Visual determination of the quality of concrete. Handy ways to determine the grade of concrete

The result of work on the creation of concrete and reinforced concrete structures is highly dependent on both the quality of the components used to prepare the concrete mixture, and on the observance of technological conditions at each stage. concrete works.

Careful control must be carried out at the following stages:

receipt and storage of materials used in the course of concrete work - sand, cement, gravel, crushed stone, reinforcement, etc .;
creation and installation on site of elements of the reinforcement structure;
creation and assembly of formwork elements;
preparation of formwork and base for concrete placement;
preparation and transportation of the concrete mixture to the place of laying;
maintenance of a concrete structure during the period of its critical or design strength (curing).

All components of the future concrete structure are checked for compliance with GOST standards. Their characteristics are analyzed in accordance with a unified methodology specially designed for laboratories at construction enterprises.

Quality control of materials

In the course of reinforcement operations, the quality of work and materials is checked upon receipt of the reinforcement - the factory markings (presence of tags) are checked, the brands comply with the declared requirements of the designers. The processes of storage and transportation are accompanied by checking the correct placement of reinforcing steel by grades, grades and sizes, preserving its quality characteristics after delivery to the construction site. geometric shape and dimensions, correctness of welded seams and their quality. Exposed in the concreting block and combined in general design the reinforcement elements are analyzed for compliance with the specified dimensions and position according to the tolerances.

Work on the installation of formwork elements is carried out with verification of the correctness of their installation, construction of fasteners, the tightness of the junction of the panels at the joints, the correspondence of the assembled formwork and the reinforcement structure (ensures the formation of a protective layer of a given thickness). The spatial position of the formwork is analyzed by leveling and linking to the axes in several separate sectors, the accuracy of the calculated dimensions is determined by measurements using measuring tool... Formwork construction tolerances are specified in GOST R 52085-2003, GOST R 52086-2003 and reference literature. Before placing the concrete mixture, the surfaces of the formwork are checked for cleanliness and the quality of the application of lubricants.

Preparation and placement of concrete mix

The introduction of the components of the mixture into the mixer is accompanied by a thorough check of the dosed portions, the duration of mixing, the density and the degree of concrete mobility. The control of the mobility of the concrete mixture is carried out at least twice per work shift, its indicators should not be 10 mm less or more than the calculated ones, density tolerances - no more than 3%.

The procedure is performed with monitoring the parameters of the mixture - for the absence of seizure, delamination, loss of mobility due to drying.

At the place of concrete work, it is important to monitor the height of the dumping of the mixture, the duration of vibration with the achievement of uniform compaction, to prevent the stratification of the mixture, the formation of voids and cavities in its structure.

Vibration compaction of the concrete mixture is carried out under visual control, the criteria are the degree of its settlement, the formation of cement laitance, and the completion of the release of air bubbles. More precisely, the compaction results are analyzed using radioisotope densitometers, which calculate the density of the concrete mixture by measuring the degree of absorption of gamma radiation.

In the process of concreting structures of a large area, the compaction of the concrete mixture is determined using several cylindrical sensors, externally resembling probes, placed depending on the thickness of the mixture to be laid. The higher the density of concrete, the lower its resistance electric current, passed through the concrete mixture - the operation of the sensors is based on this principle. They are installed near vibration installations, informing the operator about the achievement of the required density by sound and light signals.

Assessment of the strength of concrete by its samples

Find out complete quality characteristics concrete is possible in only one way - by testing its strength by compressing specially made concrete cubes until it is possible to completely destroy them.
The cubes are made at the same time as the concrete is being placed, and they are held in exactly the same conditions as the main concrete structures. Typically, 160 mm cubes are tested for compression.

Depending on the class of concrete, three test cubes of the same size are required. To assess the characteristics of foundations intended for various designs, cubes are formed from every 100 cubic meters of concrete. When creating massive foundation structures designed for the installation of technological equipment, samples for strength tests are prepared from each next 50 cubic meters of concrete, and for foundations for frame and thin-walled (lightweight) structures, cubes must be made from each new batch of concrete with a volume of 20 cubic meters.

A relatively complete assessment of the strength of a concrete structure can be obtained by drilling cores in its body, followed by testing the samples for compressive strength.

Indestructible methods for testing concrete strength

In addition to laboratory studies of the strength characteristics of concrete samples from specific batches, there are methods indirect assessment concrete structures and structures without any destruction. Among them, the most popular is the mechanical method, based on the relationship between the surface hardness of concrete and its compressive strength, as well as pulse-ultrasonic, the use of which is based on measuring the speed of longitudinal ultrasound waves directed into the concrete structure and the degree of their complete attenuation.

Strength tests reinforced concrete the method of mechanical action is carried out using an instrument called a sclerometer. Consider the versions of this device designed to determine the strength of concrete.

Kashkarov's hammer... It must be installed with the side with the ball on the surface of the concrete structure, then hit back side an ordinary bench hammer. After hitting on concrete surface and potholes will remain on the reference bar, the measurement of which will determine the surface compressive strength of the concrete. The design of Kashkarov's hammer must comply with GOST 22690-88.

Schmidt's hammer... An impact rod is located in its body - after removing the blocking, it is necessary to fully extend it, then press it against the concrete surface, pressing the impact rod into the body until it is completely immersed in it and hits the concrete. The impact of a rod hammer will cause the device to bounce and move the measuring mechanism along the scale with markings - in the process it is important to keep the tool strictly perpendicular to the surface of the concrete structure. Hammer bounce distance - depends on the surface strength of the concrete, i.e. the higher it is, the greater the distance the hammer will move. The principle of operation of modern analogues of the Schmidt hammer, equipped with an electronic measuring scale, does not differ from its mechanical counterparts.

Special devices for ultrasound examinations concrete, for example, UKB-1, also allow you to determine the strength of concrete structures. They generate ultrasound, according to the speed of movement of which through the thickness of concrete, its strength characteristics are determined. If the technological conditions meet certain requirements - the use of materials with similar characteristics, the technology compliance with the established standards, etc. - the accuracy of the data on the strength of concrete will be quite high.

Quality control of concrete work in winter

In low temperature conditions, following the procedures described above will not be sufficient. In addition to quality control measures, additional actions need to be taken, which will be discussed below.

The condition of the concrete mixture is checked during the entire preparation period for the next batch at least once every 120 minutes. When entering the concrete mixer, unheated filler (crushed stone, gravel and sand) should not contain snow and ice, frozen grains. In the process of obtaining concrete mixtures with antifreeze additives, it is necessary to measure the temperature of dry components and water before entering them into the mixer, to determine the salt content and the temperature of the finished mixture at its outlet.

Concrete transportation is carried out with a one-time check for a change in the state of the covering and insulation materials, the quality of heating and thermal insulation of containers in which the mixture is transported and into which it enters after delivery.

If, before placing the concrete mixture, it is performed, then it is required to control its temperature during the heating of each new portion.

At the construction site, immediately before starting work on laying the mixture, an inspection is carried out interior walls formwork, foundations of the concreted area and reinforcement structure to ensure that there is no snow or ice. The outer walls of the formwork must be thermally insulated in accordance with the technological conditions, it will heat the base of the area to be concreted and the zones of its interface at the joints with the formwork.

In the process of placing concrete, its temperature is monitored at the stage of unloading from the vehicle, then the temperature readings are taken again, but after the completion of concrete placement. Concreting areas not covered by formwork should also be assessed for technological compliance in terms of waterproofing and thermal insulation characteristics.

Measurements of the temperature of concrete passing the stage of curing in winter conditions are carried out in the following order:

when using the technologies of preheating, "thermos" and heating in the specified temperature and humidity conditions (hothouse), temperature measurements should be taken every two hours during the first day, at less than two times during a shift over the next three days and once every 24 hours during the further aging period;
when laying concrete containing antifreeze additives, its temperature must be measured three times during each day from the moment of completion of the work until it reaches the design strength;
when carrying out electric heating of a concrete structure, during its temperature rise with an interval of up to 10 ° C per hour, the temperature should be measured every two hours, then at least twice during each shift.

After concrete structure the term will pass aging and recruitment design strength, as well as the dismantling of the formwork will be carried out, the air temperature is measured at least once during each work shift. Temperature data for a concrete structure is obtained by drilling narrow wells and immersing thermometers in them, as well as using special technical thermometers. It is extremely important to monitor temperature changes in sectors potentially subject to high cooling (protrusions and corners), as well as heating - areas close to heating electrodes, an area of direct contact with thermoactive formwork elements. Recording of information on temperatures is carried out in a special sheet.

If concrete is heated using electrodes, it is necessary to measure the current and voltage in the supply transformer twice for each shift, and enter these data into the log.

Strength laboratory testing of concrete specimens is carried out in accordance with the standard procedure outlined above. In addition, at the place of concrete work, additional sample cubes are created for testing the strength:

In a situation where test pieces are kept at low temperatures, it is necessary first to withstand them at temperatures from +15 to +20 o C, and then check their strength characteristics.

If a set of strength characteristics of a concrete structure is provided using electrical elements, induction or infrared heating, or in a thermally active formwork, then obtaining samples for testing such concrete is most often impossible. The only way to monitor the strength of concrete in such situations is to strictly ensure the design temperature conditions.

In addition to assessing the strength by breaking sample cubes and drilled cores, it is necessary to check with non-destructive methods - for example, using Schmidt and Kashkarov hammers. It is important to carefully register each operation within the framework of quality control carried out in accordance with the technologies of concrete work, since upon acceptance of the object, this documentation will be presented to the commission. We remind you - acceptance concrete base, the concreting block, where the concrete mixture is to be laid, is drawn up by an act, then the temperature control logs are kept in a given order and in accordance with the established forms.

Construction is a rather laborious process. In order to exclude extra costs and not to waste time, it is worth taking good care of the quality of the materials. First of all, you need to think about how to check the grade of the concrete mix.

The ordered solution does not always correspond to the characteristics specified in the document. If the added raw materials for the production of concrete do not correspond to the proper proportions, the quality of the mortar will automatically change. To accurately identify the brand, it is necessary to conduct a quality assessment.

The concrete grade is an indicator showing the ultimate compressive strength. M300-400 grades are suitable for construction. М100-250 have minimum strength and are suitable only for auxiliary work. Much depends on the provider chosen. It is worth looking for trusted companies with a good reputation that can provide Required documents on the offered products. If for some reason you doubt the honesty of the supplier, you should think about further researching the solution for compliance with the specified brand.

Determination of the grade of concrete can be done by different methods:

Laboratory expertise;
Ultrasonic method;
Self check.

Each method differs in the percentage of accuracy and has certain subtleties.

Contact methods of verification

Contact verification is carried out in two ways. The first one - with the help of professional equipment - a sclerometer. The device determines the strength by means of a shock pulse. The sclerometer can be mechanical and electronic, and its price ranges from 10 to 35 thousand, a purchase for a one-time use is simply not rational for an ordinary buyer.

The second method involves sending a sample to a laboratory. First, you need to carry out a number of manipulations:

To prepare wooden box volume of 15 cm³;
Pour the purchased solution into the mold directly from the concrete mixer tray, pre-moisten the box with water. Seal the poured solution by making several punctures with fittings;
Place the sample for 28 days in the same conditions as the main structure;
The frozen sample is taken to the laboratory for research. Evaluation can be done at intermediate setting stages (3, 7 and 14 days).

The examination will issue a conclusion on the study of a sample of this brand, its compliance with the established standards.

Testing samples in the laboratory

Ultrasound technique

Ultrasonic devices, in addition to studying strength, are used for flaw detection. The speed of propagation of ultrasound in concrete reaches 4500 m / s.

The calibration relationship between the speed of sound propagation and the compressive strength of concrete is fixed in advance for each mixture composition. In the case of using 2 dependencies for concretes of alternative or unknown compositions, inaccuracy may arise in determining the strength. The ratio "strength - ultrasound speed" is influenced by a number of factors, from the fluctuations of which, in this case, it is necessary to build on when applying ultrasonic testing:

Preparation method concrete mortar;
Quantity and grain size composition;
Change in cement consumption by more than 30%;
Possible cavities, cracks and defects in the finished structure;
Concrete compaction level.

Ultrasonic testing is suitable for mass testing of structures of any shape, as well as for continuous monitoring of strength or strength reduction. The disadvantage of the method is the error in the transition from acoustic indicators to strength. It is not worth checking the quality of high-strength grades with ultrasonic equipment, the permissible range is limited to classes B7.5 ... B35 (10-40 MPa), in accordance with GOST 17624-87.

Self-check methods

Testing in a laboratory or special means does not always justify itself. This applies to those cases when small building on private territory... Poured and frozen solution can be checked at home in several ways. If it does not meet the necessary requirements, you can use a paid expertise and compensate the damage from the supplier.

Smoothness check

Take a close look at the frozen structure. It should be smooth, the presence of patterns indicates non-compliance with the filling rules. Such a solution most likely froze through, which will significantly reduce its strength. In fact, concrete of the M300 brand will become in its properties as M200-250.

Voicing test

You can check on the sound of the impact. For this, a hammer or piece is taken. metal pipe, weighing no more than 0.5 kg. Ringing tonality is important here when striking. A dull sound indicates low strength and poor compaction. And when cracks, crumbs appear, it is necessary to completely or partially replace the structure.

Visual assessment

The method involves checking the characteristics of the solution upon acceptance. You can highlight such moments as:

Color - a high-quality mixture of gray with a bluish tinge, if yellowness is clearly manifested in the cement milk, clay impurities or slag additives are present in the mixture. A brown or red color is characterized by an excess of sand or aggregate in an unacceptable amount, it is wiser to refuse a solution with an uneven shade altogether;
The correct consistency is homogeneous, without lumps or clots and resembles moist soil;
Excess water - determined by pouring a small amount of the mixture into the pit, you should get a cake without layers and cracks;
The purchased mortar of inadequate quality begins to delaminate even during transportation, the mixture cannot be removed with a shovel or fed through a sleeve.

If a mixer is delivered, it is possible to determine the quality of concrete without inspection only by using the documents provided. In this case, it all depends on the good faith of the seller.

Checking concrete with a hammer and chisel

A hammer and a chisel is the simplest answer to the question of how to check the quality of concrete pouring. For this, a hammer test is carried out. A chisel is attached to the surface of a completely dried foundation, and a blow is struck with medium force. If the resulting dent exceeds 1 cm, strength class B5 (M75), less than 0.5 cm - B10 (M150). A small dent remains on B15-25 (M200-250), a slight mark appears on B25 (M350).

It is necessary to take a hammer weighing 300-400 grams.

All the methods described have their advantages and disadvantages; for the accuracy of the result, it is worth seeking help from specialists. Laboratory, ultrasound and shock-impulsive studies are more reliable and comprehensive. Quality directly depends on the characteristics of the constituent components, compliance with proportions, storage and transportation conditions. Therefore, you can protect yourself by choosing a trusted supplier with a good reputation, this will significantly reduce the risk of problems in the future.

By purchasing or building private house on concrete foundation it is necessary to very 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 by using universal tool will be covered in this article.

Non-destructive methods of concrete quality control

First of all, you should carefully examine the surface. The surface must be smooth. If the filling was carried out in winter time there should be no "patterns" on the concrete. If they are, it means that during the pouring period the concrete froze through, which reduces the strength of the structure to 50-100 kg / cm2;
Quality control using a hammer weighing at least 0.5 kg. Knock on the concrete structure and hear the tone. Ringing tonality and the absence of damage indicate the high quality of concrete and strength at a level of at least 200 kg / cm2; ringing sound and hammer prints 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 - poor quality concrete, strength no more than 100kg / cm2;
Visible surface defects in the form of a significant number of pores "speak" of poor compaction. In addition, this is a one hundred percent guarantee of poor quality concrete preparation. If it is a concrete structure in the open air, there is a high risk of gradual destruction in the cycle: "moisture penetration, moisture freezing, destruction of a micro layer of concrete", etc.

Method of checking the quality of concrete with a hammer and chisel

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

Place the chisel on the surface to be tested 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 constructions. Assessing the impact mark:

The trace is barely noticeable - high quality concrete corresponding to the B25 brand;
The trace is very noticeable - concrete grade B15-B25;
Strong indentations formed. The concrete began to paint - B10 grade concrete;
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 the concrete before pouring. To do this, it is necessary to fill in a sample with dimensions of 100x100x100 cm. Until the concrete has set, pierce it with a concrete rod to release air.

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

Assumption! If the construction time is tight, the sample can be transported 7-14 days after pouring. Moreover, in the laboratory it should be called exact time excerpts.

In addition to determining the quality of concrete with improvised means, there are the following methods that require special tool, devices and installations:

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

The correct choice and quality control of concrete is a guarantee of the strength, durability and safety of the future structure. It is very scrupulous to approach the issue of choosing a supplier, a method of delivering concrete and using a concrete solution.

Concrete foundations

The main load-bearing element of the entire building is the foundation. It is divided into different kinds... There are pile or block foundations, but most often in the construction of private houses, tape, columnar or combined structures are used. In this case, the quality of the concrete used for the construction of foundations is very important. This method is very popular due to its affordability, ease of construction and high strength of the resulting structures.

The choice of the grade of concrete is very important, the strength of the structure depends on it. For private houses, concrete from the 200th grade can be used. However, the fact that you ordered concrete of the grade you need does not mean that such a solution will be delivered to you. Less important indicators when using concrete are the degree of its ramming, the conditions of laying and setting.

How to choose a supplier

Conscientious manufacturers always control the process of making concrete, its composition and the quality of components. But how do you choose such a supplier? There are several ways:

You can contact companies that supply concrete for large construction projects. You can find their contacts at the foremen at such facilities.
Owners of newly built houses can also help make the choice of concrete for the foundation. That being said, you should examine the condition of their foundations. If you notice defects in the form of salt, cracks and delamination, then this indicates a low quality of concrete.
When choosing supplier sites, pay attention to those where there is not only a contact phone number, but also the organization's addresses, information about the company, registration data, etc.
When buying concrete, ask for a product passport with stamps. Moreover, he must go to each car separately. There must be specified grades for strength, mobility, frost resistance, time and day of shipment. It is better not to take handwritten passports without seals. It is advisable to buy Gostovsky concrete, not commercial.
It is also necessary to preserve the supply agreement. This way you can file a complaint with the manufacturer.

But the quality control of concrete must be carried out in any case.

Transportation can affect the fluidity of the mixture, its consistency. If the vehicle is driven over bumps at high speed, the homogeneity of the solution may be impaired. As a result, large concrete elements will settle to the bottom, and the liquid will rise. This solution cannot be used. Of course, the solution can be mixed, but it is better not to take it at all. It is also worth doing when transporting it open.

The choice of concrete should be made taking into account the time taken for transportation. If this time is exceeded, the concrete may delaminate. It should be within 2-3 hours. And in order to save time, it is better to unload directly into the formwork.

Concrete quality control

It can be done in several ways. The visual method is as follows:

When delivering concrete, the composition must be of a uniform consistency.
You can do a test fill. The concrete should not either run out of water or fall out in lumps. This indicates its heterogeneity.
A check for excess water is performed as follows: when pouring a small part of concrete into the pit, a cake should form without cracks and layers. If the composition looks like lumps in a liquid substance, then it is of poor quality.
Good concrete has grey colour. Brown color indicates an overabundance of sand, red indicates bad aggregates. However, when using plasticizing additives, the color of the concrete may differ from the gray. The uneven coloring should also alert. It is better to refuse such a composition.

Also, a test can be performed by a concrete quality control laboratory:

To do this, you need to pour the brought concrete into a wetted wooden box. Seal the composition by puncturing it with fittings. Place the box in a room with a specified humidity level and standard temperature. After 28 days, the sample is taken for testing.
Do not forget that you need to take a sample and pour it into molds to check the quality of concrete directly from the machine. You also need the driver to sign the sample collection report.
The laboratory uses a special device to test the quality of concrete.

How to pour the mixture

The choice of concrete grade is as important as correct styling mixtures. It is done in this way:

First you need to check the base in the pit. The fill base must be free from dust and clean. To do this, before pouring the mixture, the bottom of the pit is cleaned with air pressure.
Before pouring, the entire formwork is wetted lime milk or emulsions. This will protect the concrete from strong adhesion to the formwork and facilitate its dismantling.
Filling should be carried out in full in one day. This is needed to get a solid monolithic construction... On large objects, work is carried out by several teams from different machines at the same time.

To supply concrete, use a gutter with a length of 1.5 m. It must move to different points of the foundation belt, otherwise you will not be able to evenly distribute the concrete along the belt. For concrete to flow well, it is very important to make the right choice of cement for concrete. But if you cannot move the chute along the belt, you will have to lengthen it. This will allow you to move the end of the gutter to the desired location.

The easiest way to pour the mixture is with a concrete pump. The consumption will be higher, but the productivity will increase. Moreover, the unit can supply mortar to a length of 50 m. Thus, it is possible to fill from one machine at different points of the base.
The distance at which the mixture is dropped should not be more than 200 cm.
Concreted in layers of 5-10 cm, without interrupting the pouring.
After pouring, the concrete is tamped. You can find out how the choice of a vibrator for concrete is made in our other article.

It is best to compact the concrete with a downhole device. Choosing a vibrator for concrete will help increase the structural strength. In this case, the device is immersed in each layer separately, moving it inside the layer. It is not necessary to buy such a unit, you can rent it or order a rammer from a specific company.
If you do not want to buy a rammer, you can simply pierce the concrete in different places with reinforcement. However, this is very difficult, since you need to poke into concrete almost every square centimeter.

To protect the solution from exposure external factors after pouring, it is covered with a film. But for uniform drying, you will need to remove the film 4 times a day and pour water on the concrete. They do this for the first three days, then for another three days the procedure is carried out three times a day. However, instead of watering, you can choose a steam generator for steaming concrete, it is more efficient.
Installation of walls begins after complete setting of the concrete (after four weeks). By this time, the concrete strength will be maximum, as can be judged by the test results.

Quality control after pouring

You have already figured out how to choose the grade of concrete for the foundation, but it is also worth learning about ways to control the hardened foundation. For this, an ultrasound or a sclerometer can be used.

You can do this yourself. To do this, you need a chisel and a hammer weighing in the range of 300-800 g. The procedure is carried out as follows:

The chisel is placed at 90 degrees to the base and hit on it.
If the chisel fits easily into the base, then grade 70 grout or even lower was used.
When the tool is deepened by 3-7 mm, it can be said that the concrete grade was used in the range of 70-100.
Small holes with a depth of 2-3 mm indicate a concrete grade of 100 or 200.
When using a loaf with a brand of 200 and above, a small mark will be left as a result of the impact.

To make the result more accurate, such tests are carried out on different parts of the base.

Standards

The grade of the concrete composition affects the strength of the base after the mortar has completely set. This indicator is marked with the letter M and a digital indicator ranging from 50 to 500. It is measured in kgf / cm3. The indicator shows the compressive strength of concrete. For small structures, 100-150 brand foundations are sufficient. For individual houses need concrete grade 200-300. High grade concrete is used for the manufacture of load-bearing reinforced concrete structures.

The correct choice of plasticizer for concrete will increase its frost resistance. This figure indicates the total number of freeze and thaw cycles that the solution has held. It is marked with the letter F and a digital indicator in the range of 50-500. For our latitudes, concrete of medium frost resistance is suitable.

Another important indicator is water resistance. It is marked with the letter W and is in the range of 2-12 kgf / cm2. The number indicates the concrete's ability to withstand water pressure. For foundations for an individual house, you can take concrete with an indicator W 2-4. In the construction of swimming pools, concrete with a water resistance index of 8-12 is used.

The choice of crushed stone for concrete should be made taking into account the loads on the structure

There are visible signs by which you can determine the quality of concrete "by eye". Workers who are engaged in construction and work closely on pouring ready mixes, you should be trained to distinguish the quality of the imported mixture by visual signs in order to exclude the use of a low-quality product.

The quality of concrete can be determined by eye by the following features:
- lack of fat content and viscosity, which are typical for a layered concrete mixture,
- significant heterogeneity of the produced concrete is noticeable,
- the difference in color: as a standard, concrete has a dirty greenish color,
- on the surface of the concrete mix, there should be laitance, not turbid water.

All these signs indicate that the mixture should not be allowed to be stacked. Such a solution stratifies already on the way during the transportation period; it is often impossible to extract the mass even with a shovel, let alone feeding it through the sleeve.

Mediators.

It is no secret that in any region there are regular customers, some of them are resellers. It is in the case of working with a concrete reseller that it is most easy to run into a deception.

What can you expect from such cooperation:
- substitution of the concrete grade. You ordered concrete of the M200 brand, and they brought you M100. At the same time, everything is written correctly in the documents. Visually, the solutions are almost indistinguishable. The result of the deception will appear later, when the solution dries.
- cheating on the volume of shipped concrete solution. It is very difficult to calculate without errors the cubic meters required for filling at the facility.
- deception on the water. The driver loads a smaller volume and dilutes himself with water until the right amount... As a result, concrete strength is significantly lost.
- in addition to dishonest suppliers, there are also hired workers at the construction site who can also dilute the delivered concrete with water ... for example, in order to make it easier to lay.

The recommendations described below will help not to become deceived by the buyer and not to pay after the completion of the work.

How to avoid deception on concrete?

Order only from stationary concrete plants and conclude contracts. For each ordered batch, require a package of documents, and they must be factory-made, and not written “on the knee”, have a name, brand, time of shipment from the factory, concrete class, mobility, water resistance, frost resistance, signatures and seals. Take a sample from each machine for analysis by an independent laboratory.

Unfortunately, only a standard dice compression test, and non-destructive methods control with a sclerometer (Schmidt hammer), and an ultrasonic test method can confirm the true grade of concrete you purchased. Alas, by that time a month will have passed ... But if you have a full package of documents in your hands, and your concrete began to crack suddenly, you have a lot of chances to restore justice by winning the case in court. There are already such winners.

Ephemeral.

Unfortunately, even these measures may not save you from deception. In light of the almost constant economic crisis, they cheat not only on substitution, unfortunately, there are a lot of one-day companies that allegedly sell concrete and cement mortars.

The first sign of such a company is the site through which you found the seller. The presence of a landline phone in the list of company coordinates already gives a chance to buy concrete from a real-life seller. The presence of only a cell number should already alert! The second sign is very cheap concrete. Concrete cannot be cheap. It is enough to compare the prices of competitors in one region, as it becomes clear that low price questionable. Why is it low? ... And of course, reviews and additional information on the net. Search engines have information on the name of the company, by phone, by e-mail and other coordinates. Use search engines - spending half an hour - save a large amount.