Problem:

Very often, Customers have a question of initializing the type of seam in a building structure through which water enters. Indeed, this issue is very serious and requires certain building knowledge.

I propose to consider in more detail the deformation sedimentary and temperature ("cold") seams and understand the difference between them.

What is an expansion joint?

Expansion joint - designed to reduce loads on structural elements in places of possible deformations arising from fluctuations in air temperature, seismic events, uneven ground settlement and other influences that can cause dangerous own loads that reduce the bearing capacity of structures. It is a kind of section in the building structure, dividing the structure into separate blocks and, thereby, giving the structure a certain degree of elasticity. For the purpose of sealing, it is filled with an elastic insulating material.

Depending on the purpose, the following expansion joints are used: temperature, sedimentary, anti-seismic and shrinkage.

What is a temperature "cold" seam?

The “cold” concreting joint is the weakest point of the concrete structure, which is formed as a result of technological features production of monolithic works. That is, during the construction of a building, a monolithic foundation slab, and then the walls rest on it. In the same way, they rest on the finished walls monolithic overlap. We consider seams in terms of possible leaks and it is necessary to mention here that there are many technologies for waterproofing such seams.

Why are seam leaks dangerous?

Leakage of expansion joints is not dangerous - in such joints there are no important structural elements, but the leakage of "cold" joints is a concern, since they contain load-bearing reinforcement, which is subject to corrosion. Reducing the diameter of the reinforcement by tenths of a millimeter has a very serious effect on the bearing capacity. Consequently, the "cold" concreting joints require repair and reinforcement through injection work.

How to fix leaks?

Practice shows that at the construction stage, work on sealing the seams is either not performed (not counting the laid foam) or is performed extremely poorly! Already at the stage of preparing the object for delivery, widespread leaks of the seams appear, which will not allow the construction object to be handed over to the State. commissions!

In such situations, the most EFFECTIVE, FAST and CHEAPEST method is INJECTION WATERPROOFING from IC LLC "Vertical Group" (www.injekt.pro)!

Is it possible to perform injection waterproofing on my own?

It is possible, but on one condition that you already have extensive experience with polymer compositions. It is also necessary to take into account a very complex and often very long stage preparatory work, where you have to apply the most non-standard technical solutions that. Another feature is the ability to work with vacuum pump, since the thing is extremely expensive and requires periodic complex Maintenance, up to its complete disassembly and assembly.

Based on all of the above, it remains to be concluded that it is most convenient and as cheap as possible for Zakachik to contact a specialized company for injection waterproofing, such as Vertical Group.

! Most effective solution the problem of leakage of expansion joints is injection waterproofing!

The main advantage of injection waterproofing is guaranteed positive result, which can be observed already in the first minutes after the completion of injection waterproofing.

MAIN ADVANTAGES OF INJECTION WATERPROOFING OF JOINTS:

High speed of work - a team of 4 specialists per shift can perform waterproofing up to 10 m.p. expansion joint

There is no need to carry out preparatory work that requires coordination with government agencies or the owners of neighboring buildings - all work is carried out from the side of the premises (from the basement)

Low cost of the complex of works, as there is no expensive preparation stage

There is no seasonal factor, since the work can be performed by the method of local heating of the structure

Stages of work:

1. Main stages of work - SEALING THE DEFORMATION JOINT

1) Visual inspection, local opening of the seam, verification and clarification of the adopted technical solutions

2) Clearing the expansion joint

3) Placement in the design position of the cord "Vilaterm"

4) Installation of injection packers - MC-Injekt

5) Preparation for work of the injection gel MC-Injekt GL95TX

6) Delivery of injection gel MC-Injekt GL95 TX with a two-component pneumatic pump (for example, MC-I 700)

2. The main stages of work - SEALING THE "COLD" JOINT

1) Visual inspection, local local opening of the seam, verification and clarification of the adopted technical solutions

2) Sealing the expansion joint

3) Installation of injection packers - MC-Injekt

5) Preparation for work of injection material - MC-Injekt 2300 , MC-Injekt 2300Top or MC-Injekt2700 *

6) Supply of injection material with a pneumatic pump (for example, MS-I 510 or MS-I 700)

7) Quality control of work performed

* the type of material used is determined depending on the type of joint leakage.

Important! The performance of work on injection waterproofing requires extensive experience in this area and does not forgive mistakes, since the cost of equipment and injection materials is quite high.

LECTURE #8

EXTERIOR WALLS OF LOW-RISE BUILDINGS AND THEIR ELEMENTS

Lecture plan.

General requirements.

Deformation seams.

Wall classification

Structural elements of walls.

General requirements and classification

One of the most important and complex structural elements of a building is outer wall (4.1).

External walls are subject to numerous and varied force and non-force influences (Fig. 4.1). They perceive their own weight, permanent and temporary loads from ceilings and roofs, wind effects, uneven deformations of the base, seismic forces, etc. From the outside, the outer walls are exposed to solar radiation, precipitation, variable temperatures and humidity of the outside air, external noise, and from the inside - to the influence of heat flow, water vapor flow, noise.

Fig.4.1. Loads and impacts on the structure of the outer wall.

Performing the functions of an external enclosing structure and a composite element of facades, and often a supporting structure, the external wall must meet the requirements of strength, durability and fire resistance corresponding to the capital class of the building, protect the premises from adverse external influences, provide the necessary temperature and humidity conditions of the enclosed premises, have decorative qualities. Simultaneously design outer wall must meet the industrial requirements, as well as the economic requirements of minimum material consumption and cost, since the outer walls are the most expensive structure (20 - 25% of the cost of all building structures).

In the outer walls, there are usually window openings for lighting the premises and doorways - entrances and exits to balconies and loggias. The complex of wall structures includes the filling of window openings, entrance and balcony doors, open space designs. These elements and their interfaces with the wall must meet the requirements listed above. Since the static functions of walls and their insulating properties are achieved by interacting with internal load-bearing structures, the design of external wall structures includes the solution of interfaces and joints with floors, internal walls or framing.

expansion joints

The outer walls, and with them the rest of the building structures, if necessary and depending on the natural-climatic and engineering-geological conditions of construction, as well as taking into account the features of space-planning decisions, are cut vertically. expansion joints(4.2) of various types: temperature-shrinkage, sedimentary, anti-seismic, etc. (Fig. 4.2).

Fig.4.2. Expansion joints: a - temperature-shrinkage; b – sedimentary type I; c – sedimentary type II; d - anti-seismic.

Thermal shrinkage seams arrange in order to avoid the formation of cracks and distortions in the walls caused by the concentration of efforts from exposure to variable temperatures and shrinkage of the material (masonry, monolithic or prefabricated concrete structures, etc.). Temperature-shrinkage joints cut through the structures of only the ground part of the building. The distances between the temperature-shrinkage joints are assigned in accordance with climatic conditions and the physical and mechanical properties of wall materials. So, for example, for external walls made of clay bricks on a mortar grade M50 and more, the distance between the temperature-shrinkage seams of 40 - 100 m is taken according to SNiP II-22-81 "Stone and reinforced masonry structures". In this case, the smallest distance refers to the most severe climatic conditions.

In buildings with longitudinal bearing walls seams are arranged in the area of ​​​​adjacency to transverse walls or partitions; in buildings with transverse load-bearing walls, seams are often arranged in the form of two paired walls. The smallest joint width is 20 mm. The seams must be protected from blowing, freezing and through leaks with the help of metal compensators, sealing, and insulating liners. Examples of constructive solutions for temperature-shrinkage joints in brick and panel walls are given in Figure 4.3.

Fig.4.3. Details of the device of expansion joints in brick and panel buildings: a - with longitudinal load-bearing walls (in the area of ​​​​the transverse stiffening diaphragm); b - with transverse walls with paired internal walls; c - in panel buildings with transverse walls; 1 - outer wall; 2 - inner wall; 3 - insulating insert in a wrapper made of roofing material; 4 - caulk; 5 - solution; 6 - flashing; 7 - floor slab; 8 - outer wall panel; 9 - the same, internal.

Sedimentary seams should be provided in places of sharp differences in the number of storeys of the building (sedimentary seams of the first type), as well as in case of significant uneven deformation of the base along the length of the building, caused by the specifics of the geological structure of the base (sedimentary seams of the second type). Sedimentary seams of the first type are prescribed to compensate for differences in vertical deformations ground structures high and low parts of the building, in connection with which they are arranged similarly to temperature-shrinkage only in ground structures. The design of the seam in frameless buildings provides for the installation of a sliding seam in the zone of support of the floor of the low-rise part of the building on the walls of the high-rise building, in frame buildings - the hinged support of the crossbars of the low-rise part on the columns of the high-rise building. Sedimentary seams of the second type cut the building to its entire height - from the ridge to the base of the foundation. Such seams in frameless buildings are designed in the form of paired frames. The nominal width of the sedimentary joints of the first and second types is 20 mm.

Temperature and sedimentary seams

To prevent deformations in structures, they are divided into compartments (along the length) by vertical gaps - expansion joints. The need for such seams is determined by external conditions and geometrical parameters of the structure.

With any dressing system chosen, the construction of the wall begins with the laying of corners. It is important to arrange the dressing of the seams in the corners not only in such a way that the selected dressing pattern is observed in the outer versts of both intersecting walls, but also so that the dressing is performed with maximum overlap of the seams.

According to their purpose, expansion joints are temperature and sedimentary. The location of the expansion joints must be indicated in the project.

Sedimentary seams

Sedimentary seams are arranged to prevent uneven settlement of the structure along the length. These seams divide the building or structure into compartments along the entire height of the structures: from the base of the foundation to the eaves. The foundation, divided into compartments by a sedimentary seam, is called a split foundation. The device of the sedimentary seam in the laying of the foundation and the wall looks different (Fig. 34).

Figure 34. The device of the sedimentary seam in brickwork: a) foundation (plan); b) wall (plan); c) longitudinal section along the foundation and wall; 1 - laying the foundation; 2 - masonry walls; 3 - sedimentary seam; 4 - sheet pile; 5 - gap under the tongue for upsetting

The seam must be perpendicular to the wall or foundation. In the place of the seam, the bricks are not tied up with each other, instead they arrange a gasket from waterproofing material in two - three layers (roofing felt, roofing felt, fiberglass, etc.). The seam in the foundation is made straight, in the wall - with a tongue (protrusion on one side of the seam and a depression on the other side). The thickness of the tongue is usually half a brick, less often - a quarter of a brick. A gap of 1-2 bricks (rows) of masonry is left above the edge of the foundation under the tongue and groove to prevent pressure from the tongue on the foundation masonry in case of uneven settlement. All joints between the foundation masonry and the wall masonry must be sealed to protect the wall from moisture penetration from the foundation.

If the foundation is made of another material (for example, reinforced concrete), the principles of the settlement joint do not change.

The thickness of the sedimentary seam in the brickwork should be 10–20 mm, so the arrangement of the seams does not affect the change in the length of the building (it simply replaces part of the vertical seams of the masonry).

On the outside of the walls, the sedimentary seams are sealed with tarred tow, silicone sealant or a special seal. Moreover, the first option (with tarred tow) is ineffective, so if possible, you should choose another option. On the outside of the foundation, a clay castle or other waterproofing option is arranged.

The need for the device of sedimentary seams arises in several cases.

1. Connection new wall to the old one. In this case, the seam can be arranged without a tongue, since the groove is cut into old wall- hard work.

2. The adjunction of one part of the building to another: for example, when a veranda or porch adjoins the main part of the building, and the foundation for the extension can be arranged with less material consumption (smaller section). In this case, the settlement of the porch and the main part of the building will be different, and in the absence of a settlement joint, cracks and other deformations of the masonry may occur.

3. Construction on soils with uneven settlement. This property of the soil base can be judged by the buildings on the site, the surface of the earth without cultivation (you can see a pronounced subsidence of the soil on it) or geological surveys. If it is not possible to determine the state of the soil according to the last option, the first two are resorted to. It is important to remember that cracks in buildings can be caused not only by uneven settlement of the soil base, but also by design errors (incorrect calculation of the foundation, lack of settlement joints in a long wall, etc.). However, if the buildings nearby have cracks, it is better when erecting new design in any case, provide for sedimentary seams in it.

Temperature joints

Temperature (temperature-shrinkage) seams protect the building or structure from deformations (cracks, masonry ruptures, distortions, masonry shifts along the seams) associated with changes in air temperature and the structures themselves. At low temperatures masonry tends to shrink, and in the heat - to expand. So, for every 10 m of length, a brick structure shrinks by 5 mm when the temperature changes from 20 ° C to -20 ° C. In addition, temperature differences can occur in different parts of the building.

Expansion joints divide the building into compartments along the entire height of the walls, not including the foundation. That is, unlike sedimentary seams, the foundation is not separated by temperature seams. The device of the expansion joint in a brick wall is similar to the device of the sedimentary one: in the form of a sheet pile with a layer of insulating material and sealed with sealant on the outside of the wall. The sealant for sealing the expansion joint must be designed for all temperatures possible during the operation of the building or structure.

The thickness of the expansion joint in brickwork should be 10–20 mm. If the masonry is carried out at an air temperature of 10 °C or more, the thickness of the joint can be reduced.

The need for an expansion joint arises with a large length of brick walls and with significant differences in air temperature between the winter and summer periods of the year. Building regulations ( SNiP II-22-81 "Stone and reinforced masonry structures") establish the maximum allowable distances between expansion joints in brick walls. These distances depend on the average outdoor temperature of the coldest five-day period of the year, the type of brick and the brand of mortar. In the most difficult climatic conditions, the maximum allowable distance between expansion joints in heated buildings in ceramic brick masonry is 50 m, in masonry silicate brick- 35 m. Since the walls of individual buildings rarely reach such a length, the expansion joints in them are practically not satisfied. For unheated enclosed buildings, the maximum wall length without expansion joints can be: in ceramic brickwork - 35 m, in sand-lime brickwork - 24.5 m. For unheated open buildings (for example, brick fences) these standard values ​​are respectively equal to 30 m and 21 m.

In this article we will talk about what are expansion joints in concrete floors and similar structures and why they are needed. We will also consider the main types of these structural elements and ways to implement them.

Main features and necessity of application

In the photo - filling the cavity of the seam with silicone sealant

For experienced builders the tendency of concrete to crack during the drying stage of the mixture is not a secret. But it turns out that the tendency to cracking persists during the subsequent operation of the finished object ().

Such processes can be triggered by thermal and shrinkage expansions of the material. And if the emerging stresses are not compensated in a timely manner, the destructive process will negatively affect the state of the entire structure.

Competent and timely arrangement of expansion joints in concrete floors allows minimizing the negative impact of temperature and shrinkage expansions and thus providing a construction site or structure with a long service life.

Statistics on the use of structures equipped with seams show that they are able to withstand factors such as:

• temperature fluctuations;
• shrinkage processes;
• change in the parameters of moisture content in the ambient air;
• chemical reactions in the thickness of the floor;
• creep of concrete.

Expansion joints are a prerequisite for the organization of monolithic concrete floors and, in accordance with building codes, are used if:

• the floor has a complex configuration;
• the screed area is more than 40 m²;
• one of the sides of the room is more than 8 m long;
• the floor temperature during operation is higher than necessary.

Expansion joints in concrete according to SNiP are located:

• near doorways
• along the perimeter of the walls;
• at the junction of the floor and other concrete structures.

Types of commonly used seams

The most commonly used types of expansion joints are:

• shrinkage;
• insulating;
• structural.

Let's take a closer look at the features of each of the above categories:

• Shrink seams;

The concrete coating hardens and dries unevenly, that is, the top layer dries faster than the bottom. As a result, the level of the screed on the edge is slightly higher than in the center.

This is a natural process, but its result is the resulting stresses and, as a result, the formation of cracks. To prevent such consequences allows the use of shrinkage seams.

The seams are cut to a depth of 1/3 of the thickness of the concrete screed. Cutting is done immediately after the end finishing coatings. On an industrial scale, cutting is carried out by means of a joint cutter with the function of water irrigation of the cutter.

Important: When doing such work with your own hands, at the stage of average concrete moisture, slats of the required dimensions are installed, which can later be removed and a seam of the desired shape can be obtained.

• insulating seams;

This type of expansion joint is used in concrete structures in order to prevent the transfer of deformations to the screed from capital architectural structures.

Elements of this type are located mainly along the perimeter of the foundation around the columns and along the walls. In this case, a joint cutter is not used. Special elastic insulating material, the price of which is low, is laid along the line of passage of the future seam before applying the concrete solution.

• Structural seams;

This type of delimitation is used if a break is made during the laying of the screed. That is, the seam connects the previously laid and subsequently applied layers of concrete.

The shape of this separating element is complex and in cross section resembles a tongue-and-groove connection. When arranging, a joint cutter is not used, and work is carried out mainly on raw concrete using rails.

Distance between seams

In the photo - compensation gaps in the floor screed, laid by hand

Temperature shrinkage joints are used to limit stresses, but in order for them to effectively perform their function, it is necessary to correctly calculate their location and, above all, the distance from each other ().

In accordance with generally accepted standards, the distance between the separating elements should be no more than 150 meters for buildings of a heated type based on prefabricated structures and 90 meters for buildings erected using monolithic and precast-monolithic structures.

Important: If the building is unheated, then the declared distance between expansion joints in reinforced concrete should be reduced by 20%.

Sealing of separating elements

At objects with increased requirements for the hydrophobicity of floor screeds, it becomes necessary to seal the joints.

This is explained by excess moisture, getting into the cavity of the separating element, contributes to the gradual peeling of the coatings. Moreover, the destructive process becomes more intense as the air temperature in the room rises.

By sealing in time, you can prevent the negative effects of excessive moisture. In addition, properly performed sealing prevents the possibility of clogging of the joint cavity.

An important point is the choice of sealant. In this case, it is necessary to take into account the operating conditions and the loads exerted on the concrete pavement.

Among the commonly used sealants, the following compositions should be noted:

• silicones
• polybutylene mastics;
• cold and hot curing thermoplastics based on bitumen or butyl rubber;
• thermosets based on polyurethanes, vinyl acetates and polysulfides.

It should be taken into account that floor coverings, within industrial facilities, should not only be easily cleaned of dirt by dry and wet cleaning, but also withstand significant mechanical loads at the same time.

Considering the requirements for such floors, it can be assumed that the sealant must be both hard enough to withstand loads, but also elastic to prevent chipping.

Self-contained waterproof expansion joint

Let's see how, using diamond drilling holes in concrete, you can make a separating element on an already dry screed.

• At the first stage, with the help of laces or a long plaster rule, a line is drawn along which we will cut the strobes. On average, the width of the ditch should be 20-30 cm, and the depth 3-4 cm.
• After we have made all the necessary markings, we cut the concrete with a wall chaser, setting the cutter to the desired depth. Given that the cutting of reinforced concrete with diamond wheels is performed to a small width, we cut several strobes. We cut down the concrete with a perforator, trying to make it as even as possible.
• In the middle we lay out a temporary profile, for this flat slats up to 5 cm wide are suitable or aluminum profile, which is used when installing drywall.
• On both sides, the profile is poured with concrete. After about 1-2 hours, the profile is dismantled.
• After the concrete is completely dry, the resulting gap is filled with sealant and smoothed out.

Conclusion

Now you know what the instructions for the separation seam device are, and you also got a general idea of ​​\u200b\u200bhow to handle this job yourself (

Movement joints in floors (inside and outside: floors, terraces, patios, flat roofs)

Expansion joints are cuts (gaps) in the concrete floor structure, dividing (crushing) the total area into separate sections in order to reduce and evenly distribute loads on the floor. Thus, increasing the integrity and performance of both each section individually and the entire structure as a whole.

Functions of expansion joints:

1. minimize possible deformations by separating monolithic concrete for a certain number of plots
2. the ability to avoid costly repairs with the replacement of the underlying and finishing coating
3. increase resistance to dynamic loads, thereby increasing the service life of the structure

The need to perform expansion joints in a concrete (or cement-sand) screed is due to the fact that the floor structure experiences various loads and stresses. Which, individually or in combination, can significantly worsen the condition of the floor.

The concrete floor experiences the following loads:

• thermal expansion
• changeable humidity regime
• dynamic loads (from operating equipment, mechanisms, people)
• loads transmitted from adjoining structures (wall, parapet, foundation, etc.)
• ground settlement, as a result of the settlement of the building and the movement of structures relative to each other
• stresses arising in the body of concrete during its hardening (concrete shrinkage)

The expansion joints are general concept, which includes different kinds seams that differ from each other in their device (performance) and functional purpose. In concrete (cement-sand) screeds, three types of seams are used.

The device of expansion joints

Types of expansion joints:

• insulating
• shrinkage
• structural

Seams

The device of insulating joints

Insulating joints are carried out mainly along the perimeter at the junction of the screed (horizontal plane to vertical) to walls, parapets, foundations, columns, built-in bulky equipment. the main task insulating joints to exclude rigid adhesion of the end face of the screed with the adjacent structure.

Why make insulating seams

The device of expansion joints of this type is used in concrete floor structures in order to prevent the transfer of deformations to the screed from capital architectural structures. Each building construction must be independent of those with which it borders. This is necessary so that the stress that occurs in one element is not transmitted to other structural components of the building. That is, the screed when expanding should not put pressure on the wall. In turn, the wall, with possible movement, should not “pull” the floor behind it.

How to make insulating seams

Before the screed device along the perimeter of the walls is fixed special tape from elastic material. This is a damper tape, which is a strip of polyethylene foam. Other names: edging, edge tape. At its core, damper tape is a roll of polyethylene foam, cut into strips of a certain width. From this we can conclude that in the absence of a damper tape, it can be replaced with a material with similar properties, namely, ordinary rolled polyethylene foam (isolon, foilizol, penofol) independently cut into strips with a width according to the thickness of the screed + 2 cm (with a margin). Moreover, it will be several times cheaper compared to buying a branded damper tape.

Branded damper tape	Homemade damper tape

Insulating joints are made to the full thickness of the screed along the perimeter of walls and partitions, as well as around columns, if any. The thickness of the gap is about 6÷10 mm. The height of the tape should be a few cm higher from the level of the screed. You can attach the tape pointwise liquid nails or support with a solution, the point is that before pouring the screed it is adjacent to vertical plane, and then the screed itself (under its own weight) will tear it apart. After the screed has dried, the tape is not removed, but is cut off with a clerical knife “flush” with the floor level.

Particular attention should be paid to the correct execution of insulating joints near the columns. In addition to laying the damper between the concrete and the column, it is also necessary to correctly cut the insulating joints.

Installation of insulating joints around columns

Consider the four options shown in the sketch above. If the cutting of the insulating joints is not performed at all (see option “c”), subsequently cracks will appear from the corners of the columns. Cutting seams parallel to the faces of the column in option “d” does not save, since cracks can go both from the cut corners and from the corner of the column to the corner of the seam (if this distance is higher than the allowable one).

The best options are considered to be "a" (circle) and "b" (a square in which the corners are rotated by 45 ° relative to the corners of the columns). These two options benefit from the fact that the distance from the corners of the column to the insulating joint is minimal (no more than two or three screed thicknesses are allowed). At the same time, the corners of the insulating joint of option “b” are correctly joined with the temperature-shrinkage ones. In option “a” (circle), there are no corners at all, but this option, due to its difficult implementation, is practically never found on real objects.

Structural seams

Where the floor area is such that an uninterrupted supply of concrete mix to fill the floor at a time - structural seams should be made (other names: work, cold, construction seams). In other words, these are seams that are caused by a technological break in work. They delimit the sections of the screed laid in different time(usually yesterday/today).

Why do construction seams

Sections of the floor screed, which were carried out with technological interruptions, gain strength unevenly (yesterday's faster than today's), so the floor must be divided into separate fragments. Otherwise, incorrect joining of concrete poured at different times can subsequently lead to delamination, cracking and a decrease in the strength of the floor structure.

How to make construction seams

The simplest (but not the most reliable) way of joining different sections of the screed is performed according to the ridge (or tenon-groove) principle. The essence of this method is that after pouring the next section, the end edge must be formed in the form of a ridge. In this case, when pouring, fresh concrete enters the grooves of the hardened one. It is possible to perform a semblance of a comb at the end with the help of metal cones, transverse rails. Or, as an option, fill the bars with a certain step on the formwork.

A more progressive and reliable way to install a structural expansion joint is to use metal profiles. Deformation profiles are ready-made (factory) structures of various sizes and purposes. The floors mainly use profiles made of steel and aluminum guides with a rubber-like compensating insert. By type of installation metallic profile can be both built-in and overhead.

overlay profile	Embedded Profile

On large, critical objects, structural seams must be carried out according to the project. In which the designer, taking into account the operating conditions and all the applied loads, will competently design the structural joint assembly. If any changes occur during the process of jointing (for example, the location, width of the joint or the need to replace the material), then the mechanism for the construction of an expansion joint must be agreed on a new one with the design organization.

Thermal shrinkage seams

This type of expansion joints prevents cracking of the screed due to shrinkage and thermal expansion of concrete. Timely and correct execution of temperature-shrinkage joints can significantly increase the bearing capacity and service life of the concrete floor.

The device of shrinkage seams

Why shrink seams

The main task of shrinkage joints is to minimize the possibility of chaotic cracking of the floor screed.

The nature of the appearance of cracks is as follows. Regardless of which solution is used to screed the floor, classic or semi-dry, maturation (drying, hardening) of concrete occurs unevenly. Upper layer dries faster and shrinks more strongly than the lower one, since when dried, freed from water, any cement mortar decreases in volume. As a result, the upper layers, shrinking, cease to correspond in volume to the lower ones. This leads to the fact that the screed tends to wrap up, the edges become higher than the middle, thereby internal stresses arise in the concrete body, leading to the formation of cracks.

Cracks are a kind of rest (breath) screeds, with the help of which internal stresses are removed.

To reduce these negative processes and ensure control of cracks in concrete screed, it is necessary to cut expansion joints. They prevent chaotic cracking of the floor screed during its hardening. This technique allows you to create straight stripes of slack, thereby, as it matures and tends to wrap, the seams open a little, and cracks do not form randomly, but in predetermined places.

How to make shrink seams

The recesses are cut with a professional tool - a seam cutter, with small volumes you can get by with an ordinary grinder (angle grinder). The procedure is carried out on freshly laid concrete, 4÷10 hours after pouring (at low temperatures, the work can be extended up to 24 hours). Work should be carried out as soon as the concrete has gained sufficient strength so that it is not damaged by the blade, but before random cracks can occur in the concrete. To do this, the worker makes a trial seam a few hours after the start of concrete hardening. If, when cutting a test joint, aggregate particles fall out of the concrete body, then it is too early to start work. It is necessary to start when the blade, together with the concrete, cuts the grains of the aggregate. Subsequently, the seams are filled with polyurethane sealant.

General rules for the device of temperature-shrinkage seams:

1. The depth of the seam should be 1/3 of the thickness of the screed. This depth is sufficient to create a slack zone in the screed, and during shrinkage, the concrete will crack in this zone, that is, it cracks in a direction, and not randomly.
2. Cutting width. For interior spaces 3 ÷ 5 mm, for outdoor (roofs, terraces) - from 5 to 20 mm.
3. Marking for cutting seams is performed with a chopping cord or chalk for a rope
4. The sequence of cutting joints begins with the concrete laid earlier. In this case, in case of rapid drying of the screed (e.g. in hot weather or a warm room) and possible premature formation of cracks, every third or fourth seam should be cut, and only then intermediate
5. The shape of the plot (map) should, if possible, be square, the length should not exceed the width by 1.5 times.
6. Seam cutting is performed in the mutually perpendicular direction with an interval (step):
   - for indoor areas, an area of ​​20 sq.m. is considered indivisible (if item 5 is fulfilled), if the area is more than 20 sq.m., then expansion joints should be performed. At the same time, on large areas, the seams are cut along the axes of the columns (map no more than 6x6 m) and joined with the corners of the insulating seams.
   - for outdoor structures (roofs, terraces, walkways) - the seams divide the screed from cement-sand mortar on sections no larger than 6 × 6 m, and from sandy asphalt concrete - on sections no more than 4 × 4 m. In cold pavements with bearing slabs 6 m long, these sections should be no more than 3 × 3 m.

When cutting seams, there is no need to strive for maximum dimensions cards (6x6 m.), If you have doubts about the composition of concrete or that you cannot create optimal conditions after his departure, then make the cards smaller. The smaller the size of the area limited by the seams, the less the risk of formation of chaotic cracks in it. Less map means less cracks. But here you need to take into account that if the size of the cards decreases, then their number increases. Accordingly, the molding of the seams increases. More seams - more work and material for their device, but less unwanted cracks.

These rules are general (introductory), they cannot be universal instruction for use, since each case (object) is individual, and there may be some nuances. The best option is the presence of a project in which the designer takes into account all the factors affecting the floor ( design features underlying layer, dynamic loads, humidity conditions, temperature regime, etc). Based on this, the designer calculates: seam spacing, depth, width, etc.

Video: cutting expansion joints

Conclusion: The device of expansion joints is a forced measure dictated by realities and building codes (SP 17.13330.2011, SP 29.13330.2011, SNB 5.08.01-2000, DBN V.2.6.-22-2001).

Can it be argued that the implementation of all expansion joints is guaranteed to eliminate possible cracks? Unfortunately no. Since the device of seams is just a part of the protective complex. The cracking of the screed can be affected by: a weak (defective) base, the water content in the mixture is higher than normal, improper care behind the screed during its maturation, humidity level, temperature difference, etc.

In other words, it is very difficult to make a concrete floor without the slightest crack. What are the examples of large construction hypermarkets, where the industrial floor (topping) has cracks, a "spider line". After all, it is not necessary to say that construction hypermarkets (selling all kinds of mixtures and aware of all technologies) saved on floors. Therefore, it is important to understand the nature of the cracks (width, depth, whether the screed “boils”) and their consequences for a particular top coat. That is, the presence of cracks is not always the defect, after which it is necessary to dismantle the entire screed and make a new one.

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