Materials that do not allow the formation of shrinkage cracks. Cracks in concrete

Cracks in the foundation after pouring concrete

Cracks in the foundation after pouring are a frequent occurrence when doing construction with your own hands or by the forces of unskilled workers. There are many reasons for their formation and it is rather difficult to independently establish a specific one. Below we will consider what causes the appearance of cracks in a concrete structure and how you can deal with them.

In itself, the occurrence of cracks in the strip foundation is not something catastrophic. Sometimes they appear as a result of natural soil shrinkage under a monolithic structure. If the preliminary soil study was carried out correctly and its results were taken into account when designing the foundation, then the grid of shallow depressions will not lead to critical consequences.

On the contrary, if the cracks on the foundation after pouring have uneven "torn" edges and the depth of the recesses exceeds 10 cm, in this case it is necessary to urgently take effective measures to rescue the situation. Complete dismantling may be required concrete base and replacing it with a new one built in accordance with building regulations. Depending on the location and direction of the crack after pouring the foundation, it can be divided into the following types:

Variety of foundation cracks

1. Horizontal - directed parallel to the main working reinforcement in the foundation. Most often they are the least problematic and maintainable. The main reasons for their formation are shrinkage phenomena in the underlying soils or in the concrete itself.
2. Vertical - perpendicular to the main reinforcing bars of the concrete structure. Quite dangerous if they grow in size. Even without finding them, home owners may face unpleasant manifestations of a change in the linearity of the base of the house in the form of jamming of doors or windows in the openings.
3. Inclined cracks are located at one or another angle to the horizon line. They are the most dangerous from the point of view of maintaining the integrity of the foundation and the structure itself as a whole. As a rule, a combination of several factors leads to their formation.

Reasons for the formation of cracks in the foundation

The appearance of cracks in the foundation of a house can occur for several different reasons, most often associated with a violation of the technology for making the base of the house or poorly conducted studies of the state and type of soil at the site construction works... Below we will consider the main factors affecting concrete cracking.

1. Incorrect calculation bearing capacity the foundation or its excess due to the use of certain construction materials not taken into account can lead to cracks, which will be almost impossible to cope with. This happens for several reasons - the manufacture of a strip foundation with reduced linear dimensions in order to save concrete, the use of plastic reinforcement instead of steel, which has a low degree of longitudinal tension, and also when using an unsuitable grade of concrete. The quality of the main binder, cement, also plays an important role in the construction of the foundation. Excessive storage time, wetting and clumping directly in bags during long-term storage - all this can lead to a decrease in the quality of concrete and, as a consequence, a decrease in its strength characteristics.
2. The behavior of the soil at the site of the installation of the house is also a common reason for which shrinkage cracks occur in the foundation. Level rise groundwater as a result of the excessive amount of precipitation that fell during the spring-autumn period, it can negatively affect the modes of soil heaving. Excess of the calculated fluctuations of the base also leads to the formation of cracks, which often self-destruct when the soil conditions return to normal. Unstable temperature regimes in winter can have a similar effect. Frequent thaws, alternating with severe frosts - for better conditions for the stability of the concrete foundation.
3. Violation of technology foundation works can be expressed in a whole complex of various mistakes made by private developers or teams of unskilled workers. The most common are the following:

Causes of cracks in the foundation

• Use of steel reinforcement with multiple traces of corrosion, which can negatively affect the internal state of concrete;
• Incorrect mating of the reinforcing belt in the corners of the foundation and at the joints with the partitions. It is not recommended to connect the reinforcement in these places with the end method. It is better to install rods in the corners and at the joints, pre-bent at an angle of 90 °.
• When concrete is poured from a mixer and there is no wooden or metal tray, the mixture is often poured into one corner of the strip foundation and spread on a stretcher or spread with shovels. In this case, the consistency of concrete and the ratio of liquid and solid fractions are disturbed. Long breaks are also critical when pouring the base of the house, for example, when there is not enough concrete. In case of unforeseen disturbances in operation, the gravel-sand-cement mixture may thicken. To save money, it is re-diluted with water, not observing the required proportion, which leads to a significant decrease in the quality of concrete.
• A great influence on the occurrence of internal stresses in concrete is exerted by the speed of its curing from the outside and from the inside. The presence of frost, strong wind, rain or heat negatively affects the solidification of the mixture. It is for this purpose that the surface concrete pouring it is necessary in the first few days to cover with a damp burlap or roofing felt to adjust the drying speed.

Crack research and measurement

If cracks appear a few months or years after the foundation slab was poured, do not panic. A thorough investigation of the problem should be carried out. First, decide on the direction of the grooves, their length and depth. According to modern building codes, permissible cracks in the foundation after pouring can have a width not exceeding 0.4 mm.

Even if a grid of small recesses is found in the base of the house, it is not recommended to immediately start repairing them. Builders advise observing the dynamics of crack behavior. A simple way is used for this. It consists in installing a lighthouse on a crack, which is a strip of tissue paper or a small plaster cake.

Study of foundation cracks

Before installing the lighthouse, the surface of the foundation around the crack must be carefully dedusted and cleaned of lagging concrete particles. It is convenient to use a metal brush, a soft nylon bristle brush and a vacuum cleaner for this. After that, a strip of paper is smeared around the edges with high-quality universal glue and glued to the foundation along the edges of the recess. It is best to do this in the widest part of the cracks.

Monitoring the state of the lighthouse should be carried out at intervals of 3-5 days. In case of crack expansion, the tape, glued in tightness, will peel off from one side or break. This speaks of the widening of the deepening in the foundation and the need for immediate action. A plaster beacon cracks when cracks grow, which is also a signal for immediate action.

Methods for eliminating foundation cracks

If, after pouring the foundation, cracks appeared on the surface, and as a result of long and careful observations it was possible to establish that their growth is absent or insignificant, it is necessary to take measures to eliminate the depressions. This must be done due to the negative effect on concrete of moisture in all its forms - dew and fog, rain, snow and ice.

Ice has a particularly harmful effect on the base of the house. From the school physics course, everyone knows about the significant expansion of water when it freezes. Moisture trapped in the crack will act on its walls, which will certainly lead to the expansion of the deepening and the destruction of concrete up to a critical scale.

Currently, there are several common and affordable ways to remove acceptable cracks in the foundation. The first of them refers to small depressions that appear in an hour and a half after pouring the mixture. This is usually due to insufficient concrete compaction. In the inquiries of the grief builders, the problem most often sounds like "flooded the foundation - cracks appeared."

If cracking of fresh concrete is observed, it must be re-compacted thoroughly with a construction vibrator. The same operation, in order to avoid the occurrence of cracks, is recommended to be performed directly when pouring a tape or slab concrete base of the house.

If cracks are found after pouring and hardening of the concrete mixture on the surface of the foundation, they can be dealt with with a finely dispersed sand-cement mortar. It is prepared before starting work, applied to the surface of the cracked base of the house and rubbed with a trowel or float. A more reliable option are special repair compounds for foundations, implemented in the form of ready-made dry mixes of a complex composition.

More complex and expensive methods are used to not only get rid of cracks in the foundation, but also to significantly increase its bearing capacity. We are talking about the so-called injection method and the manufacture of additional concrete base under the existing one. The first option involves drilling inclined holes in the base and walls of the house and pumping special fastening solutions into them. For the second, typical for incorrectly calculated strip foundations, an additional base with a large depth and support area is mounted under it.

Classification of cracks in concrete

Causes of occurrence

How and how to seal

How to fix it yourself

In concrete, cracks appear almost always, even in new buildings, because the pouring technology is not always followed, or a substandard mixture is used. They also happen from age, and although it may seem that there is no salvation, everything will crumble, you should not despair: you can still fix it. Cracks in concrete are the result of deformation from external loads or from the occurrence of internal stresses.

Classification of cracks in concrete

Bending: perpendicular to the axis of the tensile bending reinforcement. They start from the edge and end at the zero line.

Shear cracks appear in the area of \u200b\u200btransverse stress and arise from bending stresses. They usually run diagonally to the reinforcement axis.

Through faults appear at central tension and go through the cross section.

Joint failures often occur in the anchorage area of \u200b\u200bthe bars and run parallel to the reinforcement. They occur in the corners of a strip-type foundation with improper anchoring or when poor-quality concrete is used, they lead to flaking of the protective layer of the pour. Typical causes of support deformation: heaving, soil subsidence, rise when saturated with water, etc.

Internal stress deformations

This stress occurs when the temperature difference on the surface and inside the concrete mass. The reason is the rapid cooling of the surface from cold air, water, or when a large amount of heat is radiated during the process of cement hydration. If the stresses exceed the strength of the material, surface cracks appear in the concrete. They go into a depth of several cm. Among the reasons for the occurrence of cracks are stresses from the sharp drying of the outer layer from exposure to air temperature or sunlight from high temperature air.

According to the standards for conditions of variable freezing-thawing, the presence of shrinkage, surface technological cracks on the surface is allowed, but their width should not exceed 0.1 mm (GOST 13015-2003). It is believed that surface cracks after pouring in concrete are perpendicular to the axes of the reinforcement up to 0.4 mm in size, or up to 0.3 mm. but running along the reinforcement does not lead to a critical decrease in durability. It is only necessary to control the size of their opening, it is believed that these are permissible cracks in concrete, only they should be repaired on time.

Causes of occurrence

Since the tensile strength of concrete structures is low, then when they dry, they shrink and shrink cracks in the concrete. The reasons for their formation are divided into three categories:

1. Cracks affecting the strength of the structure ("Constructive"). They do not result in emergency condition structures. Structural cracks are often caused by:

a) Design errors;
b) mistakes during construction;
c) changes in the conditions of detention with overloads of the structure in excess of the design loads;
d) emergencies, such as explosion, earthquake, etc .;

2. Fire cracks... They can be constructive or non-constructive (structural). Delamination of the top layer is always observed.

3. Non-structural cracks... Include reasons not included in paragraphs. 1 and 2. They are divided into several types:

a) From plastic shrinkage;
b) temperature-shrinkage cracks in concrete at the initial stage;
c) shrinkage when dry;
d) cracks due to reinforcement corrosion.

How and how to seal

When repair work usually a wet cement "paste", a binder solution, a mixture with polyester or epoxy resin, and purchased repair mixtures are used.

Repair of cracks (up to 3 mm.) Is carried out with a cement "test" or a special mixture. Mixing proportions: 1 part of Portland cement to 3 parts of water and sand + PVA glue. Large caverns and areas of loose concrete are sealed with crack sealant.

The most popular repair is injection. The essence of the method is that the work is carried out by "injecting" polymer materials into cavities without replacing the elements of the structure itself. The method is especially applicable for large volumes of work.

To repair vertical surfaces, they are covered with a mixture consisting of concrete mortar with polymer additive. For the additive, furyl alcohol (0.35% of the total mass) and 0.02% of sulfanol are suitable. After drying, the hardened mixture is additionally covered with polyurethane sealant.

Repairs can also be carried out by creating a layer of the same material on the surface. However, the use of this method is not always rational, since it is labor intensive and leads to an increase in construction weight, increasing the load on the foundation.

How to fix it yourself

By themselves, cracks in the concrete foundation are a source for the subsequent destruction of the structure. To restore the monolith yourself, you must first inspect the damage and determine the repair method.

The grout should be started by cleaning the surface with a brush, detergent and water. Remove excess water. Remove all exfoliated fragments with a metal brush. Degrease the areas to be restored (with a preparation containing acid). Small cracks are cut with a spatula and deepened to 5 mm: this way the solution fills the space more easily. We strengthen the deep ones: with a "grinder" we saw through the transverse grooves.

If the reinforcement is visible in the depths, it must be cleaned and treated with an anti-corrosion agent. Pieces of wire with a diameter of 4 mm are placed in the cleaned furrows.

A primer is applied over the entire repaired surface with a brush, its thickness is 3 mm. Then, without waiting for the final drying, we apply the repair mixture.

One of the most common and dangerous defects concrete surface is cracking. Cracks in concrete after pouring, during operation or after machining can occur due to the influence of a huge number of factors.

The reason for this defect may be hidden both in the improper preparation of the solution, and in its transportation, laying or illiterate care.

Reasons for surface cracking

The causes of cracks in concrete can be very different.

There is a division of these factors into the following groups:

1. Even at the stage of preparing the solution, an error may be made in the technology for preparing the building material, for example, the ratio of such components of the solution as water and cement may be violated. As a result of such violations construction material will refer to another brand, and therefore will not meet the stated requirements;
2. Too long process of transporting concrete mass can lead to the beginning of such a process as "welding" of concrete;
3. An error in calculations at the design stage may lead to the fact that an excessively high load will be exerted on the finished monolith already at the operation stage finished product... In this case, the cause of cracks may be insufficient reinforcement;
4. Difficult operating conditions. So, for example, the designers may not take into account the presence of heaving soils on the building site;
5. Violation of the technology for working with the mixture at the construction site:
   • You can often meet with such a situation when water is added to the solution so that it is more convenient to pour and level it. But excess moisture interferes with the normal curing process;
   • Also, cracks in reinforced concrete structures can be the result of improper laying of steel reinforcement or insufficient compaction of the concrete mass at the stage of pouring, as well as improper installation of formwork panels;
6. Construction of additional extensions to the object without taking into account the additional load on its surface.

Classification of cracks in concrete

Instructions for eliminating defects that have arisen are primarily based on the type of crack.

There are the following types of such defects:

1. Through. It occurs due to the action of axial tensile forces or forces with a low level of eccentricity;
2. Cracks in the stretched zone. Are the result of the bending of the product or are located perpendicular to the reinforcement rods;
3. Defects caused by shear force or shear cracks. Such cracks are directed at an angle to the reinforcement rods;
4. Cracks parallel to the reinforcement bars can occur in the anchorage area if it is improperly manufactured, as a result of soil heaving or in case of uneven settlement monolithic construction;
5. Small cracks can occur due to temperature changes on the surface of the concrete product and its inner layers;
6. Hair cracks can also occur due to temperature changes, but their depth does not exceed a couple of millimeters.

Defect elimination methods

In a freshly applied solution, defects of this kind can be eliminated without special costs, simply by re-compacting the mixture.

Note! A solution is considered to be freshly applied, after pouring no more than 1-2 hours have passed.

Well, in order to remove cracks in an already frozen structure, you will have to use one of the following methods:

• Injection method... A repair compound is injected into the crack under pressure;

Note! Some repair compounds can, in addition to sealing cracks, also displace water from the formed cavity, but their price will be noticeably higher.

• Embedding method, providing for filling the defect with a concrete composition.

Crack sealing

This method is most often used in practice, because every owner can handle it with his own hands without the help of professionals.

Council. As a rule, for its implementation, it is necessary not only to fill the void with a solution, but also to pretreat the surfaces in order to ensure the best adhesion.

In order to independently repair cracks on the surface, it is necessary to prepare or purchase the following materials and tools:

• Sander;
• Chisel;
• Putty knife;
• Hammer;
• Brush with hard metal rods;
• Vacuum cleaner;
• Trowel;
• Brush;
• Rake or rule;
• Pure water;
• Cement flour;
• Wire;
• Glue;
• Metal trowel.

Now it remains to answer the questions about how to cover up the cracks and how to do it correctly?

This task involves the execution of the following stages of repair work:

1. Preparatory activities. First, you need to inspect the crack itself and identify weak points around it. Further, using a chisel and a hammer, it should be expanded and deepened to at least 5 mm. This is necessary so that the repair composition is reliably entrenched in its depth and does not fall out;

Council. If the need arises, you can deepen the crack using the sharp edge of the trowel.

1. Now the crack should be thoroughly rinsed, removing the remaining dirt and particles of cement stone. To completely remove dust from the surface, use a vacuum cleaner. Using a sponge will dry the crack and rid it of excess moisture;
2. If the reinforcement was exposed during the expansion of the crack, then before starting work with the solution, the metal should be treated with primers with anti-corrosion action;
3. In order to carry out the filling, professionals recommend using a sandy mortar consisting of cement and sand in a ratio of 1 to 3. PVA glue can also be added to such a solution;

Council. Sufficiently deep surface defects should be filled in several layers, be sure to moisten each layer to ensure high-quality filling and uniform drying of the solution.

1. In some cases, cracks should be reinforced using small pieces of reinforcing metal wire;

1. The surface of the crack filled with mortar is carefully leveled with a trowel;
2. The remaining protruding parts of the mortar should be sanded with a specialized grinder.

How to prevent cracking of the monolith

The most common and most common cause of cracks in concrete is non-compliance with the proportions of water and cement in the mortar. It is this violation of technology that leads to a decrease in the quality of the concrete itself and subsequent cracking in an intensive mode. It is for this reason that special attention should be paid to these proportions when working with concrete.

In addition to this error, in the process of mixing the concrete mixture, the compaction of the mortar with the help of specialized vibrators is of considerable importance. You should not underestimate the importance of correct and competent in the process of drying and hardening.

Council. In order to prevent too strong evaporation of moisture from the surface and to prevent uneven drying of the mass, cover the solution with a damp cloth.

Particularly dangerous can be cracks that appear on the surface, the operation of which is carried out in conditions of temperature drops with frequent transitions over the 0-degree mark.

The fact is that when moisture freezes, which gets into the very depth of the crack, it expands, deepening and expanding the size of the defect. The result of such processes can be the exposure of metal reinforcement and the occurrence of corrosion, which will lead to a decrease in the strength of the entire structure.

In order to detect cracking in a timely manner and eliminate this defect before irreparable consequences occur, the concrete surfaces should be regularly inspected, the identified defects should be fixed and sealed. Thus, you will have the opportunity to localize cracking at the earliest stage and reduce the amount of repair work performed.

Council. In no case do not allow yourself to be lazy and postpone the repair for later, even if we are talking about very small defects.

Finally

Cracks on the concrete surface, whether shrinkage cracks in concrete according to SNiP or cracks in foam concrete, are the first sign that something was done wrong during the construction process. And if you cannot undo what has been done already, then you should take care of it already at the operation stage, repairing the defect immediately after its occurrence and preventing the growth of cracks and an increase in their number.

And the video in this article will tell you even more about what cracks are and how to deal with them.

A situation often arises when the builder cannot understand why the concrete cracked after pouring. This is a fairly common phenomenon that leads to a deterioration in the performance of the material and its gradual destruction. We want to talk about the causes of cracks and how to prevent this phenomenon.

Cracking is a common occurrence when working with concrete.

Cracks in concrete

Cracking of concrete structures leads to a decrease in their quality.

Cracking of concrete is a widespread phenomenon that occurs for a number of reasons, and for the convenience of considering this topic, individual cases of this phenomenon should be classified.

So, all cracks can be divided into three large groups:

Structural crackss. They pose a threat to the integrity of the structure and its bearing capacity, appear, as a rule, due to external reasons and designer errors;

Structural or non-structural cracks... Potentially hazardous, in case of insufficient remedial measures lead to more serious damage and loss of quality, load-bearing capacity and structural integrity. They arise due to internal processes during the hydration reaction and concrete gaining strength;

Cracks caused by fire... Includes both structural and structural damage. A distinctive feature is the stratification of the top layer of concrete.

The photo shows a typical example of a structural crack.

Damages of the first group include violations of integrity caused by increased loads on parts, a mismatch of the strength of the material with real loads, errors of the architect in design, errors in the design of the composition of the mixture, soil movements, natural disasters, impacts, explosions, etc.

Important!
Cracking is often observed due to mistakes when preparing concrete with your own hands.

The price of ready-mixed concrete hits the budget, but repairing a poor-quality foundation is much more expensive.

Structural defects are distinguished by a high opening width, great depth, through character, long length and special localization. Prevention of such damage is associated with competent design and calculation of loads, the use of high-quality materials, taking into account the peculiarities of geology and concerns, mainly, the technical and design preparation of construction.

It is practically impossible to take into account the influence of natural disasters and accidents, man-made disasters and wars, the same applies to violations due to fires.

After fires, concrete cracking is almost always observed.

The second group of defects refers to violations of the structure and integrity of the material as a result of natural physical and chemical processes occurring in concrete at all stages of its maturation, especially at the initial ones.

There is a whole spectrum of phenomena that lead to the appearance of such defects:

• Plastic shrinkage cracks... They arise as a result of intense evaporation of moisture from the surface and as a result of uneven shrinkage and compaction of the mass;
• Thermal shrinkage destruction... They appear due to the effect of thermal expansion-contraction of materials caused by heating and uneven cooling of the mixture;
• Shrinkage defects when the solution dries... They arise due to an uneven decrease in the volume of concrete during drying;
• Cracks due to reinforcement corrosion... With active rusting, steel expands and can break concrete.

An example of shrinkage damage.

Important!
Preventing the appearance of cracks is a much more efficient and rational way than fixing and repairing them.
For successful prevention, you must know the causes of defects.

Causes of occurrence

Most damage is caused by natural causes.

If everything is clear with the reasons for the appearance of structural defects, then structural violations should be considered in more detail. So let's start in order.

Plastic shrinkage is a process that occurs at the very beginning of the life of the solution. Here there is such an effect as intense evaporation of moisture from the open surface of the laid concrete. As a result, the mass of the solution actively decreases in volume, while the lower layers remain in the same size, and the upper layer is covered with a network of fine hair cracks.

Plastic shrinkage and moisture evaporation lead to hairline cracks.

Also, in the first period of the mortar's life, when laying, the process of shrinkage and compaction of the concrete mixture under the action of gravity begins. In case of insufficient compaction with a vibrating tool, a moment occurs when the concrete has already grabbed, and its compaction continues. This leads to fractures.

Thermal shrinkage deformations appear due to the reaction of cement hydration, which occurs with the release of heat. The solution heats up, increasing in volume, while the hardening areas crack. The reverse process also affects - the upper layer cools down and decreases, while the lower one remains in the same size or increases, the result is material ruptures.

Thermal shrinkage damage.

Shrinkage cracks during drying are caused by the fact that the set material decreases in volume. This is typical for any type of concrete, glue and other hardening and drying substances. Usually observed in unreinforced structures and products of flat, extended or non-standard shape, this is how large-area concrete screed, plaster and similar structures crack.

Important!
Drying shrinkage often leads to worsening of other types of cracks and an increase in their degree of opening.

Corrosion rupture of concrete products.

The penetration of moisture into the concrete structure leads to corrosion of the metal inside it. As a result, the reinforcing bars expand and break the stone.

Prevention

Proper care will prevent damage.

To avoid the appearance of defects and fractures in concrete, you should adhere to the rules that contain instructions for concreting.

For the sake of brevity, here are three main points:

Prepare the mixture correctly and maintain the recipe. Excess water or cement has the most detrimental effect on the quality of concrete and leads to the appearance of defects;

Place mortar in accordance with accepted standards: use vibration compaction, aeration, and other standard procedures;

Take care of the concrete after laying. The object can be covered with a film, its surface can be moistened with water, if necessary, concrete can be heated, the formwork can be insulated, and expansion joints should be cut in large screeds.

Moistening the surface prevents cracking.

Important! Observe the conditions of concreting, namely: work in the correct temperature regime, control humidity, monitor changes in weather conditions, do not violate the framework under which work can be performed, do not neglect the technology of caring for hardening concrete and use high-quality materials.

For concreting critical units and structures, it is better to use high-quality ready-mixed concrete, since a home-made product most often demonstrates the listed phenomena, and they are different at the same time.

Protect material from sudden temperature changes.

Important! Do not dilute concrete with water and do not add cement to it, this is a gross violation of technology and interference in the formulation of the mixture, the result of which is predictable.

Cracks lead to the fact that further processing and construction procedures lead to an aggravation of the state of the structure, only cutting of reinforced concrete with diamond wheels and diamond drilling of holes in concrete does not destroy it. To avoid such defects, the technology should be strictly observed concrete works, which is detailed in the video in this article.