In modern conditions, there are many technologies that make it possible not to stop the construction process even in winter. If the temperature drops, it is necessary to maintain a certain level of heating of the concrete mixture. In this case, the construction of houses, various objects does not stop for a minute.
The main condition for carrying out such work is to maintain a technological minimum at which the solution will not freeze. Electric heating of concrete is a factor that ensures the implementation of technological standards, even in winter. This process is rather complicated. Nevertheless, it is actively used everywhere at various construction sites.
Electric heating
Electric heating of concrete is a rather complex and expensive process. However, to prevent the effect of low temperatures on the hardening cement mixture, it needs to provide a number of conditions. In winter, cement hardens unevenly. To prevent such a deviation from the norm, electric heating technology should be used. It contributes to the constant process of solidification of the mixture throughout the entire area.
Concrete is able to solidify evenly at a temperature that will be close to +20 º. Forced electric heating becomes an effective tool in the preparation of mortars.
Most often, electric heating technology is used for such purposes. If a simple warming of an object becomes insufficient, such an alternative can solve the problem of unevenly setting concrete.
Construction companies can choose one of several approaches. For example, electric heating can be carried out using a conductor such as a PNSV cable, or using electrodes. Also, some companies resort to the principle of heating the formwork itself. At present, they can also use the induction approach or infrared rays for similar purposes.
Regardless of which method the management chooses, the heated object must be insulated without fail. Otherwise, uniform heating will be unrealistic.
Warming up with electrodes
The most popular method of heating concrete is the use of electrodes. This method is relatively inexpensive, because there is no need to purchase expensive equipment and devices (for example, a wire like PNSV 1,2; 2; 3, etc.). The technology of its implementation also does not present great difficulties.
The fundamental principle of the technology presented is the physical properties and characteristics of the electric current. When passing through concrete, it releases a certain amount of thermal energy.
When using this technology, it is not necessary to supply voltage to the electrode system above 127 V if there is a metal structure (frame) inside the product. The instruction for electric heating of concrete in monolithic structures allows the use of a current of 220 V or 380 V. However, a higher voltage is not recommended.
The heating process is carried out using alternating current. If a direct current is involved in this process, it passes through the water in the solution and forms electrolysis. This process of chemical decomposition of water will impede the performance of its functions, which the substance has in the hardening process.
Types of Electrolytes
Electric heating of concrete in winter can be carried out using one of the main types of electrodes. They can be string, rod and made in the form of a plate.
Core electrolytes are installed in concrete at a short distance from each other. To create the presented product, scientists use metal fittings. Its diameter can be from 8 to 12 mm. The rods are connected to various phases. The presented devices are especially irreplaceable in the presence of complex designs.
Electrolytes, which are in the form of plates, are characterized by a fairly simple wiring diagram. Their devices must be placed on opposite sides of the formwork. These plates are connected to different phases. The current passing between them will heat the concrete. The plates may be wide or narrow.
String electrodes are necessary in the manufacture of columns, pillars and other elongated products. After installation, both ends of the material are connected to different phases. This is how heating occurs.
Cable heating PNSV
Electric heating of concrete with the PNSV wire, the technological map of which will be considered a little further, is considered one of the most effective technologies. In this case, the wire acts as a heater, and not the concrete mass.
When laying the presented wire in concrete, it turns out to warm the concrete evenly, ensuring its quality when dried. The advantage of such a system is the predictability of the period of operation. For high-quality heating of concrete in conditions of lowering temperature, it is very important that it increases smoothly and evenly over the entire area of the cement mortar.
The abbreviation PNVS means that the conductor has a steel core, which is packed in PVC insulation. The cross-section of the wire when carrying out the presented procedure is selected in a certain way (PNSV 1,2; 2; 3). This characteristic is taken into account when calculating the amount of wire per 1 m cubic cement mixture.
The technology for heating concrete with wire is relatively simple. Along the armature frame, electrical communications are allowed. Fasten the wire in accordance with the manufacturer's recommendations. In this case, when feeding the mixture into the trench, formwork or conductor mixture, the pouring and operation of the solidified substance will not be damaged.
When laying out, the wire should not touch the ground. After pouring, it is completely immersed in a concrete environment. The thickness of the wire, subzero temperatures in this climate zone, and resistance will affect the length of the wire. The applied voltage will be 50 V.
Cable application technique
Electric heating of concrete with the PNSV wire, the technological map of which consists in laying the product in a container immediately before pouring, is considered a reliable system. The wire must have a certain length (depending on the conditions of its use). Due to the good thermal conductivity of concrete, the heating is smoothly distributed throughout the thickness of the material. Thanks to this feature, it is possible to increase the temperature of the concrete mixture to 40 º, and sometimes even higher.
The PNSV cable is allowed to be supplied to the network, the electricity of which is supplied by the substations KTP-63 / OB or 80/86. They have several degrees of undervoltage. One substation of this type is capable of heating up to 30 m³ of material.
To increase the temperature of the solution, it is necessary to spend about 60 m of the PNSV 1.2 grade wire by 1 m³. In this case, the ambient temperature can be up to -30 º. Heating methods can be combined. It depends on the massive structure, weather conditions, specified strength indicators. Another important factor for creating a combination of methods is the availability of resources at the construction site.
If concrete manages to gain the required strength, it can resist destruction due to low temperatures.
Other wire heating options
The technology for heating concrete PNSV cable is effective provided that all instructions and requirements of the manufacturer are observed. If the wire goes beyond the concrete, it is very likely to overheat and fail. Also, the wire must not touch the formwork or the ground.
The length of the wire presented will depend on the conditions in which the wire is used. For their work requires the operation of a transformer. If, using the PNSV wire, the use of such a system is not very convenient, there are other varieties of conductive products.
There are cables for the operation of which you do not need to apply power to special transformers. This makes it possible to save a little money on the maintenance of the presented system. Conventional wire has a wide range of applications. However, the PNSV wire, which was discussed above, has wider capabilities and scope.
Heat gun application scheme
Concrete heating by wire is considered one of the newest and most effective technologies. However, more recently, no one knew about her. Therefore, a rather costly but simple method was used. Shelter was built over the surface of the cement. For this method, the concrete base should have a small area.
Heat guns were brought to the constructed tent. They pumped up the required temperature. This method was not without certain drawbacks. It is considered one of the most time-consuming. Workers need to build a tent, and then control the operation of the equipment.
If we compare the heating of concrete with a wire and the method of using thermal units, it becomes clear that the old approach will require more costs. Most often, certain equipment of an autonomous type of work is purchased. They run on diesel. If there is no access to the usual fixed network on the site, this option will be the most advantageous.
Thermomats
A heating wire or infrared film can serve as the basis for the creation of special thermomats. They are quite effective. The only condition is the flat surface of the concrete base. Some varieties of heaters presented can work as windings on columns, elongated blocks, poles, etc.
When using matte technology, a plasticizer is added to the solution itself, which allows to accelerate the drying process. However, they can also prevent the formation of crystallization of water.
When using the technologies presented, it should be remembered that there are special documents governing the electrical heating of concrete in the winter. SNiP draws the attention of construction organizations to the need for constant monitoring of the temperature indicators of this substance.
Cement mix should not overheat above +50 º. It is as unacceptable for the technology of its production, as well as large frosts. At the same time, the cooling and heating rate should not be faster than 10 º per hour. To avoid mistakes, the calculation of concrete electrical heating is carried out in accordance with applicable standards and sanitary requirements.
Infrared mats can replace cable analogs. They can be used for wrapping curly columns, other elongated objects. This approach is characterized by low energy consumption. Concrete structures under the influence of infrared rays begin to quickly lose moisture. To prevent this from happening, you need to cover the surface with an ordinary plastic film.
Heated formwork
Electric heating of concrete in winter can be carried out immediately in the formwork. This is one of the new ways that is very effective. Heating elements are installed in the formwork panels. In the event of failure of one or more of them, the dismantled equipment is dismantled. It is being replaced with a new one.
Equipping infrared heaters directly in the form in which concrete hardens has become one of the successful decisions made by managers of construction companies. This system is able to provide the required conditions for the concrete product in the formwork, even at a temperature of -25 º.
In addition to high efficiency, the presented systems have a high efficiency. It takes quite a bit of time to prepare for heating. This is extremely important in severe frosts. The profitability of heating formwork is determined higher than that of conventional wired systems. They can be used repeatedly.
However, the cost of the presented variety of electric heating is quite high. It is considered disadvantageous if it is necessary to heat the construction of non-standard dimensions.
The principle of induction and infrared heating
In the above systems of thermomats and formwork with heating, the principle of infrared heating can be used. To clearly understand the principle of operation of these systems, it is necessary to delve into the question of what infrared waves are.
Electric heating of concrete using the presented technology takes as a basis the ability of sunlight to heat opaque, dark objects. After heating the surface of a substance, heat is evenly distributed throughout its entire volume. If the concrete structure in this case is wrapped with a transparent film, when heated, it will transmit rays into the concrete. In this case, heat will be trapped inside the material.
The advantage of infrared systems is the lack of requirements for the use of transformers. The disadvantage is that experts call the impossibility of the heating provided to evenly distribute heat throughout the entire structure. Therefore, it is used only for relatively thin products.
The induction approach in modern construction is rarely used. It is more suitable for structures such as girders, beams. This is affected by the complexity of the device presented equipment.
The principle of induction heating is based on the fact that a wire is wound around a steel rod. It has a layer of insulation. When an electric current is connected, the system produces an induction disturbance. This is how the concrete mix heats up.
Having considered the electrical heating of concrete, as well as its main methods and technologies, it can be concluded that it is advisable to apply one or another method in a production environment. Depending on the type of manufactured structures, production conditions, technologists choose the appropriate option. A scrupulous approach to concrete hardening technology allows us to produce high-quality products, screed, foundations, etc. Every builder should know the rules for working with cement in the winter.