What is crushed stone in concrete. What fraction of crushed stone is needed for concrete? The ratio of the brand of concrete and brand of crushed stone

For the manufacture of a concrete mix, several basic components must be used. This list includes sand, cement, water and aggregate. In the role of the latter, crushed stone is most often used. This building material is represented by several varieties, each of which has its own characteristics.

Why do you need crushed stone in concrete

Crushed stone is a bulk material that is obtained by crushing rocks, including boulders and gravel. In other words, rubble is commonly understood as stones of irregular shape, which can belong to different rocks.

Dealing with the question of why crushed stone is added to concrete, several features need to be emphasized. This building material is not always used during the preparation of a concrete mixture, however, its inclusion in the composition allows us to solve a number of problems:

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

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

1. The presence in the composition of several fractions of crushed stone. If there are only large stones in the mixture, then air pockets may occur during the laying process, and therefore the strength will decrease.
2. The maximum size of the stones depends on the design features. The fraction must be less than ⅔ than the smallest distance between adjacent reinforcing bars. Another 1 calculation option is based on the width of the finished product - the stones should not exceed ⅓ of this indicator.

The main characteristics of crushed stone

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

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

Classification

Loose 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 as a result of crushing non-metallic rocks, most often it is a monolithic rock. The quality of granite building material is regulated by GOST 8267-93. In terms of strength, this material is superior to other types of filler.

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

In construction work, the average 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, mining uses the technology of dispersing rocks after mining from a 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 footpaths, the filling of reinforced concrete products, and the construction of sites.

Limestone

Sedimentary rocks are used to obtain limestone gravel. The stones in this case are calcium carbonate. The advantage is the minimum cost.

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

Due to its low strength, limestone material is of limited use. It is suitable for the construction of paths with a small load, works in the printing and glass industries, and the preparation of cement mortar.

slag

Under the slag rubble, it is customary to understand stones of various sizes, which are obtained from the slag used in production.

• large;
• average;
• small;
• screening.

You can use such a filler for cooking. The most common area of ​​application is thermal insulation.

Secondary

Secondary crushed stone is called for the reason that 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 the low cost.

Among the shortcomings, one can indicate low strength and frost resistance. Despite this, secondary raw 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 chosen carefully. There is no universal option, therefore, when choosing, it is necessary to take into account what concrete is being prepared for.

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

Fraction

When choosing which crushed stone is needed for concrete, you should be extremely careful about the selection of grain sizes. Large stones should be used in those 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 the brand of concrete and brand of crushed stone

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

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

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 of creating this mixture may be different, but the ingredients do not change. Sometimes, for a special type of 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 why is it needed?

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 varieties of crushed stone, each of which is used in a certain type of construction work:

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

Granite crushed stone is considered the most optimal for use in construction. However, it should be borne in mind that it is also the most expensive in terms of price.

Crushed stone is added to concrete for several reasons, one of which is that crushed stone, as a cheaper material compared to cement, but with a high degree of density and hardness, perfectly replaces it when creating a concrete mixture. In addition, crushed stone has other advantages compared to cement. It reduces creep, and the percentage of shrinkage of the mixture. Crushed concrete is much less likely to crack than conventional cement mix, 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 mix, it should be added carefully to the mixture of sand and cement. 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 with increased hardness to it - it will be much more efficient to mix large, medium and small crushed stone with a mixture of sand and cement. This will allow you to produce really strong and reliable concrete, minimizing the amount of cement in the overall mixture.

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

Most often, concrete using crushed stone is produced 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 roads can do without crushed stone of a large fraction.

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

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

Concrete is a modern building material, for the self-production of which it is necessary not only to have a table with concrete proportions at hand, but also to select and purchase the right ingredients: cement, sand in bags or in bulk, and, of course, solid filler - crushed stone or gravel.

The question arises: what crushed stone is needed for concrete? We recommend crushed granite fraction 5-20. But first things first.

Solid fillers

Let's start with the fact that formally any hard rock is suitable as the main filler: crushed granite, gravel, limestone, expanded clay, even crushed brick or asphalt. But there are some nuances here. Each of the listed fillers has a certain strength, which greatly limits the possibilities of application. For example, the construction of a critical structure is unthinkable with the use of broken bricks. Conversely, casting medium quality paving slabs using crushed granite in concrete is nothing more than a cost overrun.

Any solid filler - whether crushed granite or gravel - has its own strength, which is characterized by its brand. Concrete a priori cannot be stronger than fillers. It is impossible to obtain M500 concrete from cement grade M400.

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

So, we present to your attention a table with an approximate correspondence between the brand of crushed stone and the brand of concrete.

A slight deviation in one direction or another is acceptable, regulated by the ratio of sand and cement. To increase the strength of concrete with low strength of crushed stone, more cement is added to the mortar.

In practice, concrete M-250 and below is made using gravel, and concrete grade M-300 and above is mainly made on granite.

The ProBeton company carries out sale and delivery of concrete both on gravel, and on granite crushed stone. In addition, we can sell crushed granite and gravel separately.

What fraction needs crushed stone for concrete?

Crushed stone is divided into fractions according to its size. A fraction is a range of overall dimensions of a cell in a sieve through which crushed stone is poured in order to sort it. For example, a fraction of 20-40 means that the dimensions of the crushed stone range from 20 to 40 mm, i.e. stones of this size successfully “slid” into a 40x40 mm cell, but did not “crawl” into a 20x20 mm cell.

When answering the question of what kind of crushed stone is needed for concrete, let's face it: in our concrete we use crushed granite fraction 5-20 - the overall dimensions of each stone range from 5 to 20 mm. It is often possible to observe how crushed stone of fraction 20-40 is used everywhere as a filler in concrete - this is not entirely justified. Concrete from crushed stone of such a fraction is unevenly filled with solid filler, as a result of which the strength of the cast structure is reduced. If the building is being built with a margin of safety, you can save a little and use a fraction of 20-40, in all other cases it is better to overpay a little for a fraction of 5-10 or 5-20, and leave large pieces of granite to road builders as dumping during road construction or railroad tracks.

When starting construction work using concrete mixtures, it is necessary to clearly understand which fraction will need crushed stone for concrete. The mortar filler makes up the largest proportion of the volume, so crushed stone is no less important than cement in determining the quality of concrete. It is crushed stone that determines the durability and strength of concrete, it determines the plasticity of the solution, reduces shrinkage and consumption of cement, reducing the cost of work.

Concrete crushed stone is selected based on the tasks to be solved during the construction and operation of finished concrete structures. The pressure to which the concrete path is subjected is many times different from the load on the foundation of the building. Just as the conditions for the foundations of light buildings differ from the requirements for the foundations of multi-storey buildings. And although many factors influence the choice of crushed stone for concrete, there are certain rules that must be observed.

To fill the foundation for the construction of a large structure, a mixture of fine fractions of 5 - 20 or 5 - 10 mm crushed granite is used. Cuboid-shaped grains are well rammed together. A large grain of 20 mm gives strength to the solution, and smaller grains from 5 mm fill the voids between the large ones, forming a dense mass. Such concrete has good strength and frost resistance, but increases the consumption of cement.

For foundations for small buildings, crushed gravel of an average fraction of 20-40 mm is suitable. A solution with an average grain size is less plastic and harder to ram and reinforce, but it has a margin of safety and a low price.

For concrete floors, paths, blind areas, paving slabs, limestone and secondary types of crushed stone with fine grains and increased flakiness are used. Crushed stone with a lamellar grain shape increases the consumption of cement, and is poorly compacted, but is the most economical.

The use of crushed stone from rocks is standardized by GOST 8267, from metallurgical slag by GOST 5578, and from thermal power plants of slag by GOST 26644.

Since concrete gains strength within six months or more, the strength of crushed stone is taken three to five grades higher to guarantee reliability.

Gravel crushed stone is slightly inferior in characteristics, but cheaper than granite, and is classified by grades M800 - M1000 and F200. It is used both independently and in a mixture with granite to reduce the cost of construction.

Both types of crushed stone are used for the manufacture of heavy concrete. Limestone, recycled and slag are used to produce lightweight concrete.

The shape of crushed stone grains affects the quality of concrete, the more it resembles a cube, the denser it will lie in a given volume and the greater its strength. The lamellar and needle-shaped grains form a loose solution, are less durable and are less compacted.

In concrete solutions, crushed stone with a grain size of 5 to 70 mm is used. The finer the crushed stone, the higher its cost, since it requires large production costs.

For pouring foundations for individual cottages, fine crushed stone fractions of 3–8 mm are more often used; 5 - 10 mm; 10 - 20 mm and 5 - 20 mm. They are used both alone and for economy, mixed with medium fractions. For pouring a reinforced belt, preference is also given to small fractions of 5 - 10 mm and 10 - 20 mm. The smallest formwork size rarely reaches 35 cm and the middle fractions fill the reinforced belts worse and form many voids.

Crushed stone of an average fraction of 20 - 40 mm is used in the foundations of houses, ceilings, the manufacture of beams, floors, load-bearing structures. It is used both in private construction and for the construction of industrial facilities.

Large fractions of crushed stone 25-60 mm; 20-70 mm; 40–70 mm is used for large volumes of concrete work in the construction of multi-storey buildings. And it is used in a mixture with crushed stone of medium and small fractions. For individual houses, this fraction is almost never used.

When carrying out construction work, it is necessary to carry out a high-quality selection of building materials. It is important to understand their classification and production methods. For the manufacture of concrete and reinforced concrete products, the main component is crushed stone.

Varieties

Crushed stone is a non-metallic material that is obtained by crushing large pieces of hard rocks. Mining takes place in quarries and often by means of blasting.

Classification

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

Used as

• aggregate in the production of concrete;
• for the construction of roads and railways;
• for landscape design;
• for decorative purposes.

It is important to distinguish this building material from gravel. Gravel - rock fragments formed in natural conditions as a result of weathering. It has a rounded shape. In contrast, crushed stone is produced artificially, by crushing, and it has relatively sharp edges.

• granite. The most expensive, because it is the most resistant to environmental conditions and resistant to stress. It is used to produce particularly hard concretes.
• gravel. They are mined in quarries or from the bottom of reservoirs (sand and gravel mixture). This type has a lower price, but is inferior to granite in quality. Crushed stone, mined as a result of crushing gravel from a quarry, is preferable to mined from the bottom of a reservoir. This is due to the fact that its surface is rougher than that of the one mined from the bottom. This improves adhesion to the sand-cement mortar. In the construction of low-rise buildings and in suburban construction, the use of crushed gravel is allowed.
• Limestone(dolomite). It is mined by crushing sedimentary rocks (limestones). It has relatively low strength. This type is used to create reinforced concrete products with a small load. The main advantage is the low price.
• Secondary- obtained by crushing recycled concrete products.

Limestone crushed stone is subject to the negative effects of water - dissolution (especially in an acidic environment).

The secondary view has a low price, but also the lowest quality. The use of this type of building materials in critical structures is not recommended.

An important characteristic of this building material is flakiness - this is an indicator of the shape of the grains (flat or needle-shaped).

The strength of a concrete product directly depends on the strength of the crushed stone used.

Classification by strength grades

• for concrete grade M400-500, crushed stone grade 1200 is used;
• for M300 - 1000;
• for M200 - 800;
• for M100 - 600.

The principle of selecting the size of the crushed stone fraction

• 0-5 mm - a by-product of crushing rocks, used when backfilling tracks;
• 5-10 mm - used for concrete products in conjunction with a larger filler;
• 5-20 mm - the most popular, used to create reinforced concrete products;
• 20-40 mm - middle fraction;
• 25-60 mm - used to create the foundations of railway tracks;
• 40-70 mm - for large concrete structures;
• -70-120 mm - rubble stone, used in the construction of foundations.

It is impossible to create strong concrete using bad gravel.

You can not use crushed stone with the same fraction size. Since this can create voids in the concrete, which will reduce its quality and stability. When creating critical reinforced concrete structures, a mixture of crushed stone of sizes 5-10 mm and 10-20 mm is used.

Reference! Fraction 5-20 mm is considered universal.

Pouring concrete using such a fraction is more expensive, but its quality is higher. It will be more durable. Such crushed stone is suitable for pouring: foundations, slabs, ceilings. For concrete garden paths, any fractions are used. For pouring floors and blind areas, crushed stone of a small fraction is used, since the thickness of the concrete layer is small.

This building material is an important component for the production of concrete. An incorrectly selected fraction of this building material can lead to the creation of a poor-quality reinforced concrete product.