How to heat concrete: methods of heating with a wire, welding machine Antifreeze additives Thermos method. How is concrete heated with a welding machine? What do we need

The concrete screed is poured not only in summer, when the weather is warm, but also in winter, when the temperature rarely rises above zero. As is known from the school physics course, water at sub-zero air temperature is converted from a liquid state into a solid state, and therefore in winter, it will be necessary to heat the concrete with a welding machine, since water is part of this material.

Today, such methods of concrete heating are actively used, such as heating a cable specializing in this procedure with the help of PNSV, heating with the help of specialized thermomats, however, it is the welding machine that continues to be most popular, the operation of which we will consider.

Briefly about the main

The welding machine is a self-contained installation for welding work on metal parts, cutting materials through electric arc welding. Welding units have, in addition to the main elements for the production of welding work, additional elements.

Auxiliary elements of the welding unit:

• Welding current generator;
• A device used for air-plasma cutting of metals;
• Block of voltage of idling installation;
• Heating unit for concrete and other solid materials.

concrete properties

Many people believe that concrete hardens in just a few days, but this popular belief is very erroneous, since the material in question is aged for almost a month, namely 28 days. However, even during this period, according to experienced professionals, the concrete does not completely harden, since the hardening process can continue for years.

It has been proven that concrete after 28 days receives the main qualitative characteristics: strength, frost resistance, water resistance. That is why it is not recommended to subject the concrete screed of the foundation or floor to all kinds of loads during the time indicated above.

Warming up with a welding device

To warm up the concrete base at the construction site, builders often use special devices, but ordinary welding machines may occur on the way to realizing this need. The primary issue in solving the problem is additional electrodes, the role of which can be perfectly handled by pieces of reinforcement.

The fittings, in turn, are mounted evenly throughout the work area, which is covered with sawdust. Sawdust serve as an excellent addition to the thermal insulation layer of the concrete surface. In addition, sawdust will reduce moisture evaporation to a minimum. Further, the fittings are interconnected by a wire in such a way that parallel circuits come out.

The direct and return welding wires are connected to the circuits, while paying attention to the fact that they close to each other. With the help of an incandescent bulb, we learn about the presence of voltage, while the bulb must be installed between the circuits. During the heating of the reinforcement, it is necessary to diligently monitor the heating temperature of the concrete itself so that overheating does not occur. Temperature control is performed by using any thermometer.

The above method of heating the concrete surface contributes to excellent heating of the material, while not requiring the use of any additional complex equipment during the procedure. In spite of everything, it is preferable to use a welding machine for small working surfaces of concrete.

It is strongly not recommended to close the welding circuit to concrete reinforcement, since this method will not bring the expected result, and the bill for electricity consumption will be very unattractive. There are several ways to warm up.

Other methods of heating concrete:

1. Heating with electrodes;
2. Warming up by application of infrared waves.

Heating the concrete surface with electrodes

The method of heating the concrete surface by means of electrodes is based on the passage of an electric current. In turn, there are several types of electrodes that can perform excellent service during the heating of the concrete surface.

Types of electrodes:

• Strip;
• lamellar;
• Strings;
• Rod.

Concrete heating must be carried out taking into account the area of ​​​​the working surface, safety regulations and safe handling specifically with the welding machine. Before using a welding fixture to warm up a work surface, whether it is a concrete floor screed, foundation or anything else, you should consult with competent and experienced professionals.

Solidification of concrete compositions occurs with the participation of liquids. However, with the onset of cold weather, the water begins to freeze, which greatly complicates the setting of concrete. That is why most large construction sites are equipped with special electric heaters.

But what about home craftsmen? In such cases, warming up the concrete can help. This heating method is ideal for building small concrete structures at home.

For high-quality heating of a hardening concrete structure, builders will need:

• transformer welding device for 200 amperes;
• heating wire PNSV with a diameter of 1.5 mm;
• aluminum cable AVVG;
• cotton tape;
• tool for non-contact determination of the current strength.

PNSV wire.

The process of heating concrete from PNSV cable includes the following steps:

1. Cutting the wire into small pieces to warm up the loops.
   As a rule, 17 meter lengths are sufficient for the implementation of electrical heating of concrete.
2. Tying the prepared segments to the reinforcement frame.
   At this stage, it is important to ensure that the concrete layer above the loops does not exceed 4 centimeters.
3. Connection of a garter with a conductive insulated aluminum wire.
   The technological map implies the connection of loops in a serpentine way.
4. Extending connected aluminum cables and connecting them to the welding machine.
5. Insulating wires with cotton tape.
   The marking of the insulating material should be placed at the ends of the wires.

The number of heating loops directly depends on the power of the welding appliance. For a device with a maximum current of 250 amps, you can use no more than 8 wires of PNSS.

As a rule, the complete solidification of the structure heated by the PNSV wire is 40 hours.

Heating of concrete with electrodes

Heating with electrodes is one of the most popular methods for heating a cement-sand mixture in cold weather.

Schematic diagram of a transformer for heating concrete.

There are several types of electrodes used for this type of work:

1. Lamellar.
   Conductive elements are made in the form of a plate. Similar heating elements are installed on the inside of the formwork to ensure good contact with the sand-cement mixture. Heating of concrete is carried out due to the appearance of an electric field near the plate heating elements.
2. Strip.
   A similar version of heating devices is mounted on both sides of the formwork. The principle of operation of strip electrodes is identical to plate electrodes: when current is applied around the heating elements, an electric field arises that heats up the concrete structure.
3. Strings.
   String-type heating elements are often used for heating cylindrical concrete structures, such as columns. The electrodes are connected to the center of the structure, surrounded by conductive formwork. To simplify the connection of conductive elements to each other, the power wires protruding from the formwork are bent in the shape of the letter G.
4. Rod.
   In appearance, this model of heating elements resembles fittings. The installation of rod elements is carried out inside the concrete, which allows heating even the most complex structures.

There are cases when longitudinal metal bars placed in the formwork can be used instead of electrodes. This method is simple and efficient, but has a high consumption of electrical energy.

Use of welding machines

Concrete heating is a widely used method that provides good structural heating performance with the additional use of various types of heating elements.

The use of modern transformer welding is a completely safe process that does not pose a danger if safety standards are observed.

Warming up concrete in winter with a welding device is very effective. This method allows you to effectively process up to 100 cubic meters of cement-sand mixture at temperatures up to -40 degrees Celsius.

Most modern welding machines are equipped with additional modules:

• frozen soil heating unit;
• block for drying electrodes;
• voltage reduction module;
• electric current generator.

Before heating concrete with a welding device, you should check for additional options that greatly simplify the process of heating a concrete structure in winter.

Scheme of heating concrete structures.

Heating the cement-sand mixture using a transformer-type welding device consists of the following steps:

1. Uniform arrangement of reinforcement segments along the poured area.
2. Connection of electrodes in two parallel circuits.
3. Installation of a control bulb of an incandescence.
4. Direct and feedback wiring.

In the event that water evaporates too quickly from the surface of the cement-sand structure, it makes sense to cover the site with a small amount of sawdust.

Connecting the heating system to the cement-sand structure is carried out in several stages:

• connection of conductive aluminum cables with a welding device;
• checking each loop with current clamps;
• increasing the power of the device up to 50% after an hour of operation and up to 100% two hours after turning on the heating;
• current control within 25 amperes.

Features of the methods

Heating concrete with a welding machine has its own characteristics:

• the heating time of the concrete structure is seriously dependent on the ambient temperature;
• the poured cement-sand mixture should be covered with a thin layer of sawdust in order to avoid excessive evaporation of water from the thickness of the cement-sand mixture;
• excessive overheating of the structure should be avoided.

The technology of heating concrete with electrodes includes two types:

1. Through.
   This type of heating is used for concrete structures that have a complex shape or a large thickness. As a rule, with this heating method, all electrodes are installed at a distance of at least 30 millimeters from the formwork.
2. Peripheral.
   The electrodes are installed on the surface of the structure. The method allows you to remove the heating elements after solidification of the site filled with concrete.

When heating with electrodes, the following factors should be considered:

• evaporation of moisture, due to which it is necessary to constantly regulate the current supplied to the electrodes;
• the heated surface must be completely covered with heat-insulating material in order to increase the efficiency of the electrodes and reduce heat losses;
• with rod heating, all electrodes should be placed at the same distance, in order to avoid overheating of individual sections;
• inefficiency of electrode heating for small structures;
• the need to measure the current temperature of the cement-sand mixture at certain intervals;
• connection of conductive elements for heating concrete with electrodes should be developed individually for each case.

Warming up concrete with a welding machine is in many ways similar to the method of electrodes.

Heating of concrete with a welding machine.

When using a welding device, experts recommend:

• isolate the surface of the heated structure to avoid serious heat losses;
• try to limit the loss of water when using a welding device to warm up a reinforced concrete structure;
• connect to the welding machine only electrodes suitable for current work;
• install an incandescent test lamp to check the voltage;
• constantly monitor the temperature of the structure and prevent overheating;
• do not close the welding circuit to intra-concrete reinforcement, since this method is incredibly energy-consuming.

Heating concrete structures with special cables has serious advantages over heating using a transformer welding device:

• powered by a household electrical network 220 volts;
• significant reduction in the setting time of concrete;
• high economy;
• relatively simple design;
• the possibility of automatic temperature maintenance in a monolithic structure.

Conclusion

Warming up concrete with a welding machine is one of the most popular and effective methods of increasing the rate of solidification of structures in winter. Drying a site concreted in winter can be done in three ways: using a PNSV cable, using electrodes, or using a transformer welding unit.

The heated area should be isolated from the environment with sawdust or other material to avoid loss of water and heat. The best conditions for warming up concrete can be achieved by selecting the optimal electrodes for a particular type of pouring work.

In general terms, the scheme for heating concrete with a welding machine remains exactly the same as with a step-down transformer - the difference is that in this case the power of the unit will be less. This method is acceptable for small objects and at home is almost ideal, given that you do not have to look for additional power. For example, we use a 250A machine when pouring a small 4 × 5m slab, and as additional material we will show you a video in this article on this topic.

Welding transformer BRIMA TIG 250

Concrete heating

Note. According to SNiP 13.03.01-87 on load-bearing structures, if the average daily temperature outside drops below 5⁰ C, the concrete should be electrically heated. This is used to prevent the formation of an ice film around the reinforcement in fresh mortar.

At home, it is possible to heat concrete with a welding transformer.

Using a heating loop

Schematic diagram - how to heat concrete with a welding machine

Note. In addition to loops, heating of fresh concrete structures can be carried out by the electrode method, in heating formwork, liquid installations, by induction and infrared radiation.

If the solidification of the solution occurs with malfunctions in the temperature regime (the mixture freezes), then the strength drops sharply and the surface turns out to crumble - this is immediately evident when cutting reinforced concrete with diamond wheels or diamond drilling holes in concrete.

Heating of reinforced concrete structures with heating loops according to the principle of supplying the maximum current to the cable is needed mainly for platforms (slab foundations) of floors and less often for walls, when the room itself is not heated. Such circuits, as a rule, are powered through step-down transformers, which have voltage regulation - this allows you to maintain the required thermal power, depending on changes in air temperature outside. This method is more economical than the electrode one (see also the article “Aerated concrete wall chaser: structural features and application”).

What do we need

PNSV (Heating Wire Steel Type Vinyl Sheath)

• So, as we have already said, we need a transformer, which means that at home for these purposes we will use the power of the welding machine - in our case up to 250A, although more is possible, but we will specifically consider the minimum in order to learn how to get the most out of it. In addition, as the instructions require, we will need a PNSV wire - in this situation, we will cut pieces of 18m each.
• We also need an aluminum single wire with a cross section of 2.5-4 mm2 (APV is suitable), cotton insulating tape and pliers, current clamps. And, of course, such work can be done only in those areas where there is a 220V power source - it can be a power line, but also (this happens at the beginning of construction) you can use a carburetor or diesel (more economical) generator.

PNSV resistance depending on cable thickness

Getting Started

This is what the setup will look like

We have a 250A welding machine, now we need a PNSV, the amount of which we will calculate based on the formula R = U / I, and if we know that U = 220V, I = 250A, then R = U / I = 220/250 \u003d 0.88 ohm.

What follows from this - if we have a maximum of 250A at the output, then in order not to overload the device, we will make 8 loops of 25A each with our own hands - this will be quite enough. To do this, take a piece of PNSV 18 m long and 3.0 mm in diameter (0.05 cm / meter) - this will be enough for a 4 × 5 m slab.

You clean the ends of the PNSV by 40-50 mm and connect an aluminum wire to each of them (copper can, of course, be used, but the price of aluminum is much lower) - make sure that the twist is tight - the correct operation of our design will depend on this. The length of the aluminum wire will depend on how far you can install the welding machine - it will be more advisable to bring it as close as possible. If these ends turned out to be short - do not be discouraged - they can be increased at any time to the required length, just carefully isolate the twist (see also the article “Pigments for concrete: main characteristics, scope and methods of self-preparation”).

Laying loops on a metal reinforcing cage. A photo

Now we need to lay the PNSV, distributing it evenly over the entire area so that the twists with aluminum are inside the poured slab, but in no case touch the metal frame! Best of all, if you manage to pass the PNSV between two crates - inside the frame - so the cable will be inside just in the middle of the plate, like butter in a sandwich between two pieces of bread of the same thickness.

When pouring the mortar, you can easily displace the wire, so it should be tied to the reinforcement with pieces of insulated aluminum, but be careful not to damage the insulation on the PNSV - this will make heating the concrete with a welding machine efficient and safe.

You can also cut the PNSV into pieces in one loop and pull out the aluminum ends from each so it will be much easier to thread the wire between the reinforcement bars in the frame, only here you need to be careful not to confuse the ends. It is best to mark them with an insulation marker (put the + and - signs).

To connect the welding machine, you can use cables - ground and the one that goes to the holder, or screw the aluminum wire directly to the terminals. Try to connect the circuit as soon as possible after pouring and turn the voltage regulator to a minimum, turn on the breaker and check the voltage.

At first, a jump to 240-250A is possible, but as the mass warms up and solidifies, it will fall, and you can gradually increase it as needed.

Conclusion

Since you need to heat the concrete with a welding machine gradually, check the voltage every 2 hours, gradually increasing it (see also the article “Concrete footing: what it is and how it is done correctly”).

In about 8 hours you will reach the maximum and within 3 days the stove should dry (but this is not the degree of exploitation).

Construction work on the construction of objects is carried out all year round. Often, builders produce concreting to form solid structures in winter. It is important to ensure the strength of the monolith and prevent water crystallization. When heating concrete, it is important to maintain the required temperature of the mixture and create favorable conditions for cement hydration. Let us dwell on the heating technology based on the use of infrared rays and electricity. Consider the advantages and disadvantages of each method.

How is concrete heated in winter?

Faced with the need to perform concreting in difficult climatic conditions, builders take measures to maintain the temperature of the mixture that meets the requirements of the technology. Concrete containing water hardens under standard conditions within four weeks. How to do it right? After all, moisture at a negative temperature crystallizes, increasing in volume, and can cause cracking.

To ensure a favorable temperature, the following methods are used:

• electric heating, for which the PNSV wire is used. The cable is laid inside the structure and concreted;
• electric heating using a transformer for welding. The wire for heating the concrete is energized through steel rods;
• formwork heating of the concrete mass. Panel formwork elements contain electric heaters;

Pouring concrete in winter at temperatures below zero requires the provision of certain temperature conditions under which the mortar can normally harden

• heating with infrared rays. Radiation in the infrared spectrum directed at the concrete mass increases its temperature;
• preliminary increase in the temperature of the solution. It is heated before concreting, maintaining the required temperature during pouring and solidification;
• construction of special tent-type structures. They are covered with polyethylene or tarpaulin and heated with a heat gun.

To select the optimal heating method, you should make calculations and analyze all the nuances. It is necessary to take into account the possible level of costs and only then give preference to a particular method. Consider the specifics of each method.

We connect the wire for heating the concrete PNSV

Using a heating cable for concrete, you can achieve a positive temperature of the mixture in the winter months. The workflow is simple. It is necessary to lay the cable marked PNSV in the structure to be concreted and supply voltage to it from the source of electrical energy.

This heating method is often preferred due to its serious advantages:

• increased efficiency. A properly laid heating cable, which is chosen by calculation, can maintain the temperature necessary to set a significant amount of concrete;

As a rule, the power supply of the PNSV cables is carried out through substations with several stages of low voltage.

• economy. Electricity consumption is acceptable. This allows you to invest in the estimate of construction activities and prevent cost overruns;
• maintaining the concrete structure. When connecting the wire to a source of electrical energy, cracking of the concrete mass and the formation of air pores in it are excluded;
• universality. Electric heating technology can be applied to solid building structures that are made of conventional or reinforced concrete.

Along with undeniable advantages, the technology also has weaknesses:

• needs to perform preparatory work, during which the wire is laid. A flexible cable for concrete heating requires careful placement in a reinforced structure and is laid according to the drawing;
• requires the use of a step-down transformer. The technical characteristics of the equipment for reducing the supply voltage should allow smooth adjustment of the heating of the concrete mixture in the required range.

A wire of a special design is used, which consists of the following elements:

• conductive core;
• protective insulation.

Cable selection is carried out after performing calculations, taking into account the following parameters:

• voltage at the output of the transformer;
• section of the conductive part;
• the total length of the laid cable.

The temperature of the structure should not fall below the technologically determined minimum

When performing work, observe the following recommendations:

• lay the wire on a cleaned surface, avoiding damage;
• form cable loops evenly, avoiding kinks.

When buying a PNSV wire, check that the products comply with the certificate. The reputation of the cable manufacturer plays an important role. The technology of using a wire for heating a concrete mixture has much in common with the method of forming a heated floor.

How is concrete heated by a welding machine

The technical characteristics of the welding transformer make it possible to use it for heating the concrete mix. The device regulates the current that is supplied to the electrodes.

The equipment is used in the manufacture of the following structural elements of buildings in winter:

• supporting columns;
• capital walls;
• various fences.

The supply voltage is applied to the following conductive elements:

• reinforcing bars;
• wire with a cross section of 0.6–0.8 cm;
• steel plates.

Perhaps the most common heating method is to pass an electric current through the concrete using electrodes.

Work performance technology:

1. Stick the electrodes into the liquid mixture.
2. Apply voltage and adjust current.

When heating vertical structures of a small area, one conductive rod can be used. In this case, the voltage from the transformer is applied to the reinforcing cage and the steel bar inserted into the solution.

For effective warm-up, observe the following guidelines:

• immerse the electrodes at intervals of 0.8–1 m;
• smoothly regulate the current, providing the required temperature.

Technology advantages:

• ease of implementation;
• possibility of application on various objects;
• fast installation and connection.

The disadvantages include:

• increased consumption of electrical energy;
• costs associated with the impossibility of secondary use of electrodes.

When performing work, it is important to comply with safety requirements.

With the help of such electrodes, it is possible to heat structures of any shape, even the most complex ones.

Electric heating of concrete using a special formwork

To ensure a positive temperature of the hardening concrete mixture, builders also use prefabricated formwork of a panel structure. Its peculiarity is the equipping of unified shields with quick-detachable electric heaters.

Advantages of application:

• accelerated dismantling of electric heaters. The design provides easy access for replacement and service;
• versatility. The formwork is assembled from individual elements with standard dimensions and can be used repeatedly;
• efficiency. Formwork allows you to heat up the increased volume of concrete at temperatures up to -20 degrees;
• increased efficiency of use. Increased profitability and low cost are characteristic of this method;
• quick assembly of the structure. The accelerated assembly of the formwork elements reduces the installation time.

Along with the advantages, there are weaknesses:

• increased cost of formwork;
• the impossibility of using with a curvilinear shape of the object.

Shields with heaters are used in the construction of large objects.

The installation of the heating system is carried out immediately before pouring the solution into the formwork

Infrared concrete heating

Infra-red beams allow to carry out the directed warming up of the concrete mass to the set temperature. The strength of the radiation and the depth of heating vary depending on the distance between the infrared heater and the surface of the concrete mass.

Heating method using thermomats:

1. Additives are added to the concrete mix for accelerated hardening.
2. Special infrared mats are laid on the surface of the array.
3. The power cable is connected and electrical voltage is applied.

The technology allows heating concrete structures in a horizontal position.

Advantages of this method:

• small power consumption;
• ease of implementation;
• heating intensity control;
• the possibility of heating concrete through the formwork panels.

Weak sides:

• accelerated evaporation of moisture from the concrete mixture, which needs additional protection from drying out;
• increased costs associated with the purchase of thermomats to heat the increased space.

Despite the existing shortcomings, the infrared method is in demand in the construction industry.

This method is especially often used when performing screeding in winter.

Using pre-warmed solution

The method of heating the concrete mix before concreting is the simplest. The technological algorithm provides for the following operations:

• heating the concrete solution at the stage of mixing the components;
• pouring the heated mixture directly at the work site.

For the practical implementation of this technology, special calculations are made to determine the operating temperature.

This takes into account:

• the amount of poured concrete;
• time for transportation and filling;
• ambient temperature.

In case of deviations in the calculations, additional heating is carried out by any of the known methods.

Conclusion

Making a decision on choosing the optimal heating method requires a professional approach. It is important to study the technological features of each method and determine the economic feasibility of its application. The recommendations of professionals will help to understand the advantages and disadvantages of the heating technologies used.

When electrical heating of concrete at temperatures below + 5 ° C, special oil or air ones are used to lower the voltage of the 200 or 380 V network. But in the case of small volumes, when pouring the foundation in a summer cottage with your own hands, for example, it is sometimes more rational to use a welding machine (two-phase), which is often already available, rather than buying or renting the same one. A method for the so-called "home conditions".

Such a solution takes place, although it is associated with certain difficulties. Let's try to understand them for the types of heating elements PNSV wires and electrodes.

Heating of concrete with a welding machine and PNSV wire

The scheme of work here is exactly the same as when using oil transformers. All the subtlety in the calculations. So, to heat concrete with a welding transformer, together with a wire, we need a 150-250 A welder, an aluminum cable of cold ends, an ammeter (pliers) and tape, on a fabric basis.

For example, I will give a calculation for heating a plate of 3.8 m 3 with a size of 4x5x0.19 m at an air temperature of about -12 ° C and a 250 A welding machine. So, we cut the PNSV wire into segments 18 meters long. The length was determined empirically and for your case, it may be different. Each of these segments is capable of withstanding current up to 25 A. Accordingly, for a total of 250 amperes, 10 segments can be used. But in order not to go to extremes and leave a small margin, we will focus on 8 wires.

To each piece of PNSV, on both sides, we twist an aluminum wire of such a length that the twist itself is in the concrete, and the cold ends reach the transformer. We isolate the twist itself with electrical tape.

We lay the pieces of wire, tying them to the fittings with plastic fasteners or insulated wire to avoid a short circuit. For a slab, the wire can be fixed just below the top reinforcing layer. The outputs of each wire must be marked, for example (+) and (-). Or you can separate the ends on different sides of the structure. It is also very convenient to connect the phases (pluses separately, minuses separately) to each other on an insulated surface (textolite) with terminals.

After pouring concrete, we immediately connect our terminals to the direct and reverse outputs of the welding machine, set to the minimum current. We measure the current on the welding wires (should be up to 240 A) and on each segment (should be up to 20 A). As the current heats up, the current will drop, and it will need to be increased on the device.

As a result, a plate of these dimensions acquired the required strength in 40 hours. Also, after pouring concrete, it is recommended to cover it with a protective film to prevent drying out. At extremely low temperatures, a layer of insulation can be placed on top of the film.

A video on laying the PNSV wire can be viewed below:

Warming up concrete with a welding machine and electrodes

With this method, the heating elements are implanted in concrete. And the current flows directly through the solution. From this follows the main disadvantage of heating with a welding machine along with electrodes: the danger of electric shock to nearby people. Voltage up to 36 V is considered safe. If it is higher, then care must be taken to prevent people and animals from entering the heated object. It is also believed that such reinforcing electrodes quickly wear out the welding transformer.

The electrodes (reinforcement bars) are placed in the structure, connected in series in such a way that two segments isolated from each other are obtained. I connect a direct wire to one of them, and a return wire to the other. To control the current between the two electrodes, an incandescent lamp is connected (optional). It is very important to measure the temperature of the concrete to prevent its dehydration and cracking. Do not forget to cover the filled structure with foil and insulation to prevent heat and moisture loss.