Classification of cracks in concrete
Causes
What and how to close
How to fix oneself
In concrete, cracks appear almost always, even in new structures, because the filling technology is not always observed, or an unconsolidated mixture is used. They also happen from the 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 - the result of deformation from external loads or from the occurrence of internal stresses.
Classification of cracks in concrete
On the bend: perpendicular to the axis of the reinforcement, loaded by bending stretching. They start from the edge and end at the zero line.Cracks in the shear appear in the region of the transverse force and result from stresses on the bend. They, as a rule, pass diagonally to the reinforcement axis.
Through-faults appear at the central extension and go through the cross section.
Violations in joints often occur in the area of anchoring the rods and run parallel to the armature. Occur in the corners of the tape-type foundation with incorrect anchoring or when poor-quality concrete is used, they lead to the layering of the protective layer of pouring. Typical causes of deformation of the support: punching, subsidence of soil, rise at saturation with water, etc.
Deformation from internal stress
This stress occurs when there is a temperature difference between the surface and inside the concrete mass. The reason is the rapid cooling of the surface from cold air, water, or by radiating a large amount of heat during the hydration of the cement. If the stresses exceed the strength of the material - surface cracks appear in the concrete. They go to the depth of a few cm. Among the causes of the appearance of cracks are the stresses from the sharp drying out of the outer layer from exposure to air temperature or sunlight with high air temperature.The norms for variable freezing-thawing allow the presence of shrinkage, surface technological cracks on the surface, however, their width should not exceed 0.1 mm (GOST 13015-2003). It is believed that surface cracks after casting in concrete are perpendicular to the axes of the reinforcement up to 0.4 mm, or up to 0.3 mm. But going along the reinforcement, do not lead to a critical decrease in longevity. It is necessary only to control the size of their disclosure, it is believed that these are cracks permissible in concrete, only it is necessary to repair them in time.
Causes
Since in concrete structures the tensile strength is small, then after drying, they shrink and give shrinkage cracks in the concrete. The reasons for their education are divided into three categories:1. Cracks affecting the strength of the structure ("Constructive"). They do not lead to an emergency condition of the structure. Constructive cracks are often caused by:
a) Design errors;
b) errors in the construction;
c) changes in conditions of maintenance with overloads of the structure in excess of design loads;
d) emergency situations, such as an explosion, an earthquake, etc.;
2. Cracks from fires. Can be constructive or non-constructive (structural). Stratification of the upper 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 of concrete in the initial stage;
c) shrinkage during drying;
d) cracks due to corrosion of the reinforcement.
What and how to close
When repair work is usually used wet cement "dough", a binder solution, a mixture with a polyester or epoxy resin, as well as purchased repair mixes.Repair of cracks (up to 3 mm.) Is carried out by cement "test" or special mixture. Mixing proportions: 1 part Portland cement to 3 parts water and sand + PVA glue. Large caverns, and places with exfoliated concrete are closed using a sealant for cracks.
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. Particularly applicable method for large volumes of work.
To repair vertical surfaces they are covered with a mixture consisting of a concrete solution with a polymer additive. For the addition, furyl alcohol (0.35% of the total mass) and 0.02% of sulfanol are suitable. On drying, the frozen mixture is additionally covered with a polyurethane sealant.
Repair can also be done by creating a layer of the same material on the surface. However, the application of this method is not always rational, because it is laborious and leads to an increase in the construction mass, increasing the load on the foundation.
How to fix oneself
In themselves, cracks in the foundation of concrete are the source for the subsequent destruction of the structure. To restore the monolith itself, you must first inspect the damage and determine the repair method.The seal should be started by brushing with detergent and water. Surplus water remove. Remove all the fragments with a metal brush. The surfaces to be repaired should be degreased (with acid-containing preparation). Minor cracks are cut with a spatula and are buried up to 5 mm: so the solution fills the space more easily. We strengthen the deep ones: we cut the transverse grooves with the "Bulgarian".
If the reinforcement is seen in the depths, it must be cleaned and treated with an anticorrosive agent. In the cleared furrows lay pieces of wire with a diameter of 4 mm.
On the whole surface to be repaired with a brush, apply a primer, its thickness is 3 mm. After that, without waiting for the final drying, we apply a repair mixture.
Often there is a situation when the builder can not understand why the concrete cracked after pouring. This is a fairly common phenomenon, which leads to a deterioration in the performance characteristics of the material and its gradual destruction. We want to talk about the reasons for the occurrence of cracks and ways to prevent this phenomenon.
The appearance of cracks - a frequent phenomenon when working with concrete.
Cracks in concrete
Cracking of concrete structures leads to a decrease in their quality.
Concrete cracking is a widespread phenomenon that occurs for a variety of reasons, and for the convenience of considering this topic, it is necessary to classify individual cases of manifestation of this phenomenon.
So, all the cracks can be divided into three large groups:
In the photo - a typical example of a structural crack.
The damage to the first group includes integrity violations caused by increased loads on the parts, inconsistency of the strength of the material with real loads, architect's mistakes in the design, mistakes in the design of the mixture, soil movements, natural disasters, blows, explosions, etc.
Important!
Often there is a cracking due to errors in the preparation of concrete with their own hands.
The price of ready-mixed concrete hits the budget, but the repair of a poor-quality foundation is much more expensive.
Structural defects are characterized by a high opening width, great depth, through nature, 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 features of geology and concerns, mainly, technical and design training for construction.
To take into account the impact of natural disasters and accidents, technogenic catastrophes and wars is almost impossible, the same applies to violations due to fires.
After fires, cracking of concrete is almost always observed.
The second group of defects refers to the structure and integrity of the material as a result of the natural physical and chemical processes taking place in the concrete at all stages of its maturation, especially at the initial stages.
Here there is a whole spectrum of phenomena leading to the appearance of such defects:
- Cracks from plastic shrinkage. Occur due to intensive evaporation of moisture from the surface and as a result of uneven shrinkage and compaction of the mass;
- Thermal shrinkage failure. Appear because of the effect of temperature expansion-compression of materials caused by heating and uneven cooling of the mixture;
- Shrinkage defects when the solution dries out. Occur due to uneven reduction in the volume of concrete during drying;
- Cracks due to corrosion of reinforcement. With active rusting, steel increases in volume and can break concrete.
Example of shrinkage damage.
Important!
Preventing the appearance of cracks is a much more efficient and rational way than eliminating and repairing them.
For successful prevention, you should know the causes of the defects.
Causes
Most damage occurs due to natural causes.
If everything is clear with the causes of 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 takes place at the very beginning of a solution's life. There is an effect such as intensive evaporation of moisture from the exposed 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 by a network of thin hair cracks.
Plastic shrinkage and evaporation of moisture lead to hairy fissures.
Also during the first period of life of the mortar during laying, the process of shrinkage and compacting of the concrete mixture under the action of gravity begins. If there is insufficient compaction with the vibration tool, a moment arises when the concrete has already seized, and its compaction continues. This leads to faults.
Temperature-shrinkage deformations appear due to the hydration reaction of cement, flowing with the release of heat. The solution heats up, increasing in volume, while the hardening areas crack. Also, the reverse process is affected - the top layer cools and decreases, while the lower one remains in the same size or increases, the result is the discontinuities of the material.
Temperature-shrinkage damage.
Shrinkage cracks during drying are caused by the fact that the grasped material decreases in volume. This is typical for any type of concrete, glue and other hardening and drying substances. Usually observed in non-reinforced structures and products of a flat, extended or non-standard shape, so the concrete screed of a large area, plaster and similar structures crack.
Important!
Shrinkage upon drying often leads to aggravation of other types of cracks and an increase in the degree of their opening.
Corrosive rupture of reinforced concrete.
Penetration of moisture inside the concrete structure leads to corrosion of the metal inside it. As a result, reinforcing bars increase in volume and tear the stone.
Prevention
Proper care helps prevent damage.
To avoid the appearance of defects and faults in concrete, it is necessary to adhere to the rules that contain the instruction for concreting.
For brevity, we give three main points:
Humidification of the surface prevents it from cracking.
Important! Observe the conditions of concreting, namely: work in the correct temperature regime, monitor the humidity, watch for changes in weather conditions, do not break the framework at which you can do the work, do not neglect the technology of care for hardening concrete and use high-quality materials.
For concreting responsible units and structures it is better to use high-quality commercial concrete, as a homemade product most often demonstrates the listed phenomena, and different at the same time.
Protect the material from sudden changes in temperature.
Important! Do not dilute concrete with water and do not add cement to it, this is a gross violation of the 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 construction, only cutting the reinforced concrete with diamond circles and diamond drilling holes in the concrete does not destroy it. To avoid such defects, it is necessary to strictly follow the technology of concrete work, as detailed in the video in this article.
The foundation of any structure is the main component of the future building. It depends on the type and quality of the house. This is the base that performs the carrier function, and provides stability and durability.
Depending on the use of different materials, the characteristics of the erected structure, its number of storeys, a foundation is made, ready to provide the structure with the required load-bearing capacity.
The main task of the base is to evenly distribute loads to the entire surface of the foundation, including the total weight of the structure. On how effectively it will perform its basic function, the durability and good indicators of the operational capability of the structure will depend.
Cracks as a result of errors in calculations
When choosing the type of foundation with the necessary indicators of bearing capacity, two basic groups of factors emerge: natural and anthropological.
The first group includes the features of the construction site: the maximum depth of freezing, the presence of water and their level in the soil, the nature of these soils.
The second group is the factors conditioned by human activity. They include all the facilities that are near the construction site and limit the design possibilities of the future building. In this case, it is possible to limit the height and number of storeys of the erected building.
Correctly calculated load-bearing capacity of the base will avoid partial deformation of the foundation, a violation of its integrity or even complete destruction.
This mainly happens when trying to save on the device a base with a calculated load. If, on the other hand, a larger load-bearing capacity is laid, additional unnecessary expenses will be required.
Errors in the process of priming
Sometimes the appearance of cracks in the foundation is a direct consequence of violations during the construction of the foundation. And, despite the fact that the majority of builders do not consider a number of emerging chipping and cracking very serious, their appearance is by no means the norm to be followed.
Indeed, most cracks are eliminated after repairing the substrate. But, in order that they do not appear again, it is necessary to identify the root cause of their occurrence. Having understood the reason, it is possible to choose the best way to solve this unpleasant problem.
The most probable reasons for this destruction of the integrity of the surface experts call not only the wrong calculations, but also the attempt of the owners of houses to arrange the erection of the ground with their own hands.
Among the miscalculations, the following errors are possible:
- incorrectly installed formwork, which does not allow you to get the necessary monolithic structure after the end;
- poorly reinforced interior of the basement;
- insufficient depth of the base for seasonal freezing of soil in the given building site;
- choice of inappropriate quality of concrete for pouring, which does not guarantee resistance to the impacts of soils and loads;
- inconsistency of the laid down characteristics of the base and a change in the structure during the erection and after, for example, an additional superstructure of the floor;
- the water penetrates into the concrete base due to un-made or improperly executed drainage.
Harmful influence of external factors
Groundwater forces (1); punching of freezing soil (2); force of impact on the lateral parts (3,4) affecting the foundation
In addition to structural violations and non-compliance with all mandatory steps, it is possible to damage the foundation slab after exposure to some natural factors.
Cracks on the foundation after pouring concrete
A frequent phenomenon in the construction of their own hands or the forces of unskilled workers are cracks in the foundation after pouring. The reasons for their formation are numerous and it is quite difficult to independently establish a specific one of them. Below we will consider what causes the appearance of cracks in the concrete structure and how to deal with them.
In itself, the appearance of cracks in the ribbon foundation is not something catastrophic. Sometimes they appear as a result of natural shrinkage of soil under a monolithic construction. If the preliminary study of soils was carried out correctly and its results were taken into account in the design of the foundation, the net of shallow depressions will not lead to critical consequences.
On the contrary, if cracks on the foundation after pouring have uneven "torn" edges and the depth of the depressions exceeds 10 cm, in this case, urgent measures must be taken to save the situation. It is possible that it will be necessary to completely dismantle the concrete base and replace it with a new one, built in accordance with the building rules. Depending on the location and direction of the crack after the foundation is poured, it can be divided into the following types:
Variety of foundation cracks
- Horizontal - are directed parallel to the main working reinforcement in the foundation. Most often, they are the least problematic and repairable. The main reasons for their formation are shrinkage phenomena in the underlying soils or in the concrete itself.
- Vertical - perpendicular to the main reinforcing rods of the concrete structure. Dangerous enough if the size increases. Even without finding them, the owners of the house can face unpleasant changes in the linearity of the house's base in the form of jamming doors or windows in the apertures.
- The inclined cracks are located at some angle to the horizon line. They are the most dangerous in terms 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.
The causes of cracks in the foundation
The appearance of cracks in the foundation of the house can occur for several different reasons, most often associated with a violation of the technology of manufacturing the base of the house or poorly conducted studies of the condition and type of soil in the place of construction. Below, we consider the main factors affecting the cracking of concrete.
- Incorrect calculation of the load-carrying capacity of the foundation or its excess due to the use of certain construction materials that are not taken into account can lead to the appearance of cracks, which it will be practically impossible to cope with. This happens for several reasons - the production of a basement foundation with reduced linear dimensions in order to save concrete, the use of plastic instead of steel reinforcement, having a low degree of longitudinal stretching, and also when using concrete of an inappropriate grade. An important role in the construction of the foundation is played by the quality of the main binder, cement. Exceeding the time of its storage, wetting and clumping directly in bags during long storage - all this can cause a decrease in the quality of concrete and, as a consequence, a decrease in its strength characteristics.
- The behavior of the soil on the site of installation of the house is also a frequent reason for the appearance of shrinkage cracks in the foundation. The rise in the groundwater level as a result of the excessive amount of precipitation that fell during the spring-autumn period may negatively affect the modes of soil swelling. Excess of calculated vibrations of the base also leads to the formation of cracks, which often self-destruct when the soil conditions return to normal. A similar effect can also have unstable temperature conditions in the winter. Frequent thaws, alternating with severe frosts - on the best conditions for the stability of the concrete foundation.
- Violation of the technology of foundation works can be expressed in the whole complex of various errors allowed by private developers or teams of unskilled workers. Among the most common are the following:
Causes of cracks in the foundation
- Use of steel reinforcement with multiple traces of corrosion, which can adversely affect the internal state of the concrete;
- Incorrect conjugation of the reinforcing belt at the corners of the foundation and at the junction with the partitions. It is not recommended to perform connection of reinforcement in these places by the end method. It is better to install cores and joints, pre-bent at an angle of 90 °.
- When pouring concrete from a mixer and the absence of a wooden or metal tray, often the mixture pours out in one corner of the ribbon foundation and is carried on stretchers or distributed by shovels. In this case, the consistency of the concrete and the ratio of the liquid and solid fractions are disturbed. Just as long interruptions are more critical when pouring the base of the house, for example, if there is insufficient amount of concrete. In the event of unforeseen interference in the operation, the gravel-sand-cement mixture may thicken. For economy, it is re-diluted with water, not respecting the required proportion, which leads to a significant decrease in the quality of concrete.
- The large 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 adversely affects the solidification of the mixture. It is for this purpose that the surface of the concrete pouring is necessary in the first few days to be covered with a wet sack or roofing material to adjust the drying speed.
Investigation and measurement of cracks
In the event that a few months or years after the foundation slab has been poured, cracks appear, do not panic. A thorough investigation of the problem should be conducted. First, determine the direction of the depressions, their length and depth. According to modern building codes, the allowed cracks in the foundation after pouring can have a width not exceeding 0.4 mm.
Even in case of detection of a grid of small depressions in the base of the house, it is not recommended to start repairing them instantly. Builders are advised to monitor the dynamics of the behavior of cracks. For this, a simple method is used. It consists in installing a beacon on the crack, which is a strip of thin paper or a small plaster small cake.
Investigation of foundation cracks
Before installing the lighthouse, the surface of the foundation around the crack should be carefully dust-free and cleaned of lagging concrete particles. For this, it is convenient to use a metal brush, a soft nylon fleece brush and a vacuum cleaner. After that, a strip of paper is smeared around the edges with a quality universal glue and is glued to the foundation along the edges of the groove. Do it better in the widest part of the cracks.
Observation of the state of the lighthouse should be carried out with a periodicity of 3-5 days. In case of expansion of a crack, the tape pasted into the tightness will be peeled off from one side or ruptured. This indicates the expansion of the deepening in the foundation and the need for immediate action. The gypsum beacon splits with crack growth, which is also a signal for immediate action.
Methods for eliminating foundation cracks
If cracks appeared on the surface after foundation pouring, 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 depressions. This must be done because of the negative impact on moisture of concrete in all its forms - dew and fog, rain, snow and ice.
Especially the harmful effect on the base of the house is provided by ice. From the school course of physics everyone is aware of a significant expansion of water during freezing. The moisture trapped in the crack will act on its walls, which will certainly lead to an expansion of the depression and the destruction of concrete up to critical scales.
Currently, there are several common and available ways to remove the allowable cracks in the foundation. The first of these refers to small depressions that appear an hour and a half after the mixture is poured. This, as a rule, is due to insufficient compaction of concrete. In the woes of the builders, the problem most often sounds like "flooded the foundation - cracks appeared".
If cracking of fresh concrete is observed, it must be repeatedly carefully compacted with a construction vibrator. The same procedure to avoid the occurrence of cracks is recommended to perform directly when pouring a tape or slab concrete base of the house.
If cracks are detected after pouring and hardening of the concrete mixture on the surface of the foundation, they can be controlled with a sand-cement mortar of finely dispersed composition. It is prepared before the beginning of work, put on the surface of the cracked base of the house and rubbed with a trowel or grater. A more reliable option is special repair compounds for foundations, realized as ready dry mixtures of complex composition.
More complicated and expensive methods that allow not only to get rid of cracks in the foundation, but also significantly increase its load-bearing capacity. We are talking about the so-called injection method and the manufacture of an additional concrete foundation under the existing one. The first option involves drilling sloping holes in the base and walls of the house and pumping in them special fastening solutions. At the second, typical for incorrectly calculated tape foundations, below it an additional base with a large depth and support area is mounted.