed 1/3 minimum size specific building element, for example, its tape width.
The durability and strength of concrete structures primarily depend not only on how quality materials used, but also on how correctly the mixture is selected. In order to obtain high-quality concrete, it is necessary to take into account all the details of its preparation.