Concrete is a modern building material, the preparation of which requires the following components: sand, cement and solid filler (gravel or crushed stone). Crushed stone is a bulk building material obtained by crushing rocks (gravel, granite or limestone). After this, the crushed stone is divided into fractions depending on the size of the grains. Sometimes crushed stone is mined using a quarry method, using the sifting method.
This material reduces shrinkage and creep of concrete, increases its strength and durability. The shape of the crushed stone influences the convenience of pouring concrete. For example, spiny and flat material will reduce the strength of the concrete mortar, increase cement costs, and reduce frost resistance.
There are the following types of crushed stone:
- granite;
- gravel;
- limestone.
There is also secondary and slag crushed stone. The secondary type is made from construction waste, fragments of concrete, reinforced concrete, brick, etc. Slag crushed stone is made from slag generated in metallurgical production. But its scope of application is limited due to the content of harmful components.
Permissible content of harmful components in the filler
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 airfield, bridge and road surfaces. In this case, much attention is paid to the transfer of significant dynamic loads.
Concrete on granite crushed stone is also used in critical areas (floor slabs, columns, walls). The material must guarantee resistance to dynamic and static pressure.
The following quality indicators of crushed granite stone are distinguished:
- compression density;
- fraction;
- density;
- flakiness.
The bulk density of a material is the ratio of the volume of crushed stone to the area it occupies. All natural voids and distances between grains are taken into account. This is an important indicator for construction and transportation. Bulk density must be distinguished from simple density, which is an indicator of the building material from which crushed stone is made.
Crushed granite should have fractions from 5 to 150 mm. A fraction of less than 5 mm is granite screenings with small grains. Screening is used in decorative design lawns, flower beds, flowerpots, etc. Such crushed stone is rarely used as an additional component in concrete mortar. The use of such a fraction is permitted when used as a fine sand aggregate having a particle size modulus of no more than 2.5.
A material fraction of 5-20 mm is considered fine. It ensures high reliability and durability of foundations, reinforced concrete and road structures. The cost of such an additive is low.
The average fraction of granite crushed stone has grain sizes of 20-40 mm. It is used as an additive to concrete mortar when constructing foundations in large industrial facilities.
Large aggregate with grain sizes of 40-70 mm is intended for the construction of foundations for massive objects. Larger sizes of material can be used when constructing a rubble concrete foundation. But such crushed stone is rarely used as a concrete filler.
By technical specifications, granite crushed stone is sufficient 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 with crushed granite, 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.
Also crushed gravel Depending on the size of the fractions, it is divided into the following types: - fine with grain sizes up to 10 mm;
- medium with grains 10-20 mm in size;
- large – grain size is no more than 40 mm.
Features of crushed limestone
The level of frost resistance of crushed limestone is about 50-100 cycles, which does not allow the use of this building material in capital construction in high latitudes.
The material is the most accessible filler 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.
According to frost resistance, strength and some parameters secondary crushed stone inferior to material made from natural raw materials. But such crushed stone is widely used in the form of coarse aggregate for concrete, the strength of which is 5-20 MPa; in landscaping; in road construction; when strengthening weak soils.
Features of slag crushed stone
Slag crushed stone is obtained by crushing metallurgical waste slag or by special processing of fiery liquid slag melts. 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 material is 2.5-40 MPa, average density 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.
Additional components must be added to any concrete mixture, on which the final strength and all important characteristics will depend. To obtain high-quality composition It is necessary to use several elements - water, cement and high-quality filler. In most cases, crushed stone for concrete is used as a filler, which has good characteristics, suitable for construction. To obtain a high-quality composition, it is necessary to study all the main characteristics of crushed stone, as well as the varieties that can be used.
Experienced builders know that to prepare concrete, it is necessary to use cement, sand and water. To obtain different strengths, different proportions are used, but all components remain unchanged.
But in some cases, to create a special durable concrete, other components are added to the mixture, but the principle of creating the solution will not change. A building material such as crushed stone is used as a filler. As many people know, this stone has an uneven surface, and therefore the adhesion of the resulting composition will be much better.
Adding crushed stone to concrete has become popular for several main reasons, one of which is that the material is the cheapest compared to cement, but it has greater hardness and density. In addition, when crushed stone is added to a concrete solution, creep and the percentage of shrinkage of the mixture are reduced.
Concrete containing crushed stone will also crack less than regular cement mortar, but at the same time the water resistance will increase, as well as the density of the composition.
When crushed stone is added to concrete, you should be aware of certain nuances. Even despite the fact that crushed stone is a rather large filler and increases the density of the mixture, it must be added to the composition very carefully. The formation of “air pockets” is possible. This suggests that when making strong concrete, you cannot add only large crushed stone with increased hardness to the solution. It will be more effective to mix different fractions of different diameters with cement and sand. Thus, it is possible to produce a truly durable and reliable composition, while saving on cement, which is poured into the overall mixture.
Also, you should not add only fine crushed stone to the composition. To get high-quality concrete, not so much cement is required, and therefore the effect will be much more noticeable if you use different sizes of stones.
Concrete with crushed stone is very often used for the construction of hydraulic reinforced concrete structures, bridges, tunnels, stone supports and the construction various foundations. Gravel is also often used for decorative purposes during construction. landscape design. Coarse crushed stone is indispensable for construction purposes during the construction of roads.
If you want to add crushed stone to concrete, you must also take into account that the quality and strength of the mixture will be affected by the absence of dust and other impurities. That is why it is advisable to study GOST standards when purchasing crushed stone. The content of impurities should not exceed 2% of the total mass. The lower the indicator, the better the quality of the mixture. If there are any doubts after purchase, the crushed stone should be washed with water from a hose. This way it will be possible to remove a large number of impurities.
Main characteristics of crushed stone
Main characteristics:
- The average density should be 1.4-3 grams per cubic centimeter.
- Compressive strength is determined by the tensile strength of the rock when clamped and the crushability of the resulting material.
- Flakiness. This is a characteristic that determines the plane of crushed stone. In construction, angular plate forms of the material are used. Depending on this, there are several types of stone groups. The cuboid shape is considered the best and best, since it helps achieve good compaction.
- Crushed stone fraction for concrete. This parameter determines the dimensions of the material used.
- Frost resistance. This indicator will indicate in what temperature ranges crushed stone can be used. Used to mark the letter F, as well as a number indicating the cycles that crushed stone can withstand during thawing and freezing. Crushed stone marked F300 has the best quality. This parameter is especially important to observe in Russian construction conditions, since the air temperature in winter and summer is very different.
- Radioactivity. This parameter indicates the natural radioactive background of the material. If the package says first class, then it can be used in any work. The second class is used for the construction of road surfaces.
Classification of crushed stone
Depending on the method of extraction of the material, crushed stone is divided into several varieties.
Granite
Granite crushed stone is a non-metallic material extracted from hard rocks. In most cases, monolithic rock is used for mining. To get quality material, use GOST 8267-93.
Types of fractions in millimeters:
- 5-10;
- 5-20;
- 20-40;
- 40-70;
- 70-120.
The most popular fraction in construction is considered to be the fraction with a diameter of 5-20 mm, which is quite often used for the construction of asphalt and the creation of concrete.
This type of crushed stone is used for the construction reinforced concrete structures, during the construction of roads, as well as railway tracks, sidewalks and road platforms.
Gravel
This type of material is produced by dispersion after extraction from quarries. Stones are also obtained by crushing rocks. During mining, GOST 8267-93 is used. In terms of strength, the material is not inferior to the previous variety. The advantages of the material include low background radiation, as well as low cost.
Building materials are divided into several types:
- Gravel is stones of river and sea origin.
- Crushed crushed stone, which is produced after processing hard rocks.
Fractions in millimeters:
- 3-10;
- 5-40;
- 5-20;
- 20-40.
The material is used to fill reinforced concrete structures, as well as in civil engineering, during the construction of platforms and pedestrian paths.
Limestone
A similar variety is obtained by processing sedimentary rocks and limestone. Crushed stone is calcium carbonate and is sold at the lowest prices.
There are several fractions (in millimeters):
- 20-40;
- 5-20;
- 40-70.
The limestone type is used for the glass and printing industries, in the production cement mortars, as well as during the construction of roads on which a small load is applied.
Slag
Crushed slag is friction waste used to produce certain types of chemicals. Depending on the size, crushed stone is divided into several sizes:
- Large.
- Average.
- Small.
- Crushed stone screening.
Secondary
The material is obtained after processing construction waste, concrete, brick or asphalt. During production, we adhere to GOST 25137-82. This material is produced using the same technology as other types of crushed stone. The main advantage is low cost. In terms of strength and frost resistance, it is inferior to natural varieties of stones. Despite not the highest characteristics, crushed stone is used in road construction to strengthen weak soil. It is used as a filler for concrete mortar. Before purchasing, it is advisable to choose a specific type of building material that is suitable for a specific purpose, and also read the quality certificate that each seller must provide.
Criterias of choice
In order to purchase high-quality crushed stone for concrete, you need to familiarize yourself with the basic selection criteria. The quality of the resulting composition will depend on this.
Fraction
It is important to choose the right gravel or crushed stone - what fraction, to be more precise. The crushed stone fraction is a combination various particles approximately the same size in pour concrete. Crushed stone will make up the majority of the entire solution, and, therefore, the quality of the resulting foundation will depend on its characteristics.
Crushed stone added to concrete will minimize the shrinkage process, and also increase the strength characteristics and make the foundation more resistant to loads. The strength of the mortar will depend on the strength of the concrete mixing. For this indicator direct meaning affects the density of concrete. To reduce the number of voids formed in the solution, it is necessary to correctly select the fraction of crushed stone and sand. Most best option– use crushed stone of large and small fractions so that the voids between large elements are filled with small particles.
The ratio of concrete grade and crushed stone grade
The connecting link in any concrete composition is cement. Portland cement, which contains 80% calcium silicates in its composition, is considered good for concrete. The increased content of this substance ensures good adhesion of the resulting solution. Frost resistance indicators are also high, which is especially important in construction conditions in Russia. For construction, cement grade M500 is usually used. It must be stored in specially prepared premises.
Crushed stone is necessary to give strength to concrete. In most cases, fractions from 8 to 40 millimeters are used. It is important to ensure that various impurities and dirt do not fall into the composition. If you prepare the solution yourself, then use several types of crushed stone with different shapes.
To select the ideal ratio of all components, you should familiarize yourself with the manufacturer’s requirements for a specific brand of cement and brand of crushed stone. For example, to create a gazebo and flower bed, as well as small paths, you can use ordinary M100 cement. For the construction of a private house M250. For structures that will be subject to heavy loads - M400 or higher. There is no need to choose a brand with a reserve, since this way it will be useless to spend money on the necessary mixture.
There is also the option to use online calculator calculations and calculate all proportions.
After studying this information, you can understand what crushed stone is needed for concrete.
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.
Adding rubble forms the skeleton concrete structure, in which the filler can be up to 90%.
The largest expenditure of financial resources is on cement. To save money, you need to strive to reduce costs while maintaining sufficient quality. The most important 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, upon individual order, you can obtain 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.
Crushed stone is a bulk building material on an inorganic basis with different sizes fractions (grains). It is most often used as a non-binding filler in concrete, which allows future structures and their foundations to withstand operational stresses. Crushed stone is added to the solution both to reduce its cost and to give it strength and elasticity after hardening, reducing shrinkage and the risk of deformation.
The material is obtained by crushing rocks or industrial waste, as a result - the stones have various shapes and remain rough, which increases their adhesion to cement and sand. The size of concrete crushed stone fractions is affected by the maximum value individual elements, it is appropriately labeled, which makes selection and purchase easier. Depending on this, the solution acquires certain properties, in particular - the addition of large rock increases the strength during setting, and small stones - density (promotes better filling of voids).
Varieties
This material is classified according to several criteria: the type of raw materials used, the size and shape of crushed particles, frost resistance and strength. Crushed stone is made from hard granite, metallurgical and construction slag, gravel and limestone rocks. The stronger the raw material, the stronger the load it can withstand future design. Eg, the best option granite will be used for pouring the foundation, and gravel will be optimal in terms of price and quality. Depending on the shape of the crushed stone fractions and their percentage in the total mass, three types of mixtures are distinguished:
- Cuboid (from 12 to 15%), the densest.
- Regular (18–35%), with an average distance between particles.
- Flaky (from 25%), with a high content of grains with a lamellar or needle shape (width and thickness less than 3 times the length).
But the main indicator that determines the properties of crushed stone for concrete remains the size of the fractions. The standard ones include: from 3 to 8 mm (eurocrushed stone), 5–20, 10–20, 20–40, 25–60, 20–70, 40–70. Crushed stone with fractions from 5 to 10, 10–15, 15–20, 70–120, 100–300 is considered non-standard. How smaller size, the more expensive the building material, this is due to the complexity technological process when crushing it and more thoroughly sifting. In some cases, it is possible to mix a coarse fraction of crushed stone and small stone chips, the latter being used as an accompanying filler.
The most popular sizes are 20–40 mm, this is due to the low cost of this brand, but for pouring a foundation or when high requirements for the strength of concrete, it is better to buy backfill with grains from 5 to 10 mm or 5–20.
Markings
Depending on the frost resistance of the material, they are distinguished: F15, F25, F50, F100, F150, F200, F300, F400. The grade is not related to the size of the crushed stone fraction and is determined by the number of cycles of thawing or defrosting or saturation and drying in a solution of sodium sulfate. For mixing concrete, the optimal frost resistance is 300 or more (this is sufficient for pouring foundations and frequently used external structures). This indicator must be written down in the crushed stone passport, as well as the size of the fractions.
The main marking implies strength source material during compression, crushability when crushing rock and the degree of wear during grinding in a drum. The indicator indicates the resistance of concrete external influences like the weight of a vehicle or the load on a foundation. High-strength crushed stone grades include M1200–1400, very weak grades include M200; the norm is considered to be the percentage of grains obtained from weak rocks (when compressed in a water-saturated state of up to 20 MPa). For comparison, in the M300 this figure exceeds 15%, in the M1400 - no more than 5.
The ratio of crushed stone and concrete grades
The strength of the solution is determined by its fillers, the characteristics of which are indicated in the attached instructions or on the packaging. In practice, this means that M400 cement will not produce M500 or higher concrete; the corresponding ratio of grades is presented in the table:
Determining the strength of concrete depending on the fraction of crushed stone is approximate, but deviations are allowed. The latter are regulated by changing the ratio of sand or cement, adding granite chips. But in general, to obtain the required grade, it is important to observe strict proportions of the solution. Before choosing what crushed stone is needed for concrete, it is recommended to determine the intended purpose of the structure and calculate future loads. For a solution up to M250, gravel is sufficient; the use of non-standard sizes grains High-strength grades (M300 and more) require the addition of granite screenings, preferably with square fractions up to 20.
According to building regulations, the content of crushed stone with increased coarseness in the mixture varies from 1 to 20%, and undersized crushed stone should be within 20% of the total mass. If crushed stone with a fraction of up to 20 mm is used for concrete, problems with the distribution of voids do not arise. When this indicator increases to 40 mm, another type of filler (with different, smaller grain sizes) should be added to the solution. Accordingly, choosing a filler with a grain size of up to 70 mm implies adding at least three different options crushed stone fractions. The size cannot be less than 2/3 of the distance between the longitudinal reinforcement, but also no more than 30% of the smallest element of the building structure.
Examples of using
Fine-grained mixtures are needed in the manufacture decorative items made of concrete, artificial stone, paving slabs, it is also added to the composition for asphalt or other road surface. The use of too fine filler for pouring foundations and structures load-bearing walls not economically feasible, plus the risk of shrinkage and deformation increases. The medium and most popular crushed stone fraction (20–40 and 10–20) is better suited for creating large and small concrete structures. This perfect option for pouring the foundation. To prepare a high-quality solution, you should use a concrete mixer; it is difficult to achieve uniformity when mixing crushed stone, sand and binder cement manually.
Material with a fraction from 40 to 70 is classified as coarse-grain, and is needed when constructing massive buildings and mixing concrete in large volumes. It is better not to add it to solutions when pouring the foundation without adding auxiliary fillers of other sizes. Such material is difficult to obtain, the required quantity is calculated in advance, and its delivery is ordered separately. Crushed stone with a coarse fraction of 100 mm or more is called rubble or building stone; it is used mainly for decorative purposes, and not for preparing concrete. The same applies to small granite chips, but the latter is indispensable when creating self-leveling floors and as an auxiliary additive.
Particular attention is paid to the choice of filler when making mortar for pouring the foundation. The base can withstand maximum loads, therefore for of this type work requires concrete with a strength of at least M300. Accordingly, you need a granite filler of at least M1200, although for country houses gravel may be added. Recommended fractions of crushed stone for the foundation: 5–10, 10–20, 20–40, it is advisable to buy grades with square shape grains