Reinforced concrete structures are durable and durable, but it is no secret that in the process of the construction and operation of buildings and structures in reinforced concrete structures there are unacceptable defamations, cracks, damage. These phenomena can be caused by either deviations from the project requirements in the manufacture and installation of these structures, or design errors.

For rate current status Buildings or structures conduct iron survey concrete structuresdefining:

• Compliance with the actual dimensions of the designs by their design values;
• The presence of destruction and cracks, their location, nature and causes of appearance;
• The presence of explicit and hidden deformations of structures.
• The state of the reinforcement for the disorders of its clutch with concrete, the presence of breaks and manifestation of the corrosion process.

Most corrosion defects visually have similar signs, only a qualified examination may be the basis for appointing the methods of repair and restoring structures.

Carbonization is one of the most frequent causes of the destruction of concrete structures of buildings and structures in environments with high humidityIt is accompanied by the conversion of calcium-stone calcium hydroxide in calcium carbonate.

Concrete is able to absorb carbon dioxide, oxygen and moisture, which is saturated atmosphere. This not only significantly affects the strength of the concrete structure, changing its physical and chemical properties, but negatively affects the reinforcement, when concrete damage, entering the acid medium and the beginning to collapse under the influence of detrimental corrosion phenomena.

Rust, which is formed during oxidative processes, contributes to an increase in the volume of steel reinforcement, which, in turn, leads to faults of reinforced concrete and bare of rods. Golden, they wear out even rapidly, it leads to even more rapid destruction of concrete. Using specially designed dry mixes and paint coatings, it is possible to significantly increase the corrosive resistance and durability of the structure, but before this it is necessary to carry out its technical expertise.

The survey of reinforced concrete structures consists of several stages:

• Detection of damage and defects on their characteristic features and their careful inspection.
• Instrumental I. laboratory research Characteristics of reinforced concrete and steel reinforcement.
• The implementation of verification calculations based on the results of the survey.

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. To examine reinforced concrete structures used required tools And attorneys. Results, respectively, valid standards and standards are reflected in the competently compiled final conclusion.

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

• geometric sizes of structures and their sections;
• the presence of cracks, openings and destruction;
• states of protective coatings (paints and varnisions, plasters, protective screens, etc.);
• defunctions and deformations of structures;
• impairment of fittings with concrete;
• presence of reinforcement;
• state of anchoring of longitudinal and transverse reinforcement;
• The degree of corrosion of concrete and reinforcement.

When determining the geometric parameters of structures and their cross sections, all deviations from their project position are recorded. Determination of the width and depth of cracks should be performed on the recommendations specified above.

The width of the disclosure of cracks is recommended to be measured primarily in the places of maximum disclosure and at the level of the stretched zone of the element. The degree of crack disclosure is compared with the regulatory requirements for the limit states of the second group, depending on the type and conditions of the design of the structures. Cracks should be distinguished, the appearance of which is caused by stresses that manifested in reinforced concrete structures in the process of manufacture, transportation and installation, and cracks due to operational loads and environmental impact.

To cracks that appeared during the period of operation of the facility include: technological, shrinkage, caused by rapid drying of the surface layer of concrete and cutting volume, as well as cracks from concrete swelling; caused by uneven cooling of concrete; Crackers arising in the precast concrete elements in the process of storage, transportation and installation, in which the structures were subjected to power influences on their own weight according to the schemes not provided for by the project.

To the cracks that appeared in the operational period include: cracks resulting from temperature deformations due to violations of the requirements of the temperature seams; caused by unevenness of the pound basis, which may be due to violation of the requirements of the device of sedimentary deformation seams, earthworks in close proximity to the foundations without ensuring special measures; Conditioned by force acts exceeding the carrying capacity of reinforced concrete elements.

Powerful cracks should be considered from the point of view of the stress-deformed state of the reinforced concrete structure.

In reinforced concrete structures, the following types of cracks are most common:

• a) in bending elements working on the beam diagram (beams, runs), cracks, perpendicular (normal) longitudinal axis, due to the appearance of tensile stresses in the zone of maximum bending moments, inclined to the longitudinal axis caused by the main tensile stresses in the distress zone Forces and bending moments (Fig. 2.32).

Fig. 2.32.

working on the Balochy scheme

• 1 - normal cracks in the zone of the maximum bending moment;
• 2 - inclined cracks in the zone of the maximum transverse force;
• 3 - cracks and fragmentation of concrete in a compressed zone.

Normal cracks have the maximum disclosure width in extremely stretched fibers of the cross section of the element. Inclined cracks begin to reveal in the middle part of the side of the element - in the range of maximum tangent stresses, and then develop toward the stretched face.

The formation of inclined cracks at the reference ends of beams and runs is due to their insufficient bearing capacity of inclined sections.

Vertical and inclined cracks in the spanites of beams and runs indicate the insufficient carrier ability to bending the moment.

The fragmentation of concrete compressed zone of cross sections of the bending elements indicates the exhaustion of the carrying capacity of the structure;

b) Cracks may occur in the plates:

in the middle part of the slab, having a direction across the working span with the maximum disclosure on the lower surface of the plate;

on supporting areas, having a direction across a working span with a maximum disclosure on the top surface of the plate;

radial and end, with a possible disappearance of the protective layer and the destruction of the concrete plate;

along the reinforcement along the bottom plane of the wall.

Cracks on supporting plates of slabs across the working span indicate an insufficient bearing capacity of the bending reference point.

The development of fractures of power origin on the lower surface of the plates with a different aspect ratio is characteristic (Fig. 2.33). In this case, the concrete compressed zone may not be broken. Concrete crushes compressed zone indicates the danger of complete destruction of the plate;

Fig. 2.33. Characteristic cracks on the bottom surface of the plates: A - working on the beam diagram at / 2 //,\u003e 3; b - opened by contour at / 2 //, 1.5

b) Vertical cracks on columns and horizontal cracks are formed in the columns.

Vertical cracks on the edges of the columns can appear as a result of excessive bending of reinforcement rods. Such a phenomenon may occur in those columns and their zones where the clamps are rarely delivered (Fig. 2.34).

Fig. 2.34.

Horizontal cracks in reinforced concrete columns are not direct danger, if their width is small, but through such cracks can enter the moistened air and aggressive reagents, causing metal corrosion,

The appearance of longitudinal cracks along the reinforcement in compressed elements indicates the destruction associated with loss of stability (by releasing) longitudinal compressed reinforcement due to insufficient number of transverse reinforcement;

• d) the appearance in the bending elements of the transverse, perpendicular longitudinal axis of the element, the crack passing through the entire section (Fig. 2.35) can be associated with the effect of an additional bending moment in the horizontal plane, perpendicular to the plane of the action of the main bending moment (for example, from horizontal forces, arising in crane beams). The same character has cracks in stretched reinforced concrete elements, but at the same time cracks are viewed on all the faces of the element, they are squeezed;
• e) cracks on supporting sites and faces of reinforced concrete structures.

Detected cracks in the ends of the pre-intense elements oriented along the reinforcement indicate a violation of the anchoring of reinforcement. The inclined cracks in the bedroom areas crossing the zone of pre-stressed reinforcement and extending to the lower edge of the edge of the support (Fig. 2.36);

e) elements of the lattice of diagonal reinforced concrete farms may experience compression, stretching, and in support nodes - action

carrying forces. Characteristic damage

Fig. 2.36.

• 1 - with violation of the anchoring of strenuous reinforcement;
• 2 - Ply

insufficiency

indirect

reinforcement

Fig. 2.35.

planes

denia in the destruction of individual sections of such farms are shown in Fig. 2.37. In addition to cracks, 2 (Fig. 2.38) of type 1, 2 damage (Fig. 2.38), the appearance of horizontal cracks in the lower preframed belt of type 4 (see Fig. 2.37) indicates the absence or lack of transverse reinforcement in the compressed concrete. Normal (perpendicular to the longitudinal axis) of type 5 cracks appear in stretched rods in the insecurity of the crack-resistant elements. The appearance of damage in the form of type 2 shoes indicates the exhaustion of concrete strength in separate sections of a compressed belt or on the support.

Fig. 2.37.

pre-stressed belt:

1 - an inclined crack at the support node; 2 - broken shoes; 3 - Light and vertical cracks; 4 - horizontal crack; 5 - vertical (normal) cracks in stretched elements; 6 - inclined cracks in a compressed farm belt; 7 - Cracks in the bottom belt node

Defects in the form of cracks and detachment of concrete along the reinforced concrete elements can be caused by corrosion destruction of the reinforcement. In these cases, there is a violation of the clutch of longitudinal and transverse reinforcement with concrete. Violation of the adhesion of reinforcement with concrete due to corrosion

Fig. 2.38.

install the clutch of the surface of the concrete (with emptiness listened).

Longitudinal cracks along the reinforcement with a clutch impaired with concrete can be caused by temperature stresses in the operation of structures with systematic heating over 300 ° C or the consequences of a fire.

In bending elements, as a rule, the appearance of cracks causes an increase in the deflection and corners of the turn. Unacceptable (emergency) can be considered the defaults of the bent elements more than 1/50 of the span with the width of the cracks in the stretched zone of more than 0.5 mm. The values \u200b\u200bof extremely permissible deflection for reinforced concrete structures are given in Table. 2.10.

The definition and assessment of the condition of coating of reinforced concrete structures should be made according to the method described in GOST 6992-68. At the same time, the following main types of damage are recorded: cracking and detachment, which are characterized by the depth of destruction of the upper layer (to primer), bubbles and corrosion foci, characterized by the focus size (diameter), mm. The area of \u200b\u200bindividual types of coating damage is expressed approximately as a percentage in relation to the entire painted surface of the design (element).

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

In the process of visual surveys, an estimated assessment of concrete strength is produced. The method is based on the appealing of the surface surface with a hammer mass of 0.4-0.8 kg directly along the purified mortar section of concrete or in a chisel installed perpendicular to the surface of the element. More call sound When climbing, it corresponds to a stronger and dense concrete. The day of receipt of reliable data on the strength of concrete should be applied to the methods and devices shown in the section on the monitoring of strength.

If there are moistened sections and surface high-fishing on concrete structures, they determine the magnitude of these sites and the reason for their appearance. The results of the visual inspection of reinforced concrete structures are fixed as a map of defects deposited on schematic plans or cuts of the building, or make up defect tables with recommendations for the classification

The value of the maximum permissible deflection of reinforced concrete

Constructions

Table 2.10

Note. Under the action of constant, lengthy and short-term loads, the beams and slabs should not exceed 1/150 span and I / 75 departure console.

catalog of defects and damage with the assessment of the category of status of structures.

To assess the nature of the corrosion process and the degree of impact of aggressive media, there are three main types of corrosion of concrete.

The type of corrosion processes include all the processes of corrosion that occur in concrete under action. liquid media (aqueous solutions) capable of dissolving the components of cement stone. The components of the cement stone dissolve and are taken out of cement stone.

The II type of corrosion includes processes under which chemical interactions occur - exchange reactions - between cement stone and solution, including exchange of cations. The resulting reaction products or easily soluble and are made from the structure as a result of diffusion or filtration flow, or deposited as an amorphous mass that does not have astringent properties and does not affect the further destructive process.

This type of corrosion represent processes arising under the action to concrete solutions of acids and some salts.

To the III form of corrosion include all the processes of corrosion of concrete, as a result of which the reaction products accumulate and crystallize in the pores and capillaries of concrete. At a certain stage of development of these processes, the growth of crystal formations causes the occurrence of raising voltages and deformations in the enclosing walls, and then leads to the destruction of the structure. To this kind, corrosion processes under the action of sulfates associated with the accumulation and growth of hydrosulfoaluminum crystals, gypsum, etc. The destruction of concrete in structures during their operation occurs under the influence of many chemical and physical and mechanical factors. These include the inhomogeneity of concrete, elevated voltages in the material of various origins, leading to microinders in the material, alternate moisturizing and drying, periodic freezing and thawing, sharp drops of temperatures, the effects of salts and acids, leaching, violation of contacts between cement stone and aggregates, steel corrosion Armatures, destruction of aggregates under the influence of alkali cement.

The difficulty of studying the processes and factors to determine the destruction of concrete and reinforced concrete is explained by the fact that, depending on the conditions of operation and the service life of the structures, there are simultaneously there are many factors leading to changes in the structure and properties of materials. For most structures in contact with air, carbonization is a characteristic process that weakens the protective properties of concrete. Concrete carbonization can cause not only carbon dioxide available in the air, but also other acidic gases contained in an industrial atmosphere. In the process of carbonization, carbon dioxide air penetrates the pores and capillaries of concrete, dissolves in pore liquid and reacts with hydroalumum of calcium oxide, forming a weak-soluble calcium carbonate. Carbonization reduces the alkalinity of the moisture contained in the concrete, which leads to a decrease in the so-called passivating (protective) action of alkaline media and corrosion of reinforcing in concrete.

To determine the degree of corrosion destruction of concrete (degree of carbonization, composition of neoplasms, structural disorders of concrete), physico-chemical methods are used.

The study of the chemical composition of the neoplasms arising in concrete under the action of an aggressive medium is produced using differential-thermal and X-ray-structural methods performed in laboratory conditions on samples selected from the exploited structures. The study of structural changes of concrete is performed using a manual magnifying glass that gives a slight increase. Such an inspection allows you to study the surface of the sample, to identify the presence of large, cracks and other defects.

With the help of a microscopic method, you can identify the mutual location and the nature of the adhesion of cement stone and aggregate grains; Contact condition between concrete and reinforcement; form, size and pore form; Size and direction of cracks.

The determination of the depth of the carbonization of concrete is produced by changing the pH hydrogen indicator.

If the concrete is dry, wet the surface of the chip with clear water, which should be so much so that the visible film of moisture is not formed on the surface of the concrete. Excess water is removed with clean filter paper. Wet and air-dry concrete moisturizing does not require.

A 0.1% solution of phenolphthalene in ethyl alcohol is applied to the chole concrete with a dropper or pipette. When the pH is changed from 8.3 to 14, the color of the indicator varies from colorless to bright crimson. The fresh flow of concrete sample in the carbonized zone after applying the phenolphthalein solution on it is gray, and brightly raspberry paint acquires in the non-commissioned zone.

About a minute after the application, the indicator is measured by a ruler with an accuracy of 0.5 mm from the surface of the sample to the boundary of the brightly colored zone in the direction normal to the surface. The measured value is the depth of concrete carbonization. In concrete with a uniform structure of pores, the boundary of the brightly painted zone is usually located in parallel to the outer surface. In concrete with a non-uniform structure of pores, the border of carbonization can be winding. In this case, it is necessary to measure the maximum and middle depth of the carbonization of concrete. Factors affecting the development of corrosion of concrete and reinforced concrete structures are divided into two groups: related properties external environment - atmospheric and groundwater, industrial environments, etc., and caused by the properties of materials (cement, aggregates, water, etc.) of structures.

For exploited structures, it is difficult to determine how many and what chemical elements remains in the surface layer, and whether they are able to further continue their destructive action. Assessing the risk of corrosion of concrete and reinforced concrete structures, it is necessary to know the characteristics of concrete: its density, porosity the amount of emptiness, etc.

Processes of corrosion of reinforced concrete structures and methods of protection from it are complex and diverse. The destruction of the reinforcement in concrete is due to the loss of protective properties of concrete and the access to it moisture, air oxygen or acid-forming gases. Corrosion of reinforcement in concrete is an electrochemical process. Since the reinforcement steel is heterogeneous under the structure, as in contact with it, all conditions are created for the flow of electrochemical corrosion.

The corrosion of reinforcement in concrete occurs when the alkalinity of the surrounding electrolyte reinforce is reduced to the pH, equal to or less than 12, with carbonization or corrosion of concrete.

In assessing the technical condition of the reinforcement and mortgage parts affected by corrosion, it is primarily necessary to establish a type of corrosion and areas of lesion. After determining the type of corrosion, it is necessary to establish sources of exposure and reasons for corrosion of reinforcement. The thickness of corrosion products is determined by the micrometer or using instruments that measure the thickness of non-magnetic anti-corrosive coatings on steel (for example, ITP-1, MT zones, etc.).

For the reinforcement of the periodic profile, the residual severity of reefs after stripping should be noted.

In places where corrosion products began to preserve well, it is possible to approximately judge the depth of corrosion in relation to their thickness.

where 8 a. - the average depth of continuous uniform corrosion of steel; - thickness of corrosion products.

The identification of the state of the valves of elements of reinforced concrete structures is performed by removing the protective layer of concrete with the exposure of the working and assembly reinforcement.

The exposure of the reinforcement is made in the places of the greatest attenuation of corrosion, which are detected by the detachment of the protective layer of concrete and the formation of cracks and spots of rusty color, located along the rods of the reinforcement. The diameter of the reinforcement is measured by a caliper or micrometer. In places where the reinforcement has undergone intensive corrosion, which caused the decay of the protective layer, is produced thorough sweep Its from rust before the appearance of a metal shine.

The degree of corrosion of the reinforcement is estimated according to the following features: the nature of corrosion, color, density of corrosion products, the area of \u200b\u200bthe affected surface, the cross-sectional area of \u200b\u200bthe reinforcement, the depth of corrosion lesions.

With continuous uniform corrosion, the depth of corrosion lesions is determined by measuring the thickness of the rust layer, with a peptic - measurement of the depth of individual ulcers. In the first case, a sharp knife is separated by a rust film and its thickness is measured by a caliper. In this case, it is assumed that the depth of corrosion is equal to either half of the thickness of the rust layer, or half of the difference in the design and valid diameters of the reinforcement.

With ulcerative corrosion, it is recommended to cut pieces of fittings, rust remove etching (immersing fittings in a 10% hydrochloric acid solution containing 1% inhibitor-urotro-pin), followed by washing with water. Then the reinforcement must be immersed by 5 minutes into a saturated solution of sodium nitrate, remove and rub. The depth of the ulcers is measured by an indicator with a needle reinforced on a tripod.

The corrosion depth is determined by the indicator arrows indicative as the difference in the edge of the edge and the bottom of the corrosion ulcers. When detecting areas of structures with increased corrosion wear associated with local (concentrated) effects of aggressive factors, it is recommended to first pay attention to the following elements and components nodes:

• Supported assemblies of rafter and subcupile farms, near which waterfronts are located inland drain;
• Ferm's top belts in the nodes of accession to them aeration lamps, windproof panels;
• Top belt of subcording farms, along which endand roofs are located;
• Farm support nodes that are inside brick walls;
• top parts of columns inside brick walls;
• The bottom and bases of columns located at or below the floor level, especially when wet cleaning indoors (hydraulic);
• plots of columns of multi-storey buildings passing through the overlap, especially when wet cleaning dust indoors;
• Plots of the plates of the coating, located along the funds, at the funnel of the inner drain, in the outer glazing and the ends of the lanterns, at the ends of the building.

In civil and industrial construction, the most used are reinforced concrete structures. When erending, exploitation of various buildings, structures are often detected by their various damage In the form of cracks, deflection, other defects. This happens due to deviations from the requirements of project documentation during their manufacture, installation or caused by designer errors.

The company designer has a group of expert engineers who have profound knowledge in various areas of construction and the peculiarities of technological processes in industrial buildings, which is especially important when examining railway construction. The main goal, for which the survey of reinforced concrete structures will occur - establishing the current state of these elements with clarifying the causes of the identified deformations, the degree of wear of its individual elements. During the examination, the real strength, the rigidity of the concrete, its physico-technical condition, detect damage, determine the reasons for their appearance. The task consists not only in the search for various defects of concrete and reinforced concrete structures, but also in the preparation of recommendations for the customer to correct the situation for the normal future operation of the facility. It becomes possible only after a detailed study of structures from reinforced concrete, concrete.

Causes of the need for examination

To determine the supporting ability of structures, their states, buildings and structures are examined at the request of the customer. They can be implemented according to a certain schedule or the need for their conduct arises after man-made accidents, natural disasters.

Survey of concrete structures, reinforced concrete is required if:

• it is planned to reconstruct the building, facilities, if necessary, its republic, changes in the functional purpose of the room, which can increase the load on the supporting structures;
• there are deviations from the project (discrepancies between real project and erected object);
• there were obvious deformations of elements of buildings, structures that exceed admissible, according to regulations, values;
• exceeded regulatory time Buildings services;
• structures are physically worn;
• structures, buildings were subjected to natural, technological impacts;
• there was a need to study the features of the work of railway structures in difficult conditions;
• there is any expertise.

Stages of surveys

Concrete and reinforced concrete designs can be of different types Both forms, however, their research methods remain the same for all, and the work performed have a clear sequence. The survey is aimed at identifying concrete strength, the degree of propagation of corrosion processes in metal reinforcement.

For a complete examination of the designs, experts must gradually perform:

• preparatory work (documentation study);
• field work (visual, detailed study directly at the facility using special tools);
• laboratory tests of samples taken;
• analysis of the results, calculation, determination of the causes of the appearance of defects;
• issuance to the customer of survey results with recommendations.

The work of experts on the survey of railway structures begins with the study of the entire available project documentation provided by the Customer of the Services, the analysis of the source materials used on the facility.

Next, a direct survey of an object is already carried out, which allows to obtain an idea of \u200b\u200bits real state. A preliminary existent examination of prefabricated structures is carried out for the detection of their explicit defects.

At the stage of visual examination of buildings and structures can be detected:

• visible defects (cracks, salts, destruction, damage);
• rales of reinforcement, the real state of its anchoring (longitudinal, transverse);
• the presence of complete or partial destruction in various sections in concrete, reinforced concrete;
• displacement of individual elements, supports in structures;
• constructive defunctions, deformation;
• corrosive places of concrete, reinforcement, violation of their clutch between themselves;
• damage to protective coatings (screens, plaster, paintwork);
• plots with modified concrete color.

Instrumental examination

With a detailed examination, during the work, the following actions are carried out by specialists:

• the geometric parameters of structures and their sections are measured, the size of external damage, defects;
• detected defects with marks them are recorded. characteristic signs, location, width, depth of damage;
• the strength, characteristic deformations of concrete, reinforcement to the instrumental or laboratory method of examination are checked;
• calculations are held;
• designs are tested for strength load (if necessary).

During the detailed examination, concrete characteristics in terms of frost resistance, strength, abrasability, density, homogeneity, water permeability, degree of corrosion damage are estimated.

These properties are determined by two ways:

• laboratory tests of concrete samples, which are selected from the design with its integrity impairment;
• survey of ultrasound, mechanical testers, moisture meters, other instruments using non-destructive test methods.

To examine the strength of the concrete, the zones of its visible damage are usually selected. To measure the thickness of the protective concrete layer during a detailed examination, non-destructive testing technologies are also used using electromagnetic testers or its local autopsy is made.

The level of corrosion of concrete, the reinforcement and its elements is determined by the chemical and technical and laboratory methods of the study of the samples taken. It is determined by the form of the destruction of concrete, the spread of the process on the surfaces, capture the valves with steel elements of rust.

The actual state of fittings is also found out after collecting data on it and comparing them with the design parameters of working drawings. The survey of the state of the reinforcement is carried out by removing the layer of concrete to gain access to it. For this, places are selected, where there are obvious signs of corrosion in the form of rusty spots, cracks in the location zone of reinforcing rods.

An examination of structural elements is carried out by opening in several places depending on the object area. If there are no explicit signs of deformations, then the number of openings is small or they are replaced by engineering sounding. The survey may include the definition of loads with their impact on the design.

Processing survey results

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

1. Circuits are drawn up, statements where the deformations of the building, structures indicating them characteristic features (deflection, rolls, breaking breaks, etc.).
2. The causes of the appearance of deformations in concrete, structures are analyzed.
3. According to the results of the survey, the carrying ability of the structure is calculated, which will show the actual 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 what the test protocol is drawn up.

After that, a technical conclusion is drawn up with the findings of specialists who represent the Customer:

• estimated view on the technical condition of structures, determined by the degree of damage, features of the identified defects;
• defective statements, tables, descriptions, results of instrumental and laboratory tests of samples taken during examination;
• new technical certificate or a refined old document on the building, construction;
• conclusions about probable causes of damage in concrete structures, reinforced concrete (if detected);
• conclusions about the possibility of exploiting the building, the construction further;
• recommendations for eliminating defects (if possible) in several options (restoration, strengthening of structures).

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

• - geometric sizes of structures and their sections;
• - presence of cracks, off and destruction;
• - states of protective coatings (paintwork, plasters, protective screens, etc.);
• - defunitions and deformations of structures;
• - disorders of adhesion of reinforcement with concrete;
• - availability of reinforcement;
• - the state of anchoring of longitudinal and transverse reinforcement;
• - degrees of corrosion of concrete and reinforcement.

The definition and assessment of the state of paint coatings of reinforced concrete structures should be made according to the method described in GOST 6992-68. At the same time, the following main types of damage are recorded: cracking and detachment, which are characterized by the depth of destruction of the upper layer (to primer), bubbles and corrosion foci, characterized by the focus size (diameter), mm. The area of \u200b\u200bindividual types of coating damage is expressed approximately as a percentage in relation to the entire painted surface of the design (element).

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

In the process visual examinations An estimated assessment of concrete strength is produced. In this case, you can use the clutch method. The method is based on the appealing of the surface surface with a hammer mass of 0.4-0.8 kg directly along the purified mortar section of concrete or in a chisel installed perpendicular to the surface of the element. At the same time, minimum values \u200b\u200bobtained as a result of at least 10 shots are taken to assess the strength. A more ring sound when climbing corresponds to a stronger and dense concrete.

If there are moistened sections and surface heaps on concrete structures, they determine the magnitude of these sites and the reason for their appearance.

The results of the visual inspection of reinforced concrete structures are recorded as a map of defects deposited on schematic plans or cuts of buildings, or make up defect tables with recommendations on the classification of defects and damage with the assessment of the category of status of structures.

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

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

Evaluation of the technical condition of reinforced concrete structures on external features

	Signs of design status
I - Normal	On the surface of the concrete of unprotected designs of visible defects and no damage, there are no small separate potholes, chips, hair cracks (not more than 0.1 mm). Anticorrosive protection of structures and mortgage parts has no disorders. The surface of the reinforcement during the opening is clean, there is no corrosion of the reinforcement, the depth of neutralization of concrete does not exceed half the thickness of the protective layer. The approximate strength of the concrete is not lower than the project. The color of the concrete is not changed. The magnitude of the deflection and the width of the cracks do not exceed the permissible
II - satisfactory	Anticorrosion protection of reinforced concrete elements has partial damage. In some areas, traces of corrosion of distribution fittings or clamps, corrosion of working reinforcement with separate points and spots appear in places of the short size of the protective layer. loss of cross section of working reinforcement no more than 5%; Deep ulcers and rust plates are not. Anticorrosive protection of mortgage parts is not detected. The depth of the neutralization of concrete does not exceed the thickness of the protective layer. Changed the color of the concrete due to the cut, the detachment of the protective layer of concrete when attacking. Flowing faces and edges of frozen designs. The approximate strength of concrete within the protective layer below the project is not more than 10%. Create requirements existing normsrelating to the limit states of the I group; The requirement of norms on the limit states of the Group II can be partially violated, but normal operating conditions are provided.
III - unsatisfactory	Cracks in a stretched concrete zone exceeding their permissible disclosure. Cracks in a compressed zone and in the zone of main tensile stresses, the deflection of elements caused by operational effects exceed by more than 30% permissible. Concrete in the stretched zone at the depth of the protective layer between the rods of the reinforcement will easily crumble. Plastic rust or ulcers on rods of bare working reinforcement in the zone of longitudinal cracks or on mortgage parts, causing a decrease in the area of \u200b\u200bcross section of rods from 5 to 15%. Reducing the approximate strength of concrete in a compressed zone of bending elements to 30 and in the rest of the sections - up to 20%. Schedules of individual rods of distribution reinforcement, releasing the clamps, the rupture of individuals, except for the clamps of the compressed farms elements due to the corrosion of the steel (in the absence of cracks in this zone). The area reduced against the requirements of the norms and project is the area of \u200b\u200bsupporting the prefabricated elements with the coefficient of K \u003d 1.6 (see Note). High water and air permeability of wall panels
IV - pre-emergency or emergency	Cracks in structures experiencing alternating effects, cracks, including intersecting the reference zone of anchoring of stretched fittings; breaking the clamps in the zone of the inclined crack in the middle spans of multiplet beams and plates, as well as layered rust or ulcers, causing a decrease in the area of \u200b\u200breinforcement cross section of more than 15%; releasing fittings compressed design zone; deformation of mortgage and connecting elements; Waste anchors from plates of mortgage parts due to corrosion steel in welded seams, disorder of joints of prefabricated elements with a mutual displacement of the latter; Supply supports; significant (more than 1/50 span) deflection of bending elements in the presence of cracks in the stretched zone with a disclosure of more than 0.5 mm; breaking clamps of compressed farms elements; breaking clamps in the zone of oblique crack; breaking individual rods of working reinforcement in a stretched zone; The fragmentation of concrete and cutting the aggregate in the compressed zone. Reducing concrete strength in a compressed zone of bending elements and in the rest of the sections more than 30%. Reduced against the requirements of the norms and project is the area of \u200b\u200bthe prefabricated elements. Existing cracks, defamations and other damage indicate the danger of destruction of structures and the possibility of their collapse

Notes: 1. To assign a structure to the state categories listed in the table, a sufficient presence of at least one feature characterizing this category. 2. The prestressed reinforced concrete structures with high-strength reinforcement, having features of the II category II, refer to the III category, and having signs of category III - respectively to IV or V categories depending on the risk of collapse. 3. With reduced standards against the requirements of the standards and the design of the prefabricated elements, it is necessary to conduct an indicative calculation of the support element to the slice and concrete crumplement. The calculation takes into account the actual loads and strength of concrete. 4. The assignment of the examined design to a category of state in the presence of signs noted in the table, in complex and responsible cases, should be carried out on the basis of the analysis of the stress-strain state of structures performed by specialized organizations.

Determination of concrete strength mechanical methods

Mechanical methods of non-destructive testing When examining structures are used to determine the strength of the concrete of all types of normalized strength controlled according to GOST 18105-86.

Depending on the method used and the instruments of the indirect characteristics of strength are:

• - the value of the rebound of the bridge from the surface of the concrete (or the drummer pressed to it);
• - parameter of the impact pulse (impact energy);
• - the size of the imprint on the concrete (diameter, depth) or the ratio of the diameters of the fingerprints on the concrete and the standard sample when the indenter is impaired or indenting the indenter into the surface of the concrete;
• - the value of the voltage required for the local destruction of concrete when the metal disk is glued to it, equal to the separation of the separation, divided into the area of \u200b\u200bprojection of the surface of the separation of concrete to the disc plane;
• - the value of the effort required for the brightness of the concrete section on the rib of the design;
• - The value of the effort of local destruction of concrete when the anchor device is pulled from it.

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

The instruments of the mechanical principle of operation include: the reference hammer of Kashkarova, Schmidt hammer, a hammer of the Fizteel, a gun TNC, a hammer of Poland, and others. These devices make it possible to determine the material strength in terms of the magnitude of the bridge in the surface layer of structures or the magnitude of the rebound of the bridge from the design of the structure when applied Calibrated impact (gun tinking).

Fiztele hammer (Fig. 1) is based on the use of plastic deformations building materials. When hitting the hammer on the surface of the structure, a hole is formed, by the diameter of which the material strength is evaluated. The place of construction on which prints are applied is pre-cleaned from the plaster layer, grouting or painting. The process of working with the hammer of Fizdel is as follows: the right hand take over the end of a wooden handle, the elbow is based on the design. The elbow blow of the middle force is caused by 10-12 beats on each site of the structure. The distance between the impact hammer prints should be at least 30 mm. The diameter of the formed well is measured with a caliper with an accuracy of 0.1 mm over two perpendicular directions and take the average value. Of total The measurements made in this area are eliminated by the greatest and smallest results, and by the rest, the average value is calculated. Concrete strength is determined by the average measured diameter of the imprint and tariff curve, pre-built on the basis of a comparison of the diameters of fingerprints of the hammer ball and the results of laboratory tests on the strength of concrete samples taken from the design on the instructions of GOST 28570-90 or specially made from the same components and on the same Technologies that the materials of the examined structure.

Concrete strength control methods

Method, Standards, Devices	Test scheme
Ultrasonic GOST 17624-87 Devices: UKB-1, UBB-1M UCB16P, UV-90PC Concrete 8-URP, UK-1P
Plastic deformation Devices: KM, PM, Dig-4 Elastic rebound Devices: km, Schmidt sclerometer GOST 22690-88.
Plastic deformation Hammer Kashkarova GOST 22690-88.
Targeted with disks GOST 22690-88. GPNV-6 device
Rib ribs design GOST 22690-88. GPNS-4 device with URS device
Running with a rocky GOST 22690-88. Devices: GPNV-5, GPNS-4

Fig. 1. Molotok I.A. Fiztele:1 - a hammer; 2 - a pen; 3 - spherical nest; 4 - ball; 5 - angular scale

Fig. 2. Tarising schedule for determining the strength of concrete when compressed by the hammer of Fiztele

Fig. 3. Determination of the strength of the material, with the help of hammer K.P. Kashkarova:1 - body, 2 - metric handle; 3 - rubber handle; 4 - head; 5 - steel ball, 6 - steel reference rod; 7 - angular scale

Fig. 4. Calibration curve for determining concrete strength hammer Kashkarova

In fig. 2 shows a target curve to determine the strength limit when compressing the hammer of the Fiztele.

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

The distinguishing feature of the Kashkarov hammer (Fig. 3) from the hammer of the Fizteel is that there is a hole between the metal hammer and spangled ball into which the control metal rod is introduced. When hitting the hammer over the surface surface, two imprints are obtained: on the surface of the material with a diameter d. and on the control (reference) rod with a diameter d. e. . The ratio of the diameters of the finished fingerprint depends on the strength of the material being examined and the reference rod and is almost independent of the speed and force of the impact of the hammer. According to the average value of the magnitude d./d. e. From the tariff graph (Fig. 4) determine the strength of the material.

At least five definitions should be performed on the test site at a distance between the concrete prints at least 30 mm, and on a metal rod - at least 10 mm.

To the instrument based on the method elastic reboundThese are a pistol Tsniskii (Fig. 5), Borovoy's gun, Schmidt's hammer, a sclerometer km with a rod drummer and others. The principle of operation of these devices is based on measuring the elastic rebound of the drummer at a constant kinetic energy. metal spring. The platoon and the descent of the brine are carried out automatically when the drummer is contaplied with the surface. The magnitude of the bounce of the Boyhead fixes the pointer on the device scale.

Fig. 5. Pistol Tsniski and spring pistol S.I. Borovoye to determine concrete strength non-destructive method: 1 - Drummer 2 - body, 3 - scale, 4 - fixture of the instrument readings, 5 - Handle

To modern means to determine the strength of concrete concrete on a non-destructive shock-pulse method, the onyx-2.2 is applied, the principle of operation of which is to fix the parameters of a short-term electrical pulse arising in the sensitive element when the concrete is shocking, with its conversion to the value of strength. After 8-15 shots on the scoreboard, the average strength value is issued. A measurement series ends automatically after the 15th strike and the average strength value is displayed on the table of the instrument.

The distinctive feature of the sclerometer KM is that a special combos of a certain mass with a spring with a predetermined rigidity and pre-voltage strikes the end of a metal rod, called the drummer pressed by another end to the surface of the tested concrete. As a result, the battle is bounces off from the drummer. The degree of rebound is marked on the scale of the device using a special pointer.

The dependence of the validity of the bounce of the drummer from the strength of concrete is set according to the tariff tests of concrete cubes of 151515 cm in size, and the target curve is built on this basis.

The strength of the design material is detected by the testimony of the graduated scale of the device at the time of application of shocks for the test element.

The method of concrete strength in the body of the structure is determined by testing the breakdown with the cream. The essence of the method is to evaluate the strength properties of concrete along the effort required for its destruction, around the hole of a certain size when the expansion cone fixed in it or a special rod embedded in concrete is applied. An indirect indicator of strength is the discrepancing force required for the exhaust embedded in the body of the anchor designs along with it with its concrete at the depth of sealing h. (Fig. 6).

Fig. 6. Scheme of testing by the method of separation with the rocking when using anchor devices

When testing by the rolling method, the sections should be located in the low voltage zone caused by the operational load or enhanced the compression of pre-hard fittings.

Concrete strength on the site is allowed to determine the results of one test. Plots for testing should be chosen so that fittings do not get into the exhaust zone. In the test area, the thickness of the design should exceed the depth of the entrance of the anchor at least twice. When punching the hole with a jumper or drilling the thickness of the structure in this place should be at least 150 mm. The distance from the anchor device to the edge of the structure should be at least 150 mm, and from the adjacent anchor device - at least 250 mm.

When conducting tests, three types of anchor devices are used (Fig. 7). Anchor devices of type I are installed on construction during concreting; Anchor devices of types II and III are installed in pre-prepared sheets, punched in the concrete drilling. Recommended depth of the holes: for an anchor of type II - 30 mm; For an anchor type III - 35 mm. The discon's diameter in the concrete should not exceed the maximum diameter of the bellped part of the anchor device by more than 2 mm. Inserting anchor devices in structures should provide a reliable adhesion of an anchor with concrete. The load on the anchor device should increase smoothly at a speed of no more than 1.5-3 kN / s up to the exterior of it with the surrounding concrete.

Fig. 7. Types of anchor devices:1 - working rod; 2 - work rod with a slot cone; 3 - work rod with a full expansion cone; 4 - support rod, 5 - Segment corrugated cheeks

The smallest I. the greatest size The pulled part of the concrete, equal to the distance from the anchor device to the borders of the destruction on the surface surface, should not be different from another more than twice.

When determining the concrete class, the design of the rib construct is used by the GPNS-4 type (Fig. 8). The test diagram is shown in Fig. nine.

Budget parameters should be taken: but\u003d 20 mm; b.\u003d 30 mm, \u003d 18.

At the test site it is necessary to carry out at least two concrete chips. The thickness of the tested design should be at least 50 mm. The distance between adjacent chips should be at least 200 mm. The load hook must be installed in such a way that the magnitude "A" is not different from the nominal more than 1 mm. The load on the test design should grow smoothly at a rate of no more (1 ± 0.3) kn / s up to the cliff of concrete. At the same time, the loading hook should not occur. The results of the tests in which fittings were exposed at the place of the chip, and the actual depth of the spanning differed from the more than 2 mm given more than 2 mm are not taken into account.

Fig. 8. The device for determining the strength of concrete by the rib of ribs:1 - test design, 2 - Brown-up concrete, 3 - URS device, 4 - Device GPNS-4

Fig. 9. Concrete Test Scheme in Design Rib Rib Design Constructions

Single meaning R. i. Concrete strengths on the test site are determined depending on concrete compression voltages b. and meanings R. i.0 .

Compressive voltages in concrete b. In force during testing period, determine the calculation of the structure, taking into account the valid sizes of sections and load values.

Single meaning R. i.0 Concrete strength on the plot under the assumption b. \u003d 0 determined by the formula

where t. g. - correction coefficient, taking into account the size of the aggregate, taken equal: at maximum aggregate size of 20 mm and less - 1, with a large size of more than 20 to 40 mm - 1.1;

R. iY. - Conditional strength of concrete, determined by schedule (Fig. 10) by the average value of the indirect indicator R

P. i. - The effort of each of the rocks performed on the test site.

When testing the rib ribbling method on the test section, there should be no cracks, concrete chips, spills or shells height (depth) more than 5 mm. Plots should be located in the zone of the smallest stresses caused by the operational load or force of the compression of pre-hard fittings.

Fig. 10. The dependence of the conditional strength of the concrete RIY from the force of Skol Ri

Ultrasonic Method for determining concrete strength.The principle of determining the strength of concrete with an ultrasonic method is based on the presence of a functional connection between the rate of propagation of ultrasonic oscillations and the strength of concrete.

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

Concrete strength in structures are determined experimentally on established calibration dependences "Ultrasound distribution speed - concrete strength V.=f (R)"Or" Ultrasound distribution time t. - Strength of concrete t.=f (R)" The degree of accuracy of the method depends on the thoroughness of building a target schedule.

The target graph is built according to the data of the sound and strength tests of control cubes prepared from the concrete of the same composition, by the same technology, with the same hardening mode as products or structures to be tested. When building a target schedule, you should be guided by the instructions of GOST 17624-87.

To determine the strength of concrete, the ultrasonic method applies instruments: UKB-1, UBB-1M, UK-16P, "Concrete-22", etc.

Ultrasonic measurements in concrete are carried out by ways of end-to-end or surface sound. Concrete test diagram is shown in Fig. eleven.

Fig. 11. Methods of ultrasonic concrete sounding:but - test diagram by the method of pass-through sound; b. - the same, surface sound; UP - Ultrasound transducers

When measuring the ultrasound distribution time by the method of pass-through sound, ultrasonic converters are installed from opposite sides of the sample or design.

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

where t. - time distribution of ultrasound, ISS;

l. - Distance between the centers of the installation of converters (the base of the sound), mm.

When measuring the proliferation time of ultrasound, the ultrasonic converters are installed on one side of the sample or design according to the scheme.

The number of measurements of the ultrasound spread time in each sample must be: with end-to-end sound - 3, with superficial - 4.

Deviation of a separate result of measuring the time of ultrasound propagation in each sample from the average arithmetic value of the measurement results for this sample should not exceed 2%.

Measuring the time of the ultrasound distribution and determination of concrete strength is made in accordance with the instructions of the passport (technical condition) of this type of device and instructions of GOST 17624-87.

In practice, there are no cases when there is a need to determine the strength of the concrete of exploited structures in the absence or inability to build a calibration table. In this case, the determination of concrete strength is carried out in the zones of structures made from concrete on one form of large aggregate (single batch designs). Ultrasound propagation rate V. Determine at least 10 sections of the examined area of \u200b\u200bthe structures, according to which the average value is determined. V. The following sections in which the speed of ultrasound spread has the maximum V. Max and minimal V. min values, as well as a plot where speed has a magnitude V. n. the most close to the value V.And then scorched from each planned section of at least two cores, which determine the values \u200b\u200bof strength in these areas: R. MAX, R. min R. n. respectively. Concrete strength R. H. Determine the formula

R. MAX / 100. (five)

Factors but 1 I. a. 0 calculate according to formulas

When determining the strength of concrete on samples selected from the design, the instructions of GOST 28570-90 should be guided.

When performing a condition of 10%, it is allowed to approximately determine the strength: for concrete strength classes to B25 by the formula

where BUT - The coefficient determined by testing at least three cores cut out of the designs.

For concrete classes of strength above B25, concrete strength in exploited structures can also be estimated by a comparative method, based on the characteristics of the structure with the greatest strength. In this case

Such structures like beams, riglels, columns should be performed in the transverse direction, the stove - by the smallest size (width or thickness), and the ribbed plate - the thickness of the rib.

With careful testing, this method gives the most reliable information about concrete strength in existing structures. The disadvantage of it is a large complexity of work on the selection and testing of samples.

Determination of the thickness of the protective layer of concrete and armature location

To determine the thickness of the protective layer of concrete and the armature location in the reinforced concrete construction during surveys, magnetic, electromagnetic methods according to GOST 22904-93 or methods of translucent and ionizing radiation according to GOST 17623-87 are used with a selective control check of the resulting results by punching the furrow and immediate measurements.

Radiation methods are usually used to examine the condition and quality control of prefabricated and monolithic reinforced concrete structures in the construction, operation and reconstruction of specially responsible buildings and structures.

The radiation method is based on the transmission of controlled structures by ionizing radiation and receiving information about its inner structure Using the radiation converter. Displaying reinforced concrete structures is produced using radiation of X-ray devices, radiation of closed radioactive sources.

Transportation, storage, installation and adjustment of radiation equipment are carried out only by specialized organizations that have a special permit for the specified work.

The magnetic method is based on the interaction of the magnetic or electromagnetic field of the device with steel reinforced concrete fittings. Anchor Construction Concrete Armature

The thickness of the protective layer of concrete and the location of the reinforced concrete construction is determined on the basis of experimentally established dependence between the testimony of the device and the specified controlled parameters constructions.

To determine the thickness of the protective layer of concrete and the location of the reinforcement from modern devices Used in particular ISM, С - 10Н (TU25-06.18-85.79). The IZ-10N device provides a measurement of the thickness of the protective layer of concrete depending on the diameter of the reinforcement within the following limits:

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

The device ensures the definition of the location of the projections of the axes of the reinforcement rods on the surface of the concrete:

• - diameters from 12 to 32 mm - with a thickness of the protective layer of concrete no more than 60 mm;
• - diameters from 4 to 12 mm - with a thickness of the protective layer of concrete no more than 30 mm.

When the distance between the rods of the reinforcement is less than 60 mm, the use of the type of izards is inappropriate.

The determination of the thickness of the protective layer of concrete and the diameter of the reinforcement is performed in the following order:

• - before testing, the technical characteristics of the applied instrument with the corresponding design (expected) values \u200b\u200bof the geometric parameters of the reinforcement of the controlled reinforced concrete structure are compared;
• - If inconsistencies technical characteristics The device to the parameters of reinforcement of the controlled structure must be established by an individual graduation dependence in accordance with GOST 22904-93.

The number and location of the controlled design sites are prescribed depending on:

• - objectives and conditions of testing;
• - features of the design solution of the design;
• - manufacturing technologies or construction technologies, taking into account the fixation of reinforcement rods;
• - conditions of operation of the structure, taking into account the aggressiveness of the external environment.

Working with the instrument should be made in accordance with the instructions for its operation. In the fields of measurements on the surface of the design there should be no surveys with a height of more than 3 mm.

With the thickness of the protective layer of concrete, the smaller measurement limit of the applied instrument, the tests are carried out through a laying of a thickness of (10 ± 0.1) mm from a material that does not have magnetic properties.

The actual thickness of the protective layer of concrete in this case is defined as the difference between the measurement results and the thickness of this gasket.

When controlling the location of steel reinforcement in the concrete structure, for which there is no data on the diameter of the reinforcement and the depth of its location, determine the armature location scheme and the diameter is measured by opening the structure.

For an approximate determination of the diameter of the reinforcement rod, the location of the reinforcement is determined on the surface of the reinforced concrete structure.

Install the device converter on the surface of the structure, and on the scales of the device or by individual graduation dependency Determine several values \u200b\u200bof the thickness of the protective layer of concrete pr. For each of the alleged diameters of the reinforcement rod, which could be used for reinforcement of this design.

Between the converter of the device and the surface of the concrete design, the gasket is set to the appropriate thickness (for example, 10 mm), measurements are again carried out and the distance for each alleged diameter of the reinforcement rod is determined.

For each diameter of the reinforcement rod, values \u200b\u200bare compared pr. and ( aBS - e.).

As an actual diameter d. take the 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.

Indices in the formula are indicated:

s. - a pitch of longitudinal reinforcement;

r - step of transverse reinforcement;

e. - the presence of gasket;

e. - Packing thickness.

Measurement results are logged in a magazine that is shown in the table.

The actual values \u200b\u200bof the thickness of the protective layer of concrete and the location of steel reinforcement in the design of measurements are compared with the values \u200b\u200bset by technical documentation on these structures.

The measurement results are drawn up by the protocol that must contain the following data:

• - the name of the conducted design (its conditional designation);
• - the volume of the party and the number of controlled structures;
• - type and number of the applied device;
• - numbers of controlled areas of structures and the scheme of their location on the design;
• - design values \u200b\u200bof geometric parameters of reinforcement of controlled design;
• - results of tests;
• - reference to a guidance and regulatory document regulating the test method.

Record measurement results of the thickness of the protective layer of concrete concrete concrete structures

Defining the strength characteristics of reinforcement

The calculated resistance of intact fittings is allowed to take on project data or on the standoff standards of reinforced concrete structures.

• - for smooth reinforcement - 225 MPa (class A-I);
• - for reinforcement with a profile, whose crests form a knitting pattern - 280 MPa (class A-II);
• - For the reinforcement of the periodic profile, whose crests form a drawing "Christmas tree", - 355 MPa (class A-III).

Hard reinforcement from rolling profiles is accepted in calculations with calculated resistance when stretching, compression and bending equal to 210 MPa.

In the absence of necessary documentation and information, the class of reinforcement steels is established by the test of samples cut from the design with comparison of the yield strength, time resistance and relative elongation at a break with GOST 380-94.

The location, the number and diameter of the reinforcement rods is determined either by opening and direct measurements, or the use of magnetic or radiographic methods (according to GOST 22904-93 and GOST 17625-83, respectively).

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

• - tests of standard samples cut from structural elements, according to the instructions of GOST 7564-73 *;
• - tests of the surface layer of metal on hardness according to the instructions of GOST 18835-73, GOST 9012-59 * and GOST 9013-59 *.

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

In the selection of blanks for samples, structural elements are divided into conditional parties of 10-15 of the same type of structural elements: farms, beams, columns, etc.

All billets must be scarked in places of their take and brand are marked in the diagrams attached to the materials of the examination of structures.

The characteristics of the mechanical properties of steel - the yield strength, the time resistance and the relative elongation during the break is obtained by tensile testing of the samples according to GOST 1497-84 *.

Determination of the main calculated resistances of steel steel is made by dividing the average yield limit value to the reliability coefficient by material M \u003d 1.05 or time resistance to the reliability ratio \u003d 1.05. At the same time, the smallest value is taken for the calculated resistance R. t, R.which are found according to T and.

When determining the mechanical properties of the metal on the hardness of the surface layer, it is recommended to use portable portable devices: Poland-Hytte, Bauman, VPI-2, VPI-ZK, etc.

The data obtained when testing on hardness are translated into the characteristics of the mechanical properties of the metal according to the empirical formula. So, the dependence between the hardness of the brinel and the time resistance of the metal is established by the formula

3,5H. b. ,

where N. - Bringel hardness.

The identified actual characteristics of the reinforcement are compared with the requirements of SNiP 2.03.01-84 * and SNiP 2.03.04-84 *, and the valuation of the operational fitness of the reinforcement is given on this basis.

Determination of concrete strength by laboratory testing

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

Sampling is selected by drinking cores with a diameter of from 50 to 150 mm in areas where the weakening of the element does not have a significant effect on the carrying ability of structures. This method gives the most reliable information about concrete strength in existing structures. The disadvantage of it is a large complexity of work on the selection and processing of samples.

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

The essence of the method consists in measuring the minimum efforts that destroy the samples of concrete chosen or discharged from the design under static loading with a constant load growth rate.

Form I. nominal sizes Samples, depending on the type of testing of concrete, GOST 10180-90 must be consistent.

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

For the base with all types of tests, a sample is taken with the size of the working section of 150150 mm.

Concrete sampling sites should be prescribed after visual inspection of structures, depending on their intense state, taking into account the minimum possible reduction in their bearing capacity. Samples are recommended to select from places remote from the joints and edges of the structures.

After removing sampling, the selection site should be embedded with fine-grained concrete or concrete from which structures are made.

Plots for drinking or sawing concrete samples should be selected in places free from reinforcement.

To bring out samples from concrete structures drilling machines type IE 1806 for TU 22-5774 with cutting tool In the form of ring diamond drills such as SKA on TU 2-037-624, GOST 24638-85 * E or carbide end drills according to GOST 11108-70.

For cutting samples from concrete structures, sawing machines of URB-175 types for TU 34-13-10500 or URB-300 for TU 34-13-10910 with a cutting tool in the form of cut 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 from concrete structures that ensure the manufacture of samples that meet the requirements of GOST 10180-90.

Testing samples on compression and all types of stretching, as well as the choice of test and loading schemes are produced according to GOST 10180-90.

The supporting surfaces of the samples experienced on the compression, in the case when their deviations from the surface of the press plate of more than 0.1 mm must be corrected by applying a layer of leveling composition. Cement dough, cement-sandy solution or epoxy compositions should be used as typical.

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

Concrete strength of a test sample with an accuracy of 0.1 MPa when tested for compression and up to 0.01 MPa with tensile tests are calculated by formulas:

on compression;

on axial stretching;

on stretching when bending,

BUT - the area of \u200b\u200bthe working section of the sample, mm 2;

but, b., l. - Accordingly, the width and height of the transverse section of the prism and the distance between the supports when testing samples for stretching during bending, mm.

To bring concrete strength in a tested sample to concrete strength in the base size sample and the strength form obtained according to the specified formulas, are recalculated by formulas:

on compression;

on axial stretching;

on stretching when splitting;

on stretching when bending,

where 1, and 2 are coefficients that take into account the ratio of the cylinder height to its diameter taken in the compression tests in the table., when tensile tests when splitting in Table. and equal units for samples of another form;

The large-scale coefficients that take into account the shape and the dimensions of the cross section of the test samples are determined experimentally according to GOST 10180-90.

from 0.85 to 0.94

from 0.95 to 1.04

from 1.05 to 1.14

from 1.15 to 1.24

from 1.25 to 1.34

from 1.35 to 1.44

from 1.45 to 1.54

from 1.55 to 1.64

from 1.65 to 1.74

from 1.75 to 1.84

from 1.85 to 1.95

from 1.95 to 2.0

The test report should consist of the sampling protocol, the results of testing samples and the corresponding reference to the standards on which the test was carried out.

Research Group "Security and Reliability"

Construction Examination, Building Survey, Energy Audit, Land Management, Design

It is no secret that in the process of the construction and operation of buildings and structures in reinforced concrete structures there are unacceptable defignments, cracks, damage. These phenomena can be caused by either deviations from the project requirements in the manufacture and installation of these structures, or design errors.

Assess the physical state of the design, establish the causes of damage, to determine the real strength, crack resistance and the stiffness of the structure are intended to examine reinforced concrete structures. It is important to correctly evaluate the carrying ability of the structures and develop recommendations for their further operation. And this is possible only as a result of a detailed home study.

The need for such a survey arises in cases of studying the peculiarities of the work of structures and structures in difficult conditions, during the reconstruction of a building or structure, in the process of conducting examination, if there is in the designs of retreats from the project, and in a number of other cases.

The survey of reinforced concrete structures consists of several stages. At the initial stage, a preliminary examination of the structures is carried out in order to identify the presence of fully or partially destroyed areas, the reinforcement breaks, damage to the concrete, the displacement of the supports and elements in the prefabricated structures.

At the next stage, it is familiar with the design and technical documentation, then a direct examination of reinforced concrete structures is followed, which makes it possible to obtain a valid picture of the state of structures and their work under operating conditions. Depending on the tasks set, concrete strength may be assessing non-destructive methods, as well as finding out the actual reinforcement, which consists in collecting data on the real state of reinforcement, and comparison with the parameters contained in the working drawings, as well as in a selective verification of the correspondence of the actual reinforcement project.

Since the active loads can differ significantly from the design, analyzes the intense state of the structures. For this, actual loads and impact are determined. If necessary, internal tests can be continued. At the end, a construction and technical conclusion is issued.

We work for this principle:

1 You dial our number and ask the questions important for you, and we give them exhaustive answers.

2 After analyzing your situation, we define the list of questions that our experts should give answers. A contract for conducting a survey of reinforced concrete structures can be concluded as in our office and immediately at your facility.

3 We will come to you at a convenient time for you and conduct a survey of reinforced concrete structures.

After the work, using special devices (destroying and non-destructive testing), you will receive a written construction and technical conclusion in the hands, in which all defects will be reflected, the causes of their occurrence, photo report, design calculations, assessment of restoration repair, conclusions and recommendations.

The cost of the survey of reinforced concrete structures is from 15,000 rubles.

The deadline for obtaining a conclusion is from 3 working days.

4 Many customers need to leave a specialist without subsequent concluding. The construction and technical expert will conduct a survey of reinforced concrete structures, based on the results of which will give an oral conclusion with the conclusions and recommendations on the spot. Decide on the need to compile a written conclusion on the results of the study, you can later.

The cost of leaving our expert is from 7000 rubles.

5 In our company there are designers and designers who, on the basis of our conclusion, can develop a draft elimination of deficiencies and project enhancement project.