Inspection of concrete and reinforced concrete structures. Inspection of reinforced concrete structures of buildings Inspection of concrete and reinforced concrete building structures

Inspection of concrete and iron concrete structures- an important part of the survey of a building or structure as a whole.

In this article, we reveal an approach to inspecting concrete and reinforced concrete structures. The durability of the building depends on the qualified performance of this part of the building survey.

Inspection of concrete and reinforced concrete structures of a building is carried out both as part of regular inspections during operation, and before the superstructure or reconstruction of the building, before the purchase of a building or when structural defects are detected.

Correct assessment of the state of concrete and reinforced concrete structures allows you to reliably assess their bearing capacity, which will ensure further safe operation or add-on / extension.

Evaluation of the technical condition of concrete and reinforced concrete structures by external signs is carried out on the basis of:

1. determination of the geometric dimensions of structures and their sections; These data are necessary for carrying out verification calculations. For an experienced specialist, sometimes, it is enough to visually assess the clearly insufficient dimensions of the structure.
2. comparison of the actual dimensions of structures with the design dimensions; The actual dimensions of the structures play a very important role as dimensions are directly related to calculations bearing capacity... One of the tasks of the designers is to optimize the dimensions, in order to avoid overspending building materials, and, accordingly, the rise in the cost of construction. The myth that designers include multiple safety factors in their calculations is actually a myth. The safety factors and safety factors are of course present in the calculations, but they are in accordance with SNiP for design 1.1-1.15-1.3. those. not so much.
3. the correspondence of the actual static scheme of work of structures adopted in the calculation; The actual scheme of loads of structures is also very important, since if the design dimensions are not observed due to construction defects, additional loads and bending moments in structures and assemblies may occur, which sharply reduces the bearing capacity of structures.
4. the presence of cracks, spalling and destruction; The presence of cracks, spalling and destruction is an indicator of unsatisfactory performance of structures, or indicates poor quality of construction work.
5. location, nature of cracks and width of their opening; By the location of the cracks, their nature and the width of their opening, the specialist can determine the likely cause of their occurrence. Some types of cracks are acceptable SNiP in reinforced concrete structures, others may indicate a decrease in the bearing capacity of the building structure.
6. condition of protective coatings; Protective coatings are called so because they must protect building structures from adverse and aggressive influences. external factors... Violation of protective coatings, of course, will not lead to instant destruction of the building structure, but it will affect the durability.
7. deflections and deformations of structures; The presence of deflections and deformations can give a specialist the opportunity to assess the performance of a building structure. Some bearing capacity calculations building structures are carried out according to the maximum permissible deflections.
8. signs of violation of adhesion of reinforcement to concrete; The adhesion of the reinforcement to the concrete is very important because concrete does not work in bending, but only in compression. Bending work in reinforced concrete structures is provided by reinforcement, which is prestressed. The lack of adhesion of reinforcement to concrete indicates that the bearing capacity of the reinforced concrete structure for bending has decreased.
9. the presence of a break in the reinforcement; Reinforcement ruptures indicate a decrease in bearing capacity up to the emergency category.
10. state of anchorage of longitudinal and transverse reinforcement; Anchoring the longitudinal and transverse reinforcement ensures the correct operation of the reinforced concrete building structure. Violation of the anchoring can lead to an emergency condition.
11. the degree of corrosion of concrete and reinforcement. Corrosion of concrete and reinforcement reduces the bearing capacity of the reinforced concrete structure, because reduced concrete thickness and reinforcement diameter due to corrosion. The thickness of the concrete and the diameter of the reinforcement are one of the important values ​​in calculating the bearing capacity of a reinforced concrete structure.

The size (width) of the crack opening in concrete is measured in the areas of their greatest opening and at the level of the reinforcement of the stretched zone of the element, because this most fully gives an idea of ​​the performance of the building structure.

The degree of crack opening is determined in accordance with SNiP 52-01-2003.

Cracks in concrete are analyzed from the point of view of structural features and the stress-strain state of a reinforced concrete structure. Sometimes cracks appear due to a violation of manufacturing technology, storage and transportation.

Therefore, the task of a specialist (expert) is to determine the probable cause of cracks and to assess the effect of these cracks on the bearing capacity of a building structure.

During the inspection of concrete and reinforced concrete structures, specialists determine the strength of the concrete. For this, the methods are used non-destructive testing or conduct laboratory tests and are guided by the requirements of GOST 22690, GOST 17624, SP 13-102-2003. During the survey, we use several non-destructive testing devices (shock-impulse method IPS-MG4, ONIKS; ultrasonic method UZK MG4.S; device for separation with spalling POS, and also, if necessary, use the "Kashkarov hammer"). We give a conclusion about the actual strength characteristics according to the readings of at least two devices. We also have the opportunity to conduct research on selected samples in the laboratory.

In civil and industrial construction, reinforced concrete structures are among the most used. During the construction, operation of various buildings, structures, they are often found various damage in the form of cracks, deflections, and other defects. This happens due to deviations from the requirements of the design documentation during their manufacture, installation, or caused by mistakes of the designers.

The Konstruktor company has a team of expert engineers with deep knowledge in different areas construction and features technological processes in industrial buildings, which is especially important when examining reinforced concrete structures. The main goal for which the inspection of reinforced concrete structures is carried out is to establish the current state of these elements with the identification of the causes of the identified deformations, to establish the degree of its wear individual elements... During the examination, the real strength, stiffness of concrete, its physical and technical condition are determined, damage is identified, and the reasons for their occurrence are determined. The task is not only to search for various defects in concrete and reinforced concrete structures, but also to prepare recommendations for the customer to correct the situation for the normal further operation of the facility. This becomes possible only after a detailed study of structures made of reinforced concrete and concrete.

Reasons for the need for examination

To determine the bearing capacity of structures, their condition, an examination of buildings and structures is carried out at the request of the customer. They can be carried out according to a certain schedule or the need for their implementation arises after man-made accidents, natural Disasters.

Inspection of structures made of concrete, reinforced concrete is required if:

• reconstruction of the building, structure is planned, if necessary, its re-profiling, changes functional purpose premises, which can increase the load on the supporting structures;
• there are deviations from the project (inconsistencies were found between real project and the erected object);
• there were obvious deformations of elements of buildings, structures that exceed the permissible, according to the standards, values;
• the standard service life of buildings has been exceeded;
• structures are physically worn out;
• structures, buildings have been exposed to natural, man-made impacts;
• there was a need to study the features of the work of reinforced concrete structures in difficult conditions;
• any kind of examination is carried out.

Survey stages

Concrete and reinforced concrete structures can be of different types and shapes, however, the methods of their research remain the same for everyone, and the work carried out has a clear sequence. The survey is aimed at identifying the strength of concrete, the extent of the spread of corrosion processes in metal reinforcement.

For a complete inspection of structures, specialists must step by step perform:

• preparatory work (study of documentation);
• field work (visual, detailed study directly at the facility using special tools);
• laboratory tests of taken samples;
• analysis of the results, carrying out calculations, determining the causes of defects;
• delivery of survey results to the customer with recommendations.

The work of specialists for the inspection of reinforced concrete structures begins with a study of all available project documentation, the service provided by the customer, analysis of the raw materials used at the facility.

Further, a direct examination of the object is carried out, which makes it possible to get an idea of ​​its real state. A preliminary external examination of prefabricated structures is carried out for the detection of their obvious defects.

At the stage of visual inspection of buildings and structures, the following can be identified:

• visible defects (cracks, spalling, destruction, damage);
• breaks of reinforcement, the real state of its anchorage (longitudinal, transverse);
• the presence of complete or partial destruction in various areas in concrete, reinforced concrete;
• displacement of individual elements, supports in structures;
• structural deflections, deformations;
• corrosive places of concrete, reinforcement, violation of their adhesion to each other;
• damage to protective coatings (screens, plaster, paintwork);
• areas with changed concrete color.

Instrumental examination

With a detailed examination in the process of work, specialists carry out the following actions:

• the geometric parameters of structures and their sections, the dimensions of external damage, defects are measured;
• detected defects are registered with marks of their characteristic features, location, width, depth of damage;
• strength, characteristic deformations of concrete, reinforcement are checked by instrumental or laboratory examination method;
• calculations are carried out;
• structures are tested for strength by loading (if necessary).

In the course of a detailed examination, the characteristics of concrete are assessed in terms of frost resistance, strength, abrasion, density, uniformity, water permeability, and the degree of its corrosion damage.

These properties are defined in two ways:

• laboratory tests of concrete samples that are taken from the structure in violation of its integrity;
• examination by ultrasonic, mechanical testers, moisture meters, other instruments using non-destructive testing methods.

For testing the strength of concrete, areas of visible damage are usually selected. In order to measure the thickness of the protective concrete layer during a detailed examination, non-destructive testing technologies are also used with the help of electromagnetic testers or its local opening is done.

The level of corrosion of concrete, reinforcement and its elements is determined by chemical-technical and laboratory methods for studying the samples taken. It is installed according to the type of concrete destruction, the spread of the process on surfaces, the capture of reinforcement with steel elements by rust.

The actual state of the reinforcement is also found out after collecting data about it and comparing them with the design parameters of the working drawings. Inspection of the condition of the reinforcement is carried out by removing the concrete layer to gain access to it. For this, places are selected where there are clear signs of corrosion in the form rust stains, cracks in the area of ​​reinforcing bars.

Inspection of structural elements is carried out by opening it in several places, depending on the area of ​​the object. If there are no obvious signs of deformations, then the number of openings is small or they are replaced by engineering sounding. The survey may include the determination of loads and their effects on structures.

Processing of examination results

At the end of the examination of concrete and reinforced concrete structures, the results are processed as follows:

1. Diagrams, statements are drawn up, where the deformations of the building, structures are recorded, indicating their characteristic features(deflections, rolls, faults, distortions, etc.).
2. The reasons for the appearance of deformations in concrete and structures are analyzed.
3. Based on the results of the survey, the bearing capacity of the structure is calculated, which will show the real state of the object and the likelihood of its trouble-free operation in the future. In the laboratory, samples of materials taken from structures of structures, buildings are tested, on the basis of which a test report is drawn up.

After that, a Technical Opinion is drawn up with the conclusions of specialists, which are presented to the customer:

• an appraisal opinion on the technical state of structures, determined by the degree of their damage, the characteristics of the identified defects;
• defective statements, tables, descriptions, results of instrumental and laboratory tests of samples taken during the examination;
• new technical certificate or an updated old document for a building, structure;
• conclusions on the probable causes of damage to structures made of concrete, reinforced concrete (if found);
• conclusions about the possibility to operate the building, the structure further;
• recommendations for the elimination of defects (if possible) in several versions (restoration, reinforcement of structures).

Reinforced concrete structures are strong and durable, but it is no secret that in the process of erecting and operating buildings and structures in reinforced concrete structures, unacceptable deflections, cracks, and damage occur. These phenomena can be caused either by deviations from the design requirements in the manufacture and installation of these structures, or design errors.

To assess the current state of a building or structure, a survey of reinforced concrete structures is carried out, which determines:

• Correspondence of the actual dimensions of structures to their design values;
• The presence of destruction and cracks, their location, nature and reasons for their appearance;
• The presence of explicit and hidden deformations of structures.
• The state of the reinforcement for a violation of its adhesion to concrete, the presence of ruptures in it and the manifestation of the corrosion process.

Most of the corrosion defects visually have similar signs, only a qualified inspection can be the basis for the appointment of methods of repair and restoration of structures.

Carbonation is one of the most common causes of destruction of concrete structures of buildings and structures in environments with high humidity, it is accompanied by the transformation of calcium hydroxide cement stone to calcium carbonate.

Concrete is capable of absorbing carbon dioxide, oxygen and moisture, which are saturated with the atmosphere. This not only significantly affects the strength of the concrete structure, changing its physical and Chemical properties, but negatively affects the reinforcement, when the concrete is damaged, it gets into an acidic environment and begins to collapse under the influence of harmful corrosion phenomena.

Rust, which is formed during oxidative processes, contributes to an increase in the volume of steel reinforcement, which, in turn, leads to fractures of reinforced concrete and exposure of rods. Bare, they wear out even more rapidly, this leads to an even faster destruction of concrete. Using specially developed dry mixes and paint coatings, it is possible to significantly increase the corrosion resistance and durability of the structure, but before that it is necessary to conduct its technical expertise.

Inspection of reinforced concrete structures consists of several stages:

• Identification of damages and defects by their characteristic features and their thorough examination.
• Instrumental and laboratory research characteristics of reinforced concrete and steel reinforcement.
• Calibration calculations based on the survey results.

All this contributes to the establishment of the strength characteristics of reinforced concrete, the chemical composition of aggressive media, the degree and depth of corrosion processes. For inspection of reinforced concrete structures are used necessary tools and certified devices. The results, in accordance with the current regulations and standards, are reflected in a well-written final conclusion.

Assessment of the technical condition of structures based on external features is based on the determination of the following factors:

• - geometric dimensions of structures and their sections;
• - the presence of cracks, spalling and destruction;
• - condition of protective coatings (paints and varnishes, plasters, protective screens and etc.);
• - deflections and deformations of structures;
• - violations of adhesion of reinforcement to concrete;
• - the presence of a rupture of the reinforcement;
• - state of anchorage of longitudinal and transverse reinforcement;
• - the degree of corrosion of concrete and reinforcement.

Determination and assessment of the state of paint and varnish coatings of reinforced concrete structures should be carried out according to the method described in GOST 6992-68. In this case, the following main types of damage are recorded: cracking and delamination, which are characterized by the depth of destruction of the upper layer (to the primer), bubbles and corrosion foci, characterized by the size of the focus (diameter), mm. The area of ​​certain types of damage to the coating is expressed as an approximate percentage in relation to the entire painted surface of the structure (element).

The effectiveness of protective coatings when exposed to an aggressive production environment is determined by the state of concrete structures after removing the protective coatings.

In progress visual examinations an approximate assessment of the strength of concrete is made. In this case, the tapping method can be used. The method is based on tapping the surface of the structure with a hammer weighing 0.4-0.8 kg directly on the cleaned mortar area of ​​concrete or on a chisel installed perpendicular to the surface of the element. In this case, to assess the strength, it is taken minimum values received as a result of at least 10 blows. A louder tapping sound corresponds to a harder, denser concrete.

In the presence of wetted areas and surface efflorescence on the concrete of structures, the size of these areas and the reason for their appearance are determined.

The results of visual inspection of reinforced concrete structures are recorded in the form of a map of defects, plotted on the schematic plans or sections of the building, or tables of defects are compiled with recommendations for the classification of defects and damage with an assessment of the category of the state of structures.

External signs characterizing the state of reinforced concrete structures in four categories of states are given in table.

Assessment of the technical condition of building structures based on external signs of defects and damage

Assessment of the technical condition of reinforced concrete structures by external signs

Notes: 1. To classify a structure as a condition category listed in the table, it is sufficient to have at least one feature characterizing this category. 2. Prestressed reinforced concrete structures with high-strength reinforcement, having signs of category II of state, belong to category III, and those with signs of category III - respectively to IV or V categories, depending on the danger of collapse. 3. When the bearing area of ​​precast elements is reduced against the requirements of the norms and the project, it is necessary to carry out an approximate calculation of the supporting element for shear and crush concrete. The calculation takes into account the actual loads and the strength of the concrete. 4. The assignment of the examined structure to one or another category of state in the presence of signs not noted in the table, in difficult and critical cases, should be made on the basis of analysis of the stress-strain state of structures performed by specialized organizations

Determination of concrete strength mechanical methods

Mechanical methods of non-destructive testing during the inspection of structures are used to determine the strength of concrete of all types of rated strength, controlled in accordance with GOST 18105-86.

Depending on the applied method and devices, indirect strength characteristics are:

• - the value of the rebound of the striker from the concrete surface (or the striker pressed against it);
• - parameter of the shock impulse (impact energy);
• - the dimensions of the indentation on concrete (diameter, depth) or the ratio of the diameters of the indentations on the concrete and the reference specimen when the indenter is hit or the indenter is pressed into the concrete surface;
• - the value of the stress required for local destruction of concrete when tearing off a metal disk glued to it, equal to the pull-off force divided by the area of ​​the projection of the concrete tear-off surface onto the plane of the disc;
• - the value of the effort required to chip a section of concrete on the edge of the structure;
• - the value of the force of local destruction of concrete when the anchor device is pulled out of it.

When conducting tests by mechanical methods of non-destructive testing, one should be guided by the instructions of GOST 22690-88.

To devices mechanical principle actions include: Kashkarov's standard hammer, Schmidt's hammer, Fizdel's hammer, TsNIISK's pistol, Poldi's hammer, etc. TsNIISK).

Fizdel's hammer (Fig. 1) is based on the use of plastic deformation of building materials. When struck with a hammer on the surface of the structure, a hole is formed, according to the diameter of which the strength of the material is assessed. The place of the structure to which the prints are applied is pre-cleaned of the plaster layer, grouting or painting. The process of working with Fizdel's hammer is as follows: the right hand is taken by the end of the wooden handle, the elbow is supported on the structure. With an elbow blow of medium strength, 10-12 blows are applied to each section of the structure. The distance between the impact hammer marks must be at least 30 mm. The diameter of the formed hole is measured with a caliper with an accuracy of 0.1 mm in two perpendicular directions and the average value is taken. From the total measurements made in this area, exclude the largest and smallest results, and the rest calculate the average value. The strength of concrete is determined by the average measured diameter of the indentation and a calibration curve previously constructed on the basis of a comparison of the diameters of the hammer ball imprints and the results of laboratory strength tests of concrete samples taken from the structure according to the instructions of GOST 28570-90 or specially made from the same components and according to the same technologies that the materials of the surveyed structure.

Concrete strength control methods

Method, standards, instruments	Test scheme
Ultrasonic GOST 17624-87 Instruments: UKB-1, UKB-1M UKB16P, UF-90PC Beton-8-URP, UK-1P
Plastic deformation Devices: KM, PM, DIG-4 Elastic rebound Instruments: KM, Schmidt sclerometer GOST 22690-88
Plastic deformation Kashkarov's hammer GOST 22690-88
Breakaway with discs GOST 22690-88 GPNV-6 device
Chipping the rib of the structure GOST 22690-88 GPNS-4 device with URS device
Shearing off GOST 22690-88 Devices: GPNV-5, GPNS-4

Rice. 1. The hammer I.A. Fizdelya:1 - hammer; 2 - pen; 3 - spherical socket; 4 - ball; 5 - angular scale

Rice. 2. Calibration chart for determining the ultimate strength of concrete in compression with Fizdel's hammer

Rice. 3. Determination of the strength of the material, using a hammer K.P. Kashkarova:1 - frame, 2 - metric handle; 3 - rubber handle; 4 - head; 5 - steel ball, 6 - steel reference bar; 7 - angular scale

Rice. 4. Calibration curve for determining the strength of concrete with Kashkarov's hammer

In fig. 2 shows a calibration curve for determining the ultimate strength in compression with a Fizdel hammer.

The method for determining the strength of concrete, based on the properties of plastic deformations, also includes Kashkarov's hammer GOST 22690-88.

A distinctive feature of Kashkarov's hammer (Fig. 3) from Fizdel's hammer is that there is a hole between the metal hammer and the rolled ball, into which a control metal rod is inserted. When struck with a hammer on the surface of the structure, two imprints are obtained: on the surface of the material with a diameter d and on a control (reference) rod with a diameter d eh . The ratio of the diameters of the resulting prints depends on the strength of the material being examined and the reference rod and practically does not depend on the speed and force of the blow applied by the hammer. Average value d/d eh the strength of the material is determined from the calibration schedule (Fig. 4).

At the test site, at least five determinations must be made with the distance between the indentations on the concrete not less than 30 mm, and on the metal rod - not less than 10 mm.

Devices based on the method of elastic rebound include the TsNIISK pistol (Fig. 5), Borovoy's pistol, Schmidt's hammer, KM sclerometer with a rod impactor, etc. The principle of operation of these devices is based on measuring the elastic rebound of the striker at a constant kinetic energy of a metal spring. The cocking and descent of the striker are carried out automatically when the striker touches the test surface. The magnitude of the striker's rebound is fixed by a pointer on the scale of the device.

Rice. 5. Pistol TsNIISK and S.I. Borovoy to determine the strength of concrete by a non-destructive method: 1 - drummer, 2 - frame, 3 - scale, 4 - fixture of the reading of the device, 5 - handle

TO modern means to determine the compressive strength of concrete by the non-destructive shock-impulse method, the ONIKS-2.2 device is used, the principle of operation of which is to fix the parameters of a short-term electrical impulse that occurs in the sensitive element in the sensitive element when it hits concrete, with its transformation into a strength value. After 8-15 strokes, the average strength value is displayed on the scoreboard. The series of measurements ends automatically after the 15th impact and the average strength value is displayed on the instrument panel.

A distinctive feature of the KM sclerometer is that a special striker of a certain mass, using a spring with a given stiffness and pre-stress, strikes the end of a metal rod, called a striker, pressed with the other end to the surface of the concrete being tested. As a result of the impact, the striker bounces off the striker. The degree of rebound is marked on the scale of the device using a special pointer.

The dependence of the rebound value of the striker on the strength of concrete is established according to the data of calibration tests of concrete cubes with a size of 151515 cm, and on this basis a calibration curve is constructed.

The strength of the material of construction is determined by the readings of the graduated scale of the device at the time of striking the tested element.

The shear strength test is used to determine the strength of concrete in the body of the structure. The essence of the method consists in assessing the strength properties of concrete by the force required for its destruction around a borehole of a certain size when pulling out an expanding cone fixed in it or a special rod embedded in concrete. An indirect indicator of strength is the breakout force required to pull out the anchor device embedded in the body of the structures together with the surrounding concrete at the embedment depth h(fig. 6).

Rice. 6. Scheme of the test by the method of separation with spalling when using anchor devices

In the shear pull test, the sections shall be located in the zone of lowest stresses caused by the service load or the compression force of the prestressed reinforcement.

The strength of concrete on the site is allowed to be determined based on the results of one test. Test areas should be selected so that reinforcement does not fall into the tear-out zone. At the test site, the thickness of the structure should be at least twice the embedment depth of the anchor. When punching a hole with a bolt or drilling, the thickness of the structure in this place must be at least 150 mm. The distance from the anchor device to the edge of the structure must be at least 150 mm, and from the adjacent anchor device - at least 250 mm.

During the tests, three types of anchor devices are used (Fig. 7). Type I anchoring devices are installed on structures during concreting; anchor devices of types II and III are installed in pre-prepared boreholes, punched in concrete by drilling. Recommended hole depth: for type II anchor - 30 mm; for anchor type III - 35 mm. The borehole diameter in concrete should not exceed the maximum diameter of the recessed part of the anchor device by more than 2 mm. Sealing of anchor devices in structures must ensure reliable adhesion of the anchor to concrete. The load on the anchor device should increase smoothly at a rate of no more than 1.5-3 kN / s until it breaks out together with the surrounding concrete.

Rice. 7. Types of anchor devices:1 - working rod; 2 - working rod with expanding cone; 3 - working rod with a full expansion cone; 4 - support rod, 5 - segmented grooved cheeks

Smallest and largest dimensions of the torn out part of concrete, equal to the distance from the anchor device to the boundaries of destruction on the surface of the structure, should not differ from one another by more than two times.

When determining the class of concrete by the method of chipping the rib of the structure, a device of the GPNS-4 type is used (Fig. 8). The test scheme is shown in Fig. 9.

Loading parameters should be taken: a= 20 mm; b= 30 mm, = 18.

At the test site, at least two concrete spalls must be carried out. The thickness of the test structure must be at least 50 mm. The distance between adjacent chips must be at least 200 mm. The load hook must be installed so that the "a" value does not differ from the nominal by more than 1 mm. The load on the tested structure should grow smoothly at a rate of no more than (1 ± 0.3) kN / s until the concrete is chipped off. In this case, there should be no slippage of the load hook. The test results, in which the reinforcement was exposed at the site of the spall, and the actual spalling depth differed from the specified one by more than 2 mm, are not taken into account.

Rice. 8. Device for determining the strength of concrete by spalling ribs:1 - the structure under test, 2 - chipped concrete, 3 - URS device, 4 - device GPNS-4

Rice. 9. Scheme of testing concrete in structures by shearing the rib of the structure

Single value R i the strength of concrete at the test site is determined depending on the compressive stresses of concrete b and values R i 0 .

Compressive stresses in concrete b valid during the test period are determined by calculating the structure, taking into account the actual dimensions of the sections and the values ​​of the loads.

Single value R i 0 concrete strength at the site under the assumption b= 0 is determined by the formula

where T g- a correction factor that takes into account the aggregate size, taken equal to: with a maximum aggregate size of 20 mm or less - 1, with a size of more than 20 to 40 mm - 1.1;

R iy- the conditional strength of concrete, determined according to the graph (Fig. 10) by the average value of the indirect indicator R

P i- the effort of each of the spalling performed at the test site.

When testing by spalling ribs, there should be no cracks, concrete chips, sagging or cavities with a height (depth) of more than 5 mm in the test area. The sections should be located in the zone of the lowest stresses caused by the operational load or the compression force of the prestressed reinforcement.

Rice. 10. Dependence of the conditional concrete strength Riy on the cleavage force Pi

Ultrasonic method for determining the strength of concrete. The principle of determining the strength of concrete by the ultrasonic method is based on the presence of a functional relationship between the propagation speed of ultrasonic vibrations and the strength of concrete.

The ultrasonic method is used to determine the compressive strength of concrete of classes B7.5 - B35 (grades M100-M400).

The strength of concrete in structures is determined experimentally according to the established calibration dependences of the "velocity of propagation of ultrasound - strength of concrete V=f (R)"Or" ultrasound propagation time t- concrete strength t=f (R)". The degree of accuracy of the method depends on the accuracy of the calibration schedule.

The calibration schedule is based on the sounding data and strength tests of control cubes made of concrete of the same composition, using the same technology, with the same hardening mode as the products or structures to be tested. When constructing a calibration schedule, one should be guided by the instructions of GOST 17624-87.

To determine the strength of concrete by the ultrasonic method, instruments are used: UKB-1, UKB-1M, UK-16P, "Beton-22", etc.

Ultrasonic measurements in concrete are carried out by means of through or surface sounding. The concrete test scheme is shown in Fig. eleven.

Rice. 11. Methods of ultrasonic sounding of concrete:a- test scheme by the through sounding method; b- the same, superficial sounding; UP- ultrasonic transducers

When measuring the propagation time of ultrasound by the through sounding method, ultrasonic transducers are installed on opposite sides of the sample or structure.

Ultrasound speed V, m / s, calculated by the formula

where t- ultrasound propagation time, μs;

l- distance between the centers of the installation of transducers (sounding base), mm.

When measuring the propagation time of ultrasound by the surface sounding method, ultrasonic transducers are installed on one side of the sample or structure according to the scheme.

The number of measurements of the propagation time of ultrasound in each sample should be: with through sounding - 3, with surface sounding - 4.

The deviation of a separate measurement result of the ultrasound propagation time in each sample from the arithmetic mean of the measurement results for this sample should not exceed 2%.

Measurement of the propagation time of ultrasound and determination of the strength of concrete are carried out in accordance with the instructions of the passport ( technical conditions application) of this type of device and the instructions of GOST 17624-87.

In practice, there are often cases when it becomes necessary to determine the concrete strength of the structures in operation in the absence or impossibility of constructing a calibration table. In this case, the determination of the strength of concrete is carried out in the zones of structures made of concrete on one type of coarse aggregate (structures of one batch). Ultrasound propagation speed V are determined in at least 10 sections of the surveyed area of ​​structures, according to which the average value is determined V. Next, areas are marked in which the propagation speed of ultrasound has a maximum V max and minimum V min values, as well as the section where the speed has a value V n closest to the value V, and then drilled from each target area at least two cores, which determine the strength values ​​in these areas: R max, R min, R n respectively. Concrete strength R H determined by the formula

R max / 100. (5)

Odds a 1 and a 0 is calculated by the formulas

When determining the strength of concrete using samples taken from the structure, one should be guided by the instructions of GOST 28570-90.

When the 10% condition is met, it is allowed to roughly determine the strength: for concretes of strength classes up to B25 according to the formula

where A- coefficient determined by testing at least three cores cut from structures.

For concretes of strength classes above B25, the strength of concrete in operating structures can also be estimated comparative method, taking as a basis the characteristics of the structure with the greatest strength. In this case

Structures such as beams, girders, columns should be sounded in the transverse direction, the slab should be sounded in the smallest size (width or thickness), and the ribbed slab - in the thickness of the rib.

With careful testing, this method provides the most reliable information about the strength of concrete in existing structures. Its disadvantage is the large laboriousness of work on the selection and testing of samples.

Determination of concrete cover and reinforcement location

To determine the thickness of the protective layer of concrete and the location of reinforcement in a reinforced concrete structure during examinations, magnetic, electromagnetic methods are used in accordance with GOST 22904-93 or methods of transillumination and ionizing radiation in accordance with GOST 17623-87 with selective control verification of the results obtained by punching furrows and direct measurements.

Radiation methods, as a rule, are used to examine the condition and control the quality of prefabricated and monolithic reinforced concrete structures during the construction, operation and reconstruction of especially critical buildings and structures.

The radiation method is based on transillumination of controlled structures with ionizing radiation and at the same time obtaining information about its internal structure using a radiation converter. Radiation of reinforced concrete structures is carried out using radiation from X-ray machines, radiation from sealed radioactive sources.

Transportation, storage, installation and adjustment of radiation equipment is carried out only by specialized organizations that have a special permit to carry out these works.

The magnetic method is based on the interaction of the magnetic or electromagnetic field of the device with the steel reinforcement of a reinforced concrete structure. anchor construction concrete fittings

The thickness of the concrete cover and the location of the reinforcement in the reinforced concrete structure are determined on the basis of the experimentally established relationship between the readings of the device and the specified controlled parameters of the structures.

To determine the thickness of the concrete cover and the location of reinforcement from modern devices used in particular ISM, IZS-10N (TU25-06.18-85.79). The IZS-10N device measures the thickness of the concrete cover depending on the reinforcement diameter within the following limits:

• - when the diameter of the reinforcement rods is from 4 to 10 mm, the thickness of the protective layer is from 5 to 30 mm;
• - with a diameter of reinforcement rods from 12 to 32 mm, the thickness of the protective layer is from 10 to 60 mm.

The device provides determination of the location of the projections of the axes of the reinforcement bars onto the concrete surface:

• - with diameters from 12 to 32 mm - with a concrete cover not more than 60 mm thick;
• - with diameters from 4 to 12 mm - with a concrete cover not more than 30 mm thick.

When the distance between the reinforcement rods is less than 60 mm, the use of IZS-type devices is impractical.

Determination of concrete cover thickness and reinforcement diameter is carried out in the following order:

• - prior to testing, the technical characteristics of the device used are compared with the corresponding design (expected) values ​​of the geometric parameters of the reinforcement of the controlled reinforced concrete structure;
• - if the technical characteristics of the device do not correspond to the parameters of the reinforcement of the controlled structure, it is necessary to establish an individual calibration dependence in accordance with GOST 22904-93.

The number and location of the controlled sections of the structure are assigned depending on:

• - the purpose and conditions of the tests;
• - features of the design solution of the structure;
• - technology of manufacturing or erection of a structure, taking into account the fixation of reinforcing bars;
• - operating conditions of the structure, taking into account the aggressiveness of the external environment.

Work with the device should be carried out in accordance with the instructions for its operation. At the measurement points on the surface of the structure, there should be no sagging with a height of more than 3 mm.

When the thickness of the protective concrete layer is less than the measurement limit of the device used, the tests are carried out through a gasket with a thickness of (10 ± 0.1) mm made of a material that does not have magnetic properties.

The actual concrete cover in this case is determined as the difference between the measurement results and the thickness of this pad.

When monitoring the location of steel reinforcement in the concrete of a structure, for which there is no data on the diameter of the reinforcement and the depth of its location, determine the layout of the reinforcement and measure its diameter by opening the structure.

For an approximate determination of the diameter of the reinforcing bar, the location of the reinforcement is determined and fixed on the surface of the reinforced concrete structure using an IZS-10N device.

The device transducer is installed on the surface of the structure, and several values ​​of the concrete cover thickness are determined using the device scales or individual calibration dependence pr for each of the assumed reinforcing bar diameters that could be used to reinforce the structure.

A spacer of appropriate thickness (for example, 10 mm) is installed between the device transducer and the concrete surface of the structure, measurements are taken again and the distance is determined for each assumed diameter of the reinforcing bar.

For each diameter of the reinforcing bar, the values ​​are compared pr and ( abs - e).

As actual diameter d take a value for which the condition is satisfied

[ pr -(abs - e)] min, (10)

where abs- indication of the device, taking into account the thickness of the gasket.

The indices in the formula indicate:

s- pitch of longitudinal reinforcement;

R- pitch of transverse reinforcement;

e- the presence of a gasket;

e- the thickness of the gasket.

The measurement results are recorded in a journal, the form of which is shown in the table.

The actual values ​​of the concrete cover thickness and the location of the steel reinforcement in the structure according to the measurement results are compared with the values ​​established by the technical documentation for these structures.

The measurement results are documented in a protocol, which should contain the following data:

• - the name of the tested structure (its symbol);
• - batch size and number of controlled structures;
• - type and number of the device used;
• - numbers of controlled sections of structures and a diagram of their location on the structure;
• - design values ​​of the geometric parameters of the reinforcement of the controlled structure;
• - the results of the tests carried out;
• - a reference to the instructive and normative document regulating the test method.

Form of recording the results of measuring the thickness of the protective layer of concrete of reinforced concrete structures

Determination of strength characteristics of reinforcement

The design resistances of undamaged reinforcement are allowed to be taken according to design data or according to the design standards of reinforced concrete structures.

• - for smooth reinforcement - 225 MPa (class A-I);
• - for reinforcement with a profile, the ridges of which form a helical line pattern - 280 MPa (class A-II);
• - for reinforcement of a periodic profile, the ridges of which form a herringbone pattern - 355 MPa (class A-III).

Rigid reinforcement made of rolled profiles is taken in calculations with a design tensile, compression and bending strength of 210 MPa.

Without necessary documentation and information, the class of reinforcing steels is established by testing samples cut from the structure with a comparison of the yield strength, ultimate strength and elongation at break with the data of GOST 380-94.

The location, number and diameter of reinforcing bars are determined either by opening and direct measurements, or by using magnetic or radiographic methods (according to GOST 22904-93 and GOST 17625-83, respectively).

To determine the mechanical properties of steel in damaged structures, it is recommended to use the following methods:

• - testing of standard samples cut from structural elements, in accordance with the instructions of GOST 7564-73 *;
• - tests of the surface layer of metal for hardness in accordance with the instructions of GOST 18835-73, GOST 9012-59 * and GOST 9013-59 *.

It is recommended to cut blanks for samples from damaged elements in places that have not received plastic deformations during damage, and so that after cutting, their strength and stability are ensured.

When selecting blanks for samples, structural elements are divided into conditional batches of 10-15 of the same type structural elements: trusses, beams, columns, etc.

All blanks must be marked in the places of their taking and the marks are indicated on the diagrams attached to the materials for the inspection of structures.

The characteristics of the mechanical properties of steel - yield strength t, ultimate strength and elongation at break - are obtained by tensile testing of specimens in accordance with GOST 1497-84 *.

The determination of the main design resistances of steel of structures is made by dividing the average value of the yield point by the material safety factor m = 1.05 or the ultimate strength by the safety factor = 1.05. In this case, the calculated resistance is the smallest of the values R T, R, which are found, respectively, by m and.

When determining the mechanical properties of metal by the hardness of the surface layer, it is recommended to use portable portable devices: Poldi-Hutta, Bauman, VPI-2, VPI-Zk, etc.

The data obtained during the hardness test are converted into characteristics of the mechanical properties of the metal according to the empirical formula. So, the relationship between the Brinell hardness and the temporary resistance of the metal is established by the formula

3,5H b ,

where N- Brinell hardness.

The revealed actual characteristics of the reinforcement are compared with the requirements of SNiP 2.03.01-84 * and SNiP 2.03.04-84 *, and on this basis the serviceability of the reinforcement is assessed.

Determination of concrete strength by laboratory tests

The laboratory determination of the concrete strength of existing structures is carried out by testing samples taken from these structures.

Sampling is carried out by cutting out cores with a diameter of 50 to 150 mm in areas where the weakening of the element does not significantly affect the bearing capacity of structures. This method provides the most reliable information about the strength of concrete in existing structures. Its disadvantage is the high labor intensity of work on the selection and processing of samples.

When determining the strength for samples taken from concrete and reinforced concrete structures, one should be guided by the instructions of GOST 28570-90.

The essence of the method consists in measuring the minimum efforts that destroy concrete samples drilled or sawn out of a structure under static loading with a constant load growth rate.

The shape and nominal dimensions of the samples, depending on the type of concrete testing, must comply with GOST 10180-90.

It is allowed to use cylinders with a diameter of 44 to 150 mm, a height of 0.8 to 2 diameters when determining the compressive strength, from 0.4 to 2 diameters when determining the tensile strength at splitting, and from 1.0 to 4 diameters when determining the strength at axial tension.

For all types of tests, a sample with a working section size of 150–150 mm is taken as the basic one.

Concrete sampling sites should be designated after visual inspection of structures, depending on their stress state, taking into account the minimum possible reduction in their bearing capacity. It is recommended to take samples from places far from joints and edges of structures.

After sampling, the sampling sites should be sealed with fine-grained concrete or concrete from which the structures are made.

Areas for drilling or cutting out concrete samples should be selected in places free of reinforcement.

To drill out samples from concrete structures, use drilling machines type IE 1806 according to TU 22-5774 s cutting tool in the form of circular diamond drills of the SKA type according to TU 2-037-624, GOST 24638-85 * E or carbide end drills according to GOST 11108-70.

To cut samples from concrete structures, sawing machines of the URB-175 type according to TU 34-13-10500 or URB-300 according to TU 34-13-10910 are used with a cutting tool in the form of cutting diamond disks of the AOK type according to GOST 10110-87E or TU 2- 037-415.

It is allowed to use other equipment and tools for making samples of concrete structures, ensuring the production of samples that meet the requirements of GOST 10180-90.

Testing of samples for compression and all types of tension, as well as the choice of the test and loading scheme is carried out in accordance with GOST 10180-90.

The supporting surfaces of the samples tested for compression, in the case when their deviations from the surface of the press plate are more than 0.1 mm, must be corrected by applying a layer of a leveling compound. The cement paste should be used as typical, cement-sand mortar or epoxy compositions.

The thickness of the layer of the leveling compound on the sample should be no more than 5 mm.

The strength of the concrete of the test specimen with an accuracy of 0.1 MPa during compression tests and with an accuracy of 0.01 MPa during tensile tests is calculated by the formulas:

for compression;

axial tension;

tensile bending,

A- the area of ​​the working section of the sample, mm 2;

a, b, l- respectively width and height cross section prisms and distance between supports when testing specimens for tensile bending, mm.

To bring the strength of concrete in the tested sample to the strength of concrete in a sample of the base size and form of strength obtained according to the indicated formulas, recalculate according to the formulas:

for compression;

axial tension;

tensile splitting;

tensile bending,

where 1, and 2 are coefficients that take into account the ratio of the height of the cylinder to its diameter, taken during compression tests according to the table, during tensile splitting tests according to table. and equal to one for samples of a different shape;

Scale factors that take into account the shape and dimensions of the cross-section of the tested samples are determined experimentally in accordance with GOST 10180-90.

The test report shall consist of a sampling report, the results of the test of the samples and an appropriate reference to the standards against which the test was carried out.

Cost of inspection of reinforced concrete structures
from 17,000 rubles

Reinforced concrete structures are strong and durable objects. If they were built in strict accordance with the project, then in the future there should be no problems with their operation. If you are even sure that the object is flawless in terms of the materials used, it is worth regularly monitoring it. The fact is that even the most durable buildings are exposed to aggressive factors and their resistance to corrosion begins to decrease.

Our experts professionally investigate civil and industrial building and structures in Moscow and recommend ordering a survey of reinforced concrete structures of buildings:

• Before commissioning.
• Within 2 years after commissioning.
• At least once every 10 years.
• Before the purchase.
• Before redevelopment, reconstruction.
• If the object has reached the end of its service life.
• After natural disasters and man-made accidents.

Prices for inspection of reinforced concrete structures

In all these situations, the purpose of the survey is to determine the technical condition, identify defects, and establish their causes. Only a detailed study of reinforced concrete objects will make it possible to achieve these goals. Inspection of the condition of objects should be carried out only by experts who have the right to work in this area, that is, have received access to SROs to carry out activities in the field of construction expertise.

Our advantages

Experienced professionals

Our specialists, who have been working in this field for many years, have a full range of practical knowledge.

Quality of work

Carrying out work takes a minimum of time, while the quality always remains at its best

Wide range of services

Our company specializes in providing a range of services

Affordable prices

Affordable prices with high quality work

How we are working?

Although reinforced concrete structures are diverse, their examination is carried out according to a single algorithm:

• Preparation and study of technical, project documentation.
• Field work. They are carried out directly at the facility. Experts conduct visual, detailed research. They on this stage use ultra-precise equipment that allows you to determine the strength and other characteristics of materials.
• Laboratory tests of those samples that were taken at the previous stage.
• Analytical work with the results obtained, identifying the causes of defects. Note that the most common reasons for the destruction of reinforced concrete structural elements is leaching, carbonation, rust, etc.
• Drawing up a technical opinion and issuing it to the customer.

Calling our experts, you will specify the prices for the service: they will name preliminary rates for the examination of reinforced concrete structures of buildings. The exact amount will be calculated after reviewing the terms of reference.