Heating of concrete with electrodes in winter time

A dozen years ago in the winter period, almost all construction work lost its intensity. This was due, first of all, to minus temperatures. But if the workers were able to dress warmly, then it was extremely problematic to perform concreting in such conditions. However, after a while, a very effective method appeared - heating the concrete with electrodes and using an electric cable. Let's take a closer look at the features of this method and talk about its feasibility.

What is it for?

Before delving into this topic, you need to talk about what is actually used. The fact is that any concrete has in its composition a certain amount of water. It is quite natural that at minus temperatures it forms ice crystals. The latter lead to the fact that a large pressure on the pores of the concrete, which eventually leads to a partial or complete destruction of the structure. The ultimate strength in this case is significantly reduced, and performance deteriorates.

Another dangerous factor is the freezing of water during the setting (hardening). The fact is that at low temperatures the interaction of the concrete mixture and water slows down. This stops the hardening process, making it uneven. That is, there is no need to talk about any declared strength. Nevertheless, today there is more than one scheme for heating concrete with electrodes, which allows to keep the humidity-temperature characteristics within the permissible range.

On the methods of winter concreting

It is worthwhile to draw your attention to the fact that not only the electrode is used today. Due to the fact that sometimes this method is not suitable, or its use is too expensive for developers. In addition, much depends on the conditions (temperature, humidity, purpose of the future design). For this simple reason, there are a number of other ways of concreting during the winter. For example, heating in the heating formwork. This method is very effective and good, but it is advisable only with a small thickness. By the middle of the concrete it will still be a little freezing and the thicker it is, the more harmful the effect of the minus temperature will be. Also there are antifreeze additives, making the mixture more resistant to frost. There is an induction heating and with the help of special wires. But the most popular method is to use electrodes.

When do you use electrodes?

Each of the above described methods is used in this or that situation. As for the electrodes, this is not a universal solution either. For example, when pouring a concrete slab it is completely ineffective. In this case, it is better to use a heating wire. But if it is a question of any vertical design, then electrode heating will be an excellent solution.

By the way, sometimes a natural insulation is used, which is often not enough. In this case, the electrode is suitable as an additional heater. But we need to understand that the wider the design, the lower the efficiency and the higher the cost, but we will return to this issue. Fortunately, today the technology of warming concrete in this way is mastered and widely used by builders from all over the world. Nevertheless, most of the buildings in the Russian Federation use wire heating.

The advantages of this method

It should be noted that the technology of warming concrete with electrodes implies only 3 workers. This is a significant advantage, as many people do not need it. In addition, it is worth mentioning the effectiveness of the method. This solution provides not only a uniform grasp of the mixture, but also does not violate the integrity of the structure. This is a very important point, since such a factor directly affects the strength and durability of the product. Another important factor is the simplicity and high speed of installation. This is especially true during a severe frost. In addition, one can not help saying that it is often sufficient for a column to use only one electrode.

We considered the strengths , but now it makes sense to say about the disadvantages, which are also there.

Disadvantages of preheating with electrodes

In our case, we need to talk about using wire rod fittings as electrodes. Usually it is selected with a diameter of 8-10 millimeters, which is enough for effective work. It would seem that there may be flaws, but they do exist.

First, this is a fairly large energy expenditure. Each electrode will consume about 50 A. At the same time, it is necessary to use step-down transformers. For example, a model for 80 kW pulls not so much. Therefore, in addition to the electrodes, you need to buy additional equipment, which is quite expensive.

Another significant drawback, due to which many developers circumvent this method by the side - is high cost. The fact is that the electrodes from the rod are disposable. After they are installed, they remain forever in the body of the structure, and it is not possible to extract them. But those who still decided to use this method, are satisfied. The strength of the structure is maintained for a long time, and the performance characteristics are at a high level.

Warming of concrete with electrodes: technology

And now let's briefly consider the essence of this method. As noted above, it is not suitable for pouring concrete slabs, only for columns, walls, as well as diaphragms. After the pouring works have been completed, metal rods are inserted into the walls. They are supplied with voltage through a step-down transformer. Usually, the interval between two adjacent electrodes is chosen from 60 to 100 centimeters, which depends both on the weather and the configuration of the object.

From the step-down transformer, three phases are applied to the valve, as a result of which the space between the electrodes warms up and freezes are eliminated. It should be noted that the warming up of concrete in winter is based on the passage of an electric current through the water contained in the solution. As a result, we have uniform heating. It should be understood that if there is an armature frame, then the voltage should not be more than 127 V, and if there is none, you can apply 220 and 380 V, but no more.

Types of electrodes used

Currently, three types of electrodes are used. Each of them is suitable for certain situations. For example, rod electrodes, which are among the most popular, are made of reinforcement with a diameter of 8-12 mm. In the body of concrete they are installed with a calculated step, which is determined in advance. The extreme row is mounted no further than 3 centimeters from the formwork, which guarantees a full warm-up of the edges of the wall or column. It is noteworthy that such electrodes are suitable for designs of the most complex shape.

But the plate electrodes work somewhat differently. They are suspended on different sides of the formwork. As a result, an electric field is created, which heats the concrete to the desired temperature for a certain time. In principle, the heating of concrete in winter by this method is very effective. String electrodes are best suited for structures such as columns.

Warming of concrete with electrodes: wiring diagram

It is necessary to understand that the method of connection of electric heating will differ depending on the type of electrode chosen. When working with plate electrodes, one phase is fed to the first electrode, and the second to the located on the opposite side. As a result, we have two electrodes that are parallel to each other, each has a phase. In the case of rod reinforcement, the first and last electrodes in a row are connected to one phase. The rest work from the 2 nd and 3 rd phases.

I would like to note that we should not neglect the installation of transformers. They are in some cases not needed, but in most situations it makes sense to install them. So, the temperature of the concrete heating will be optimal, that is not too high, otherwise such undesirable effect as overdrying may appear. For this simple reason, it makes sense to plug all the electrodes through the step-down transformer.

Heated electric keys: important rules

For effective operation of electric heating, it is necessary to connect to different poles of the power grid. This rule is very important for execution, since if one phase is used, then there will be no result.

In addition, the closure of the chain occurs only through wet concrete. For each case, a special design is prepared, which indicates the step between the electrodes, the location of the step-down transformers and the permissible voltage.

It is worthwhile to draw your attention to the fact that some concrete grades lose their strength. For example, a loss of 20-25% is considered acceptable. Nevertheless, before starting the technological heating of concrete, it is recommended to withstand it for some time without heating it.

A few details

Here we are with you and examined what is the heating of concrete with electrodes. The technology may differ depending on the electrodes used. However, it should be noted that it is advisable to use special additives to improve the final quality and strength of the concrete mixture. For example, calcium chloride, added to slag Portland cement, can reduce the loss of strength and hardening time by 20-30%. If you noticed that even if there is a drying transformer, there is drying, then the surface must be moistened with water or turn off the heating for a while.

Conclusion

Here we are and we examined the heating of concrete with electrodes. Technology, as noted above, is selected according to the individual project, which is developed for each case separately. This allows not only to save money and time of the builder, but also to optimally place the electrodes, as well as speed up the process of solidification of the concrete mixture. Sometimes it is advisable to use other methods of heating, for example, heating wires. Of course, this is quite expensive, but very effective. In principle, this is all information on this topic. Remember that the key role is played by compliance with the technology during the installation of electric heating.