What is the concept of a crack? What are the causes of normal and abnormal cracks in concrete?

There are various reasons why cracks occur in concrete, but the root cause is that the tensile stress in the concrete exceeds the tensile strength of the concrete. Specifically, it can be attributed to three reasons: temperature and humidity changes, excessive deformation due to external loads, and improper construction methods. The specific types are:

1.Cracks caused by cement shrinkage. This crack appears on the surface of the concrete and is relatively small. Cement is a hydraulic material with dry shrinkage, and cracks may occur if there is not enough water due to improper maintenance in the early stage of hardening.

2.Temperature differences, cracks caused by thermal expansion and contraction effects. This kind of crack generally appears in the environment with large temperature difference and on the component or structure with a large area or length, and there is no expansion joint in the appropriate part.

3.Cracks caused by stress concentrations. This kind of crack generally appears at the yin and yang corners of the concrete slab or at the support. It is caused by insufficient reinforcement of negative moment reinforcement on the plate surface or excessive spacing of thick reinforcement.

4.Cracks caused by overload and excessive deformation caused by improper use. This type of crack usually occurs in the tension zone of the concrete flexural member.

5.Cracks caused by tensile force. In the tensioning process of prestressed reinforced concrete components after tensioning, cracks may be caused if they are not well controlled. This type of crack usually occurs at the end of the prestressed member or at the corner of the upper surface of the slab.

6.Cracks caused by uneven settlement. Due to the uneven settlement of the foundation, the foundation or ring beam, girder and other components are too tensile and cracks appear.

7.During construction, cracks will occur in the structure due to the vibration, deformation or displacement of the formwork in the initial setting stage of concrete.

8.Cracks created prematurely by loading. During construction, due to the early removal of the formwork, the concrete strength did not meet the design requirements and the load was added in advance, which caused the components to be overloaded and cracks appeared.

9.If the construction joint is not treated well, cracks may appear in the construction joint.

10.In the process of demoulding, transportation, stacking and lifting, the compression area of the component is in a tensile state due to various reasons, which may cause cracks in the component.

The products of cracking in concrete for various reasons are cracks. Normal and abnormal cracks are relative, and we cannot eliminate them but can control them. The cracks of the concrete itself are considered normal cracks, and the cracks of external factors can be classified as abnormal....

Summary. The definition of concrete crack refers to the phenomenon that cracks appear after solidification of concrete structure due to internal and external factors (proportion, weather, etc.) during the concrete pouring process.

Cracks are the main reason for the reduction of bearing capacity, durability and waterproofness of concrete structures.

What is the definition of a crack in concrete.

The definition of concrete crack refers to the phenomenon that cracks appear after solidification of concrete concrete structure due to internal and external factors (ratio, weather, etc.) during the concrete pouring process. Cracks are the main reasons for the loss of bearing capacity, durability and waterproofness of concrete structures.

Cracks in concrete structures are divided into two categories: macroscopic cracks and microscopic cracks, and the microscopic cracks of concrete are inherent in concrete. The reasons for the cracks caused by the nature of the concrete itself are: 1. Shrinkage cracks; 2. Temperature cracks; 3. The cracks caused by the first sound of the creep are discussed.

What is it called if it does not affect the quality.

Wait a minute. Concrete cracks are divided into microscopic cracks and macroscopic cracks. The micro-cracks are irregular, non-penetrating along the cross-section, and the concrete components with ruined micro-cracks are rotten because the fiber potatoes can withstand the tensile force.

What are the main causes of concrete cracks: the main causes of concrete cracks are the most complete cracks caused by loads! The causes and countermeasures of concrete cracking are all clearly explained2019-11-30 04:

21. Mingyuan Real Estate Research Institute 1, cracks caused by load concrete under conventional static, dynamic load and secondary stress cracks are called load cracks, which are mainly summarized into two types: direct stress cracks and secondary stress cracks. Direct stress cracks refer to cracks caused by direct stress caused by external loads, and secondary stress cracks refer to cracks caused by secondary stress caused by external loads. The characteristics of load cracks vary according to different loads, and present different characteristics.

This type of crack mostly appears in the tension zone, shear zone or severe vibration area. However, it must be pointed out that if there is peeling or short cracks along the compression direction in the compression zone, it is often a sign that the structure has reached the limit of bearing capacity and is a precursor to structural failure, and the reason is often that the cross-sectional size is too small. 2. Cracks caused by temperature changes Concrete has the properties of thermal expansion and contraction, when the external environment or the internal temperature of the structure changes, the concrete will be deformed, if the deformation is constrained, the stress will be generated in the structure, and when the stress exceeds the tensile strength of the concrete, the temperature crack will be generated.

In some long-span bridges, temperature stresses can reach or even exceed live-load stresses. The main characteristic of temperature cracks that distinguish other cracks is that they will expand or close with temperature changes. 3. Cracks caused by shrinkage In practical engineering, cracks caused by shrinkage of concrete are the most common.

Among the types of concrete shrinkage, plastic shrinkage and shrinkage shrinkage (dry shrinkage) are the main causes of concrete volume deformation, as well as autogeneous shrinkage and carbonization shrinkage. Plastic shrinkage, occurs in the construction process, about 4 5 hours after the concrete is poured, at this time the cement hydration reaction is intense, the molecular chain is gradually formed, there is a sharp evaporation of water and water, the concrete loses water and shrinks, and the aggregate sinks due to its own weight, so the concrete has not yet hardened, which is called plastic shrinkage. The magnitude of plastic shrinkage is very large, up to about 1%.

In the process of aggregate sinking, if it is blocked by the reinforcement, cracks along the direction of the reinforcement will be formed. At the vertical variable cross-section of the component, such as the junction of the T-beam, the box girder web and the top and bottom plate, cracks will occur on the surface along the web direction due to uneven solidification before hardening. In order to reduce the plastic shrinkage of concrete, the water-cement ratio should be controlled during construction, and the mixing should be avoided for too long time.

In our daily life, we see a lot of concrete cracks, so what are the causes of concrete cracks? Today, I will satisfy everyone's curiosity and talk about the causes of concrete cracks, I hope it can help you, and interested friends can follow along to find out.

1. Concrete is a material with very low tensile strength, to be precise, concrete is still relatively brittle in nature, so we must pay attention to the changes in temperature and humidity during construction, and the concrete construction environment is very important.

2. In addition to the impact of the environment, if the construction workers are uneven during the foundation construction, then the concrete will settle, and it is very easy to produce cracks in the later stage.

3. If the content of concrete is too large during construction, resulting in the shrinkage of concrete, the material proportioned to concrete will shrink poorly, and cracks will occur in the later stage of concrete. If you choose a cement with no guaranteed quality, the quality of the concrete must be problematic, and there will definitely be cracks in the later stage, so we are better to be careful in choosing materials.

4. In addition to the problem of materials, there may be construction technical problems of construction workers, in the construction process, the need for proportioning, mixing, transportation, watering, any defects or omissions in these processes will lead to cracks in the later stage of the concrete ground.

The above is the content and information summarized by the children about the causes of concrete cracks, I hope it can help you. If you have other questions, you can leave a message at the bottom of the platform, and we will solve the problem in time, and finally if you have any questions about home or home decoration, you can pay more attention to Qeeka Home.

Concrete is used for some large buildings of construction soil, the common use of this soil is some high-rise buildings and bridge buildings, can be said to be the soil often used in modern buildings. With the rapid development of modern economy, various cities are building high-rise buildings or building bridges, so the use of this kind of concrete has become more places, sometimes in the process of use of our buildings will appear some cracks, so what is the reason for the emergence of concrete cracks? What is the solution?

1. Causes of cracks in concrete.

1. There is a contraction and change of letter.

Generally, when the concrete is poured, the general temperature is relatively low, at this time in the process of drying, the temperature will rise, in this case, there will be a certain thermal expansion and contraction, if the cement is asymmetrical, there will be a shrinkage reaction, so that cracks appear.

2. There is a temperature difference between inside and outside.

After pouring concrete, sometimes the cement will be hydrated, and heat will be generated inside, which is difficult to dissipate, and such a temperature difference will make the concrete burst, and in this extremely unstable situation, the slippery sample is easy to crack.

Second, the solution to cracks in concrete.

1. Add expanded cement.

When we pour concrete, we can appropriately add some expanded cement or some expansion agent to the concrete, so that if the cement shrinks in the later stage, the reaction will be reduced.

2. Appropriate proportion.

In this case, we can mix concrete and cement in the right ratio to reduce the amount of water and cement and achieve a lower temperature, which can prevent cracks in the later stage and can also be repaired according to the proportion.

Classification of concrete cracks: static cracks, active cracks, developing cracks.

Cracks inevitably exist in concrete structures due to internal and external factors, and cracks are the main reason for the reduction of bearing capacity, durability and waterproofness of concrete structures.

Control: Preferential selection of slag cement with low heat of hydration to mix concrete, and appropriate use of retarding superplasticizer;

On the premise of ensuring the design strength grade of concrete, the water-cement ratio should be appropriately reduced and the amount of cement should be reduced;

Reduce the mold temperature of concrete, control the temperature difference between inside and outside of concrete (when there is no design requirement, control within 25);

timely insulation and moisturizing of concrete covering;

When mixing concrete, an appropriate amount of micro-expansion agent or expanded cement can be mixed to compensate for the shrinkage of concrete and reduce the temperature stress of concrete;

When the plane size of large-volume concrete is too large, the post-pouring joint can be appropriately arranged to reduce the external stress and temperature stress;

Large-volume concrete can be used for secondary plastering to reduce surface shrinkage cracks.

Treatment method: 1. Surface treatment closure method.

The scope of application of surface coating and surface patching envy matching method is fine and shallow cracks that are difficult to penetrate the slurry, hairline cracks whose depth does not reach the surface of the steel bar, non-leaking cracks, non-retractable cracks and inactive cracks. The surface patching (geomembrane or other waterproof brother finger piece) method is suitable for anti-seepage plugging of large-area water leakage (honeycomb surface, etc., or it is not easy to determine the specific leakage location and deformation joint).

2. Filling method.

Fill the cracks directly with repair materials, which is generally used to repair wider cracks, which is simple to operate and low in cost. Cracks with a width less than and shallow depth, or cracks with filling, cracks that are difficult to achieve by grouting method, and small-scale cracks can be treated with a V-shaped groove and then filled.

3. Grouting method.

This method has a wide range of applications, from fine cracks to large cracks, and the treatment effect is good. The use of pressure feeding equipment (pressure to fill the joint slurry into the concrete cracks, to achieve the purpose of occlusion, this method is a traditional method, the effect is very good. It is also possible to use an elastic joint repairer to inject joint injection glue into the crack, which is very convenient and the effect is ideal without electricity.

4. Structural reinforcement method.

Cracks caused by overloading, cracks that are not treated for a long time and cause concrete durability reduction, cracks caused by fire, etc., affect the structural strength can take the structural reinforcement method.

1.Shrinkage cracks and prevention of shrinkage cracks mostly appear in a period of time after the end of concrete curing or about a week after the concrete is poured. The evaporation of water in cement mortar produces dry shrinkage, and this shrinkage is irreversible.

2.Plastic shrinkage cracks and prevention of plastic shrinkage refer to the shrinkage of the surface of concrete due to rapid water loss before setting. 3.

Temperature cracks and prevention of temperature cracks mostly occur in concrete structures with large volume concrete surfaces or areas with large temperature differences. 4.Cracks caused by chemical reaction and prevention of concrete mixing will produce some alkaline ions, which will have a chemical reaction with some active aggregates and absorb water in the surrounding environment and increase in volume, resulting in loose concrete, expansion and cracking.

5.Subsidence cracks and prevention of subsidence cracks are caused by uneven and soft soil quality of structural foundation, or uneven settlement caused by unsolid backfill or water immersion; Or because the stiffness of the formwork is insufficient, the spacing of the formwork support is too large or the bottom of the support is loose, etc., especially in winter, the formwork is supported on the frozen soil, and the uneven settlement occurs after the frozen soil is thawed, resulting in cracks in the concrete structure.