When the temperature is low, the internal structure of concrete will also change, and this change will cause later construction to be impossible and the materials to fail to meet construction standards. Therefore, in order to ensure that the concrete can still reach the construction state after low temperature weather, we use early strength agents, antifreeze and other external antifreeze agents to maintain the concrete, improve the strength of the concrete, reduce the freezing point of the concrete, and treat the concrete in various forms. of maintenance.
1. The occurrence of frost damage to concrete
There are three main situations of frost damage to concrete: one. It is fresh concrete that is frozen. This situation mainly refers to the concrete being frozen before the final frost damage. In this way, the main measures we take are to re-mash the concrete after it freezes, but it must be done before the final freezing and strengthening the maintenance work of the new concrete. The concrete cannot be allowed to be roughly frozen, so that it can Guarantee the performance of concrete. Second, under the influence of low temperatures, improper construction techniques and substandard requirements will cause the concrete to freeze during the curing period or even freeze early. In this way, the physical properties of the concrete will be destroyed and the design requirements will not be met. The third type is that the concrete is frozen during construction. In this case, the long-lasting use ability and endurance of the concrete must be tested.
2. The working principle of early strength agent and antifreeze during the construction process
In autumn and winter, The construction environment is affected by temperature. Certain methods must be used to ensure that the project can continue to have liquid water and not be affected by freezing damage during the cement hydration process to ensure that the construction requirements of the entire project are met. Therefore, in order to complete the project smoothly, it is necessary to properly Adding some early strength agents and antifreeze is a more convenient, simple and effective method.
① Early strength agent and antifreeze have the effect of lowering the freezing point under negative temperature conditions, which can ensure that the concrete in the concrete can still maintain the strength of the concrete at extremely low temperatures. The liquid water content is the critical value that concrete reaches to withstand freezing damage before it is about to suffer freezing damage and is protected from freezing damage. When the temperature reaches normal temperature, the cement oxidizes rapidly and reaches the condition to continue working. ② Adding early strength agent and antifreeze agent can change the ice crystal state of concrete itself. The ice in the additive solution has its own structure that is inconsistent with the concrete structure. The defects in its own structure prevent it from causing significant damage to the concrete. After adding antifreeze, ice will appear on the surface. This is a normal phenomenon. After the temperature rises, the ice on the surface of the concrete will melt and reach a normal state, restoring its original strength. ③ Early strength agents and antifreeze agents also enable the cement to hydrate after it is exposed to low temperatures and the temperature rises, using water molecules to fill the pores in the concrete so that cracks that appear due to exposure to low temperatures can be automatically sutured. This can restore the original concrete density of the concrete.
3. Methods of using early strength agent and antifreeze to protect concrete
3.1 Early strength Application of additives and antifreeze
In modern society, the autumn and winter concrete construction methods using admixtures have been widely used in various projects. The use of this method The project efficiency and social benefits have been greatly improved. In engineering, the main functions of early-strength agents and antifreeze agents are to lower the freezing point and refine the crystal structure inside the concrete, so that the concrete can still fully maintain cement moisture even at low temperatures, reduce the speed of cement hydration, and improve microscopic aspects. The structure of concrete enables the concrete to reach a minimum critical strength. When the temperature rises, the strength of the concrete begins to gradually increase to meet the construction requirements. Antifreeze in today’s society mainly consists of some chlorine salts, nitrites, carbonates, etc. and their own compounds, that is, some inorganic salts and other compounds. Judging from the practical experience over the years, these antifreeze agents have a good effect on lowering the freezing point and slowing down the damage of concrete.
3.2 Classification of external antifreeze
According to the type and type added to concrete in autumn and winter Depending on their functions, external antifreeze mainly includes antifreeze admixtures, antifreezes, retarders and composite antifreezes.
①The function of antifreeze is mainly to increase the setting time of concrete so that it can reach critical strength in a short time, which means that in the early stage Preparations have been made for frost resistance. The internal structure of the concrete has been changed to give the concrete a certain degree of frost resistance. This will prevent frost damage under negative temperatures and ensure that the concrete meets the construction requirements. ②Antifreeze has the effect of lowering the freezing point. It can ensure that the concrete contains enough moisture even at negative temperatures, so that the concrete structure is not affected by freezing damage, thereby ensuring the quality requirements of the construction project. The use of antifreeze is A relatively simple method was used to obtain greater profit income. ③The principle of use of retarder is roughly the same as that of other antifreezes. Part of the moisture contained in concrete is bound water, while the other part is mainly gelled water that has been absorbed by the cement. The freezing point of this water is very low, and it can only be used when the temperature reaches -78°C.Only some capillaries and free water can be frozen in the composition. The main function of the retarder is to lower the freezing point of these freezeable water, reduce the amount of movable water and reduce the degree of solidification of the structure. . ④Principle of compound antifreeze. Complying with antifreeze means optimizing the configuration of the above antifreeze in a certain proportion to improve the antifreeze effectiveness of the antifreeze, showing the comprehensive strength of the antifreeze, and improving the antifreeze ability of concrete. This kind of antifreeze is called It is a composite antifreeze agent. This kind of antifreeze strives to obtain a higher antifreeze effect with the minimum amount of antifreeze raw materials, improve the effect of external antifreeze, and plays an important role in better construction in autumn and winter.
4. Precautions for early strength concrete and antifreeze in autumn and winter
If you want The first prerequisite for using these admixtures is that the raw materials must meet the requirements of seasonal construction. Raw materials are the basis of construction. If the raw materials cannot meet the requirements of low-temperature construction, then even the best antifreeze will not help. The cement used in construction is better to use Portland cement or ordinary Portland cement. The internal structure of this cement is more suitable for autumn and winter. It is strictly forbidden to use high alumina cement. Use appropriate materials to reduce the pressure during the construction process and give full play to Greater effectiveness of antifreeze.
When mixing antifreeze, you should pay attention to the different structures of different antifreezes. When mixing with other antifreezes, you should pay attention to the proportion and status issues. Some antifreeze contains insoluble or less soluble substances and should be mixed with some powdered antifreeze. If some antifreeze appears in a liquid state after mixing, it must be fully blended and made uniform. The concentration of the liquid that is successfully mixed must meet the quality standards. How to use composite antifreeze, the solubility and solubility conditions of each other should be considered during the configuration process. If there is incompatibility in Germany, the separation principle should be adopted, and they should be added to the concrete separately to exert their respective functions. If you want to speed up the emergence of antifreeze function, you can add 40°-60° hot water to the antifreeze to prepare a solution before use. Antifreeze is available in powder form. Make sure that the antifreeze does not become damp or lose its function due to exposure to the sun. When there is a small area of moisture and agglomeration, it should be polished to ensure that it meets the quality requirements for use.
Strictly control the dosage and use antifreeze with different properties according to different weather conditions. Different dosages of antifreeze will have great internal differences. Different amounts of antifreeze will have different functions. Excessive use of anticorrosives will cause the concrete to set too fast, causing greater difficulties in construction. The surface of the building will have serious salt precipitation, which will affect the quality of the exterior decoration of the entire building. . Excessive dosage will reduce the strength of the concrete itself. Not only will it not be able to effectively prevent freezing damage, but the strength will not increase after the temperature rises. However, if the dosage is insufficient, the anti-freeze function will not be achieved, and the concrete will still be affected by low temperatures.
During the mixing process, the mixing time should be longer than the time without antifreeze to ensure that the antifreeze can exist evenly in the concrete. , the strength of each part of the concrete is consistent. The transportation time and construction time should be shortened as much as possible. In order to ensure the early strength of the concrete, the temperature when entering the mold should not be too low.
When using qualified antifreeze, negative temperature curing should be used instead of steam curing. Steam curing not only fails to improve the strength but also reduces the strength, reducing the frost resistance and durability of concrete. Exposed surfaces of concrete should be covered immediately after pouring and no moisture should be added. During the initial maintenance, the temperature must not be lower than the lower temperature specified by the antifreeze. When the temperature of the concrete is below the temperature specified by the antifreeze, corresponding insulation measures must be taken.
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