Why concrete cracks: causes and ways to prevent cracks

Often there is a situation where the builder can not understand why the concrete cracked after pouring. This is a fairly common phenomenon, which leads to deterioration of the performance characteristics of the material and its gradual destruction. We want to talk about the causes of cracks and how to prevent this phenomenon.

The appearance of cracks is a frequent occurrence when working with concrete.

Cracks in concrete

Varieties

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

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

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

  1. Structural crackss. They represent a threat to the integrity of the structure and its carrying capacity, appear, as a rule, due to external causes and errors of the designers;
  2. Structural or non-structural cracks. They represent a potential danger, in the case of insufficient remedial measures, lead to more serious damage and loss of quality, bearing capacity and integrity of the structure. Arise due to internal processes during the hydration reaction and the concrete gaining strength;
  3. Cracks caused by fire. Include both structural and structural damage. A distinctive feature - the separation of the top layer of concrete.
The photo is a typical example of a structural crack.

Damage to the first group includes integrity violations caused by increased loads on parts, material mismatch with actual loads, architect's errors in design, errors in designing the composition of the mixture, ground movements, natural disasters, strikes, explosions, etc.

Note! Often there is cracking due to errors in the preparation of concrete with their own hands.

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

Конструкционные дефекты отличаются высокой шириной раскрытия, большой глубиной, сквозным характером, большой протяженностью и особой локализацией. Prevention таких повреждений связано с грамотным проектированием и расчетом нагрузок, применением качественных материалов, учетом особенностей геологии и касается, в основном, технической и проектной подготовки строительства.

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

After fires, cracking of concrete is almost always observed.

The second group of defects relates 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.

Here there is a whole range of phenomena leading to the appearance of such defects:

  • Plastic shrinkage cracks. Arise due to the intense evaporation of moisture from the surface and as a result of uneven shrinkage and compaction of the mass;
  • Температурно-усадочные разрушения. They appear due to the effect of thermal expansion-compression of materials caused by heating and uneven cooling of the mixture;
  • Shrinkage defects when drying the solution. Arise due to an uneven decrease in the volume of concrete during drying;
  • Cracks due to reinforcement corrosion. With active rusting, steel increases in volume and can break concrete.
An example of shrinkage damage.

Note! Preventing the appearance of cracks is a much more efficient and rational way than their removal and repair. For successful prevention, you should know the causes of defects.

Causes

Most damage occurs due to natural causes.

If the reasons for the appearance of structural defects are clear, 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 intensive evaporation of moisture from the open surface of the laid concrete. As a result, the mass of the solution is actively reduced in volume, while the lower layers remain the same, and the upper layer is covered with a network of thin hairline cracks.

Plastic shrinkage and evaporation of moisture lead to hairline cracks.

Also in the first period of the life of the solution during installation, the process of shrinkage and compaction of the concrete mix under the action of gravity begins. With insufficient compaction with the vibrotool, a moment arises when the concrete is already set and its compaction continues. This leads to faults.

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

Heat 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 they are observed in unreinforced structures and products of flat, extended or non-standard forms, such as a large-sized concrete screed, plaster and similar structures crack.

Note! Shrinkage during drying often leads to aggravation of other types of cracks and an increase in the degree of their opening.

Corrosion gap

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

Prevention

Proper care prevents damage.

To avoid the appearance of defects and faults in concrete, you should follow the rules that contain instructions for concreting.

For brevity, we present three main points:

  1. Properly prepare the mixture and maintain the recipe. Excess water or cement most adversely affects the quality of concrete and leads to the appearance of defects;
  2. Lay the solution in accordance with accepted standards: use a vibration seal, aeration and other standard procedures;
  3. Take care of the concrete after laying. The object can be covered with a film, its surface can be wetted with water, if necessary, it is possible to heat the concrete, insulate the formwork, and in large screeds should be cut deformation seams.
Moisturizing the surface prevents it from cracking.

Note! Observe the concreting conditions, namely: work in the correct temperature conditions, control the humidity, watch for changes in weather conditions, do not violate the framework under which you can work, do not neglect the technology of hardening concrete and use quality materials.

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

Protect material from sudden changes in temperature.

Note! Do not dilute the 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.

Conclusion

Cracks lead to the fact that further processing and construction procedures lead to a worsening of the state of the structure, only cutting reinforced concrete with diamond circles and diamond drilling of holes in concrete does not destroy it. In order to avoid such defects, one should strictly observe the technology of concrete work, which is described in detail in the video in this article.

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