In modern conditions, there are many technologies, thanks to which it is possible not to stop the construction process even in winter. If the temperature drops, it is required to maintain a certain level of heating of the concrete mixture. In this case, the construction of houses, various objects does not stop even for a minute.
The main condition for such work is to maintain a technological minimum at which the solution will not freeze. Electrical heating of concrete is a factor that ensures the implementation of technological standards even in winter. This process is quite complex. Nevertheless, it is actively used everywhere at various construction sites.
Electric heating
Electrical heating of concrete is a rather complicated 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 applied. It contributes to the constant solidification of the mixture over the entire area.
Concrete is able to harden evenly at a temperature that will be close to +20 ºС. Forced electrical heating is becoming an effective tool in the preparation of mortars.
Most often, electric heating technology is used for such purposes. If simply insulating an object is no longer enough, this alternative can solve the problem of unevenly curing concrete.
Builders can choose from 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. Currently, the induction approach or infrared rays can also be used for similar purposes.
Regardless of which method the management chooses, the heated object must be insulated without fail. Otherwise, it will be unrealistic to achieve uniform heating.
Heating 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, wire type PNSV 1, 2; 2; 3, etc.). The technology of its implementation also does not present great difficulties.
The physical properties and features of electric current are taken as the fundamental principle of the presented technology. As it passes through concrete, it releases some heat energy.
When using this technology, do not apply 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, it is not recommended to use a higher voltage.
The heating process is carried out using alternating current. If a direct current is involved in this process, it passes through the water in solution and forms electrolysis. This process of chemical decomposition of water will interfere with the performance of its functions, which the substance has in the process of hardening.
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.
Stand electrolytes are installed in concrete at a small 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 different phases. The presented devices are especially indispensable in the presence of complex structures.
Electrolytes, which are in the form of plates, are characterized by a fairly simple connection scheme. 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. Plates can be wide or narrow.
String electrodes are needed 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.
Heating with cable PNSV
Electrical heating of concrete with the PNSV wire, the technological map of which will be discussed a little further, is considered one of the most effective technologies. In this case, the wire acts as a heater, not the concrete mass.
When laying the presented wire in concrete, it turns out to evenly warm up the concrete, ensuring its quality when it dries. The advantage of such a system is the predictability of the period of work. For high-quality heating of concrete in conditions of decreasing temperature, it is very important that it rises smoothly and evenly over the entire area of the cement mortar.
The PNVS abbreviation means that the conductor has a steel core, which is packed in PVC insulation. The wire cross section during 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 cubic meter of cement mix.
The technology of heating concrete with a wire is relatively simple. Electrical communications are allowed along the armature frame. Attach the wire in accordance with the manufacturer's recommendations. In this case, when the mixture is fed into the trench, formwork or mixture, the conductor will not be damaged by the pouring and operation of the solidified substance.
The wire should not touch the ground when laying out. After pouring, it is completely immersed in the concrete environment. The length of the wire will be influenced by itsthickness, sub-zero temperatures in this climate zone, resistance. The applied voltage will be 50 V.
Cable Application Method
Electric heating of concrete with the PNSV wire, the technological map of which consists in placing the product in a container immediately before pouring, is considered a reliable system. The wire must have a certain length (depending on its operating conditions). Due to the good thermal conductivity of concrete, the heat is smoothly distributed over the entire thickness of the material. Thanks to this feature, it is possible to increase the temperature of the concrete mixture up to 40 ºС, and sometimes even higher.
The PNSV cable is allowed to be fed into the network, the electricity of which is supplied by substations KTP-63/OB or 80/86. They have several degrees of reduced voltage. One substation of the presented type is capable of heating up to 30 m³ of material.
To increase the temperature of the solution, about 60 m of wire of the PNSV 1, 2 brand should be spent per 1 m³. In this case, the ambient temperature can be up to -30 ºС. Heating methods can be combined. It depends on the massiveness of the structure, weather conditions, specified strength indicators. Also an important factor for creating a combination of methods is the availability of resources at the construction site.
If concrete can gain the required strength, it can withstand the destruction due to low temperatures.
Other wired heating options
Concrete heating technology PNSV cable is effective if all instructions are followedand manufacturer's requirements. If the wire goes beyond the concrete, it is very likely to overheat and fail. Also, the wire should not touch the formwork or the ground.
The length of the wire shown will depend on the conditions in which the wire is used. They require a transformer to work. If, using the PNSV wire, the use of such a system is not very convenient, there are other types of conductor products.
There are cables that do not need to be powered by special transformers. This makes it possible to save some 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.
Scheme of using a heat gun
Concrete heating with wire is considered one of the newest and most effective technologies. However, until recently no one knew about it. Therefore, a rather expensive, but simple method was used. A shelter was built over the surface of the cement. For this method, the concrete base had to have a small area.
Heat guns were brought to the built tent. They pushed the required temperature. This method was not without certain drawbacks. It is considered one of the most labor intensive. 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 clearthat it is the old approach that will require more costs. Most often, certain equipment of an autonomous type of work is purchased. They run on diesel fuel. If there is no access to a regular fixed network in the area, this option will be the most advantageous.
Thermomats
Heating wire or infrared film can serve as the basis for creating special thermomats. They are pretty efficient. The only condition is a flat surface of the concrete base. Some varieties of the presented heaters can work as a winding on columns, elongated blocks, poles, etc.
When using matte technology, a plasticizer is added to the solution itself, which allows to speed up the drying process. At the same time, they can also prevent the formation of water crystallization.
When using the presented technologies, it should be remembered that there are special documents regulating the electric heating of concrete in winter. SNiP draws the attention of construction organizations to the need to constantly monitor the temperature indicators of this substance.
Cement mixture should not overheat above +50 ºС. This is just as unacceptable for the technology of its production, as are severe frosts. At the same time, the rate of cooling and heating should not be faster than 10 ºС per hour. To avoid errors, the calculation of electrical heating of concrete is carried out in accordance with applicable standards and sanitary requirements.
Infrared mats can replace cable analogues. Themit is allowed to use 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 surfaces with ordinary plastic wrap.
Heated formwork
Electric heating of concrete in winter can be carried out immediately in the formwork. This is one of the new ways, which is very effective. Heating elements are installed in the formwork panels. In case of failure of one or more of them, the faulty equipment is dismantled. It is being replaced with a new one.
To equip with infrared heaters directly the form in which the concrete hardens has become one of the successful decisions taken by the managers of construction companies. This system is able to provide the required conditions to the concrete product, which is in the formwork, even at a temperature of -25 ºС.
In addition to high efficiency, the systems presented have a high efficiency. It takes very little time to prepare for heating. This is extremely important in severe frosts. The profitability of heating formwork is determined to be higher than that of conventional wired systems. They are reusable.
However, the cost of the presented variety of electric heating is quite high. It is considered unprofitable if you need to heat a building of non-standard dimensions.
Principle of induction and infraredheating
In the systems of thermomats and formwork with heating presented above, the principle of infrared heating can be used. In order to better understand the principle of operation of these systems, it is necessary to delve into the question of what infrared waves are.
Electrical 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 volume. If the concrete structure in this case is wrapped with a transparent film, when heated, it will transmit rays into the concrete. This will trap heat inside the material.
The advantage of infrared systems is the absence of requirements for the use of transformers. The disadvantage of experts is the impossibility of the presented heating to evenly distribute heat throughout the 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 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 inductive disturbance. This is how the concrete mixture is heated.
Having considered the electrical heating of concrete, as well as its main methods and technologies, we can conclude that it is advisable to use one or another methodin production conditions. Depending on the type of manufactured structures, production conditions, technologists choose the appropriate option. A scrupulous approach to the technology of concrete mixture hardening allows the production of high-quality products, screed, foundations, etc. Every builder should know the rules for working with cement in the winter.
