Problems encountered in concrete construction in winter and their solutions

Many problems are often encountered in concrete construction in winter. 

In the case of low temperature, the internal structure of concrete will also change, and this change leads to the later construction can not be carried out, the material can not meet the construction standards. 

Therefore, in order to ensure that the concrete can still reach the construction state after the low temperature weather, we use the early strength agent, antifreeze and other additional antifreeze to maintain the concrete, improve the strength of the concrete and reduce the freezing point of the concrete. curing concrete in various forms. 

1. The occurrence of concrete frost damage. 

There are three main cases of frost damage of concrete, one is that fresh concrete is frozen, which mainly refers to the freezing of concrete before the final frost damage. 

In this way, the measures we take are mainly to re-mash the concrete after freezing, but we must hurry before the final freezing, and strengthen the maintenance of the new concrete, so that the concrete can not be frozen, so as to ensure the performance of the concrete. 

Second, under the influence of low temperature, if the construction technology is improper and the requirements are not up to standard, the concrete will be frozen during maintenance or even in the early stage, so the physical properties of concrete will be destroyed and can not meet the design requirements. 

The third is the freezing of concrete during construction, in which case it is necessary to test the durability and endurance of concrete. 

2. The action principle of early strength agent and antifreeze during construction

In autumn and winter, the construction environment is affected by temperature, so it is necessary to use certain methods to enable the project to have liquid water continuously and not to be affected by frost damage in the process of cement hydration, so as to meet the construction requirements of the whole project. Therefore, in order to successfully complete, properly add some early strength agent, antifreeze is a more convenient, simple and effective method. 

The main results are as follows: (1) the early strength agent and antifreezing agent can reduce the freezing point in the case of negative temperature, and can ensure the liquid water content of concrete in the case of extremely low air temperature, which means that the concrete reaches the critical value of frost damage before it is about to suffer frost damage. to avoid frost damage. 

When the temperature reaches the normal temperature, the cement is oxidized rapidly to continue to work. 

(2) the ice crystal state of concrete can be changed by adding early strength agent and antifreeze. 

The structure of the ice in the solution of additives is inconsistent with that of concrete, and the defects of its own structure prevent it from causing significant damage to concrete. 

After adding antifreeze, there will be ice bodies on the surface, which is a normal phenomenon. 

After the temperature rises, the ice body on the concrete surface melts to the normal state and returns to the original strength. 

(3) the early strength agent, the antifreeze and the cement can hydrate the cement after the temperature rises, and use water molecules to fill the pores in the concrete, so that the cracks caused by the low temperature can be sewn automatically, thus the original concrete density of concrete can be restored. 

3. The method of using early strength agent and antifreeze to protect concrete. 

3.1 Application of early strength agent and antifreeze. 

In modern society, the concrete construction method of using admixtures in autumn and winter has been widely used in various projects, and the use of this method has greatly improved the engineering and social benefits. 

In the project, the function of early strength agent and antifreeze is mainly to reduce the freezing point and refine the internal crystal structure of concrete, so that concrete can fully retain cement moisture and reduce the speed of cement hydration even at low temperature. improve the structure of concrete from the microscopic aspect, so that concrete can reach a minimum critical strength, and when the temperature rises, the strength of concrete begins to gradually increase to meet the requirements of construction. 

Nowadays, antifreeze in society is mainly composed of some chloride salts, nitrites, carbonates and their own compounds, that is, some inorganic salts and his compounds. 

From the practical experience over the years, these antifreeze agents play a good role in reducing the freezing point and slowing down the damage degree of concrete. 

3.2 Classification of additional antifreeze. 

According to the different types and functions of adding in concrete in autumn and winter, the main antifreeze admixtures are antifreeze admixture, antifreeze, retarder and compound antifreeze. 

1 the main function of antifreeze is to improve the solidification time of concrete so that it can reach the critical strength in a short time, which means that the preparation for frost resistance has been made in the early stage, and the internal structure of concrete has been changed. so that the concrete has a certain frost resistance, so that frost damage can not occur in the case of negative temperature, and ensure that the concrete meets the construction requirements. 

(2) the antifreeze can reduce the freezing point, and can ensure that there is enough moisture in the concrete even in the case of negative temperature, so that the concrete structure is not affected by frost damage, so as to ensure the quality requirements of the construction project. the use of antifreeze is a relatively simple method to obtain a larger income. 

(3) the use principle of freeze retarder is roughly the same as that of other antifreeze agents. 

Some of the moisture contained in concrete is bound water, while the other part is mainly cemented water that has been absorbed by cement. The freezing point of these water is very low, and only when the temperature reaches-78 °, the condensation state may occur. Only some capillaries and free water belong to the frozen water in the composition, and the main function of the freezing retarder is to reduce the freezing point of these frozen water. 

Reduce the amount of movable water to reduce the degree of solidification of the structure. 

(4) The principle of compound antifreeze. 

Compound antifreeze is to optimize the above antifreeze according to a certain proportion, improve the antifreezing effect of antifreeze, show the comprehensive strength of antifreeze, and improve the frost resistance of concrete. this antifreeze is called compound antifreeze. 

This antifreeze strives to get a higher antifreeze effect with the least number of antifreeze raw materials, improves the effect of additional antifreeze, and plays an important role in better construction in autumn and winter. 

4. Attention problems of early strength agent and antifreeze of concrete in autumn and winter

If we want to use these admixtures, the first premise is that the raw materials must meet the requirements of seasonal construction, raw materials are the basis of construction, if the raw materials can not meet the requirements of low temperature construction, then even the use of good antifreeze will not help. 

The cement used in the construction had better use Portland cement or ordinary Portland cement. The internal structure of this kind of cement is more suitable for autumn and winter. It is forbidden to use high alumina cement and adopt suitable materials to reduce the pressure in the construction process and give full play to the maximum effect of antifreeze. 

In the mixed use of antifreeze, we should pay attention to the different structure of different antifreeze, and pay attention to the proportion and state when mixing with other antifreeze. 

Some antifreeze agents contain insoluble substances or substances with low solubility should be mixed with some powdered antifreeze. 

If some antifreeze show the state of liquid after mixing, it must be fully fused and uniform, so that the concentration of the liquid successfully stirred meets the requirements of quality standards. 

How to use the compound antifreeze, the conditions of solubility and solubility should be considered in the configuration process, and the separation principle should be adopted in the case of immiscibility, which should be added to the concrete respectively to play their respective functions. 

If you want to speed up the appearance of the antifreeze function, add the antifreeze solution with 40 °- 60 °hot water before use. 

Antifreeze in the form of powder, to ensure that the antifreeze is not exposed to moisture or loss of function after exposure, when there is a small range of moisture caking, it should be polished to meet the quality requirements of use. 

Strictly control the amount of antifreeze and use antifreeze with different properties according to different weather conditions. the content of antifreeze is different, and the function of antifreeze is also different. excessive use of preservatives will lead to excessive setting speed of concrete, causing great difficulties to construction, serious salt precipitation on the surface of the building, affecting the exterior decoration quality of the whole building. 

Too much content will reduce the strength of concrete itself, not only can not effectively prevent frost damage, but will not increase after the rise of temperature. 

However, if the content is not enough, the function of anti-freezing can not be achieved, and the concrete will still be affected under the influence of low temperature. 

In the mixing process, the mixing time should be longer than that without antifreeze, to ensure that antifreeze can exist uniformly in concrete, and the strength of each part of concrete is the same. 

The transportation time and construction time should be shortened as much as possible, in order to ensure that the early strength of concrete in the mold when the temperature can not be too low. 

When using compound antifreeze, negative temperature curing should be used instead of steam curing. 

Steam curing not only can not improve the strength, but will reduce the strength, frost resistance and durability of concrete. 

Concrete should be covered immediately after pouring, and no moisture should be added. 

During initial maintenance, the temperature must not be lower than the minimum temperature specified by antifreeze. 

When the temperature of the concrete is below the temperature specified by the antifreeze, corresponding heat preservation measures should be taken. 

In winter, the climate is relatively dry and the temperature is low, which has an important impact on the construction process. In order to ensure the smooth progress of the construction to prevent the cracking of concrete, we usually use early strength agent or antifreeze for curing. In the use of early strength agent and antifreeze, there are problems that we need to pay attention to. Early strength agent and antifreeze have their own different types and different scope of use. 

And there are some problems to pay attention to during the construction, but the purpose is to improve the strength of concrete and strengthen the frost resistance of concrete. 

Antifreeze and early strength agent in a relatively simple way, get a greater return, they are through pre-curing so that the concrete can still reach the construction standard after the temperature rise.

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