What is antifreeze concrete
The technical requirements of antifreeze concrete are: during the winter construction process, reliable technical measures should be taken to make the concrete solidify and harden as soon as possible after pouring, and in the future Frost heave damage shall not occur before reaching the critical strength due to frost.
When the temperature is between 0 and 4°C, the activity of water is low, the hydration reaction of cement is extremely slow, and the strength development of concrete cannot meet the requirements. When the temperature is below 0°C, most of the moisture inside the concrete freezes. When water freezes, it produces a volume expansion of 9%, which will cause permanent damage to the concrete structure. In addition, after water freezes, there is not enough liquid water in the concrete to participate in the hydration reaction of the cement, and the strength of the concrete increases very slowly or even stop.
Therefore, the concrete poured during winter construction should be mixed with early strength agent or antifreeze agent, and appropriate insulation or temperature increasing measures should be taken in the early stage of concrete setting and hardening. Make full use of the concrete’s own heat or external heat (such as electric heating method, greenhouse method, etc.) to ensure that the initial curing temperature after concrete pouring is: not lower than 10°C in severe cold areas; not lower than 5°C in cold areas, so that the concrete strength has normal Growth conditions to obtain critical freezing strength as quickly as possible.
Technical measures to be taken during winter construction
Winter construction is the season when concrete engineering quality accidents occur frequently. This is due to the short preparation time and complex technical requirements. It is caused by failure to keep up with a certain link or hasty construction. Therefore, careful planning and winter construction preparations should be made in advance based on local meteorological data statistics for many years to avoid engineering quality accidents. The technical measures adopted during winter construction mainly include:
①Material preheating method: that is, water, sand and stone are preheated before being used for mixing concrete;
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②Thermal storage and insulation method: that is, using insulation materials to cover the concrete after pouring, so that the concrete will not cool down or cool down slowly for a certain period of time after pouring;
③Warm shed method: That is to build an insulated and heated greenhouse at the construction site, so that after the concrete is poured, it can be cured under positive temperature environmental conditions in the greenhouse. It is best to stir and pour if conditions permit. Carry out in a greenhouse;
④Add early strength agent or antifreeze.
In addition, the amount of cement should be appropriately increased for concrete construction in winter, or early-strength cement should be used, as well as high-performance water-reducing agents or high-efficiency water-reducing agents to minimize water use. Quantity and other technical measures.
The purpose of taking the above technical measures is to control and increase the temperature of concrete coming out of the machine and the temperature after entering the mold, so as to ensure that the strength of the concrete has the conditions for normal growth after pouring. Freezing damage will not occur before the critical strength for freezing is reached.
About early strength agents and antifreeze
The causes of concrete damage in the world today in order of importance are: corrosion of steel bars, freezing damage in cold climates, and erosion Physical and chemical effects of the environment. Therefore, when concrete mixed with early-strength agent or antifreeze agent, care should be taken to limit the chloride content. Chloride salt is a very important factor in inducing corrosion of steel bars. Prestressed concrete and reinforced concrete should strictly follow the relevant standards and regulations to control the maximum content of chlorine salt in the concrete. Chloride ion content can avoid engineering quality accidents and causing huge waste. Many projects at home and abroad have paid a heavy price for this.
①Concrete early strength additives and components
Admixtures that can accelerate the early strength development of concrete are called It is an early strengthening agent. In actual use, most of them are compound early-strength agents. Inorganic salts are detrimental to the later strength of concrete; chloride early-strength agents can cause corrosion of steel bars; sulfate early-strength agents may cause volume expansion, reducing the durability of concrete; sodium salts Early strength agent will increase the alkali content in concrete and produce alkali-aggregate reaction with active silica aggregate. If the early strength agent is added excessively, although the early effect of the concrete is good, the later strength loss will be large, and the salt precipitation will be intensified, affecting the concrete finish; it will increase the conductivity of the concrete and increase the risk of shrinkage and cracking of the concrete. The main components of concrete early strength agent are: sodium chloride, calcium chloride, sodium sulfate, calcium sulfate, aluminum sulfate, potassium dichromate, triethanolamine, triisopropanolamine, methanol, ethanol, calcium formate, lithium oxalate , sodium acetate, etc.
②Concrete antifreeze and components
Can make concrete harden at negative temperatures and Admixtures that achieve expected performance under specified maintenance conditions are called antifreeze. The vast majority of antifreeze agents are composite admixtures. The amount of early strength components and inorganic salts of the antifreeze component should be controlled. Otherwise, improper use will cause the later strength shrinkage of concrete, corrosion of steel bars, and alkali-aggregate reactions.
The main components of concrete antifreeze are: antifreeze components (such as sodium nitrite, sodium chloride, methanol, urea, calcium chloride, potassium carbonate, etc.) , air-entraining components (such as rosin soap, rosin thermopolymer, sodium alkyl sulfonate, etc.), early strength components (such as sodium sulfate, calcium chloride, calcium nitrate, triethanolamine, etc.), water-reducing components (such as Naphthalene series, melamine, sulfamic acid, etc.).
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