The concrete mixture includes several components that allow it to provide all the necessary characteristics. IN mandatory it must contain 3 main components: cement, water and aggregate. Very often crushed stone is used as a filler because it has high performance characteristics.
To obtain high-strength concrete, high-strength types of crushed stone are used.
The strength of crushed stone can be 1000 MPa or even more. This value will depend on the type of material and its characteristics. Therefore, let's consider what crushed stone can be used for preparing concrete mixture.
Types of crushed stone for preparing concrete
Types of crushed stone: a) cube-shaped; b) acute-angled; c) wedge-shaped; d) flaky.
Crushed stone for concrete can be artificial or natural. The first option is obtained from construction waste and household waste. It is a recycled material, so it has a low cost. IN construction work it is almost never used (it is used to strengthen weak soils in places where non-federal roads are being built). The second type is obtained from rocks by crushing them. With the help of crushed stone you can reduce creep and shrinkage of soil, increase the strength and durability of concrete.
The choice of crushed stone is carried out according to such characteristics as the size of the fractions (the size of individual particles that predominate in the composition of the material). The smaller the fraction size, the smaller its number will be.
When coarse-grained crushed stone is used to ensure high strength when setting concrete, and fine-grained crushed stone is used to better fill voids and cavities.
Needled and flat crushed stone reduces the strength of the mixture, while increasing cement consumption. Its use reduces the frost resistance of concrete, so when carrying out construction work, crushed stone of this form is avoided. Let's take a closer look at each type of crushed stone that is used in construction work.
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Granite crushed stone for concrete
This material is one of the most durable ore materials. It is made by crushing natural granite. Such crushed stone is the best filler for concrete, which should have a high grade:
- airfield and road surfaces;
- critical areas that are under heavy load (columns, walls, slabs);
- bridge deck and other types of bridge structures.
The quality of granite crushed stone can be determined by such characteristics as density, compressive strength and fraction, which should be in the range of 5-150 mm. The fraction with a size of 5-20 mm is in highest demand, which is used for the construction of reinforced concrete products, bridges and road surfaces. When used, the reliability of the composition and its high performance parameters are guaranteed.
The average fraction has dimensions of about 40 mm, which is used in construction industrial facilities. The size of the coarse fraction required for the construction of large structures is 40-70 mm. Larger dimensions are used in the construction of rubble concrete foundations.
Granite material is quite durable in its performance characteristics. Its grade is in the range of 1200-1400, and frost resistance is up to 400 cycles.
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Gravel and limestone material
Crushed gravel is obtained by sifting quarry rock or by crushing natural rocks. In terms of performance characteristics, it is inferior to granite, but has more low price. This filler is widely used in the production of concrete products, in road construction and when constructing foundations. Depending on the size of the fractions, it is divided into small (up to 10 mm), medium (10-20 mm) and large (up to 40 mm).
Crushed stone made from limestone is one of the cheapest types. According to the accuracy class, several groups of such material are distinguished:
- grade M600-M800 is the result of processing limestone or dolomite. She has high performance and has big size factions;
- grade M300-M600 is made of limestone;
- grade M200 is almost never used for the production of concrete, as it has a high price.
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Dependence of concrete grade on crushed stone grade
Any hard rock is suitable as the main filler: expanded clay, limestone, gravel, granite, asphalt or crushed brick. But there are some nuances here. Each filler has a certain strength, which leads to severe restrictions on the possibility of application. For example, the manufacture of a critical structure is unthinkable using broken bricks.
The durability of a solid drive indicates its brand. A table with the approximate ratio of crushed stone is presented below.
Table 1. Selecting a grade of crushed stone for concrete
Brand of crushed stone Concrete grade M1200 M400-M500 M1000 M300 M800 M200 M600 M100 This table may have some deviations in one direction or another, but they are acceptable and can be adjusted by the ratio of cement and sand.
In practice, concrete M250 and less is made using gravel, and M300 and above is made using granite.
Concrete cannot be stronger than its fillers, that is, it is impossible to obtain M500 concrete from M400 cement. To obtain the right brand, it is necessary to select the correct proportions of all components.
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 granite crushed stone, which has increased hardness - 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 obtain durable concrete, you will need quite a bit of cement, so the effect will not be as significant as 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 not recommended to use it in construction work, especially in laying the foundation. secondary crushed stone. Despite its relative cheapness, its density is noticeably lower than that of new crushed stone.
All mixtures for cooking concrete solutions consist of 3 main components, one of which is called “filler” (filler). As such they are used various materials, including with different parameters. Therefore, there may be several answers regarding even crushed stone.
Firstly, the industry produces several types of similar products, which differ in both chemical and structural composition and certain properties (in particular, strength).
Secondly, even crushed stone of the same type can have different sizes of fractions (granules), which is why it is divided into large, small or medium.
Third, it is also important for what purposes the concrete solution is prepared, what are the specifics of its use and the further operation of the structure “created” from it.
For example, if a foundation is to be poured, the concrete must be strong enough. At the same time, if you use crushed stone with large fractions, then “pulling” the solution along the formwork and compacting it (either manually or with a vibrator) will be quite difficult. And if it has a rather complex configuration, with dense reinforcement cage, which quite often happens during individual construction?
To install a concrete floor, using the same solution is not economical, since you can prepare a “cheaper” one. In addition, the smallest crushed stone is taken, since the thickness of such a floor is usually small.
As can be seen from the above, there are many nuances in choosing crushed stone for concrete. Therefore, it is worth immediately noting that you should not be guided by any single recommendation, especially from supposedly “knowing all” people. It is clear that there cannot be a universal “recipe” in principle. Still, there are certain criteria that should be taken into account.
- The strength of the final product is determined by the corresponding characteristics of the aggregate. For example, it is impossible to obtain M500 concrete from 600 grade crushed stone.
For general guidance, here is an approximate correspondence between the strength of the hardened mortar and filler (concrete - crushed stone):
M100 – M600;
M200 – M800;
M300 – M1000;
M400 (500) – M1200.
If, when using a certain brand of crushed stone, it is still necessary to increase the strength of concrete, then it is necessary to increase the proportion of cement in the prepared solution. Some sources indicate that sand can be added to save money. This is incorrect, since this material is not “defining” in this regard.
- To ensure the specified strength of the final product, filler with same sizes granules This leads to the fact that the “fill” volume will be filled unevenly; the formation of many voids is possible, which naturally reduces the strength characteristics of concrete (tensile, displacement, compression).
For foundations for massive structures, experts recommend using not large, but smaller crushed stone (with sizes 5 - 20 and 5 - 10). It will cost a little more, but it will be more reliable. In other cases you should take different types crushed stones (according to the size of the granules) and mix. Small fractions will ensure the filling of voids that form between large ones, therefore, the density of the mass will increase.
- It is worth paying attention to such a characteristic of crushed stone as “flakiness”. It shows the degree of “flatness” of the pebble. More cuboidal granules have lower flakiness. The use of crushed stone, which has a fairly high this characteristic(with flatter fractions) entails an increase in binder consumption, which is not always justified from an economic point of view.
In addition, such a solution is quite difficult to compact, since flat crushed stone is less compacted.
For buried foundations It’s better not to use it, but, for example, it’s quite suitable for blind areas.
- The peculiarities of our climate force us to take into account such characteristics of materials as resistance to low temperatures. According to this “parameter”, the leader among similar products is crushed stone from granite rocks.
For our climate, it is not advisable (especially for the foundation) to use crushed stone with an “F” value below 150. Otherwise, you will have to additionally insulate the surfaces, which is associated with both material and time costs.
- Nowadays, quite a lot of attention is paid to environmental issues. Crushed stone has a certain radioactivity. This indicator has its own classes and is reflected in the product certificate.
It is advisable to use crushed stone of the 1st class only for arranging foundations.
Practice shows that for the preparation of concrete solutions below grade 250, in order to optimize cash costs, it is more profitable to use gravel. For solutions from M300 and above, crushed stone is taken.
If concrete is needed for the construction of a foundation, then crushed granite stone should be used as a filler.
If the possibilities for choosing products are limited, you should focus on granite crushed stone 5 - 20. Solutions based on it are more universal and can be used for various types works (bases, floors, blind areas and in a number of other cases).
If you increase the density by using smaller fractions, then you need to take into account that much more binder (cement) will be needed. And this will lead to a significant increase in the cost of construction, since this material is the most expensive (from the composition of the mixture for concrete mortar).
To reduce the cost of work, you can mix crushed granite and gravel, since the latter material is cheaper.
This article discusses the issue of selecting crushed stone for medium and heavy concrete. Although, as noted, there are several varieties of it - slag, secondary, lime and some others. If, for example, cellular concrete is being prepared, then it is clear that there is no point in using crushed stone from granite rocks, since this will cancel the advantage of foam concrete (or aerated concrete) such as low weight.
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 that 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 the performance properties of 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
Available permissible percentage content of minerals and rocks related to 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:
- 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
An additive to concrete, gravel is widely used in foundation construction, road construction and the manufacture of reinforced concrete products.
Mined crushed gravel 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. An additive to concrete, gravel is widely used in foundation construction, road construction and the manufacture 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 has only 50-100 cycles, which makes it impossible to use of this material V capital construction in 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. It is characterized by high characteristics and large fractions.
- M 200 is a group practically not used in concrete production due to the high cost of crushed stone for the 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.
01.06.2018
Concrete is modern building material, which involves the use of a mixture of cement with water, sand and any other solid material. Crushed stone is the most commonly used hard material due to its special properties and good capabilities for versatile use. 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 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.
The addition of crushed stone forms the skeleton of a concrete structure, in which aggregate can make up 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 parameter quality and its indicator determine the strength, which depends on the total density of the mass. 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 what kind of crushed stone for concrete fits better All you need to do is understand what a faction 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, 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.