Even a dozen years ago in the winter period of time, almost all construction work lost their intensity. This was due primarily to subzero temperatures. But if the workers could dress warmly, then concreting in such conditions was extremely problematic. However, after a while, a very effective way appeared - heating 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, it is necessary to talk about why this is actually applied. The fact is that any concrete has a certain amount of water in its composition. It is quite natural that at minus temperature it forms ice crystals. The latter lead to the fact that concrete pores are under a lot of pressure, which ultimately leads to partial or complete destruction of the structure. The final strength is significantly reduced, and the performance is deteriorated.
Another dangerous factor is the freezing of water during the setting (solidification) period. The fact is that at low temperature the interaction of the concrete mixture and water slows down. This pauses the solidification process, making it uneven. That is, talking about any declared strength is not necessary. Nevertheless, today there is not one scheme of heating concrete with electrodes, which allows you to keep the humidity and temperature characteristics in the allowable range.
About winter concreting methods
It is worth paying your attention to the fact that today not only an electrode is used. This is 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 methods of concreting in the winter. For example, heating in a heating formwork. This method is very effective and good, but only suitable for small thicknesses. In the middle, the concrete will still freeze a little and the thicker it is, the more harmful the effect of subzero temperature will be. There are also anti- frost additives that make the mixture more resistant to frost. There is induction heating and using special wires. But the most popular method is to use electrodes.
When are electrodes used?
Each of the above methods is used in a particular situation. As for the electrodes, then this is not a universal solution. For example, when pouring a concrete slab, it is completely ineffective. In this case, it is better to use a heating wire. But if we are talking about 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, an electrode is suitable as additional heating. But you need to understand that the wider the design, the lower the efficiency and higher cost, but we will return to this issue. Fortunately, today the technology of warming up concrete in this way has been mastered and is widely used by builders from around the world. Nevertheless, in the territory of the Russian Federation, most of the buildings use wire heating.
About the advantages of this method
It should be noted that the technology of heating concrete with electrodes implies only 3 workers. This is a significant advantage, since it does not need a lot of people. In addition, it is worth mentioning the effectiveness of the method. This solution provides not only a uniform setting of the mixture, but also does not violate the integrity of the structure. This is quite an 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 severe frost. In addition, it cannot be said that the use of only one electrode is often sufficient for a column.
We examined the strengths, and now it makes sense to say about the disadvantages, which are also here.
Disadvantages of heating with electrodes
In our case, we need to talk about using wire rod as electrodes. Usually it is picked up with a diameter of 8-10 millimeters, which is quite enough for effective work. It would seem that there may be flaws, but they are.
Firstly, this is a fairly large energy consumption. Each electrode will consume about 50 A. In this case, step-down transformers must be used. For example, an 80 kW model will not pull much. Therefore, in addition to electrodes, you need to buy additional equipment, which is quite expensive.
Another significant drawback due to which many developers bypass this method is the high cost. The fact is that wire rod electrodes are disposable. After their installation, they remain forever in the body of the structure, and it is not possible to extract them. But those who nevertheless decided to use just such a method, remain satisfied. The structural strength is maintained for a long time, and performance is at a high level.
Concrete heating with electrodes: technology
Now let's briefly review the essence of this method. As noted above, it is not suitable for pouring concrete slabs, only for columns, walls, and also diaphragms. After filling work is completed, metal rods are inserted into the walls. They are supplied with voltage through a step-down transformer. Typically, the interval between two adjacent electrodes is selected from 60 to 100 centimeters, which depends on both the weather and the configuration of the object.
Three phases are supplied to the valve from the step-down transformer, as a result of which the space between the electrodes warms up and freezing is eliminated. It is worth paying your attention to the fact that heating of concrete in winter is based on the passage of electric current through the water contained in the solution. As a result, we have uniform heating. It must be understood that if there is a reinforcing cage, then the voltage should not be more than 127 V, and if there is none, then you can supply 220 and 380 V, but no more.
Types of Electrodes Used
Three types of electrodes are currently used . Each of them is suitable for certain situations. For example, rod electrodes, which are some of the most popular, are made of fittings with a diameter of 8-12 mm. In the concrete body they are installed with a calculated step, which is determined previously. The extreme row is mounted no further than 3 centimeters from the formwork, which ensures complete heating of the edges of the wall or column. It is noteworthy that just such electrodes are suitable for structures of the most complex shape.
But plate electrodes work a little differently. They are hung on opposite sides of the formwork. As a result, an electric field is created that heats the concrete to the desired temperature for a certain time. In principle, warming up concrete in winter using this method is very effective. String electrodes are best suited for structures such as columns.
Concrete heating with electrodes: connection diagram
It must be understood that the method of connecting electric heating will differ depending on the type of electrode selected. When working with plate electrodes, one phase is fed to the first electrode, and the second to the opposite side. As a result, we have two electrodes that are parallel to each other, each has a phase. In the case of bar reinforcement, the first and last electrodes in a row are connected to one phase. The rest work from the 2nd and 3rd phase.
I would like to note that you should not neglect the installation of transformers. They are not needed in some cases, but in most situations it makes sense to install them. So, the temperature of concrete warming up will be optimal, that is, not too high, otherwise such an undesirable effect as overdrying may appear. For this simple reason, it makes sense to supply all the electrodes through a step-down transformer.
Heated Electrodes: Important Rules
For the effective operation of electric heating, it is necessary to connect to various poles of the mains. This rule is very important for execution, since if you use one phase, then there will be no result.
In addition, circuit closure occurs only through wet concrete. For each case, a special project is drawn up, in which the step between the electrodes, the location of the step-down transformers and the permissible voltage are indicated.
It is worth paying your attention to the fact that some brands of concrete lose their strength. For example, losses of 20-25% are considered acceptable. Nevertheless, before starting technological heating of concrete, it is recommended to withstand it for some time without heating.
Few details
So we have examined what is the heating of concrete with electrodes. The technology may vary depending on the electrodes used. However, it is worth noting that to improve the final quality and strength of the concrete mixture, it is advisable to use special additives. For example, calcium chloride, added to slag-Portland cement, can reduce strength loss and solidification time by 20-30%. If you notice that even if there is a step-down transformer, drying is present, then the surface must be moistened with water or the heating turned off for a while.
Conclusion
So we have examined the heating of concrete with electrodes. The technology, as noted above, is selected depending on the individual project, which is developed for each case separately. This allows not only saving money and time for the builder, but also optimally placing the electrodes, as well as significantly accelerating the hardening of the concrete mixture. Sometimes it is advisable to use other heating methods, for example, heating wires. Of course, it is quite expensive, but very effective. In principle, this is all information on this topic. Remember that adherence to technology during the installation of electric heating plays a key role.