What crushed stone is needed for concrete. How to choose the right fraction of crushed stone for the manufacture of reinforced concrete structures? Granite crushed stone for concrete

Crushed stone is a bulk building material on an inorganic basis with different sizes fractions (grains). Most often, it is used as a non-binding filler in concrete, which allows future structures and their foundations to withstand operational stresses. Crushed stone is added to the solution both in order to reduce its cost, and to give it strength and elasticity after solidification, reduce shrinkage and the risk of deformation.

The material is obtained by crushing rocks or industrial waste, as a result, the stones have various forms and remain rough, which increases their adhesion to cement and sand. The size of fractions of crushed concrete is affected by the maximum value individual elements, it is labeled accordingly, which makes it easier to choose and buy. Depending on this, the solution acquires certain properties, in particular, the addition large breed increases the setting strength, and small stones - the density (contributes to a better filling of voids).

Varieties

This material is classified according to several criteria: the type of raw materials used, the size and shape of crushed particles, frost resistance and strength. Crushed stone is made from hard granite, metallurgical and construction slag, gravel and limestone rocks. The stronger the feedstock, the stronger the load withstands future design. For example, the best option granite will be used for pouring the foundation, and gravel will be optimal in terms of price and quality. Depending on the shape of crushed stone fractions and their percentage in the total mass, there are three types of mixtures:

1. Cuboid (from 12 to 15%), the most dense.
2. Plain (18-35%), with an average distance between particles.
3. Flaky (from 25%), with a high content of grains with a lamellar or needle shape (width and thickness less than 3 times the length).

But the main indicator that determines the properties of crushed stone for concrete is the size of the fractions. The standard ones include: from 3 to 8 mm (euro crushed stone), 5–20, 10–20, 20–40, 25–60, 20–70, 40–70. Crushed stone with fractions from 5 to 10, 10–15, 15–20, 70–120, 100–300 is considered non-standard. How smaller size, the more expensive the building material, this is due to the complication technological process during its crushing and more thorough screening. In some cases, it is allowed to mix a large fraction of crushed stone and fine stone chips, the latter is used as an accompanying filler.

The most popular are sizes of 20-40 mm, this is due to the low cost of such a brand, but for pouring the foundation or with high requirements for concrete strength, it is better to buy backfill with grains from 5 to 10 mm or 5-20.

Markings

Depending on the frost resistance of the material, there are: F15, F25, F50, F100, F150, F200, F300, F400. The brand is not related to the size of the crushed stone fraction and is determined by the number of cycles of thawing or thawing or saturation and drying in a solution of sodium sulfate. For mixing concrete, frost resistance from 300 is optimal (this is enough for pouring the foundation and frequently used external structures). This indicator is necessarily prescribed in the crushed stone passport, as well as the size of the fractions.

The main marking implies strength source material in compression, crushability when crushing the rock and the degree of wear during grinding in the drum. The indicator indicates the resistance of concrete to external influences such as the weight of a vehicle or the load on the foundation. The grades of crushed stone M1200–1400 are classified as high-strength, the M200 grades are considered very weak, the percentage of grains obtained from weak rocks (when compressed in a water-saturated state up to 20 MPa) is considered the norm. For comparison, in the M300 this figure exceeds 15%, in the M1400 - no more than 5%.

The ratio of grades of crushed stone and concrete

The strength of the solution is determined by its fillers, the characteristics of which are indicated in the attached instructions or on the packaging. In practice, this means that concrete M500 or higher will not be obtained from M400 cement, the corresponding grade ratio is presented in the table:

The determination of the strength of concrete depending on the fraction of crushed stone is approximate, but deviations are allowed. The latter are regulated by changing the ratio of sand or cement, adding granite chips. But in general, in order to obtain the required grade, it is important to observe strict proportions of the solution. Before choosing which crushed stone is needed for concrete, it is recommended to determine the intended purpose of the structure and calculate future loads. Gravel is enough for mortar up to M250, it is allowed to use custom sizes grains. High-strength grades (M300 and more) require the addition of granite screenings, preferably with square fractions up to 20.

According to building codes, the content of crushed stone with increased fineness in the mixture varies from 1 to 20%, underestimated - should be within 20% of total weight. If crushed stone of fraction up to 20 mm is used for concrete, there are no problems with the distribution of voids. With an increase in this indicator to 40 mm, another type of filler should be introduced into the solution (with other, smaller grain sizes). Accordingly, the choice of a filler with a grain of up to 70 mm implies the addition of at least three different options rubble fractions. The size cannot be less than 2/3 of the distance between the longitudinal reinforcement, but not more than 30% of the smallest element of the building structure.

Examples of using

Fine-grained mixtures are needed in the manufacture decorative items from concrete, artificial stone, paving slabs, it is also added to the composition for asphalt or other road surface. The use of too fine filler for pouring foundations and structures bearing walls economically impractical, plus the risk of shrinkage and deformation increases. The average and most demanded crushed stone fraction (20–40 and 10–20) is better suited for creating large and small concrete structures. it perfect option for pouring the foundation. To prepare a high-quality mortar, a concrete mixer should be used, it is difficult to achieve uniformity when mixing crushed stone, sand and binder cement manually.

Material with a fraction from 40 to 70 refers to coarse-grained, and is needed when erecting massive buildings and mixing concrete in large volumes. It is better not to introduce it into solutions when pouring the foundation without adding auxiliary fillers with other sizes. Such material is difficult to obtain, the required quantity is calculated in advance, its delivery is ordered separately. Crushed stone with a coarse fraction of 100 mm or more is called buta or building stone, it is used mainly for decorative purposes, and not for concrete preparation. The same applies to fine granite chips, but the latter is indispensable when creating self-leveling floors and as an auxiliary additive.

Particular attention is paid to the choice of filler in the manufacture of mortar for pouring the foundation. The base can withstand maximum loads, so for of this type works require concrete, strength not lower than M300. Accordingly, a granite filler of at least M1200 is needed, although the addition of gravel is allowed for summer cottages. Recommended crushed stone fractions for the foundation: 5–10, 10–20, 20–40, it is advisable to buy grades with square shape grains.

All mixtures for the preparation of concrete solutions consist of 3 main components, one of which is called "aggregate" (filler). As such, they are used various materials, including those with different parameters. Therefore, there can be several answers regarding even crushed stone.

Firstly, the industry produces several types of similar products, which differ both in chemical and structural composition and in certain properties (in particular, strength).

Secondly, crushed stone of even one type can have different sizes of fractions (granules), therefore it is divided into large, small or medium.

Thirdly, it is also important for what purposes the concrete solution is being prepared, what are the specifics of its application and further operation of the structure “created” from it.

For example, if a foundation is to be poured, then the concrete must be strong enough. At the same time, if you use gravel with large fractions, then it will be quite difficult to “pull” the solution along the formwork, compact it (at least manually, at least with a vibrator). And if she's pretty complex configuration, with a dense reinforcing cage, which is quite often the case with individual construction?

For arranging a concrete floor, use the same solution - not in a businesslike way, since you can also prepare a more “cheap” one. In addition, the crushed stone is taken as the smallest, since the thickness of such a floor is usually small.

As can be seen from the above, there are many nuances in choosing gravel for concrete. Therefore, it should be noted right away that one should not be guided by any single recommendation, especially supposedly “knowing everything” people. It is clear that there can be no 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 respective characteristics of the aggregate. For example, it is impossible to obtain M500 concrete from crushed stone of the 600 brand.

For general guidance, we give 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 degree of concrete strength, 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 not true, since this material is not "defining" in this regard.

• To ensure the desired strength of the final product, it is impossible to use a filler with the same size granules. This leads to the fact that the volume of the "fill" will be filled with them unevenly; the formation of many voids is possible, which naturally reduces the strength characteristics of concrete (tensile, displacement, compression).

For foundations for massive structures, experts recommend using not large, but smaller crushed stone (with sizes 5 - 20 and 5 - 10). It will cost a little more, but it will be more reliable. In other cases, take different types gravel (according to the size of the granules) and mix. Small fractions will ensure the filling of voids that form between large ones, therefore, the mass density will increase.

• It is worth paying attention to such a characteristic of gravel as "flakiness". It shows the degree of "flatness" of the stone. More cuboidal pellets 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 gravel is less compacted.

It is better not to use it for deep foundations, but, for example, it is quite suitable for a blind area.

• The peculiarities of our climate make us take into account such characteristics of materials as resistance to low temperatures. According to this “parameter”, crushed stone from granite rocks is the leader among the same type of products.

For our climate, it is not advisable (especially for the foundation) to use crushed stone with an “F” index below 150. Otherwise, it will be necessary to additionally insulate the surfaces, which is associated with both material and time costs.

• Now 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 the 250th grade, 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 required for the construction of the foundation, then granite crushed stone should be used as a filler.
In case of limited options for choosing products, one should focus on crushed granite 5 - 20. Solutions based on it are more versatile and can be used for various kinds works (bases, ceilings, blind areas and in some other cases).
If you increase the density by using smaller fractions, then you need to take into account that the binder (cement) will need much more. 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 granite and gravel crushed stones, 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, calcareous and some others. If, for example, cellular concrete is being prepared, then it is clear that it makes no sense to use gravel of granite rocks, since this cancels such an advantage of foam concrete (or aerated concrete) as low weight.

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 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 automobile and railways;
• for landscape design;
• for decorative purposes.

It is important to distinguish this construction material from gravel. Gravel - fragments of rock formed in vivo 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, as the most resistant to conditions external environment and resistant to stress. It is used to produce particularly hard concretes.
• gravel. Mined in quarries or from the bottom of reservoirs ( Sand and gravel). 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 sand-cement mortar. In construction low-rise buildings and in cottage construction 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 - low price.
• Secondary- obtained by crushing recycled concrete products.

Limestone rubble is subject to negative impact water - dissolution (especially in an acidic environment).

The secondary view has a low price, but also the most poor 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 when creating bases 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.

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 certain form 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 more cheap material compared to cement, but with a high degree of density and hardness, it perfectly replaces it when creating concrete mix. 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 regular concrete. cement mixture, and its density and water resistance are much higher.

When adding crushed stone to concrete, some nuances should be taken into account. Despite the fact that crushed stone in construction terminology is a large filler and significantly increases the density of the finished concrete 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. To receive you need to 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.

Composition of concrete - how to choose the composition of concrete?

ready-mixed concrete tender

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

AT classic version The composition of concrete includes such components as a binder, water and fillers. Today, the construction industry supplements it with various plasticizers, water repellents and other additives that make it possible to produce construction works in the off-season, as well as increase specifications this material.

GOST and concrete

GOST strictly determines 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, the moisture content of the sand, and the fractions of the filler. 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 buying concrete, it is necessary to deal with such a technical indicator as W / C (water-cement module or water-cement ratio)

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

GOST regulates concrete according to:

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

Why is crushed stone in concrete?

The most common aggregate in concrete is crushed stone. Depending on the size of the granite obtained as a result of crushing, it is graded from fine to coarse fraction. 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 grains of acicular and lamellar forms per unit volume. It is the shape of the grain that determines the groups of crushed stone:

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

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

Why is there reinforcement in concrete?

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

As a result, the bending strength, compression and tension increase, as well as the temperature deformation of the concrete structure is extremely low. Depending on the diameter and profile of the section (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 mesh welding, then At (smelted from thermally compacted steels) is used in the installation of 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, 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 various mixtures to concrete to speed up the hardening process. high content calcium nitrate.

And although they contain a small amount 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 the concrete, the more pronounced the smell of ammonia.

Living or working in such premises can result in irreversible health consequences, therefore, the selection of concrete composition consists not only in knowing the brand of this building material, but also in carefully studying the manufacturer's reputation, and seriously reading the certificate for the required products.

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

In 1867 French gardener Monnier discovered and patented reinforced concrete. In the manufacture of cement pots for plants, he accidentally added pieces of metal there, 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 great in compression, and steel, as you know, in tension. Combining these materials into a single whole will achieve high performance strength, endurance, seismic resistance, fatigue failure and many others.

Order a call from the Lenbeton manager

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Crushed stone as a necessary element of concrete mortar

10/27/2014 Fillers for concrete are varied. Among them, crushed stone often leads. 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 the finished cement will be much higher. And it would seem that this is wonderful, because the work performed with such concrete would have lived for many centuries, like mountains, but there is a major nuance here. It would be very inconvenient, time-consuming and practically impossible to create buildings from such huge stone blocks, because mankind invented concrete, and actually for concrete there are already fillings. Crushed stone, acting as a filler, performs its functions at a height. 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. Because the placeholder, you should read information about it, about the size and its manufacturer. So why does concrete need crushed stone? By itself, concrete cannot be used without filler, since its volumetric shrinkage would not allow pouring the mortar and retaining its shape. Without filler, concrete could not be shaped, it would simply spread when 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 large filler, sand as a fine one. The more work is required in the thickness of the poured concrete layer, the naturally thicker the filler is selected. The volume of the filler is also often called a fraction. Without a special filler, such as crushed stone, the strength of concrete could not be fixed. Crushed stone improves the overall strength of the solution, 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 question of working with high-quality concrete is now in your main place, do not buy crushed stone without thinking and reading about its characteristics. We have already managed to tell you why there is crushed stone in concrete, now we will tell you a little about its production. Almost any crushed stone, whether it be 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 its strength, shape, grain size, and the amount of impurities contained can be determined. Crushed stone for concrete usually falls into three categories: 1. Granite crushed stone (this is crushed stone, in the production of which mainly granite was used) 2. Lime crushed stone (which is obtained as a result of limestone crushing) 3. gravel crushed stone(a product obtained by crushing rocks or sieved in granite rock) The category of crushed stone itself may also differ according to radioactivity and grain sizes.

Do not be afraid for the first time to use such materials. This type of work is the most common, and just carefully making the solution adhering to the necessary standards, the result will undoubtedly satisfy you.

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Ode to concrete

" Back

09.09.2012 21:03

WHAT YOU NEED TO KNOW ABOUT CONCRETE.

“Live a century - learn a century” - (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 at a construction site for several years. Besides, in Russian society there is a stereotype that a builder is the easiest profession, and concrete worker is the easiest of all construction specialties. Specialists of the company "Credo" will not enter into a dispute with those who think so. But they cannot indifferently observe how sometimes illiterate builders and non-builders handle concrete. And with their ignorance, they not only spoil high-quality and expensive material, which causes direct damage to the customer or themselves, but also discredits a conscientious concrete manufacturer, suggesting to 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. At the same time, most of the questions were dictated by practice.

What is concrete?

It seemed like a simple question. But few can give the correct answer to it. Concrete is artificial stone material. It uses best properties stone - its strength. But why can't you just use a stone? Because it is very laborious and expensive, and sometimes it is simply impossible to give the stone the desired shape 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 than it is to process granite. Well, it's hard to imagine interfloor overlap made of stone. Is it just vaulted ceilings made of stone on small spans. Or it is already quite 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 take tensile loads well. But if reinforcement is inserted into the concrete, then the tensile forces on the concrete will be taken by the reinforcement located inside the concrete. Everyone understands that inserting rebar into the stone and gluing it to it is also very laborious and expensive.

What is in concrete?

Concrete consists of three main components - binder, water and aggregate. For brevity, we will simply refer to the binder as "astringent". We will talk about the most common building 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 refer to cement concrete as "concrete". There are many types of cement. We will not consider its varieties. This is a topic for a separate study and is more interesting for concrete manufacturers and other specialists. The main types of aggregates are crushed stone, gravel and sand. Crushed stone differs from gravel in that it is a crushed material. In our area, most often it is a product of crushing the same gravel, but separated by fractions, that is, by size. Gravel concrete is slightly cheaper, as gravel is cheaper than crushed stone. Concretes up to certain grades are made from gravel. The main characteristics of crushed stone and gravel are size and strength. Sand is coarse-grained and fine-grained. Fillers must be selected in a strictly defined proportion. Simplistically, it can be imagined 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 are doing the right thing when they purchase ready-made gravel or crushed stone-sand mixture (GPS or SCHPS) for the preparation of concrete at the facility. In the manufacture of them in the factory, the ratio of crushed stone-sand or gravel-sand is optimal.

What qualities should concrete have?

The main physical characteristic of concrete is its strength. It is measured by special devices 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 strength in kilograms per square centimeter (kg/cm2). For example, a strength of 100 kg/cm2 means that concrete collapses when subjected to a pressure of 100 kg/cm2. Previously, and often now, this strength meant the brand 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, the grade of concrete is M100, the class of concrete is B7.5. There are special tables for matching the grade and class of concrete. Many manufacturers, for the convenience of buyers, indicate in the price lists both the brand and the class of concrete. 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 feature names speak for themselves. Frost resistance - means the number 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. Simplistically, the production of cement 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 the cement. When a strictly defined amount of water is added to cement, it turns back into stone.

Why do we need crushed stone and sand in concrete?

Indeed, when water is added, cement will turn into stone anyway. Answer: making an artificial stone only from cement is both expensive and difficult. In addition, the cement itself shrinks a lot. Therefore, aggregates are added to concrete: crushed stone or gravel and sand.

What happens if you put an arbitrary number of aggregates in concrete?

There will be concrete. But not the quality that the manufacturer wanted to achieve from him. 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 work. If the sand is more 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. It is possible with a margin, i.e. pour cement in excess. But then the economy will suffer. It will be very expensive concrete. The proportions of the components in concrete are selected by experts in the laboratory. These proportions are called "rebounds".

How much water should be added to concrete?

The amount of water is also determined in the laboratory. In order for cement to turn into stone, only 13% of water by weight of cement is enough. But in fact, in the production of concrete, they add large quantity. 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 not be possible to put it into the structure. Such concrete is mainly used in 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? Chemical additives called "plasticizers" and "superplasticizers" are used to reduce the amount of water in concrete while still maintaining qualities such as workability.

How is workability measured?

The indicator of concrete, reflecting its workability, is called "mobility". Previously, one could also come across the term "plasticity". Mobility is measured with special devices and is designated as follows: P1, P2, etc.

Is it possible to make selections for the composition of concrete, the same for the whole country?

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

Why does concrete thaw?

The 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 alternate 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 alternate freezing and thawing, and then it can collapse. How more water in concrete, the lower its frost resistance. Therefore, vibropressed paving slabs has great frost resistance. The worse the gravel, crushed stone or sand (dirty, fragile, non-frost-resistant), the lower the frost resistance of concrete. Many have watched concrete thaw out of dirty local river gravel.

Why can't water be added to the finished concrete that the supplier brought?

When ordering concrete, the buyer, in addition to the class of concrete, must indicate its mobility. The manufacturer, guided by economic considerations, produces concrete with the ordered characteristics with a minimum margin of safety. Therefore, when concrete arrives at the site, all the components in it are in the ratio and quantity that is necessary for this class of concrete, including water. By adding additional water, builders increase the VC and thereby reduce the ordered and paid characteristics. In other words, the buyer pays high class concrete, and it enters the structure with underestimated characteristics. Conclusion: it is impossible to add water at a construction site to the imported concrete. Sometimes by different reasons However, such a need 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 conscientious manufacturer should have such a specialist) will tell you what to do. You need to contact the technologist of the supplier from whom you bought the concrete. It is he who knows what components are used in the manufacture of this concrete and how to proceed in order to maintain the quality of concrete.

Does concrete need maintenance?

Quality Care behind concrete is no less important than its quality manufacturing. Some customers and builders are mistaken, 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 the preservation of the water (or moisture) that is already present in the concrete. As already mentioned, in order for concrete to turn into stone, water is needed. If the builders do not ensure the preservation of water in the concrete laid in the structure, then it will not have the strength that is ordered. What needs to be done for this? Concrete needs to be covered. Especially in sunny or windy weather. The wind often does more damage than the sun. When water evaporates from concrete, it will not be enough for concrete to gain strength. The concrete will "dry out" and will never gain the strength that was planned. With intensive evaporation of water, concrete cracks, as it shrinks sharply. After cracking of concrete, water evaporates from it through cracks even more intensively. In the future, during operation, water may enter the cracks, and the concrete will defrost. Through cracks in concrete, water and air enter the reinforcement, and it rusts and collapses. You can't watch and wait to see if the concrete starts to crack. If it starts, then 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 the concrete the word “shaken”. AT different time year in different weather, this time can be from several minutes to several hours. The experience, qualifications and skill of concrete workers are very important here. The mistake is made by those who replace the covering of concrete by watering it with water. Firstly, cement is washed out from the concrete surface, and secondly, upper layer concrete is waterlogged (increased CC). Consequence - the concrete will "crumble", peel off. What should be covered? Any vapor barrier material. For example, polyethylene film. But the process of covering is very laborious. It is necessary to cover the concrete so that, if possible, its surface is not disturbed. The film must be fixed so that it is not blown away by the wind. The position of the film must be constantly monitored. It is especially difficult for large areas, for example, on ceilings, road surfaces, etc. What is the way out? Very simple. Now many manufacturers of additives for concrete produce products for the care of concrete. it liquid materials, which are applied to the surface of the concrete, as soon as it shakes, with 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 up and turns into a film. These materials are called "film-forming materials". It is this film that allows you to keep water in concrete both in the sun and in the wind. As you know, 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 we calculate the cost of a polyethylene film, the laboriousness of its laying, preservation, cleaning, storage, taking into account the disturbed surface of concrete or the cost of water, spraying, water damage, it becomes clear that the use of film-forming materials is beneficial. In the future, this film evaporates and any concrete can be applied to the concrete. Decoration Materials, including tiles, without additional preparation. Conscientious concrete producers often sell these materials themselves. Most often, they do this not to make money, but to help builders and thereby maintain 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 basis 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, rubble from Gelendzhik quarries absorbs a very large amount of water. After concrete is laid, moisture from 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 astonished builders, who have nothing left to do but blame the concrete manufacturer and cover up the cracks, which can no longer change anything. No watering and covering will help, because shrinkage cracks form from below the concrete. The same happens when concrete comes into contact with dry wooden formwork. Which exit? The base for concrete must be moistened "to failure", 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. Formwork needs to be lubricated special materials, for example, emulsol, mining. This is done not only so that concrete does not stick to the formwork, but also so that moisture does not absorb. If there is no emulsol or mining, then it is necessary to strongly moisten the formwork, again avoiding puddles on horizontal surfaces. The exception is formwork made of laminated plywood or metal. Water doesn't go anywhere in it.

Another enemy of concrete is frost. In order for concrete to become stone, a positive temperature is necessary. Under laboratory conditions, the temperature is maintained in the region of 20 degrees Celsius. It is under such conditions that it is believed that concrete will gain its design strength after 28 days. The higher the temperature, the faster the concrete will gain strength. At the same time, one should not forget about the need to preserve moisture in the concrete. But the rapid rise in temperature when the concrete is heated is also harmful. There are internal (not visible to the eye) stresses and destruction in concrete. It is important to know this not only for those who use concrete heating. During the hardening of concrete, chemical reaction with heat release. With small structures, this only benefits concrete. At very large massive structures(most often in industrial construction, for example, powerful foundations), the concrete heats up so much that it is necessary to cool it, for example, by pouring water. Sometimes laid inside 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 object with a temperature of at least 5 degrees. Celsius. To protect concrete from freezing before it is covered or heated, special antifreeze additives are used in 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 production process. In the future, in order for the concrete to harden, it needs a positive temperature, i.e. it is necessary either to cover and thus preserve the heat that the concrete emits during hardening, or to heat it up.

In this article, we touched only on those rules, non-observance of which by builders can damage the business reputation of a concrete manufacturer and damage customers. In fact, the science of concrete is a serious discipline that is constantly evolving and requires a long study. Practicing builders need to have much less knowledge about concrete and the rules for its use than science has, but much more information than is presented in this article. The purpose of the authors of the article was to arouse interest among that part of builders and customers who do not even know the information presented in this article, and to encourage them to independently study the secrets of the concrete worker profession. For those who already know everything that has been said, it remains for the authors to point out only two points: 1. repetition is the mother of learning; 2. Nothing stands still, everything develops, including building science.