Concrete additives at sub-zero temperatures - principle of

According to building codes, the concept of winter conditions is somewhat different from the generally accepted calendar ones. In particular, it is considered to be cold time to consider conditions with an average daily temperature of about +5? С and the possibility of a nightly decrease to 0? С. As is known, at low temperatures, water crystallizes and the processes of hydration in cement-containing compounds slow down or stop altogether.

But in most of our country, this time is quite long. To stop work and wait when it becomes warmer unprofitable. Therefore, since the appearance of concrete, experts are looking for a solution to this problem.

Common types of concrete pouring in the cold

Until recently, the method of pre-heating the components of a solution to a certain temperature was considered the most common and effective, after which a warm solution was prepared and poured.

The temperature of the monolith was maintained artificially until curing of at least 50%.

• But every year the price of energy increases, and such technologies greatly increase the cost of construction. Here it is not so important than to heat the concrete - by electricity, steam or other energy-intensive methods.
• In the middle of the last century, our scientist I.A. Kiriyenko was offered another effective way to heat the monolith. Conventionally, it was called the method of "Thermos". The general instruction is quite simple, a heat insulating cover is created around the reinforced concrete. Depending on the ambient temperature, the concrete could be heated by internal processes or energy from the outside.
• Recently, science has made a qualitative breakthrough in the creation of chemically active additives that allow you to work at around the clock minus temperature. Of course, it is very convenient, there are several additives and we will talk about the most common ones.

The principle of operation and types of cold-resistant compositions

What to add to concrete at sub-zero temperatures is not an idle question. Fully, 100% universal composition does not exist.

The choice depends on many factors, primarily on the temperature itself.

• Also greatly influenced by the size of the monolith. Plus, you should consider the purpose of the product, the fact that different additives can change some of the physical qualities of concrete and that is suitable for strip foundation in a private house, may not be suitable for the construction of a bridge or a large bulk plinth.

How it works

As it is known, the main task of water in a solution is to create conditions for the crystallization of the constituents of the solution, silicates, aluminates, and so on. In the language of professionals, this is called cement hydration.

The most comfortable, without additives, the solution solidifies at a temperature of 15 - 20? С, all that is higher and especially lower, needs to create special conditions.

• The main task of this kind of additives is to reduce the setting time of the solution and reduce the time of maturation of concrete at low temperatures. That is, to reduce the level of freezing of water and at the same time do not harm the rest of the processes occurring in the solution.

Common formulations and methods of work

• Salts of monocarboxylic acids can be safely considered the most common materials for the manufacture of frost-resistant additives, among professionals this composition is known as “Potash”. The price of these formulations in the domestic market is quite acceptable.
• When concrete is poured in sub-zero temperatures, monocarboxylic acid additives must be strictly metered. For each temperature, the amount of additives is different. Such additives can be used to prepare the solution for temperatures up to minus 30? С. The lower the temperature, the more composition will be required.

Important: as mentioned earlier, an additive with illiterate use may reduce other characteristics of the solution. Therefore, the principle, the more, the better it can hurt.

• The next leader of our market is sodium nitrite. The price for it is also not very high, but this substance has a strong, acrid, unpleasant smell. In addition, this composition can easily ignite. Upon contact with certain types of modern plasticizers, toxic, toxic gases can be released.

• The maximum temperature that sodium nitrate can hold is not lower than -15? С. Experts recommend its use in the preparation of solutions on Portland cement or on slag Portland cement. Adding this additive to alumina cements is strictly prohibited.
• Sodium formate and calcium nitrate have a wide range of uses. In addition to the production of concrete products, these additives can be used in plaster and mortar solutions for brick laying. But these compositions are used only in combination with a plasticizer, since due to the accumulation of salts, voids and efflorescence can form in the monolith.

Important: solutions with the addition of additives should be prepared with their own hands at a temperature not lower than 5 - 10? С. In addition, they can not be stored for a long time, the solution must be used within an hour after mixing.

• Do not forget about domestic manufacturers, additives from the frost line, frost-styrene, etc. They are compounds of complex action. After pouring, due to the processes occurring inside the monolith, the temperature is maintained naturally and with a slight frost, you just have to cover the concrete well.

Concrete brand dependence

• According to the norms of SNiP 111-1-76, frost is dangerous for concrete only at the stage of curing. Maintain a certain temperature in the monolith need to a certain% of the fortress. For each brand of concrete, this percentage is individual.
• After the monolith grabbed, freezing was no longer so scary for him, but it was not recommended to exploit concrete goods. The fact is that after thawing, the product will ripen naturally. The active phase of solidification of the monolith is within 27 days. After this, the strengthening will continue for several more years, but much more slowly.
• If frost-resistant additives were not introduced into the composition, then for solutions with the mark M150 50% strength is sufficient. Mark M200 - M300, can be frozen at 40% strength. For M400 and more, 30% is enough. But when using an additive, the permissible strength before freezing drops by an average of 10%.

Tip: the time of mixing the composition in winter conditions should be increased at least 2 times.

Myths related to additives

• In wide use this type of additives appeared not so long ago. The people had not yet had time to figure out how comfortable this was and on this fertile soil several prejudices were born.
• The first common myth was born a long time ago, periodically with the advent of each new composition, this issue is raised, and frost-resistant additives are no exception. Handicraft masters "authoritatively" declare that such additives cause increased corrosion of the reinforcement cage.
• Take the simplest and most affordable sodium nitrite in Russia. Any average chemist or metal scientist will tell you that this is one of the inhibitors that can slow down the corrosion process. Moreover, in conjunction with plasticizers and shrinkage additives for working with monoliths, in view of increasing the strength, only diamond drilling of holes in concrete can be used, as well as cutting of reinforced concrete with diamond circles.

• The second common myth can be called a decrease in the strength of concrete. This statement was born due to the fact that in the early stages of the mortar setting, there was indeed some delay compared to pure concrete. But then the speed of strength increase significantly increases. This especially applies to the combined formulations.
• All experts, from the very beginning, advise one thing, carefully study the instructions. With an insufficient amount of additive in the solution, it may freeze. But if you add too much additive, then you risk increasing the setting time or losing a certain percentage of the strength due to the formation of gases.

In the video in this article, you can discover many useful things.

Conclusion

As a conclusion, I would like to note that when you decide what to add to concrete in sub-zero temperatures, do not forget that counterfeit products in this area of ​​production have unfortunately not disappeared from the shelves. Having laid it is not known what is in the foundation in the winter, you risk redoing all the work in the summer, especially since the price of real, high-quality compounds is quite affordable.