How to check the quality of concrete and what is needed for this? Determination of the strength of concrete: methods and their features Mechanical non-destructive methods for determining the strength of concrete.

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 the scale of the plant, waiting until the concrete reaches 100% of the design strength result is rather irrational, therefore this minimum value is used, assuming that the concrete will subsequently gain the 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 mix? 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 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.

Provide standard strength of concrete products. With the help of mixtures, high-quality pouring of foundations and monolithic building structures is carried out. Concrete of any grade can withstand tests and the maximum number of checks on the quality of cement and fillers, in mixtures and ready-made structures.

We offer solutions and concrete from the manufacturer with standard indicators that meet the requirements of GOST. Strict compliance with the standards is ensured by the use of special additives and plasticizers that meet the requirements for water resistance, frost resistance, etc. But is it possible to evaluate the quality of concrete during pouring or during setting without laboratory testing?

How to determine the quality of concrete before pouring

It is possible to know exactly certain characteristics of the mixture only in a laboratory that works at every large enterprise. After all, concretes M350 or M400 look almost the same as M100. When ordering a batch, the client is forced to trust the passport and documents for the ordered delivery, which are presented by the mixer driver. To do this, carefully review the provided certificates.

Next, you should pay attention to the brand indicated by the manufacturer, as well as the time when invoices were issued. Indeed, during the day the machine makes many trips, and the documents presented for unloading may not correspond to the batch actually delivered to the construction site. There are also signs by which experienced craftsmen can approximately evaluate the brand.

How to visually determine the brand of concrete?

• Pay attention to the shade of the mixture. Light brown indicates an excess of sand, reddish indicates slag additives or the presence of clay. The solution should be uniform, gray in color. However, the color change of the mixture may depend on the presence of various additives.
• You can determine the quality of concrete if you pour a part into a separate container (bucket, moistened mold). There should be no puddles of water on the solution.
• When pouring, delamination and cracks should not form on the surface.
• If the concrete falls like a cake, and cement laitance flows separately, this can be considered a sign of the poor quality of the mixture provided.

But it is possible to accurately check the concrete mixture only in the conditions of a specialized laboratory, and most often - after curing. Therefore, when pouring the main foundation, it is necessary to cast cubes 100x100x100 mm in size and leave to harden under standard conditions. After full maturation (28 days), the samples should be sent for testing to the laboratory.

How to determine the quality of concrete after hardening

To assess the quality of the resulting product, there are several ways that experienced builders know.

• Carefully inspect the resulting surface of the product or foundation. Concrete of a high grade should have a smooth surface, without pores and layers. If pouring work was carried out at low temperatures in winter, characteristic patterns should not appear on the surface, which indicate freezing of the mixture. The presence of patterns indicates freezing during pouring, they lower the concrete grade by 70-100 points (from M300 to M200-250);
• With a hammer that weighs no more than 500 g, knock on the foundation after gaining 70% strength characteristics. The sound must be resonant. If, with a ringing sound during a blow, hammer prints remain on the surface, this shows that the density of concrete is 150-200 kg / cm2. A dull sound indicates a low grade of the mixture, and says that the strength of which does not exceed 100 kg / cm2. And if, upon impact, cracks form on the surface or the material crumbles, it is recommended to refill.

With the help of blows on the chisel of a hammer, which has a small weight (300-400 grams), you can also find out the quality of concrete. It is necessary to evaluate how and to what depth the chisel plunges into concrete during medium-strength impacts.

• If the tip plunges deeply and easily, without falling on crushed stone or gravel, the grade is lower than M70.
• With an immersion depth of up to 5 mm, it can be assumed that the brand is equivalent to M70-M100.
• For concretes of the M100-M200 grade, when a chisel strikes, small thin layers are only separated on the surface.
• If there are no traces of the chisel at all or there is a shallow trace and there are no delaminations, it can be assumed that the concrete grade is higher than M200.

However, all these methods give only a rough estimate. Only laboratory tests can accurately determine the quality of poured concrete and the reliability of the structure. In this case, special equipment, measuring devices and tools are used. In addition to testing cast control samples (a cube with a 10 cm edge), there are many non-destructive methods for checking the quality of the mixture - ultrasonic, shock-pulse, and other devices and control methods. The methods listed above are "folk" and do not claim to be highly accurate. In addition, the reliability of the determination depends on the experience of the master who is trying to determine the brand of concrete.

How to check the performance of concrete in the laboratory

If the technology and proportions are strictly observed in the manufacture of the mixture at the enterprise, the components are selected, there are no low-quality fillers, the quality of the finished product will undoubtedly be ideal. But just in case, it is recommended to prepare samples for subsequent control. They will be checked in the laboratory by compression and an expert opinion will be issued.

In order to exhaustively accurately determine the quality of the finished concrete and its compliance with the specifications, it is necessary to pre-fabricate the formwork in the form of cubes with a rib size of 100 mm. After the concrete has matured, the samples must be delivered to the laboratory, where they know exactly how to check the brand of concrete. This procedure is carried out after compaction (vibration) and drying under the same conditions in which the general casting was carried out.

Verification and specification of the brand of the resulting concrete, as well as the issuance of a certificate should be carried out after the mixture has fully matured, after 28 days.

When actively working with building mixtures, sooner or later one has to learn to determine some characteristics by visual signs or with the help of special devices. If necessary, the quality of concrete can be checked both in the liquid state and in the hardened state, when the structure is already fully prepared.

Determining the parameters of the liquid mixture

Immediately before pouring a freshly prepared solution, it is recommended to verify the technological properties, especially if the batch was done by hand or the manufacturer does not inspire confidence. Having performed independent control, you can learn a lot about the quality of products.

Density check

By calculating the approximate mass of a substance in a certain unit of volume, one can judge which category this composition belongs to. This parameter is particularly affected by the type of placeholder. Detailed information on the density of mixtures is presented in the table.

Attention!
The first two categories of solutions are mainly used to form an additional layer.
However, in some cases, small structures can be created with their help.

Preparatory measures must be taken immediately before testing. To carry out the work you will need: a two-liter container, a trowel, scales and a metal rod for sealing. The container used is immediately weighed, after which its volume in cubic centimeters is determined.

The filled container is weighed with an error of up to a gram.

1. First, the net mass of the mixture is determined, for which the weight of the tare used for verification is subtracted. Example: 5000-400=4600 g.
2. Then the result is divided by the volume of a two-liter vessel. The result is: 4600/2000 = 2.3 kg per 2000 cm3.
3. At the last stage of calculations, it remains to find out the density in one cubic meter: 2.3×1000=2300 kg/m3.

Note!
The density of the composition can be increased by proper selection of aggregates, reducing the amount of water, as well as high-quality vibration using special equipment.

Stiffness testing

Not only the convenience of installation depends on this parameter, but also to some extent. Officially, the test is carried out using a special device in accordance with GOST 10181.1-81. The device is a cylindrical metal vessel.

In the process of determining the stiffness, the product is fixed on a vibration platform with a range of motion of 0.35 mm and a frequency of 2800 to 3200 vibrations per minute. The final indicator is the arithmetic mean of two determinations at once, taken from the same sample.

However, the price of such equipment is quite high, so individual developers do not have the opportunity to carry out research in this way. Therefore, you can use a simplified version, which provides for the presence of one vibrator.

A cubic mold with an edge of 20 cm is mounted on a vibrating table and fixed in one position. A standard cone is placed in it, designed to be filled with a solution. Vibration continues until the liquid composition is distributed horizontally. The value is determined using a stopwatch.

Mobility assessment

Testing is carried out using a standard cone made of galvanized iron or sheet steel. The amount of precipitation of this object characterizes the mobility of the solution. If the indicators are too low, then water and an astringent are added.

Hardened Material Control

The most accurate assessment of the quality of concrete is made after its final hardening, when 28 days have passed since the moment of pouring. Control can be destructive or non-destructive. In the first case, a direct sample is taken, and in the other, testing is carried out with various devices, the readings of which are not absolutely accurate.

Non-destructive methods

• The separation of the disks involves the removal of stress, which is produced by local destruction. The applied force in this case is divided by the quadrature of the surface projection.
• Rib shearing allows you to define the characteristics of linear structures such as columns, beams, and piles. The method cannot be applied if the protective layer does not exceed 2 cm.
• Shearing is the only non-destructive testing method for which calibration dependencies are officially regulated. When testing, it is possible to achieve high accuracy.
• Ultrasound quality testing involves determining the speed of waves. Distinguish between through and surface sounding. The difference lies in the location of the sensors.

• Elastic rebound provides an opportunity to measure the amount by which the striker will move after impact on the surface of the structure. Tests are carried out using spring hammers.
• The impact impulse allows you to register the energy of a perfect impact, which is formed when the striker comes into contact with the plane. Such devices are compact in size.
• Plastic deformation is based on measuring the size of the impression left after impact with a steel ball. The method is a bit outdated, but still used, due to the cheapness of the device.

Destructive methods

• Sawing a sample from a concrete structure is carried out by special equipment such as URB-175, equipped with a cutting tool like diamond discs.
  
• Drilling out is carried out using drilling machines type IE 1806. They have a diamond or carbide drill.

As a conclusion

Before purchasing a ready-made composition from a manufacturer, you need to find out if he has a quality certificate for concrete. This is not a prerequisite, but gives an indication of the reliability of the company's intentions. More detailed instructions on the topic are reflected in the video in this article.

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 an inexperienced buyer of building materials in several ways to understand 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 looked into the "barrel" of a concrete mixer truck (although, of course, you can hardly see anything there) and found that the concrete is not gray, but light brown - turn around the machines 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

There are three most effective ways to measure the strength of concrete. In this article, you will learn how and how to measure the strength of concrete, which method is more suitable for your tasks.

3 proven ways to determine the strength of concrete!

When constructing a building, special attention must be paid to determining the strength of concrete. Calculations, measurements must be carried out qualitatively, so that it is possible to approximately determine the service life of the building and some other parameters.

In science, the word "Strength" is defined as the resistance of a material to mechanical damage. There are strength standards specified in the standards and sanitary rules.

In addition to measuring a test sample in the laboratory, it is inevitable with a qualitative approach to study the concrete of the construction site in order to identify the difference, if any, and eliminate it if the concrete at the construction site for some reason turned out to be worse than the reference sample.

In total there are three ways to determine. By reducing the effect on the sample, this has the following form.

1. Destructive and non-destructive testing

1.1. Destructive way

There is a sample that is tested by exfoliating it with a press. Samples are tested on two installations. The first tries to compress the sample into a small cube. And the second is just trying to chip a piece of concrete. From their effectiveness and time of work, conclusions are drawn about the quality of concrete.

1.2. non-destructive way

It is especially good for measuring the strength of existing objects. For a non-destructive method for determining the strength of concrete, deformations are also characteristic, but their volume is much smaller.

There are two methods to measure strength without changing the structure of the material. The first is the use of mechanical percussion instruments. These include various hammers and pistols. If with the help of the first they measure the diameter of the holes after the impact, then with the help of the second - the rebound force of the impact rod - the elasticity of the material.

The greater the elasticity, the greater the overall strength.

2. Use of ultrasonic assessments.

As is known, in a dense medium, the speed of sound and ultrasonic data transmission increases. This means that the stronger the concrete, the faster the ultrasound will be transmitted through it.

There are two types of transmission - surface (for walls and floors) and through (assessment of piles, pillars, narrow supporting elements.)

3. Analytical method

It is divided into 2 types. The first, with the help of special formulas, is available to those who have received a special construction education.

The second is available to everyone and is most often used in practice. A very small piece of concrete is taken, a hammer weighing about a pound and a chisel. The chisel is placed on a piece of concrete, a hammer is lowered onto it with medium force. The hammer bounces, it is not necessary to release it again. Remove the chisel and look at the diameter. If the concrete is not damaged, then these are the best grades of concrete - from B 25 and above. If the concrete is slightly damaged (up to five millimeters), then these are medium grades of concrete - from B 10 to B 25. But if the concrete is damaged up to a centimeter, then these are relatively weak grades - from B 5 to B 10.

This method of measuring the strength of concrete is suitable for everyone, it is easy to remember, but it is also worth remembering that this method is only suitable for small construction projects - when building official large buildings in which enterprises will be located or people will live, concrete must be evaluated using invited experts and industrial formulas and installations.

Even if you, say, are repairing the roof of a private house, you will need to evaluate the strength of the concrete of the supporting structures on which this roof will rest.