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What does crushed stone affect in concrete? Brand of crushed stone for preparing concrete. Granite crushed stone for concrete

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:

1. limestone;
2. gravel, or just gravel;
3. granite;
4. 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?

1. 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.
2. 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.
3. 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 compacting the concrete mixture, the space between large crushed stone particles is occupied by more fine particles coarse aggregate, and the voids between small particles of crushed stone were 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, particles large size have a smaller specific surface area than particles small size 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 iron concrete structures according to GOST 8267-93 in quality control laboratories (department technical control) determine the grain composition check, 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:

1. 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%.
2. 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 specifications" the largest size of crushed stone for a given reinforced concrete structure should be established in the standards, in standard projects, technical conditions or working drawings 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

Selection process correct faction crushed stone, which is briefly given above, concerns mainly 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 shortest 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 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 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 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:

1. The quality (purity, absence of organic impurities) of the aggregate (crushed stone) has a significant impact on the strength of concrete. 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.
2. 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.
3. 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

Concrete is a modern building material for self-made which requires not only to have a table with concrete proportions on 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 kind of crushed stone is needed for concrete? We recommend granite crushed stone of 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 using broken bricks. Conversely, casting paving slabs of average quality using granite crushed stone in concrete is nothing more than an overspending of funds.

Any solid filler - be it granite crushed stone 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 M400 grade cement.

Dependence of concrete grade on crushed stone grade

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

Brand of crushed stone	Concrete grade
M1200	M400-M500
M1000	M300
M800	M200
M600	M100

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

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

The ProBeton company sells and delivers concrete both on gravel and granite crushed stone. In addition, we can sell granite crushed stone and gravel separately.

What fraction of crushed stone is needed for concrete?

Crushed stone is divided into fractions based on size. Fraction is a range of overall cell sizes in a sieve through which crushed stone is poured to sort it. For example, a fraction of 20-40 means that the dimensions of crushed stone range from 20 to 40 mm, i.e. stones of this size successfully “slipped” into the 40x40 mm cell, but did not “get through” into the 20x20 mm cell.

Answering the question of what kind of crushed stone is needed for concrete, let's say frankly: in our concrete we use granite crushed stone of fraction 5-20 - dimensions each pebble ranges from 5 to 20 mm. You can often see how crushed stone of fraction 20-40 is used everywhere as a filler in concrete - this is not entirely justified. Concrete made from crushed stone of this 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 safety margin, you can save a little and use the 20-40 fraction; in all other cases, it is better to overpay a little for the 5-10 or 5-20 fraction, and leave large pieces of granite for road builders as backfill when building roads or railway tracks.

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

Why do you need crushed stone in concrete?

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

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

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

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

1. Presence of several fractions of crushed stone. If there are only large stones in the mixture, then air pockets may appear during the laying process, and therefore the strength will decrease.
2. The maximum size of stones depends on the design features. The fraction must 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 the technical indicators of ready-made mixtures depend:

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

Classification

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

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

Granite

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

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

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

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

Gravel

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

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

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

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

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

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

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

Gravel material has found application in the construction of pedestrian paths, filling reinforced concrete products, 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 crushed stone is usually understood as stones of different sizes, which are obtained from 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 crushed stone for the reason that this material is obtained from construction waste, including old asphalt, bricks, 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 road construction.

Criterias of choice

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

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

Fraction

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

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

The ratio of concrete grade and crushed stone grade

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

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

Granite, limestone or crushed gravel, is an indispensable component concrete solutions determining the brand of building material and, accordingly, the strength and durability of a concrete structure or concrete product.

Crushed stone for preparing concrete mortar

As was said, the strength of crushed stone determines the strength of the final product. In other words, the strength of the foundation, floor slab, column or other structure cannot be higher than the strength of the filler.

In this regard, before considering the question of what fraction of crushed stone is needed for concrete, it is worth citing the dependence of the most popular brands of heavy concrete on the grade of crushed stone:

Crushed stone (brand)	Concrete (grade)
1200	M400-500
1000	M300
800	M200
600	M100

The numbers indicated in the grades of crushed stone and concrete represent the average compressive strength in kg/cm2. As follows from the data presented, for example, using M800 grade crushed stone as a filler, it is impossible to obtain concrete with a strength of 400-500 kg/cm2.

The principle of selecting crushed stone fraction sizes

To ensure a given grade (strength) of concrete, it is unacceptable to use crushed stone with the same fraction sizes. This will lead to the volume of structures being filled unevenly, big amount voids. This reduces tensile, compressive and torsional strength.

Concerning optimal sizes granules, for pouring critical structures (foundations, columns, floor slabs), it is recommended to use a mixture of crushed stone standard sizes“grains” – 5-10 mm and 10-20 mm.

This costs a little more, but the end result is durable, read - durable design. For pouring non-critical (lightly loaded structures): blind area, garden paths etc., it is allowed to use crushed stone of any fraction, including inexpensive granite screenings, broken brick, furnace slag and other “stone” waste.

You should also pay attention to the characteristics of the configuration of individual crushed stone granules, the so-called flakiness. Flakiness characterizes the flatness of elements.

Using crushed stone with to a large extent flakiness leads to an increase in cement consumption and a corresponding increase in construction costs. In addition, such concrete is difficult to compact. In this regard, crushed stone with a significant amount of “flaky” granules is not recommended for the construction of buried foundations. At the same time this excellent material for the construction of blind areas, paths and other concrete platforms.

• If you are limited in the choice of crushed stone fraction, focus on granite material with granule sizes from 5 to 20 mm. Concrete mortars based on it can be called “universal”, so they can be used for the construction of all types of concrete structures and products: bases, foundations, floor slabs, blind areas, columns, etc.
• If you decide to increase the density of concrete by introducing fine crushed stone into it, keep in mind that in this case the consumption of cement increases significantly. This will lead to a significant increase in construction costs. As you know, cement is the most expensive component of concrete.

This article discusses the issue of optimal sizes of crushed stone granules for structures poured with the most common, universal type of building material - heavy concrete. For concrete of other types of concrete (asphalt concrete, perlite concrete, silicate concrete, tuff concrete and other types), the recommended filler sizes will be different.

All mixtures for preparing concrete solutions consist of 3 main components, one of which is called “aggregate” (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, crushed stone of even one type can have various sizes fractions (granules), therefore 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 further exploitation a 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 she's pretty complex configuration, with a dense reinforcement frame, which quite often happens in 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 the same granule sizes cannot be used. This leads to the fact that the “fill” volume will be filled unevenly; the formation of many voids is possible, which naturally reduces strength characteristics concrete (tension, 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.

It is better not to use it for buried foundations, but, for example, for blind areas it is quite suitable.

• 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.