Concrete at negative temperatures - the use of electrical

25-05-2018

Building

As you know, the best conditions for concreting works are spring or autumn with temperatures from 10 to 20 degrees, the best result is achieved under these conditions. But sometimes you have to carry out concrete work at negative air temperatures, we will consider this option in this article, because there are a lot of features and nuances, the ignorance of which can greatly affect the final result.

Concreting requirements in winter

SNiP for concrete work at negative temperatures has the number 3.03.01-87 and is called "supporting and enclosing structures."

It is in this regulatory act that the main requirements and features of the work are defined:

The rules apply to work that is carried out at an average daily value of ambient air temperature below +5 degrees or when the lower temperature value per day is below 0 degrees.
The process of making the mixture should be carried out in a heated room. It should not be forgotten that the mixing process should be longer than in the summer period: not less than 25% of the time.
The aggregates used to prepare the solution must be heated (especially water), all dry fillers may not be heated, but they should not contain ice crystals.

In the photo: all containers intended for storing the components of the mixture must be located in the room, so you will avoid freezing them

If delivery is required from the concrete preparation site to the construction site, remember that the solution should not cool below the set temperatures, this will significantly impair its properties.
The base on which the concrete mix will be laid should exclude the possibility of the mortar freezing when it is poured. To this end, the surface, as well as reinforcing elements with a large number of them must be heated.
All surfaces must be cleared of frost and snow, this is very important, since you may encounter unpleasant surprises in the form of irregularities on the surface when removing the formwork.
In permafrost conditions, concreting at negative temperatures according to SNiP II-18-76 is carried out in strict accordance with the regulatory act, it should be used as an instruction, since the cost of errors in such conditions is too high.

The main technologies of the work in the cold period

Pouring concrete at negative temperatures can be done by a variety of methods. We consider the most common of them, which are most often used in our conditions. It is worth noting that all techniques are quite effective if used in appropriate conditions.

Electric concrete heating

This option is very popular with large industrial developers, but smaller objects also successfully use electric current as a way to maintain a positive temperature when the concrete freezes.

Depending on the characteristics of the concrete work, one of the following options can be used:

Electric heating with the help of special wires, which are produced in isolation, but due to the design features during the passage of current, generate heat and thus heat the thickness of the concrete, thereby accelerating the process of its hardening and eliminating freezing. The most commonly used wire is the PNSV, the cross section of which is calculated individually for each object, while it is better to involve specialists to avoid errors in the calculations.

When working with your hands, the process of laying the wires takes the most time - this should be done carefully, eliminating damage to the insulation

Another option is to heat the material with the help of electrodes, which are often reinforcement or any other metal pins.. This method is quite simple in terms of implementation, but its use involves the use of a large number of step-down transformers and a rather impressive power consumption, which significantly increases costs.

Electrodes are put in advance or stuck in a freshly poured solution.

Another less common option is induction heating, which uses the electromagnetic field principle to generate heat.. To use this option, you will need a transformer and an induction coil.

Note! Recently, one more interesting way to maintain a positive temperature in concrete - infrared heating - has increasingly become used. Quite a lot is known about the properties of radiant energy; it can be used to heat the surface with minimal energy, the only problem is the high cost of equipment.

Use of various additives

This method is characterized by the fact that the properties of concrete at low temperatures are significantly improved due to special additives, due to which structures gain high strength properties of concrete even under adverse conditions.

All additives can be divided into several main groups, according to which the technology of work is also different:

A “cold” thermos, when a special additive increases the exotherm of cement, that is, its heat release during the solidification process. Its use allows the composition to be heated independently. It is worth noting that this option is suitable for small frosts.
"Hot" thermos involves heating the solution in the process of mixing it to a certain temperature. After pouring the composition, the additive significantly increases the thermostatic exposure, due to which the material cools for a very long time.
Another option is the so-called cold method; special antifreeze additives are added to the mixture, which prevent surface freezing and provide high-quality curing of concrete at negative temperatures. It can be said that this is the easiest option for independent use, the price of the composition is small, and the application process is simple: add the additive to the prepared mass.

Additives of this group can be found in almost any hardware store.

Note! Carefully read the instructions for use of antifreeze components, as a rule, the proportions of their addition are directly dependent on external conditions: the lower the temperature, the more will be required.

The use of thermoactive formwork

This option involves the use of various structures, which not only create a framework for the future structure, but also provide high-quality concrete hardening at negative temperatures due to its heating.

There are the following options for such decisions:

Thermoactive formwork allows you to maintain a positive temperature even at high temperatures

Systems with electric heating elements (special grids, heating cables, heating elements, etc.). This method is simpler, and therefore is used most often.
Another interesting option is the thermo-toothed tumbler, this system is a construction with a cavity inside which hot water, oil or steam circulates. The system is complex, therefore it is used only on large objects.

Heaters

This method involves the construction of structures that ensure the maintenance of the desired temperature, while other work can be carried out in the heating room - cutting of reinforced concrete with diamond circles and diamond drilling of holes in concrete should be carried out at positive temperatures, this will provide excellent results.

Teplyak provides high-quality hardening of concrete and comfortable work

Designs can be of two types:

Stationary, assembled from shields with a gate. Most often, such options are used for large amounts of work.
Temporary greenhouses, representing a frame with a canopy of film or tarpaulin. This option is quickly built and easy to assemble.

Temporary construction can be erected from improvised means, which is an undoubted advantage

It is worth noting that all the considered options relate only to ordinary concrete, laying asphalt concrete at negative temperatures is carried out on completely different requirements. Therefore, it is important to correctly determine the nature of the work.

Conclusion

Only the observance of technology guarantees high quality of work even in the winter period. The video in this article will help to better understand some types of work and clearly show their features.