During winter construction, the water in the newly poured concrete is easy to freeze, causing the volume to increase to 9% of the original volume, seriously damaging the internal structure of the concrete, so we are constructing Some antifreeze measures must be taken. Among the many antifreeze methods, adding concrete antifreeze to concrete is a method often used in construction.
Since the 1970s, my country's concrete antifreeze has developed rapidly, and there are many brands of antifreeze. Improper selection will have a negative impact on the quality of concrete. When choosing antifreeze, be sure to choose the appropriate type of antifreeze based on concrete with or without reinforcement. Today's antifreeze types can be roughly divided into three categories: chlorine salts, chlorine salt rust inhibitors, and chlorine-free salts:
1. Chlorine salts
Chloride salt antifreeze is mainly based on sodium chloride and calcium chloride as raw materials, together with other early-strength components, water-reducing components, and air-entraining components. Compounded additives. It has good water reduction, early strength and freezing point lowering effects, but it has a rust-promoting effect on steel bars. It will cause the volume to expand to twice its original size, causing cracks in the concrete, forming a vicious cycle, and even causing damage to concrete buildings. Therefore, chloride antifreeze is only suitable for unreinforced concrete projects.
2. Chlorine salt rust inhibitor
This type of antifreeze is mainly based on chlorine salt It is mainly composed of rust inhibitors, water-reducing components, early strength components, air-entraining components and other additives. It has the effects of water reduction, early strength, antifreeze and rust prevention, and can be widely used in reinforced concrete projects.
3. Chlorine-free salts
This type of antifreeze is based on nitrite, Nitrate, carbonate and urea are the main compound additives. It has no rusting effect on steel bars, but nitrites and nitrates can cause stress corrosion. Therefore, it cannot be used in prestressed concrete projects and reinforced concrete structures in galvanized steel or in contact with aluminum and iron. Antifreeze produced from urea is rarely used now because large amounts of it pollute the environment. Antifreeze produced by regular manufacturers is often compound antifreeze. It can fully bring together the advantages of various components, which can reduce water, strengthen, lower the freezing point, accelerate the hydration of cement under negative temperature conditions, improve early strength, and reduce the damage to concrete caused by freezing stress, so this kind of antifreeze It has good antifreeze effect and is an ideal antifreeze agent in winter concrete construction.
If you choose the correct antifreeze and use it improperly, it will also affect the quality of the concrete. Therefore, you should pay attention to the following points when using concrete antifreeze:
1. Ask the manufacturer to provide product instructions, a product identification report issued by the government designated department and the manufacturer's product certificate, in order to Prevent the purchase of substandard products.
2. Within the specified temperature, the dosage must be used according to the dosage provided by the manufacturer or the cement at the construction site must be used to determine the dosage through testing, and a dedicated person must be sent to check the dosage. Take control.
3. During construction, the adaptive temperature of the admixture must be controlled according to the lowest daily temperature, so that it is safe to use.
4. If there is precipitation when using liquid antifreeze, stir it evenly before use. If powder antifreeze becomes wet and clumps, it should be ground through a 0.63mm sieve before use.
5. Active aggregates or aggregates mixed with active silica shall not be used in concrete construction. Because antifreeze contains a lot of potassium and sodium ions, it will react with active silicon oxide during the hardening process of concrete to cause concrete expansion, leading to structural damage and reducing the usability and durability of concrete.
6. When construction requirements are met during winter construction, less water must be used and the water-cement ratio must be strictly controlled as required.
7. When the temperature is lower than -5℃, hot water can be used to mix concrete. When the water temperature is higher than 65℃, the hot water should be mixed with the aggregate first. , add cement and mix. When the temperature is low and -10℃, the aggregates can be moved to a greenhouse or heating measures can be taken.
8. The exit temperature of the concrete mixture mixed with antifreeze shall not be lower than 10°C, and the mold entry temperature shall not be lower than 5°C.
9. Concrete mixed with antifreeze must not be poured on a frozen foundation. If the foundation freezes, insulation measures should be taken.
10. Before pouring concrete, the ice, snow and dirt on the formwork and steel bars should be removed, but steam should not be used to directly melt the ice and snow to avoid freezing again.
11. When the concrete mixed with antifreeze is transported to the pouring site, it should be poured within 15 minutes, and after the pouring is completed, the exposed concrete surface should be covered with plastic film or insulation material .
12. Concrete mixed with antifreeze must not be watered and cured under negative temperature conditions. The initial maintenance temperature must not be lower than the specified temperature of the antifreeze, otherwise heat preservation measures should be taken.
13. When the difference between the surface temperature of the concrete and the ambient temperature after the formwork is removed is greater than 15°C, it should be covered and cured with insulation materials.
In short, mixing in winterIn soil construction, in addition to selecting suitable antifreeze and operating in strict accordance with product instructions and specifications during construction, we also need to make more observations and comparisons during construction. After problems arise, we need to analyze and summarize more, and combine multiple methods. Only by taking these preventive measures can we effectively prevent the concrete structure from freezing.
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