To avoid unnecessary problems in the form of extra costs, including financial and moral, it is worth understanding the material with which you are going to build your house, bath or any other piece of building art. That is, you need to know how to determine the brand of concrete.

Since the basis of everything is a solid, reliable foundation that would not let us down with cracks and subsidence, we should learn to understand the methods for determining its strength. It will depend on how much weight he can bear without destruction.

Correct determination of its strength will help to avoid mistakes.

Concrete grade - a number showing the compressive strength of a concrete cube of 28-day exposure with a side of 20 cm, expressed in kg / cm².

M300-400 concrete grades are the most suitable for individual housing construction. M100-250 have a minimum degree of strength and are used as an auxiliary material. It is difficult to find brands above 500 on sale, and it is unlikely that you will need heavy-duty concrete with special additives.

The correct option, of course, is to study the accompanying documents (concrete quality certificate) from the supplier, the manufacturer. It is necessary to pay attention to whether the mixture did not separate during transportation.

Visual Definition

It is possible to determine concrete by color: the better and stronger the mixture, the blue color. If yellowness appears in the liquid (cement milk), then this indicates clay impurities or other slag additives. The thicker this liquid fraction, the higher the brand of concrete. But, in general, the color also depends on the manufacturer's specifications, on the additives that were used in the production. A well-prepared mixture should not contain impurity grains that are not covered with a solution. A denser solution should resemble moist soil.

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Contact strength test

You can test concrete for strength using a special device - a sclerometer. The purpose of the device is to determine the strength by the shock pulse method. A sclerometer costs from 11 to 35 thousand rubles. They are mechanical and electronic. It is unlikely that an ordinary buyer would like to buy such an expensive device for a one-time use.

Another option is to send a concrete sample to a specialized laboratory to determine and check the degree of strength. To do this, you need to build a wooden box measuring 15 cm², moisten it with water. The form is wetted with water so that dry wood does not draw water from the concrete mixture, worsening the process of hardening (hydration) of concrete. Since only a good interaction of cement and water affects the strength. Next, pour concrete into the prepared form. needs to be compacted. This can be done with a few hammer blows on the sides of the box, and for this, the mixture is pierced with a piece of reinforcement to release the existing air. The cube should be left to cure for 28 days, at a humidity of about 90% and an average temperature of 20°C. 28 days - this is the period in which the setting and curing of concrete occurs.

It is possible to send a concrete cube for laboratory research at the intermediate stages of hardening, this is the 3,7,14th day after the mold was made.

Determining the strength of concrete can also be done by impact testing. To carry out the test, a chisel and a hammer weighing from 400 to 800 g are required. A chisel is attached to the surface of the hardened concrete, it is struck with a hammer with medium force. If the chisel is driven in to a depth of more than 1 cm, then the strength class is B5 (grade M75), if less than 0.5 cm, then B10 (M150). Leaves a small mark-B25 (M350), a small dent-B15-B25 (M200-250).

concrete quality. How to check?

Why test concrete?

Construction of concrete today allows you to build the most resistant to loads and durable structures of buildings and structures. For this reason, this technology of capital housing construction is used not only by professional builders who build entire districts and cities with large-panel houses, but also by individuals for whom the properties of the structure being built (strength and durability) are of paramount importance. This strength and durability means that the materials and technologies used at the construction site must comply with building codes both in terms of the quality of materials and the execution of the works themselves, their sequence / parallelism, etc.

In the case of building a small single-family house, laying a strip foundation, erecting small supporting structures, you can still somehow get by with household concrete mixing plants and independently mix concrete mixes from dry building mixes; but you need to clearly understand and be aware that there will be so much work on just one batch that a team of at least two workers is needed. And during the construction of an apartment building, manual mixing of concrete mixtures is simply out of the question. There is only one way out: to order concrete with delivery - the price and quality of which will vary from "terrible" to "beautiful" depending on the manufacturer. The purpose of this article is not to analyze the producers of ready-mixed concrete in a particular region of Russia, therefore, we will give only a couple of tips that will allow the inexperienced buyer of building materials to understand in several ways how terrible or wonderful the product he has purchased.

How to check the quality of concrete by eye?

So you ordered concrete with delivery - the price of which suited you (well, since you ordered it), it remains to understand whether its quality suits you.

Here is a short list of steps to help you with this: 1. Pay attention to the color of the mixture. Ready-mixed concrete should be grey. We emphasize: pure gray color! Not in some separate places of the mixture, but a uniform pure gray color in any part of it. Let's say concrete arrived at your place, you started pouring it, or you looked into the "barrel" of a concrete mixer truck (although, of course, you can't see anything there) and found that the concrete is not gray, but light brown - turn around cars with such a mixture, since such the shade appears due to an excess of fine filler (sand) to the detriment of other components;
2. The second thing you should definitely pay attention to is the consistency of concrete. The mixture must be uniform and homogeneous in any part of it! Uniform and homogeneous not only in color, but also in composition. If the concrete is not a homogeneous mixture, and for example, does not “pour” but falls in pieces, and in other places, on the contrary, is too liquid, then the ingredients are not well mixed and the mixture is of poor quality;
3. Necessarily, in preparation for the adoption of concrete, build several boxes of a cubic shape and dimensions of 10x10x10 cm. These boxes must be moistened before pouring concrete into them. It is worth pouring a mixture from different concrete mixers into different boxes, this will allow after 28 days from the moment of pouring the concrete to give it for examination and check the quality of the mixture of one batch from different machines that deliver it. Checking the quality of the concrete mixture (analysis of hardened cubes) should be carried out in an independent laboratory, of course, for a fee. And make demands and claims to the supplier of the material, in case of non-compliance with the quality standards declared by him;
4. After the mixture has hardened, it is worth trying the good old method: hitting the concrete. If the stone begins to crumble, it means that the mixture was bad and it is necessary to dismantle the structure and repeat the pouring procedure. If the concrete mixture makes a sharp ringing after striking, then you have bought a quality building material.
5. It is also possible to check the quality of the concrete mixture after it has hardened at the construction site itself in several ways. One of them and the most effective method is the ultrasound method. It is known at what speed ultrasound passes through reference samples of ready-mixed concrete of a particular brand. Therefore, based on the speed of ultrasound passing through your wall, it will be possible to tell how your concrete corresponds or does not correspond to its declared characteristics. The administration of Mostootryad 26 hopes that this information will be useful to you. And thanks to her, you will order

Many construction works are accompanied by concrete pouring. Not many people know what indicators of concrete quality to pay attention to when buying a ready-made solution or ready-made concrete blocks. Let's consider this question, because it is quite difficult to buy concrete, the price per cubic meter of which will not ruin your company.

What to pay attention to

So, to determine the quality of the mixture, pay attention to the following indicators:

• resistance to low temperatures or frost resistance. The concrete mixture must retain strength, both during freezing and after thawing;
• waterproof. Should be taken into account in conditions of high humidity or direct contact with water;
• corrosion resistance. This indicator is important in case of further contact of the screed with caustic chemicals;
• strength. An important parameter showing the resistance of building materials to all kinds of loads.

We check

To check the solution (blocks), strength tests are carried out and a conclusion is given based on their results. Examination is carried out both after pouring the solution and after kneading.

Methods for determining the quality of concrete:

1. in the laboratory (laboratory);
2. visual;
3. contact.

When visually inspecting, it is necessary to pay attention to such characteristics of the sample as consistency, presence of excess moisture, color.

Please note that high-quality concrete has a uniform gray color. If the technology is not followed, the color of the concrete will have red or brown shades.

When using the laboratory method, preliminary work is necessary:

• pouring the mixture into specially prepared wooden boxes;
• sealing mortar with parallel puncture fittings.

After the above steps, leave the prepared sample for 28 days in a room with conditions similar to the main room. After the expiration of the period, the sample is sent to the laboratory for analysis.

The contact method for analyzing the quality of the concrete mixture is carried out using a device - a sclerometer.

Solid solution analysis

If it is necessary to analyze already hardened concrete, the following methods are used:

• destructive;
• non-destructive.

With the destructive method, test samples (cores) are drilled out and an examination is carried out.

Non-destructive analysis is carried out using special equipment - a Kashkarov hammer, as well as an ultrasonic apparatus. The results obtained are analyzed based on the indicators of the calibration curves.

Concrete analysis is an important stage of construction work and it is advisable not to neglect it, so as not to redo the work later.

Concrete is one of the most popular materials in construction, its quality and strength characteristics affect the integrity of the entire structure. Under the influence of external factors and deformation loads, the design strength usually does not match the actual results. There are several methods for diagnosing the quality of concrete. The method of separation with shearing has become widespread in practice, but specialists use other methods of verification.

Tensile strength

Each class of concrete has its own indicators, the required strength according to the norms of SNiP is listed in the table:

There is such a thing as the transfer strength of concrete - in fact, this is the cubic strength during the compression period, it initially has a lower value than the design (grade strength). On a plant scale, waiting until concrete reaches 100% of the design strength result is rather irrational, so this minimum value is used, assuming that concrete will subsequently gain design strength.

The manifestation of design strength occurs only on the 28th day, if all technologies and temperature conditions (from 30 ° C and above) are observed, a very important indicator for a concrete solution is critical strength. Experimentally, experts concluded that concrete samples that have gained critical strength (matured to a certain state) under winter concreting conditions are not subject to destruction after thawing, but continue to gain strength simultaneously with the aging process.

Unbrakable control

The method of non-destructive testing is used when measuring during the operation of an object. This is a very important indicator during the construction of structures. The integrity of concrete is not violated during such control, it is completely ready for use. Each method has its pros and cons, if the laboratory owns the instruments for each of them, then it will be possible to implement a comprehensive quality control of concrete.

How to determine the average strength in ready-made buildings after pouring the concrete mixture? To do this, use one of two methods:

• Determination of the bearing capacity to the maximum, by transferring the load to the structures up to its complete destruction. The method is not profitable from the economic side, because of the high cost - after all, after checking, the concrete becomes unusable;
• The state of buildings is determined using special devices without destroying the structure. The final results are processed using specialized software on a computer with high precision. These methods are called "non-destructive" and are calculated based on indirect signs: the energy expended on the impact, the voltage that leads to local (partial) damage to the system, the imprint.

Method of local destruction

This technique is one of the most accurate of all, since it involves the use of a calibration dependence that takes into account the change in the strength of two indicators: the degree of scale of the filler and its type.

• The shearing-off method is the most common and most accurate, based on determining the forces applied when shearing a partial structure (its ribs), but labor-intensive, since the basic law provides for drilling holes and placing anchors in the structure, which are subsequently pulled out. Disadvantage of the method: it cannot be used for thin wall panels and pouring with frequent reinforcement;
• The method of tearing off metal discs is designed for less labor than the previous method, but in practice it is used much less frequently, suitable for structures with dense reinforcement. The essence of the method consists in gluing metal discs onto the surface (several hours before the control tests), and then tearing these discs from the structure.

Impact strength control methods

Quite a popular method of non-destructive testing. What determines the choice of builders in favor of a particular method is an open question, often this is influenced by the design features, thickness, degree of reinforcement and other parameters.

These methods fix and register impact energy at the moment of equipment contact with the surface. The strength of concrete is determined by these methods simply, using the same units of measurement as when determining the compressive strength of concrete.

Control algorithm:

1. determination of the class of concrete by taking measurements;
2. carrying out manipulations of measuring strength characteristics at different inclinations to the surface of the structure;
3. processing of the received results on the computer.

Rebound method. The parameters of the magnitude of the reverse rebound, which occurs when the equipment hits the concrete plane, are determined. The Schmidt sclerometer is widely used in determining the strength. Each blow in the control process is measured on a special scale, the readings are recorded in the journal.

Plastic deformation method. The peculiarity of this method: first, the ball hits the concrete, then the imprint remaining on the surface is measured. The method is quite ancient, but it is still popular today, because it does not require special equipment and is not too expensive. For control, a Kashkarov hammer is used.

Strength determination by ultrasonic method

Ultrasonic testing of concrete for strength is the most convenient and modern method. For implementation, a special sensor is used that conducts waves through the thickness of the concrete layer. The characteristics of the wave propagation speed are compared. Disadvantage: for high-strength concrete classes, this method is not suitable.

Destructive methods

SNiP obliges construction organizations to carry out control by destructive methods.

Destructive testing methods:

• testing on special samples;
• sawing out samples from the structure itself in different places (where to take samples is prescribed by the design documentation or the designer at the work site);
• the use of cubes made at a construction site according to special regulations, taking into account all technological characteristics.

Conducting laboratory research is an expensive process, it is not always possible to implement it. You can control yourself. You should stock up on simple tools: a hammer, weighing about 800 grams, and a chisel.

When purchasing or building a private house on a concrete foundation, it is necessary to carefully control the quality of ready-made or poured concrete. Moreover, this operation can be done on your own without having special measuring equipment. How to check the quality of concrete using a universal tool will be discussed in this article.

Non-destructive methods for testing the quality of concrete

• First of all, you should carefully examine the surface. The surface must be smooth. If the pouring was carried out in winter, there should be no “patterns” on the concrete. If they are, it means that during the pouring period, the concrete froze, which reduces the strength of the structure to 50-100 kg / cm2;
• Quality control using a hammer weighing at least 0.5 kg. Tap on the concrete structure and appreciate the tone of the sound. The ringing tonality and the absence of damage testify to the high quality of concrete and strength at a level of at least 200 kg/cm2; a ringing sound and imprints from a hammer identify the antinode at the level of 150-200 kg/cm2; dull sound in the absence of damage - concrete has serious defects; dull sound and damage from impacts - concrete is of poor quality, strength is not more than 100 kg / cm2;
• Visible surface defects in the form of a significant number of pores "speak" of poor sealing. In addition, this is a 100% guarantee of poor quality concrete preparation. If this is a concrete structure located in the open air, there is a high risk of gradual destruction in the cycle: “moisture penetration, moisture freezing, destruction of the micro-layer of concrete”, etc.

Method for testing the quality of concrete with a hammer and chisel

To check the concrete, you will need a hammer weighing 500-800 grams and a steel chisel.

We set the chisel on the surface to be checked at an angle of approximately 180 degrees and hit it with medium force. For a more accurate check, a similar operation must be done in different places of the structure. Evaluate the impact trace:

• The trace is barely noticeable - high quality concrete corresponding to the B25 grade;
• The trace is very noticeable - concrete grade B15-B25;
• Strong depressions formed. Concrete began to paint - concrete grade B10;
• The chisel entered the material by more than 10 mm - concrete grade no more than B5.

With ongoing construction, it makes sense to determine the quality of concrete before pouring. To do this, it is necessary to pour a sample with dimensions of 100x100x100 cm. Until the concrete has set, it should be pierced with a concrete rod to release air.

Next, the sample is dried at an ambient temperature of 20-25 degrees Celsius and after 28 days is taken to a specialized laboratory for analysis. Thus, you can get the most accurate technical specifications and brand of concrete.

Assumption! If the construction time is running out, the sample can be transported 7-14 days after pouring. In this case, the exact exposure time should be indicated in the laboratory.

In addition to determining the quality of concrete by improvised means, there are the following methods that require special tools, fixtures and installations:

• Determination of the strength of concrete using a Fizdel hammer;
• Determination of the strength of concrete using a Kashkarov hammer;
• Ultrasonic method: determining the quality of concrete by determining the propagation time of a sound wave and its speed with special equipment.