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What to do if the concrete is cracked. The concrete slab was poured and cracks appeared.

home Formation of cracks in concrete and reinforced concrete elements negatively affects the load-bearing capacity of building structures. In addition, as a result of thermal changes, moisture and moisture can enter the room through them. various types

salt. There are many reasons for the formation of cracks. But, regardless of the source of the cracks and the nature of the damage, their occurrence requires immediate repair work.

Cracks in concrete: types and causes of formation There are two main reasons for the occurrence of cracks in concrete structures: exposure to external loads

and internal stresses in the material itself.

• Cracks that occur under the influence of external forces are divided into several types.
• Cracks in bending are located perpendicular to the longitudinal axis of the reinforcement, which is subject to tension during bending.
• Flexural cracks form shear cracks. They appear in the zone of transverse forces and are located diagonally to the axes of the reinforcing bars. Through cracks completely penetrate cross section concrete structure
• . Appear during central tension or tensile stress with low eccentricity.

In the places where reinforcement bars are connected and anchored, cracks occur during connections. They are located parallel to the reinforcing bars. The reasons for the formation of such defects are: improper anchoring of reinforcing bars in the corners of strip foundations, subsidence or heaving of the soil, incorrectly calculated or poorly secured formwork, too early loading of concrete before it has completely hardened. Cracks at connections cause delamination of the concrete element. The reasons for the formation of cracks from external influences

There may also be: incorrect choice of cross-section and location of reinforcing bars, weak compaction of the concrete element by vibration, insufficient or incorrect curing of concrete, chemical damage. In practice, there is usually a combination of several reasons.

• Internal stresses in a concrete element appear due to the difference in temperatures of the surface layer and the core. Thermal difference can be caused by the following reasons:
• too rapid and strong cooling of the concrete surface under the influence of wind, water, cold air;

Stresses caused by the temperature difference between the outer and inner layers of a concrete element can exceed the strength of concrete and lead to the formation of cracks. These cracks go several centimeters deep into the concrete element and have the ability to close when the temperatures of the outer and inner layers are equalized.
Such cracks should be distinguished from hairline cracks in concrete, which also form as a result of temperature changes. Hairline cracks are small surface cracks in concrete that are acceptable.

Methods for sealing cracks in concrete elements

Cracks that appear in fresh concrete can be eliminated using one of the proposed methods.

• If cracks appear in fresh concrete before it begins to harden (within 1-2 hours after mixing the components), then they can be eliminated by repeated vibration.
• If cracks appear during the drying process, they can be eliminated by rubbing cement or a special repair mortar into the cracks.
• If grid-shaped cracks appear approximately 8 hours after hardening, they can be repaired as follows. The surface is cleaned with a piece of foam glass or a brush. Dust is removed from the surface of the concrete element with a brush or air jet. The cleaned concrete layer is treated with cement repair compounds. After they harden, the surface is re-rubbed with foam glass or a brush.

Injection is a modern way to repair concrete surfaces

Often, the above methods for repairing concrete elements are not enough. After a short period of time, the cracks will begin to grow again. The results of the work will be reduced to nothing, and then the question arises: how and with what to permanently seal the cracks? The only one effective way, which can qualitatively eliminate this problem is crack injection.

Injection, depending on the final purpose of this operation, is divided into two types.

When injecting for waterproofing concrete structures, polyurethane compounds are injected under pressure into the pores and cracks of the material, which stop the flow of water and retain elastic properties even after polymerization is complete. The elasticity of these resins helps maintain high waterproofing characteristics under dynamic loading of concrete structures.

The use of polyurethane resins makes it possible to seal and fill not only dry and wet, but also water-filled cracks, joints and seams. Used in above-ground and underground building structures, including drinking water facilities.

Injection, carried out to strengthen and structurally bond concrete elements, is carried out with low-viscosity epoxy resins. These materials are intended for power gluing and allow you to restore the integrity of the structure and the normal transfer of internal stresses.

Concrete injection, completely restoring concrete elements using polymer and cement compositions, allows you to avoid overhaul And complete replacement designs.

Crack formation: how to prevent this process?

Repairing cracks is a labor-intensive undertaking. Therefore, when installing concrete and reinforced concrete structures It is necessary to adhere to certain rules, the implementation of which will avoid the formation of cracks.

• When manually mixing the solution, a significant amount of water is immediately added to facilitate the work, which leads to increased evaporation of moisture, too rapid hardening, and, as a result, the formation of cracks, which are called shrinkage cracks. That's why an indispensable condition To obtain a high-quality concrete mass is strict adherence to the proportions of all components of the mixture and the technological rules for its preparation: shrinkage cracks appear both as a result of a lack of water and its excess.
• When too high temperature Once the concrete dries, its hardening occurs unacceptably quickly due to the accelerated evaporation of moisture. To resolve this issue, you must protect concrete covering from a direct hit sun rays. Protective shelters can be created using plants or dense fabric. In hot weather before shelter concrete surface moistened with water.
• Cracks on the surface of the concrete layer can form due to an illiterate choice of cement brand. To completely eliminate this problem, you can use the services of specialized companies and purchase ready-made concrete produced by professionals in compliance with all technological requirements.
• Cracks may appear due to the construction of structures on problematic soils. To avoid this process, reinforcement with a metal frame is used.

The company "TD Navigator" carries out concrete work of varying complexity.

For renewal service life concrete structures, it is necessary to regularly inspect their surface, filling the small cracks that arise with mortar or sealing compounds. These measures will prevent their growth and destruction of the structure. If complex cracks that are problematic to eliminate occur, it is best to seek help from qualified specialists.

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Many who have dealt with the construction of a foundation and any other construction work involving concrete are puzzled by the problem: why do cracks appear in this solution soon after pouring? It seems that everything was done according to the instructions, professional recommendations were followed, the frozen solution itself is a very strong connection, and yet the problem arises.

In order to answer the question of why cracks appear, you need to understand the causes and factors that lead to the destruction process.

The reason why concrete cracks after pouring can be easily determined by any professional by the nature of the cracks. They can be dangerous and non-hazardous, surface and through, horizontal, vertical, inclined. Depending on the type of destruction, they can be a rupture, shear or crush.

To make it easier to diagnose the problem and definitely find out why cracks appear in concrete, we will divide the article into several parts, in each of which we will analyze its own reasons.

External factors

External factors are the impact on concrete, which can be caused by any external influence and leads to its cracking.

Rusty reinforcement is the cause of cracks in concrete after pouring

Such reasons include:

1. Unbalanced impact on concrete. For example, over time, the foundation of a building begins to sag under the influence of groundwater, and the load on one of the load-bearing sides increases noticeably. A similar situation can be abruptly caused by an explosion or impact. The concrete surface cannot withstand one-sided load and cracks. Very unstable and dangerous situation requiring immediate action.
2. Problems with interlocking design. For example, with fittings that are subject to corrosion and rust formation. A paradoxical situation. Reinforcement is used to strengthen concrete, since it does not allow it to compress and expand much, but, nevertheless, it can also cause significant harm. Rust grows and therefore requires occupying more space. Under its influence, the solution sooner or later fails and cracks.

Such problems arise very rarely, provided that everything was calculated as accurately as possible at the planning stage. If the engineering calculations are incorrect, then even a perfectly made mixture will begin to crack as it dries and, ultimately, collapse.

Internal factors

In addition to external influences, among the reasons why concrete cracks after pouring, there may be internal factors related to the composition concrete mixture and errors made during its manufacture.

Diagram of cracks in concrete

Such reasons include:

1. Evaporation of moisture. Along with sand, gravel and cement, water is an integral part for the preparation of this durable mixture; you cannot do without it. However, if there is more water than necessary, it begins to evaporate and seep under pressure, having a destructive effect on concrete. Accordingly, it is very important to maintain the required proportions during the preparation of the solution.
2. Temperature changes. A familiar situation for every resident of the country: the sun had just been shining unbearably, and then it began to rain, accompanied by an icy wind and vice versa. During the rain, a certain amount of moisture was absorbed into the frozen surface, and when the sun warmed up, the water inside heated up. As the surface of concrete cools, it begins to contract, while the internal temperature increases and causes expansion. Accordingly, the material cannot withstand opposing forces and cracks. Each time it freezes and then thaws, the crack will grow.

As you can see, a lot depends on correct composition mixture and temperature environment. These factors may be the reason why concrete cracks when it dries, resulting in the need to redo or re-pour.

Additional reasons

TO additional reasons, in which concrete cracks soon after pouring, include those that happen rarely and it is difficult to somehow protect the solution from them:

• Soil subsidence for any reason.
• The soil under the pour is too wet (this causes the concrete to rise and crack);
• The soil contracts, which also causes deformation;
• Incorrect formwork;
• Incorrect choice of reinforcement section;
• Incorrect points for placing steel rods;
• Insufficient holding of the mixture after pouring;
• Corrosion of reinforcement inside the mixture;
• Earthquake.

As you can see, despite its strength, concrete has a fairly high susceptibility to cracking. Not a single super-professional builder is able to completely resist this phenomenon, but even a beginner can reduce it to minimal manifestations. After pouring, it is recommended to use a sprayer to cover the concrete surface with special sealing mixtures, and the reinforcement should be subjected to preliminary anti-corrosion treatment.

Cracks in concrete after pouring can be caused by an earthquake!

It is important to follow the recommended proportions when preparing concrete. If cracks nevertheless form, regardless of the reasons for their appearance, it is necessary to urgently take corrective measures. Otherwise, this poses a certain threat to strength, reduces the durability of the hardened mortar and significantly damages appearance. In exceptional cases, cracks can be very dangerous and lead to the most disastrous consequences.

How to avoid cracks?

Now let's talk about what to do to prevent concrete from cracking when drying. Here are a few rules to help you with this:

• Try to ensure that shrinkage of the mixture is minimal;
• Do not allow the solution to dry out too quickly; to do this, eliminate temperature changes;
• Do not force the mixture until it is completely dry;
• Make sure that the formwork is intact;
• Make sure that moisture does not leak out through the formwork and the composition is not dehydrated;
• Insulate the concrete after pouring, let it sit for the required period;
• Any natural influences should not affect the mixture (wind, sun, rain);
• 7-9 hours after pouring, moisten the mixture additionally;

The main task is to protect concrete from external factors and temperature changes

With the help of this article, we found out why concrete cracks after pouring, what affects it, how to prevent it and what to do in case of damage that has already occurred. Below you can watch a short lecture on cracks in concrete mixtures, presented in clear and literate language.

Video instructions

• Causes of cracks

Private developers, not being professional builders, often do not understand why concrete cracks when drying.

Often, if prepared and poured incorrectly, concrete cracks and crumbles after drying.

It seems that high-quality components for concrete were used, and the proportions were maintained correctly, and the pouring technology was followed, but cracks still appear in the concrete monolith. So why does this happen and are there ways to avoid it?

Causes of cracks

Cracks in concrete can appear for a variety of reasons. Conventionally, these reasons can be divided into several large groups:

• structural;
• structural;
• influence of external factors.

Structural cracks arise due to miscalculations by designers or due to the introduction of unjustified changes to the design calculations of the structure, such as replacing the M100 grade mortar with a lower grade when pouring it or erecting an additional floor that was not taken into account in the design.

Types of cracks in concrete: a) longitudinal cracks; b) transverse cracks; c) corrosion of concrete and reinforcement; d) buckling of compressed reinforcement bars.

Such cracks are a serious threat to bearing capacity structure until its destruction. But to eliminate the causes of their occurrence, very little is needed: trust only reputable companies to carry out design calculations and do not deviate from these calculations either during concrete pouring or during further construction.

Cracks in concrete can also appear under the influence of external factors: fire, flood, soil movements due to an earthquake or nearby explosions. The reason for their appearance is practically beyond the control of human will, so their prediction is impossible.

Structural cracks are the most common and most diverse group of cracks in concrete. Often the danger of such cracks is underestimated and sufficient measures are not taken to eliminate them, which leads to the concrete monolith losing its properties. strength characteristics and its gradual destruction.

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Types of structural cracks

Structural cracks in concrete are the most common and diverse group of concrete cracks. These are actually shrinkage cracks. The reason for their appearance is the natural physical and chemical processes occurring in concrete. They are especially active at the initial stage of maturation of the concrete monolith; then their speed slows down, but the processes themselves do not stop until the concrete has completely matured.

Reasons for the formation of concrete cracks.

In other words, these damages appear in the concrete due to the drying and shrinkage of the concrete mixture after pouring. It is well known that a concrete mixture consists of 4 main components: cement (binder), sand and gravel or crushed stone (fillers) and water. Each of the components plays its own strictly defined role in creating a concrete monolith.

Freshly prepared concrete mortar has a plastic or even liquid consistency. The mixture poured into the mold begins to harden. The further this process goes, the more the cement and water contained in the concrete are reduced in volume. As a result, shrinkage of the poured mixture occurs, and in the body of the forming concrete monolith, due to the compaction of the mass, loads arise that the cement mortar, which has not yet gained sufficient strength, holding together the mixed components of concrete, is simply unable to cope.

As a result, shrinkage cracks are most often a consequence of processes occurring inside the hardening concrete monolith. Conventionally, they are divided into:

• damage from plastic shrinkage;
• temperature-shrinkage damage;
• shrinkage damage from drying out the solution.

It is very important to correctly determine the cause of damage in a concrete monolith, because the method of repair directly depends on this.

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Damage from plastic shrinkage

Scheme of crack formation due to shrinkage.

This type of damage usually occurs due to intense loss of moisture from the exposed surface of the laid concrete, resulting in uneven shrinkage and compaction of the concrete mass.

This process occurs at the very beginning of setting of the poured concrete mixture. Due to the evaporation of moisture, the surface of the solution actively loses volume, while the middle and bottom layer of laid concrete remain in their original dimensions. The result of this shrinkage is the appearance on the surface of the concrete mixture of a network of small (the width of a human hair) and shallow cracks.

Phenomena similar to those described occur with concrete during precipitation. When it rains, the surface of the concrete gets wet, and a certain amount of moisture gets inside the monolith. When the rain stops and the sun comes out, the wet surface of the concrete heats up, expanding, and cracks may appear on it.

This type of damage also includes cracks that appear in concrete under the influence of gravity. The reason for the appearance of such cracks is insufficient compaction of the concrete being laid. In this case, the following results: the forces of gravity act on the setting concrete monolith, and if insufficiently compacted areas remain in its body, then the mixture in these areas will continue to compact, breaking the integrity of the concrete monolith.

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Temperature-shrinkage damage

Scheme of processes during concrete hardening, formation of structure and formation of properties.

Such deformations occur because the cement used for the binder, in contact with water, enters into a hydration reaction, which results in the release of a large amount of heat and, in accordance with physical laws, an increase in the volume of the solution.

In the mortar being laid, this heating and increase occurs evenly, but in hardening concrete, hydration slows down in hardened areas, and continues with the same force in unhardened areas. This unevenness causes damage to the drying concrete.

The hydration reaction also has the opposite effect, which is no less dangerous for the integrity of the concrete monolith. In the hardening upper layers of the poured concrete mixture, hydration stops and they decrease in volume, while in its deeper layers the process continues and they, accordingly, increase their volume. The result of such exposure to multidirectional forces on the monolith often results in ruptures of the concrete monolith.

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Shrinkage damage from drying concrete

This type of damage usually occurs because a concrete monolith that has already set, but has not yet fully matured, continues to decrease in volume.

This is a feature not only of concrete, but also of any cement and adhesive compositions, such as cement screed, plaster, etc.

This is the most common type of shrinkage damage, and preventing the formation of such cracks is a very difficult task. In addition, such temperature damage widens and deepens small cracks in concrete that appeared from the first two types of shrinkage damage.

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How to prevent and eliminate cracks in concrete

Components for preparing concrete mixture.

It is clear to any sane person that it is better to prevent a problem from occurring than to eliminate its consequences. All this is completely true for cracks in a concrete monolith. To save yourself from unnecessary work in the future, when preparing a concrete mixture you need to follow a few simple rules.

When kneading the mixture, you need to follow the recipe and strictly observe the proportions between its components. Keep in mind that cracks can appear not only from excess water in the mixture, but also from excess cement in it.

When pouring, the concrete mixture must be compacted as much as possible. This will protect the poured mixture from damage due to the effects of gravity. Also, to prevent the appearance of cracks in the concrete being laid, reinforced belts are installed.

Concrete needs maintenance after pouring. Its main task is to prevent excessively rapid or uneven evaporation of moisture from the body of the poured concrete mixture. To do this, the mixture is covered with a moisture-proof film or burlap, and periodically - after 4-8 hours - its surface is moistened with water until completely set.

Expansion joints in concrete floors.

For large areas of filling, in order to avoid the appearance of cracks from temperature changes, it is necessary to install expansion joints. If necessary, the formwork can be insulated.

If cracks do appear, then you need to carry out work to eliminate them as quickly as possible. Cracks must be repaired with cement mortar based on Portland cement. Moreover cement mixture It is advisable to prepare it of the same brand as the poured concrete, then the uniformity of the concrete structure will not be compromised.

After sealing the cracks with cement mortar, the treated surface must be thoroughly smoothed with a brush. Then the surface is covered for 2-3 days plastic film, secured at the edges with strips or bars. The film should be periodically removed to moisten the treated surface with water.

Even the most highly professional builder will not be able to completely avoid the appearance of cracks in concrete; sooner or later they will appear. But their appearance can be delayed for a long time, and the cracks that appear can be repaired quickly and efficiently, preventing the destruction of the concrete monolith. Good luck!

The demand among consumers for both concrete and products is constantly growing. As a result, enterprises are increasing their volumes, and manufacturers are opening new factories and launching production lines. The quality of all products produced by enterprises remains important for manufacturers and their consumers.

Strength ratio table.

Quite often, those who independently carry out construction work on their site, and even professional specialists, wonder why concrete cracks? Is it possible or avoidable and what affects it?

After all, repairs when they have already begun to deteriorate are troublesome and sometimes ineffective. Therefore, it is better to do everything at once with high quality, in compliance with all the rules. The main thing is that the appearance of various deformations on the surface can be avoided, although this is not easy.

As you know, the composition includes: cement, crushed stone, sand and water. In its plastic state or fresh form, concrete has a liquid consistency. After pouring, as the mass hardens, cement and water are reduced in volume. Appearing loads that appear due to compaction of the mass, fresh concrete difficult to tolerate due to low strength.

One of the main factors for high-quality concrete is maintaining the correct proportion of all components included in the composition.

Here it is necessary to take into account not only the state of the solution, but also the conditions under which it is located, namely:

Scheme for preparing the mixture.

• when using the solution in rooms with low temperatures, chemical additives should be added to the mixture to prevent the formation of a frozen crust;
• at elevated temperatures, the solution quickly hardens, its structure changes, and after installation, when dry, it begins to quickly crack;
• To create a good fill, you should take high-quality dry mixtures, avoid drafts, observe the temperature regime and moisten the surface during the entire drying time.

Plastic shrinkage cracks

Surface deformations

Wall reinforcement diagram.

They appear due to the rapid evaporation of moisture when the coating is in a plastic state. Namely, the rate of evaporation is higher than the rate of water separation. It is important that the time for evaporation of moisture from the surface of the solution depends on temperature. As well as ambient temperature, wind speed, humidity and sun exposure.

Hot sunny weather or dry wind contribute to the appearance of this type of crack. Surface cracks are usually not deep, up to 750 mm in length. If the cracks are minor and lead to the destruction of the frozen slab, then everything can be fixed. To do this, you will need to seal all the cracks with a Portland cement solution and carefully smooth them with a brush. Cover the treated surface with plastic film for 48 hours, while securing the film along the edges of the slab with bars and strips.

Subsidence defects

Table for creating the required strength.

The resistance of the surface to compaction of plastic concrete contributes to the appearance of this type of crack. That is, this is when the hardening of the solution has already begun while simultaneously settling. This process leads from the very beginning to the formation of cracks, and the concrete slab, even before it hardens, is already destroyed.

As a rule, such cracks are wider on the surface, their depth reaches no more than 25 mm. It is important that this type of crack can reach the reinforcement, because when it hardens, the mixture seems to get stuck on the reinforcement, and the continuing solidification process entails the formation of cracks. Such cracks are best repaired after complete hardening by introducing a new solution into the cavity.

Other types of cracks

Temperature-shrinkable

At the very beginning of hardening and during the setting process, a certain amount of heat begins to be released between cement and water. This phenomenon causes an increase in the temperature of the mixture.

If the floor, ceiling or wall does not have freedom to deform, then thermal stress develops during shrinkage. This stress is tensile or compressive in nature and entails the formation of cracks on the surface.

The appearance of cracks of this type is influenced by: the temperature of the air and concrete, the type of formwork and the period of curing of concrete in it. As well as the brand of cement used and the quantitative ratio of all components in the finished solution. The damaged surface can be restored by high-quality sealing of cracks followed by application of a decorative layer.

Shrink when dry

Cracks of this nature are less common compared to other types. Basically, they appear on secondary elements without reinforcement or fills reinforced according to the requirements.

The reason for their occurrence may be improper mixing of components, excessive amounts of water, the use of low-quality aggregates and insufficient soaking time for the solution.

To prevent the product from cracking in the future, it is recommended to repair work apply a decorative waterproof coating and insulate the entire surface.

For this, you can use reinforcement or iron ties.

Cracking of concrete structures is quite common. The causes of this harmful phenomenon have been identified and systematized. However, regardless of the source of cracks, when this defect appears, immediate repair work is required.

Why do cracks occur in concrete?

There are two main reasons for the appearance of cracking in concrete structures - the influence of external factors and uneven internal stresses within the concrete thickness.

• Cracking that appears in concrete under the influence of external factors is divided into types:
• Cracks in bends located perpendicular to the axis of the reinforcement working in tension during bending;
• Shear cracks resulting from bending cracks. Located in zones of transverse stress diagonally to the reinforcement axis;
• Fissures-fistulas (through). Arise under the influence of central tensile forces; Cracks where concrete contacts anchor bolts

and reinforcing elements. Cause delamination of reinforced concrete products.

Causes of occurrence: improper anchoring and reinforcement in the corners of strip foundations, subsidence or heaving of the soil, “flimsy” or poorly fixed formwork, loading of reinforced concrete until the permissible strength gain, incorrect choice of cross-section and location of reinforcement, insufficient compaction of concrete during the pouring process, exposure to chemical agents liquids.

As practice shows, as a rule, the causes of concrete cracks are several of the listed factors.

• The causes of internal stresses that literally “tear” a concrete structure is a significant difference in temperature on the surface and in the thickness of the concrete. The temperature difference may be due to the following reasons:
• Rapid cooling of the concrete surface by wind, water or snow;
• Rapid drying of the surface under the influence of high air temperatures and direct sunlight;

Intensive heat release during the hydration of large volumes of cement located inside massive reinforced concrete products.

Methods for eliminating cracking of freshly poured concrete

• Cracks in reinforced concrete that appear before the material begins to set can be eliminated by repeated vibration treatment;
• Cracks that arise during the setting and hardening process are eliminated by rubbing cement (ironization) or repair mortar into the crack;
• The network of cracks that appeared 8 hours after pouring is eliminated using the following method. The surface is cleaned with a metal brush. The resulting cement dust is removed. The surface is treated with a repair compound and, after drying, cleaned again with a brush or foam glass.

Cracks that appear in concrete after complete hardening are eliminated by injection with polyurethane compounds. Injection technology involves injecting special compounds into the crack, which seal the crack and form an elastic “seam.”

The latter effectively restrains further crack propagation under the influence of static and dynamic loads.

Having told in this article why does concrete crack, it is impossible not to mention how to prevent this very harmful process, which ultimately leads to the complete destruction of concrete structures.

• Very often, when mixing the material themselves, inexperienced builders add a large amount of water. This results in strong evaporation and very rapid setting and hardening. The consequence is the formation of shrinkage cracks. In this regard, water must be added in small portions and the recommended consistency of the solution must be observed, even if it seems too thick;
• Concrete structures poured in conditions of high air temperature and bright sunlight must be protected with plastic film, wet cloth or special mats. If this is not possible, the surface of the concrete (at least four times during the day) is generously sprayed with water;
• To avoid the appearance of cracks from soil shrinkage, you should strictly adhere to accepted technologies concrete works: soil compaction, filling a cushion, laying reinforcing belts, etc.

In any case, before starting concrete work, you should carefully study and strictly follow the theoretical and practical recommendations of GOST and experts on: choice of brand and type of cement, type and type of reinforcement, concrete composition and other features of concrete work.

The presence of cracks in concrete indicates problems with the pouring. We will try to figure out why concrete is cracking and how serious the damage is. Cracks in concrete always appear, even in new buildings. Splitting of concrete occurs due to violation of technology or proportions during the production of the solution, or age. The formation of cracks negatively affects the load-bearing capacity of the walls, but the problem cannot be completely avoided. You should monitor the width of the cracks formed and eliminate them in a timely manner.

Causes

Cracks in concrete are a consequence of changes from external or internal load. The main reasons for the splits were combined into the following groups:

• violation of solution manufacturing technology;
• deviations in calculations, insufficient amount of reinforcement;
• unaccounted for complex geological conditions;
• violation of the structure of the solution during use (cannot be diluted with water);
• violation of concrete care conditions (the required temperature was poorly maintained);
• long-term transportation of the solution, which violated its properties;
• additional buildings not approved by the project.

Separation of cracks into groups

Splits in concrete are quite common. Having examined the nature of their occurrence, they were divided into certain types.

Constructive

The opening of cracks in the concrete of structures indicates serious violations in the calculations. They negatively affect the load-bearing capacity of the frame and reduce safety. They arise due to design violations, changes in operating conditions of the building, and poor materials.

Non-constructive (structural)

These include cracks in concrete that do not fall into the first category. They are divided into several types: damage from plastic shrinkage, temperature-shrinkage damage, damage from drying out and corrosion of the frame.

Plastic shrinkage disorders occur in several situations

Temperature-shrinkage damage

Diagram of a crack in the foundation.

At the beginning of the hardening process of the concrete mixture, a chemical reaction occurs between water and cement. The result of the reaction is heat generated. The time during which the temperature reaches its maximum is influenced by various factors: air temperature, concrete temperature, formwork material, cement brand and many others. The behavior of cement during hardening (with temperature changes) has not been fully studied. The lack of freedom to distort the ceiling during concrete shrinkage leads to an increase in temperature stress. Resistance to tensile and compressive stresses leads to cracks. You may not notice them right away, but when you find them later, you need to monitor whether the defect is expanding and choose the right method of restoration.

Drying the solution

Appearing shrinkage defects have a limited distribution area. Formed in thin ceilings, load-bearing elements without reinforcement. The main reason is considered to be disturbances in the structure of the solution.

Impact of external factors

It will cause sudden shrinkage. External factors include rainfall, snowfall, flooding, and improper operation. For example, underground soils are dangerous due to the subsidence of a separate part of the structure and the creation of uneven load distribution, which will lead to crack formation. The reason for the problems in this case is often lack of professionalism in the preparation and implementation of work.

Defect Prevention

Eliminating negative results after concrete is poured is a difficult process. It’s worth taking care at the very beginning to comply with technologies and rules that will help prevent the formation of defects:

• When mixing ingredients by hand, adding plenty of water will make the process easier. This approach leads to additional vaporization, and as a result, rapid hardening of the surface occurs. Compliance with the ratio of components is the basic rule quality solution. Excess moisture and insufficient quantity will lead to the appearance of shrinkage splits.
• The high temperature of the material and the environment leads to rapid evaporation of moisture. Pouring a concrete base at high temperatures requires additional protection. Before covering, the concrete is wetted.
• An error in choosing the quality of cement causes cracks to open after drying. Any doubts regarding the choice can be resolved by specialists offering a ready-made solution.
• Often the cause of trouble is unaccounted for problems with the soil. It is necessary to carry out sufficient reinforcement of the structure.

Systematic inspection of surfaces and identification of defects at an early stage will help to increase the service life of concrete after work.

Troubleshooting

Formations in freshly laid concrete can be corrected with additional compaction, and cracked hardened concrete can be corrected in several ways. Before you start solving the problem, you should choose the right method:

Procedure for correcting deficiencies concrete base occurs in several stages:

• revealing the problem of why concrete cracks;
• surface preparation, tapping to identify weak spots;
• expansion of the defect with a chisel up to 5 mm;
• cleaning the surface from dust with water - the sponge will remove excess moisture and dry the surface;
• treatment of existing exposed reinforcement with an anti-corrosion compound.

Afterwards, the repair solution is filled (if necessary, the defect is reinforced with wire), and the surface is leveled. The resulting defect is not always a problem for concrete. The main criteria influencing the decision to repair will be the cause of occurrence, the width of the defect, location, and exposure to air.

Water imbalance is a common cause of poor quality mortar, leading to cracks. It is worth carefully monitoring compliance with cement preparation technologies. Excess water in the solution is dangerous for surfaces when temperature conditions from zero and below. When moisture freezes, it expands, widening cracks in the concrete, after which the concrete crumbles, exposing the reinforcement. These processes reduce the strength of the building.

Try to identify deficiencies in the early stages, and do not delay correcting even minor damage.

The most dangerous thing for an individual developer is pouring a foundation in winter, which leads either to a lack of design strength or to numerous openings of cracks. However, there are technological, structural and operational reasons that are fraught with similar defects.

Clear sequence of design and manufacturing monolithic foundations given in regulatory documents SP 20.13330 – SP 25.13330, departmental standards of the VSN, technical maps of the TTK. However, mixtures, formwork and reinforcing frames are often made at home in violation of technology, proper care of the concrete is not provided, and the geological conditions in the construction site are ignored.

The main reasons why concrete cracks after pouring are violations of technology, operation, structural design and even the choice of materials.

Acceptable crack opening

The standards SP 28.13330 regulate the complete absence of cracks exclusively in unique structures or in cases where absolute impermeability of the mass is required (gases, liquids under pressure inside). The foundations of cottages do not fall into this category, therefore they are standardized by SP 63.13330 standards. There are several types of cracks in reinforced concrete products, not all of which are dangerous for the performance of the structure:

• hair - got their name from the opening width of 0.1 mm, caused by violations of the outer layer, practically do not affect the strength;
• shrinkage - mainly operational (0.3 mm), geology is not taken into account (loose, weak, unstable, bulk soils);
• horizontal - dangerous for the foundations of heavy buildings, if excessively heaving soils, since they usually cut through the thickness of the structure, after which the operation of the reinforcement frame is disrupted.

Such cracks often form after pouring; the cause may be poor-quality vibration compaction, dilution of concrete with water, or neglect of concrete care. They usually pose no threat unless they exceed acceptable limits, as shown in the following photo. They are sealed with special repair compounds. They are called shrinkage cracks in concrete (not to be confused with shrinkage of the entire structure under load).

For MZLF it is acceptable if the concrete cracks after pouring within an opening of 0.15 - 0.18 mm (ACI-224), 0.1 mm (GOST 13015) or 0.3 - 0.4 mm (German standards for opening along reinforcement , perpendicular to the working axis, respectively, after pouring).

Nature and location of cracks

Crack opening can occur after application of external loads. Therefore, there is a classification of these defects according to the type of load.

• Connection crack - concrete is destroyed parallel to the rods of the lower and upper chords, the joints of the rods. This is caused by improper anchoring (usually at T-junctions and corners) or by soil compression, uplift from over-watering, or subsidence. In addition, the culprit may be early stripping, loading of fragile concrete with masonry or frame crowns, or insufficient cross-section of reinforcement. With such cracks, there is a danger of peeling off the protective layer.
• Through crack - the culprit is central tension outside the center of the structure.
• Shear crack - usually runs diagonally to the frame rods, occurs due to transverse forces (for example, a pallet with masonry bricks was placed on the tape);
• A bending crack is perpendicular to the axis of the wall and begins at the edge of the stretched zone.

An example of strong shrinkage cracks, such cracks are already dangerous.

Situations often arise when cracks appear on the surface due to internal stresses. The main reason in this option is the significant difference in temperature between the core and the surface of the laid mixture (concreting in the heat, frost + heat released during the chemical reaction of cement with water).

If these stresses exceed the strength of the construction material, cracks can open anywhere. They penetrate deep and can close on their own when the temperatures of the layers naturally equalize.

Prevention of thermal stresses - the use of special cements. For example, with a reduced heat of hydration (marking VLH), Portland cement with slag (marking LH). An easier way is to control the temperature of the concrete before laying - within +20 degrees.

Armature

After laying reinforcement with peeling rust, cracks open after several months or even years. If the protective layer is not observed or the rods are released into the ground (for better support of the clamps), the situation is completely similar to the indicated case.

Aggressive advertising by manufacturers of composite reinforcement is aimed solely at increasing sales volumes. It is strictly not recommended for an individual developer to lay it in concrete. For example, manufacturers indicate seamlessness as the main advantage:

• the composite is easy to deliver to the building site in the form of a bay;
• however, excessive plasticity and flexibility leads to unpleasant consequences;
• instead of immediately absorbing tensile loads, the reinforcement is first pulled out;
• this is usually enough to open cracks in the concrete.

Consequences of using fiberglass reinforcement.

In addition, despite the corrugation, the structure of fiberglass and carbon composite is too smooth, adhesion to concrete components is an order of magnitude lower.

Weather

Cracks often appear in concrete after winter concreting, usually in the area of ​​concentration of voids in which water accumulates or along the reinforcement. Measures to combat the defect - high-quality sealing with the tip deep vibrator until the bubbles completely stop, large fillers are hidden, and cement laitance appears (the funnel collapses almost instantly after removing the vibrating tool).

Vertical cracks after wintering indicate incorrect calculations or no geology at all.

The next reason is the accelerated drying of exposed surfaces in the wind, cold or heat. Stresses arise inside the surface layer and cannot be eliminated. Timely and high-quality care of fresh concrete is required.

Poor quality raw materials

Cracks may open due to the cement not meeting the declared quality. Individual developers are looking for cheap prices and often do not pay attention to packaging. The bags of a manufacturer that values ​​its reputation must include:

• details - you can conduct an examination, file a complaint, at least partially compensate for the damage;
• packaging period - cement retains its properties under storage conditions for 3 months, after which it begins to “lose” its strength quite sharply;
• ratio of water and filler - for mortars and concretes;
• composition - addition of slag, grinding size significantly influence the hydration process, which is important for the thermal regime of massive structures intended for use in the ground and aggressive environments.

Concrete cracks on the surface immediately after pouring, including due to plastic shrinkage. The principle of this defect is determined by the process of formation of cement stone:

• the volume of the mixture increases with the release of heat as a result of a chemical reaction;
• the surface cools and dries faster and begins to shrink;
• in the core the process lasts more slowly and prevents surface compression;
• the result is cracks across the entire surface or individual sections of concrete.

There is no clear direction, everything depends on the circumstances. Or longitudinal cracks 1–3 mm thick and of insignificant depth appear. A wet compress made from periodically moistened sawdust, sand, and rags completely saves you from these troubles in the first three days.

Dilution with water

When ordering the mixture using mixers, developers sometimes receive delivery times of one and a half hours. After laying the first layer, time is required for compaction by vibration. Another 1 - 1.5 hours pass, the concrete begins to thicken, water is added to it.

Large shrinkage crack turning into a vertical one. When the concrete is heavily diluted with water and a vibrator is not used, this also happens.

In this case, cracks are inevitable, since the proportions balanced by the mortar unit are disrupted. Grade strength decreases, hydration time increases (water-cement ratio W/C increases).

Side view of the top crack.

"Long Run"

Downtime of mixers is expensive for the developer, so concrete is often dumped in one place and shoveled to distant areas without a tray. This leads to the separation of the mixture into separate fractions - large crushed stone is better captured by the entrenching tool, the liquid practically remains in place.

Pronounced consequences of concrete delamination.

The result is an uneven concentration of sand/crushed stone in individual areas, which cannot but affect the quality. There will be no design strength in any section of such a foundation, crushed stone is physically unable to envelop the reinforcement, cracks are inevitable.

Exceeding the technological break

The recommended technological break is 1 - 2 hours, depending on the specific pouring conditions, due to the hydration time. If the next portion is laid after the specified time on the previous layer, the tip of the deep vibrator will destroy the formed bonds without the possibility of their restoration.

In addition, a large volume of concrete on the surface of the previous layer will push through the emerging structure, which will lead to the formation of cracks and a loose consistency incapable of absorbing loads.

What can be done or methods of correction

There are several ways to repair cracks that formed immediately after concreting:

• discrepancy before setting begins - if defects were noticed on the surface within 2 hours, the concrete can be compacted with a vibrator again to completely correct the situation (time is calculated from mixing the concrete at the factory, and not from the time of laying in the formwork);
• discrepancy after setting - a solution made in a 3/1 ratio (cement, water, respectively) with the addition of 3 - 4 drops of plasticizer is rubbed into the cracks (suitable detergent), you can use a special repair mixture, which must be purchased in advance.

If a network of small cracks is found in the concrete within 8 hours from the moment of laying the formwork inside, it can be eliminated using several methods:

• cleaning with a wire brush, foam glass;
• dust removal with a vacuum cleaner;
• putty with repair compound (for example CN83 from Ceresit);
• repeated cleaning with foam glass/brush after drying.

Larger cracks in concrete are removed from dust, widened with a spatula, rubbed with compounds containing fine-grained sand, and rubbed with an abrasive tool. If the groundwater level is high and there is a possibility of their seasonal rise, injection formulations, for example Penetron or similar, should be used.

The article discusses the main reasons for the opening of cracks in concrete, which are acceptable or make operation impossible. Almost any violation of the foundation concreting technology can lead to a sharp decrease in the service life of the structure immediately after removing the formwork. Small cracks in concrete can be repaired in the first days after pouring. To solve other problems, you will need expertise, development of a reinforcement project or dismantling of a reinforced concrete structure.

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

Cracks in concrete

Varieties

Concrete cracking is a widespread phenomenon that occurs due to 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:

1. Structural cracks s. They pose a threat to the integrity of the structure and its load-bearing capacity, appearing, as a rule, due to external reasons and design errors;
2. Structural or non-structural cracks. They pose a potential hazard and, if remedial measures are insufficient, 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 the gain of concrete strength;
3. Cracks caused by fire. Includes both structural and structural damage. A distinctive feature is the delamination of the top layer of concrete.

Damage of the first group includes violations of integrity caused by increased loads on parts, discrepancy between the strength of the material and the actual loads, architect’s design errors, errors in the design of the mixture composition, ground 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 low-quality foundation is much more expensive.

Structural defects are characterized by a high opening width, great depth, end-to-end nature, large extent and special localization. Prevention of such damage is associated with competent design and calculation of loads, application quality materials, taking into account the peculiarities of geology and concerns mainly the technical and design preparation of construction.

It is almost impossible to take into account the impact of natural disasters and accidents, man-made disasters and wars, the same applies to disturbances due to fires.

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 range of phenomena that lead to the appearance of such defects:

• Cracks due to plastic shrinkage. They arise due to intense evaporation of moisture from the surface and as a result of uneven shrinkage and compaction of the mass;
• Temperature-shrinkage destruction. Appear due to the effect of thermal expansion and contraction of materials caused by heating and uneven cooling of the mixture;
• Shrinkage defects when the solution dries. They arise due to an uneven reduction in the volume of concrete during drying;
• Cracks due to corrosion of reinforcement. When rusting actively, the steel increases in volume and can tear apart the concrete.

Important!
Preventing cracks from occurring is a much more effective and efficient way than eliminating and repairing them.
To successfully prevent it, you must know the causes of defects.

Causes

If everything is clear about 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 a solution. Here an effect such as intense evaporation of moisture from the open surface of the laid concrete is observed. As a result, the mass of the solution actively decreases in volume, while the lower layers remain the same size, and upper layer covered with a network of thin hairline cracks.

Also, during the first period of the solution's life during installation, the process of mixing under the influence of gravity begins. If compaction by a vibrating tool is insufficient, a moment arises when the concrete has already set, and its compaction continues. This leads to faults.

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

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, so cracking concrete screed large area, plaster and similar structures.

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

The penetration of moisture into a concrete structure leads to corrosion of the metal inside it. As a result, the reinforcing bars increase in volume and tear the stone.

Prevention

To avoid the appearance of defects and breaks in concrete, you should adhere to the rules contained in the concreting instructions.

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

1. Prepare the mixture correctly and follow the recipe. Excess water or cement has the most detrimental effect on the quality of concrete and leads to the appearance of defects;
2. Place the mortar in accordance with accepted standards: use vibration compaction, aeration and other standard procedures;
3. Maintain concrete after installation. The object can be covered with film, its surface can be moistened with water, formwork can be used if necessary, and expansion joints should be cut in large screeds.

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

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

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

Conclusion

Cracks lead to the fact that further processing and construction procedures lead to a worsening of the condition of the structure, only cutting reinforced concrete diamond wheels and diamond drilling holes in concrete do not destroy it. To prevent such defects from occurring, you should strictly follow the technology of concrete work, as the video in this article explains in detail.