Concrete composition - how to choose the concrete composition?

tender platform ready-mixed concrete

The Lenbeton company is the first tender site for the sale of concrete in St. Petersburg. Our Company was created by a group of professionals with extensive experience in construction industry. We believe that this format of working with a client is an optimal and honest scheme for partnership relationships.

IN classic version Concrete contains components such as binders, water and fillers. Today construction industry It also complements it with various plasticizers, water repellents and other additives that allow construction work to be carried out in the off-season, and also improve the technical characteristics of this material.

GOST and concrete

GOST strictly defines the proportions in the composition of concrete and, depending on this, divides this building material into types. The ratio of components depends on the brand of cement used, sand moisture content, and filler fractions. The most common brand of concrete is 200. This brand of concrete has the following composition: cement M400 - 1 part, water - 3 parts, filler - 5 parts. Since the main binders in concrete are water and cement, before you buy concrete, you need to understand this technical indicator, as W/C (water-cement module or water-cement ratio)

The strength of concrete is inversely proportional to W/C - the lower this indicator, the stronger the building material. For concrete, it is enough for the W/C to be equal to 0.2, but such concrete will not be sufficiently plastic, so when selecting concrete, stop at a water-cement ratio of 0.3-0.5.

GOST regulates concrete according to:

• purpose - for ASG, as well as special ones (decorative, hydraulic, road, heat-resistant, etc.);
• mind binder material– skinny, fat, marketable;
• type of filler - here they are similar;
• structure - large-porous, cellular, dense and porous;
• hardening conditions - natural or special conditions;
• volumetric mass– light, especially light, lightweight, heavy and especially heavy;

Why is there crushed stone in concrete?

The most common filler in concrete is crushed stone. Depending on the size of granite obtained as a result of crushing, it is graded from fine to coarse. However, consumers are most often not aware that not only the particle size is regulated by SNiP. An important indicator is also the content of needle-shaped and lamellar grains per unit volume. It is the shape of the grain that determines the groups of crushed stone:

• cuboid – 12-15%;
• regular -18-25%;
• flakier - over 25%.

Here the percentage determines the ratio of the mass of grains of a given surface to the mass of a unit volume (density). Crushed stone must be added to concrete not only to save cement. This is mainly done for better adhesion of the solution, since the rough surface of the crushed stone particles and their acute angular shape contribute to the bonding of all components of concrete.

Why is there reinforcement in concrete?

Even under low loads, concrete structures are destroyed. A steel tensile rod works 100-200 times better. Therefore, in order for the entire concrete structure to work as a single whole, one or more reinforcing bars are inserted into the concrete. Further, under the action of vibration compaction, air pockets are almost completely removed from the concrete, and at the same time the adhesion force between the steel rods and the concrete increases.

As a result, the bending, compressive and tensile strength increases, and the temperature deformation of the concrete structure is also extremely low. Depending on the diameter and cross-sectional profile (with or without moon-shaped protrusions), the reinforcement is divided into classes from A-1 to At-7. And if class A-1 is used in non-stressed structures more often as mounting element for welding meshes, then At (melted from thermally compacted steels) is used when installing concrete structures operating in aggressive environments.

Whatever class of reinforcement or other embedded materials is used in concrete, this building material is economical, fire-resistant, technologically advanced, and also has significant indicators of biological and chemical resistance, and frost resistance.

Why is ammonia added to concrete?

If you need to buy concrete with delivery, then it is very important to study the certification documents for this material. Since unscrupulous manufacturers add to concrete to speed up the hardening process various mixtures with a high content of calcium nitrate.

And although they contain a small content of ammonium salts, which prevent the formation of lumps of calcium nitrate, ammonia gas is released as a result of the interaction. Moreover, the more ammonium salts added to concrete, the more pronounced the smell of ammonia.

Living or working in such premises can result in irreversible health consequences, so selecting the composition of concrete consists not only of knowing the brand of this building material, but also of carefully studying the reputation of the manufacturer, and seriously familiarizing yourself with the certificate for the required products.

Reinforced concrete: a gift to the construction industry from a botanist

In 1867, the French horticulturist Monier discovered and patented reinforced concrete. When making cement pots for plants, he accidentally added pieces of metal and was surprised at the solidity and durability of these products.

Today, reinforced concrete is the most important building material, which is a composite material that includes concrete and steel. The fact is that concrete itself works perfectly in compression, and steel, as you know, works in tension. Combining these materials into a single whole will allow achieving high levels of strength, endurance, seismic resistance, fatigue failure and many others.

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Crushed stone as a necessary element of concrete mortar

10/27/2014 There are various fillers for concrete. Among them, crushed stone is often the leader. Let's consider this situation in more detail. The stone from which concrete is made has its own strength. This strength compared to the strength of ready-made cement will be much higher. And it would seem that this is wonderful, because work done with such concrete would live for many centuries, like mountains, but there is a major nuance here. Creating buildings from such huge stone blocks would be very inconvenient, labor-intensive and practically impossible, which is why humanity invented concrete, and in fact, concrete was used for filling. Crushed stone, acting as a filler, performs its functions at a high level. It is also called coarse aggregate, fine aggregate is sand. The quality of the finished concrete will directly depend on the quality of the crushed stone produced. Therefore, the filler should read information about it, its size and its manufacturer. So why does concrete need crushed stone? Concrete itself cannot be used without filler, since its volumetric shrinkage would not allow pouring the solution and maintaining its shape. Without filler, concrete could not be shaped; it would simply flow as it hardened. To prevent this from happening when working with concrete, fillers such as crushed stone and sand are used. Crushed stone is classified as a coarse filler, sand as a fine filler. The more work is required in the thickness of the layer of poured concrete, the naturally thicker the filler is selected. The volume of the filler is also often called the fraction. Without a special filler such as crushed stone, the strength of concrete could not be recorded. Crushed stone improves the overall strength of the mortar, from which the required work is then produced. Crushed stone also has its own strength. It directly depends on the type of stone used in the manufacture of this product. If the issue of working with high-quality concrete is now on your top priority, do not buy crushed stone without thinking about it and reading about its characteristics. We have already told you why there is crushed stone in concrete, now we will tell you a little about its production. Almost any crushed stone, be it sandstone, granite rocks or limestone, can become a ready-made filler for concrete. So, depending on the type of stone used, crushed stone has a number of characteristics by which one can determine its strength, shape, grain size, and the amount of impurities contained. Crushed stone for concrete is usually divided into three categories: 1. Granite crushed stone (this is crushed stone in the production of which granite was mainly used) 2. Lime crushed stone (which is acquired by crushing limestone) 3. Crushed gravel (a product obtained by crushing rocks or sifted through granite rock) The category of crushed stone itself can also differ according to radioactivity and grain size.

Don’t be afraid to use such materials for the first time. This type of work is the most common, and simply by carefully making the solution and adhering to the required standards, the result will undoubtedly satisfy you.

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Ode to concrete

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09.09.2012 21:03

WHAT YOU NEED TO KNOW ABOUT CONCRETE.

“Live forever and learn” - (proverb).

“I know that I know nothing” (ancient Greek thinker Socrates).

These epigraphs are intended for those builders and customers who have decided that they know everything about concrete, since they have been working on construction sites for many years. Besides, in Russian society There is a stereotype that a builder is the simplest profession, and a concrete worker is the simplest of all construction professions. The specialists of the Credo company will not enter into an argument with those who think so. But they cannot indifferently observe how ignorantly builders and non-builders sometimes handle concrete. And with their illiteracy they not only spoil high-quality and expensive material, causing direct damage to the customer or themselves, but also discredit a conscientious concrete manufacturer, convincing the customer that the concrete was of poor quality.

For the convenience of the reader, the article will be structured in the form of questions and answers. Moreover, most of the questions were dictated by practice.

What is concrete?

It would seem a simple question. But few can give the correct answer to it. Concrete is artificial stone material. It uses the best properties of stone - its strength. But why can't you just use stone? Because it is very labor-intensive and expensive, and sometimes it is simply impossible to give the stone the required form or size. For example, there are stone (granite) curbs and there are concrete curbs. Everyone understands that a concrete curb is cheaper. It is easier to shape concrete into the desired shape than to process granite. Well, it’s hard to imagine an interfloor ceiling made of stone. Perhaps only vaulted stone ceilings on small spans. Or it’s completely difficult to find a stone 12 meters long or more. And we see reinforced concrete beams of this length on almost every bridge. In addition, both stone and concrete do not withstand tensile loads well. But if reinforcement is inserted into the concrete, then the tensile forces on the concrete will be absorbed by the reinforcement located inside the concrete. Everyone understands that inserting reinforcement inside a stone and gluing it to it is also very labor-intensive and expensive.

What is included in concrete?

Concrete consists of three main components - binder, water and aggregate. For brevity, we will simply call the astringent “astringent.” We will talk about the most common construction concrete– cement concrete. From the name itself it is clear that cement is used as a binder in cement concrete. For brevity, we will simply call cement concrete “concrete.” There are many types of cement. We will not consider its varieties. This is a topic for separate study and is of more interest to concrete producers and other specialists. The main types of aggregates are crushed stone, gravel and sand. Crushed stone differs from gravel in that it is crushed material. In our area, most often it is a product of crushing the same gravel, but separated by fractions, i.e. by size. Gravel concrete is slightly cheaper because gravel is cheaper than crushed stone. Concrete up to certain grades is made from gravel. The main characteristics of crushed stone and gravel are size and strength. Sand can be coarse-grained or fine-grained. Fillers must be selected in strictly defined proportions. In a simplified way, we can imagine that the voids between the particles of crushed stone or gravel should be filled with sand, and the voids between the sand particles should be filled with cement. Builders do the right thing when they purchase a ready-made gravel or crushed stone mixture (GPS or ShchPS) to prepare concrete on site. When producing them in a factory, the crushed stone-sand or gravel-sand ratio is optimal.

What qualities should concrete have?

The main physical characteristic of concrete is its strength. It is measured with special instruments when the concrete reaches the age of 28 days. Strength is measured in units of pressure. The most understandable and familiar to most people is the unit of measurement of strength in kilograms per square centimeter(kg/cm2). For example, a strength of 100 kg/cm2 means that concrete collapses when exposed to a pressure of 100 kg/cm2. Previously, and often now, this strength meant the grade of concrete. For example, 100 kg/cm2 meant M100, etc. According to the new GOST, the concept of “concrete class” was introduced, which takes into account not only strength, but also some other characteristics. But in this article, for simplicity, we will equate the concept of “concrete grade” and “concrete class”. For example, concrete grade M100, concrete class B7.5. There are special tables for matching the grade and class of concrete. For the convenience of buyers, many manufacturers indicate both the brand and class of concrete in their price lists. For example: concrete B 7.5 (M100). In addition to strength, concrete has other physical characteristics. For example, water resistance, frost resistance and others. The names of the characteristics speak for themselves. Frost resistance means the amount of alternating freezing and thawing that concrete can withstand without collapsing. Water resistance is the ability of concrete to prevent water from penetrating through it. Frost resistance and water resistance are closely related to each other.

What is cement and why is it needed in concrete?

The first mention of cement appeared relatively recently - in 1844. Although in one form or another (for example, volcanic ash) cement has been known since ancient times. In a simplified way, cement production can be represented as follows. Crushed rock of a special composition (marl) is fired in a kiln. During the firing process, chemically combined water is removed from the marl. As a result, clinker is formed. It is ground in special ball mills to a powder state. This powder is cement. When a strictly defined amount of water is added to cement, it turns back into stone.

Why are crushed stone and sand needed in concrete?

Indeed, if you add water, the cement will turn into stone. Answer: do fake diamond only made from cement is both expensive and difficult. In addition, the cement itself gives large shrinkage. Therefore, aggregates are added to concrete: crushed stone or gravel and sand.

What happens if you put an arbitrary amount of aggregates into concrete?

There will be concrete. But it is no longer the quality that the manufacturer wanted to achieve from it. If you put an excess amount of crushed stone, then there will be voids in the concrete that are not filled with sand and cement. Accordingly, the required strength will not be obtained. If there is more sand than normal, then the cement contained in the concrete will not be enough to “coat” each grain of sand, and the grains of sand will not stick to each other. Accordingly, strength will suffer again. You can add more cement, i.e., in excess. But then the economy will suffer. This will be very expensive concrete. The proportions of the components in concrete are selected by specialists in the laboratory. These proportions are called “selections”.

How much water should be added to concrete?

The amount of water is also determined in the laboratory. For cement to turn into stone, only 13% of the weight of cement is water. But in fact, during the production of concrete, a larger amount is added. The ratio of the amount of water to the amount of cement by weight is called the water-cement ratio (WC). In practice, it ranges from 0.3 to 0.4. If the VC is made smaller, it will be impossible to work with concrete manually. It will be very hard, thick, dry. It will be impossible to fit it into the structure. Such concrete is used mainly for vibrocompression, for example, in the manufacture of paving slabs or curbs. But with an increase in the amount of water, the quality of concrete deteriorates: its strength, water resistance, frost resistance. What to do? To reduce the amount of water in concrete and at the same time ensure such qualities as workability, chemical additives called “plasticizers” and “superplasticizers” are used.

How is workability measured?

The indicator of concrete that reflects its workability is called “workability”. Previously, the term “plasticity” could also be found. Mobility is measured with special instruments and designated as follows: P1, P2, etc.

Is it possible to make selections of concrete composition that are uniform for the entire country?

No, because in every locality there are different breeds and quality crushed stone, gravel, sand, water, cement. And all concrete selections are made for each specific case. The quality of materials changes, selections need to change.

Why does concrete defrost?

A characteristic that reflects the resistance of concrete to alternate freezing and thawing is called “frost resistance.” Frost resistance is measured by the number of cycles of alternating freezing and thawing, as a result of which the concrete begins to collapse. Frost resistance is designated as follows: F150, F200, etc. This means that concrete can withstand 150 cycles of alternating freezing and thawing, and then can collapse. The more water in concrete, the less its frost resistance. Therefore, vibropressed paving slabs have greater frost resistance. The worse the gravel, crushed stone or sand (dirty, fragile, not frost-resistant), the less frost resistance of concrete. Many have watched concrete from dirty local river gravel defrost.

Why can't you add water to the ready-mixed concrete that the supplier brought?

When ordering concrete, the buyer must indicate its mobility in addition to the class of concrete. The manufacturer, guided by economic considerations, produces concrete with the ordered characteristics with a minimum strength reserve. Therefore, when concrete arrives at the site, all components are in the ratio and quantity required for this class of concrete, including water. By adding additional water, builders increase the VT and thereby reduce the ordered and paid for characteristics. In other words, the buyer pays for a high-grade concrete, but it ends up in the structure with underrated characteristics. Conclusion: you cannot add water to delivered concrete at a construction site. Sometimes, for various reasons, such a need nevertheless arises. For example, the builders did not have time to prepare the formwork or for other reasons. The concrete has thickened. Then the buyer needs to contact the concrete supplier for advice. And the supplier’s technologist (and a bona fide manufacturer should have such a specialist) will tell you what to do. You need to contact the technologist of the exact supplier from whom you purchased the concrete. He is the one who knows what components are used in the production of this concrete and what needs to be done to preserve the quality of the concrete.

Does concrete need to be maintained?

Quality care behind concrete is no less important than its high quality manufacturing. Some customers and builders are mistaken in believing that if the concrete is of high quality, then nothing can spoil it. The addition of water has already been written above. Now let's talk about preserving the water (or moisture) that is already present in the concrete. As already stated, in order for concrete to turn into stone, water is needed. If builders do not ensure that water is retained in the concrete laid into the structure, then it will not have the strength that was ordered. What needs to be done for this? The concrete needs to be covered. Especially in sunny or windy weather. The wind often causes more damage than the sun. When water evaporates from concrete, there will not be enough water in it for the concrete to gain strength. The concrete will “dry out” and will never gain the strength that was planned. With intense evaporation of water, concrete cracks, as it shrinks sharply. After concrete cracks, water evaporates even more intensely through the cracks. In the future, during operation, water may enter the cracks, and the concrete will defrost. Through cracks in the concrete, water and air enter the reinforcement, and it rusts and collapses. You cannot watch and wait to see if concrete begins to crack. Once it starts, the process cannot be stopped. It is necessary to cover the concrete immediately after laying, as soon as the film of water disappears from its surface; we call this state of concrete the word “shake”. At different times of the year and in different weather, this time can range from several minutes to several hours. The experience, qualifications and dexterity of concrete workers are very important here. A mistake is made by those who replace covering the concrete with watering it. Firstly, cement is washed out from the concrete surface, and secondly, upper layer concrete becomes waterlogged (VC increases). The consequence is that the concrete will “crumble” and peel off. What should you cover with? Any vapor-proof material. For example, polyethylene film. But the covering process is very labor-intensive. It is necessary to cover the concrete so as not to disturb its surface, if possible. The film must be secured to prevent it from being blown away by the wind. It is necessary to constantly monitor the position of the film. This is especially labor-intensive large areas, for example, on floors, road surfaces, etc. What is the solution? Very simple. Now many manufacturers of concrete additives produce concrete care products. This liquid materials, which are applied to the surface of the concrete as soon as it is shaken, using a conventional construction or garden sprayer (sprayer). Most often it is a liquid that has the color and consistency of milk. After application to concrete, the liquid dries and turns into a film. These materials are called “film-forming materials.” This film allows you to retain water in concrete both in the sun and in the wind. As you understand, the wind does not blow it away. At first glance, it seems that the use of this material is expensive. But this is at first glance. If you count the cost polyethylene film, the complexity of its installation, preservation, cleaning, storage, take into account the disturbed concrete surface or the cost of water, work on its spraying, water damage, then it will become clear that the use of film-forming materials is beneficial. Subsequently, this film evaporates and any material can be applied to the concrete. Decoration Materials, including tiles, without additional preparation. Conscientious concrete manufacturers often sell these materials themselves. Most often, they do this not with the goal of making money, but with the goal of helping builders and thereby maintaining their business reputation, since the concrete will be better preserved and the customer will not have any complaints.

Often concrete loses moisture due to the fact that it is laid on an unprepared base or formwork. Sometimes the base for concrete is crushed stone or sand. If this material is dry, then it is able to absorb a large number of water. For example, crushed stone from Gelendzhik quarries absorbs a very large amount of water. After laying the concrete, moisture from the concrete in the area of ​​its contact with the base is intensively absorbed into the base material. As a result, the concrete quickly dehydrates and cracks in front of the amazed builders, who have no choice but to blame the concrete manufacturer and cover up the cracks, which can change nothing. No amount of watering and covering will help, because shrinkage cracks form from the bottom of the concrete. The same thing happens when concrete comes into contact with dry wooden formwork. Which exit? The base for concrete must be moistened “to capacity,” that is, until it stops absorbing water, while avoiding the formation of puddles on the base. Those builders who lightly sprinkle water on the base, for example, from a mixer, deceive themselves and the customer. This is not enough. The formwork must be lubricated special materials, for example, emulsol, processing. This is done not only to prevent concrete from sticking to the formwork, but also to prevent moisture from being absorbed. If there is no emulsol or waste, then it is necessary to heavily moisten the formwork, again avoiding puddles on horizontal surfaces. The exception is formwork made of laminated plywood or metal. The water doesn't go anywhere in it.

Another enemy of concrete is frost. In order for concrete to become stone, positive temperatures are required. In laboratory conditions, the temperature is maintained at around 20 degrees Celsius. It is under these conditions that it is believed that concrete will gain its design strength after 28 days. The higher the temperature, the faster concrete will gain strength. At the same time, we must not forget about the need to preserve moisture in the concrete. But a rapid increase in temperature when heating concrete is also harmful. Internal (not visible to the eye) stresses and destruction occur in concrete. This is important to know not only for those who use concrete heating. When concrete hardens, chemical reaction with heat release. At small structures this is only good for concrete. With very large, massive structures (most often in industrial construction, for example, powerful foundations), the concrete heats up so much that it needs to be cooled, for example, by pouring water. Sometimes they lay inside the concrete special pipes, water is pumped through them and thereby cools it.

So, concrete must be preserved from low temperatures. This is achieved by covering the concrete with films, matting, snow, etc. or warm it up. Concrete must arrive at the site at a temperature of at least 5 degrees. Celsius. To protect concrete from freezing before it is covered or heated, special antifreeze additives are used during its manufacture. They are designed for different temperatures: -5, -10, -15 degrees. etc. and significantly increase the cost of concrete. But these additives protect concrete from freezing only during the work process. In the future, for concrete to harden, it needs a positive temperature, i.e. it is necessary either to cover and thus preserve the heat that concrete releases during hardening, or to heat it up.

In this article, we touched only on those rules, non-compliance with which by builders can damage the business reputation of the concrete manufacturer and damage customers. In fact, the science of concrete is a serious discipline that is constantly evolving and requires long-term study. Practicing builders need to have a much smaller amount of knowledge about concrete and the rules for its use than science has, but a much larger amount of information than is presented in this article. The goal of the authors of the article was to arouse interest among that part of builders and customers who do not even have the information presented in this article, and to encourage them to independently study the secrets of the concrete profession. For those who already know everything stated above, the authors can only point out two points: 1. repetition is the mother of learning; 2. nothing stands still, everything is developing, including construction science.

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 making concrete and iron 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 rock. Extraction occurs in quarries and often through blasting.

Classification

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

Used as

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

It is important to distinguish this building material from gravel. Gravel is fragments of rock 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 exposure to conditions external environment and resistant to stress. It is used to produce particularly hard concrete.
• Gravel. They are mined in quarries or from the bottom of reservoirs ( Sand and gravel). This type has a lower price, but is inferior in quality to granite. Crushed stone obtained by crushing gravel from a quarry is preferable to that obtained 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 grip sand-cement mortar. In the construction of low-rise buildings and in country house 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 light loads. The main advantage is low price.
• Secondary- obtained by crushing recycled concrete products.

Limestone crushed stone is susceptible negative impact water - dissolution (especially in an acidic environment).

The secondary type 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 Flakiness 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 crushed stone fraction sizes

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

Cannot create strong concrete using poor crushed stone.

You cannot use crushed stone with the same fraction sizes. Because 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! The 5-20 mm fraction is considered universal.

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

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

The composition of concrete includes components different types, which provide its main properties. There are three main components, each of which gives the material certain properties. These include, in particular, water as a filler and cement. Additives should also be mentioned here. They are not always used, which must be taken into account. Why is additional material needed? This procedure provides greater strength to the concrete. If there is a need to introduce such a component, you need to carefully read state standards on the brand and a substance to enhance the parameters.

Crushed stone as an additional component provides greater strength to concrete.

Handling crushed stone quickly and affordably! Crushed stone is one of the types of concrete aggregates that are used quite often.

The reason for this is the fairly high performance characteristics, which crushed stone has. For example, the strength of a material of this type can reach 1000 MPa or even higher. Everything depends on the specific breed and its characteristics. It is necessary to consider this type of material in more detail, since it requires a special approach.

For foundations and structures made of heavy concrete, gravel and crushed stone are used as coarse aggregates for concrete from dense rocks in accordance with GOST 8267, from ferroalloy and blast furnace slags of ferrous metallurgy and copper smelting and nickel slags of non-ferrous metallurgy in accordance with GOST 5578 and, finally, from thermal power plant slags, GOST 26644.

Mining Features

Crushed stone is mined in the following way: hard rocks are crushed, after which a separation is made depending on the size of the grains and a fraction is established.

Crushed stone is mined in the following way: hard rocks are crushed, after which a separation is made depending on the size of the grains and a fraction is established. Sometimes it is mined in a quarry, using the sifting method. On the territory of the Russian Federation, crushed stone is mined in the largest quantities in the quarries of the Urals, here are some of them:

• Syrostankinsky quarry;
• Medvedevsky quarry;
• Satka field;
• Mednogorskoye field;
• Maly Kubais mine;
• Novosmolinsky quarry;
• Mochischensky plant;
• Rezhevsky plant;
• Kazantsevsky quarry;
• Timofeevsky quarry, etc.

The shape of individual stones is very important for the production of concrete: the more cube-shaped the stone, the more of them will fit into a given volume. On the contrary, the presence of needle-shaped elements reduces the quality of the fill. Standard size, which one fraction has, is equal to 5 to 20 mm. Crushed stone for concrete, the fraction of which falls within these limits, makes it possible to significantly increase the performance properties of concrete, and in addition, also provides a large number of other advantages. For the production of high-grade compositions, crushed stone of larger sizes is used. This makes it possible to increase the strength indicator, but at the same time, the cost of such material also increases.

Limit of harmful substances content

There is an acceptable percentage of minerals and rocks that are considered harmful impurities in the additive material for concrete:

• sulfur, sulfides (except for pyrite) and sulfates (anhydrite, gypsum, etc.) in terms of SO3 no more than 1.5% for coarse aggregate by weight and up to 1.0% for fine aggregate by weight;
• amorphous types of silicon dioxide, which dissolves in alkalis (opal, chalcedony, flint) - no more than 50 mmol/l;
• layered silicates (chlorite, mica, hydromica, etc., which are rock-forming minerals) - no more than 15% for coarse aggregate by volume and for fine aggregate - no more than 2% by weight;
• pyrite in terms of SO3 – not higher than 4% by weight;
• halogens (sylvine, halite, etc.), which also includes water-soluble chlorides, when converted to chlorine ion: not more than 0.1% for coarse aggregate by weight and not more than 0.15% for fine aggregate by weight;
• magnetite, apatite, iron hydroxides (goethite, etc.), phosphorite, nepheline, which are the minerals that form the rock - no more than 10% each individually and no more than 15% in total by volume;
• coal – not higher than 1% by weight;
• free asbestos fiber – not higher than 0.25 by weight.

The content of clay and dust particles from metamorphic and igneous rocks should not exceed 1% by weight - for concrete of all classes. The content of clay and dust particles in crushed stone from sedimentary rock should not be more than 2% by weight for concrete of class B22 and above, no more than 3% by weight for concrete of class B20 and below. The content of flaky grains in crushed stone should not exceed 35% by weight.

The following types are distinguished:

• granite;
• gravel;
• the most common type is limestone.

Granite

Granite is best used as a filler for high-quality concrete mixtures that are used when pouring road, bridge and airfield pavements.

• Which nonmetallic material is the strongest and best ensures the strength of concrete? Granite. It is obtained by crushing natural granite, whose fragments, after a directed explosion, are ground in a special unit. Granite crushed stone is best used as a filler for high-quality concrete mixtures that are used when pouring:
• road and airfield pavement and a number of other types of work. In this case, great attention is paid to the ability to withstand serious dynamic loads;
• bridge deck and other bridge structures. It should be noted that crushed stone for concrete in this case will be additionally affected by variable water levels, which is a serious problem;
• critical areas such as walls, columns and floor slabs that carry heavy loads. In such cases, crushed stone must guarantee the ability to withstand not only static pressure, but also dynamic pressure, which is important during operation.

Quality parameters:

• density;
• fraction;
• compressive strength;
• flakiness.

Material fractions

The fraction in the range of 5-20 mm is the smallest fraction; it provides high durability and reliability of the foundation.

Granite should have fractions ranging from 5 to 150 mm:

• the fraction less than 5 mm is called granite screening. It has small grains and is used as decorative design flowerpots, flower beds, lawns, etc. This is used quite rarely as an additional component in concrete. The use of this fraction is permitted when used as a fine sand aggregate with a particle size modulus of no more than 2.5;
• the fraction in the range of 5-20 mm is the smallest fraction that is best used. It is used in the construction of reinforced concrete products, bridge construction 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 characteristics, its grade ranges from 1200 to 1400, frost resistance is up to 400 cycles. Its flakiness is low, equal to only 15-18%.

Flakiness is a characteristic of grain shape; it is expressed as the percentage of needle-shaped and plate-shaped grains from the total mass.

It is possible to increase all these characteristics if you use only selected stone that has no flaws. The absence of deformation makes it possible to improve the structure and make the monolithic mass more durable.

Application

The addition of gravel to concrete is widely used in foundation construction, road construction and the production of reinforced concrete products.

Crushed gravel is obtained by sifting quarry rock or crushing natural rocks. This material is inferior in strength to granite filler. Why use it in this case, you ask? Unlike granite, this one is more affordable. The addition of gravel to concrete is widely used in foundation construction, road construction and the production of reinforced concrete products. Gravel is divided into several types:

• gravel having rounded grains, which became such under the influence of sea or river water.
• crushed, crushed or natural.

It is also divided depending on the size of the fractions:

• fine – grains up to 10 mm.
• medium – grains from 10 to 20 mm.
• large – grain size does not exceed 40 mm.

Limestone

The frost resistance of crushed limestone is only 50-100 cycles, which makes it impossible to use this material in capital construction at high latitudes.

Limestone is one of the most readily available additive materials used in construction. It contains calcite, which is why the material has the appearance of white stones, the shade of which depends on impurities and can vary: from quartz, iron or clay.

Limestone can be divided into several groups depending on the strength class:

1. M 300-600 – produced mainly from limestone.
2. M 600-800 is the result of processing dolomite and limestone. He is characterized by high performance and large size fractions.
3. M 200 is a group practically not used in concrete production due to the high cost of crushed stone for this type of material. 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.

Any concrete mixture includes a number of components on which its main characteristics depend. Of these, three components are required: water, cement and filler. Crushed stone, which has excellent performance parameters, is usually used as a filler.

To obtain particularly high-strength concrete, high-quality crushed stone is used, the strength of which can reach 1000 MPa or more. This value is determined by what material is used to produce crushed stone and what its features are. Let's consider what kind of crushed stone can be used as the basis for producing a concrete mixture.

Types of crushed stone used to prepare concrete

By type, crushed stone can be:

• cube-shaped;
• having sharp corners;
• wedge-shaped;
• Flaky.

Crushed stone used for concrete can be of artificial or natural origin. Artificial is obtained by processing household slag and construction waste. It is a recycled material, so its cost is low. It is practically not used in construction work; it is used to strengthen weak soils during the construction of not very important roads. Natural crushed stone is obtained by crushing rocks. Right choice crushed stone can reduce soil shrinkage and creep, increase the durability and strength of concrete.

An important characteristic by which the choice is made that is suitable for specific works crushed stone, this is the size of the fractions. This refers to the size of those particles that are most numerous in the material. The smaller the particle size, the lower the fraction number.

When forming a concrete mixture, crushed stone of large fractions is used where it is necessary to ensure high strength of concrete after it has set. Crushed stone of small fractions in the best possible way fills cavities and voids.

Flat and needle-shaped crushed stone reduces the strength of the concrete mixture, and cement consumption also increases. The use of such crushed stone reduces the frost resistance of the finished concrete, so this form of crushed stone is practically not used in construction. Let's take a closer look at the types of crushed stone used in construction work.

Granite crushed stone - the best for concrete

This crushed stone is one of the most durable ore materials. It is obtained by crushing natural granite. For concrete, this type of crushed stone is the most best filler, it is used for those concretes that must have a high grade:

• pavement of roads and airfields;
• the most critical building elements experiencing maximum load(walls, slabs, columns);
• various bridge structures, including bridge deck.

Granite crushed stone is characterized by its quality by the following indicators: density, compressive strength, as well as fractionation, which can range from 5 to 150 mm. The most popular fraction ranges in size from 5 to 20 mm, which is used in the construction of reinforced concrete products, road surfaces and bridges. Its use guarantees a reliable mixture composition and high performance data.

Crushed stone of the medium fraction measuring 40 millimeters is used for the construction of industrial facilities. The large fraction used to create large concrete structures has dimensions of 40-70 mm. Crushed stone of larger forms is used to make rubble concrete foundations.

The operational parameters of granite material indicate its high strength. The grade of such crushed stone can be in the range of 1200-1400, and its frost resistance reaches 400 cycles.

Gravel and limestone material

Crushed stone of gravel type is obtained by sifting quarry rocks or crushing rocks of natural origin. The performance indicators of this material are inferior to granite, but its cost is lower. This filler is actively used in the manufacture of reinforced concrete products, in road works and when creating foundations. According to its fractionation, it can be divided into small, with sizes up to 10 mm, medium (from 10 to 20 mm) and large, with a fraction size up to 40 mm.

Limestone crushed stone is one of the cheapest types of filler. Depending on the accuracy class, this material can be divided into groups:

• M600-M800 - these grades are made from limestone or dolomite, their performance is high, and the fraction sizes are large;
• M300 - M600 - grades obtained from limestone;
• M200 is an expensive brand, so it is not used when producing concrete.

Relationship between concrete grade and crushed stone grade

The main filler can be any hard rock - granite, gravel, limestone, expanded clay, crushed brick and asphalt. But there are some peculiarities in the choice of filler. The strength of a particular filler may greatly limit its use. Thus, it is absolutely impossible to use broken bricks in the manufacture of critical concrete structures.

The grade of solid filler indicates its strength. The correspondence between concrete and filler grades is presented in the table:

Brand of crushed stone	Concrete grade
M1200	M400 - M500
M 1000	M 300
M 800	M 200
M 600	M 100

This table allows for some deviations, which are quite acceptable and are determined by the ratio of sand and cement. In practice, concrete of grade M250 and less is made using gravel, and above M300 granite is used.

Concrete cannot be stronger than its fillers, so it is impossible to obtain M500 concrete from M400 cement. Obtaining the correct concrete measurement depends on the selection of the proportions of its components.

What fraction of crushed stone is needed for concrete?

For the concrete mixture, crushed stone of a fraction of 5-70 mm is used. A finer division forms the subgroups 5-10 mm, 10-20 mm, 20-40 mm and 40-70 mm. For concreting, it is better to use larger crushed stone and gravel, since the used filler will have a smaller specific surface area and exert less pressure on cement mortar, which ensures the required mobility of the mixture.

There are standards according to which high-size filler should make up from one to twenty percent of the mass, and low-size filler should make up no more than 20% of the mixture.

In accordance with SNiP 3.03.01-87, the concrete mixture must contain crushed stone of at least two fractions with a maximum particle size of up to 40 mm, and at least three fractions if the largest particles are 40-70 mm. Maximum size crushed stone should be less than 3/3 minimum distance between longitudinal reinforcing bars. Also, it should not exceed 1/3 of the minimum size of a specific building element, for example, its tape width.

The durability and strength of concrete structures primarily depend not only on how quality materials used, but also on how correctly the mixture is selected. In order to obtain high-quality concrete, it is necessary to take into account all the details of its preparation.

Getting started construction work When using concrete mixtures, it is necessary to clearly understand which fraction of crushed stone is needed for concrete. The mortar filler makes up the largest share of the volume, so crushed stone is no less important than cement for determining the quality of concrete. The durability and strength of concrete depends on crushed stone; it determines the plasticity of the solution, reduces shrinkage and cement consumption, reducing the cost of work.

Concrete crushed stone is selected based on the problems solved during the construction and operation of finished concrete structures. The pressure which is subjected to concrete path differs many times 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-story buildings. And although many factors influence the choice of crushed stone for concrete, there are certain rules that must be followed.

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

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

For concrete floors, paths, blind areas, paving slabs use limestone and secondary types of crushed stone with fine grain grains and increased flakiness. Crushed stone with a lamellar grain shape increases cement consumption and is difficult to compact, 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 plant slag by GOST 26644.

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

Concrete strength grade	Crushed stone strength grade

Granite crushed stone has the greatest strength; its strength corresponds to grades M1200 - M1400, and frost resistance to grade F400. It is used in critical structures requiring high-quality concrete, but is the most expensive.

Crushed gravel is slightly inferior in characteristics, but cheaper than granite, and is classified as 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 production 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 fit into 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 from 5 to 70 mm is used. The finer the crushed stone, the higher its cost, since it requires high production costs.

To fill the foundations for individual cottages, small fractions of crushed stone 3–8 mm are 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. Smallest size formwork rarely reaches 35 cm and the middle fractions fill the reinforced belts worse and form many voids.

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

Large fractions of crushed stone 25-60 mm; 20-70 mm; 40–70 mm is used for large volumes concrete works during 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 faction is almost never used.