Features of pouring a foundation in winter: methods of heating concrete. Heating concrete with a welding machine is a proven method

Construction work on the construction of facilities is carried out year-round. Often builders perform concreting to form solid structures in winter time. It is important to ensure the strength of the monolith and prevent water crystallization. When heating the concrete, it is important to maintain the required temperature of the mixture and create favorable conditions for cement hydration. Let's focus on heating technology based on the use of infrared rays and electricity. Let's look at the advantages and disadvantages of each method.

What methods are used to heat concrete in winter?

Faced with the need to perform concreting in complex climatic conditions, builders take measures to maintain the temperature of the mixture that meets the technology requirements. Concrete containing water hardens under standard conditions within four weeks. What is the right thing to do? After all, moisture at negative temperatures crystallizes, increasing in volume, and can cause the formation of cracks.

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

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

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

For selection the best way heating, calculations should be made and all the nuances analyzed. It is necessary to take into account the possible level of costs and only then give preference to a specific method. Let's consider the specifics of each method.

We connect the wire for heating the concrete PNSV

By using a heating cable for concrete, you can achieve a positive temperature of the mixture in the winter months. The method of performing the work is simple. A cable marked PNSV should be placed in the structure to be concreted and supplied with power supply voltage from the source electrical energy.

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

• increased efficiency. A correctly laid heating cable, which is selected by calculation, can maintain the temperature necessary to harden a significant volume of concrete;

• efficiency. Electrical energy consumption is acceptable. This allows you to invest in the estimate of construction activities and prevent overspending;
• preservation of 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;
• versatility. Technology electric heating can be used for whole building structures, which are made from ordinary or reinforced concrete.

Along with undeniable advantages, the technology also has weaknesses:

• requires preparatory work during which the wire is laid. The flexible cable for heating concrete requires care when placed in a reinforced structure and is laid according to the drawing;
• requires the use of a step-down transformer. Specifications equipment to reduce the supply voltage should allow for smooth adjustment of heating concrete mixture in the required range.

A specially designed wire is used, which consists of the following elements:

• conductor;
• protective insulation.

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

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

When performing work, observe the following recommendations:

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

When purchasing PNSV wire, check the product’s compliance with the certificate. The reputation of the cable manufacturer plays an important role. The technology of using wire to heat a concrete mixture has much in common with the method of forming a heated floor.

How concrete is heated using a welding machine

The technical characteristics of the welding transformer allow it to be used for heating the concrete mixture. The device regulates the current supplied to the electrodes.

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

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

The supply voltage is supplied to the following conductive elements:

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

Work technology:

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

When warming up vertical structures For small areas, one conductive rod can be used. In this case, the voltage from the transformer is supplied to reinforcement cage and a steel rod inserted into the solution.

To ensure effective warm-up, follow these guidelines:

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

Advantages of the technology:

• ease of implementation;
• Possibility of application at various sites;
• quick installation and connection.

The disadvantages include:

• increased electrical energy consumption;
• costs associated with the inability to reuse electrodes.

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

Electric heating of concrete using special formwork

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

Advantages of use:

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

Along with the advantages, there are weaknesses:

• increased price of formwork;
• impossibility of use if the object has a curved shape.

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

Infrared heating of concrete

Infrared rays allow for targeted heating of a concrete mass to a predetermined temperature. The radiation strength and heating depth vary depending on the distance between infrared heater and the surface of the concrete mass.

Method of heating using thermomats:

1. Additives are added to the concrete mixture to accelerate 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 of concrete structures located in a horizontal position.

Advantages of this method:

• low power consumption;
• ease of implementation;
• heating intensity control;
• possibility of heating concrete through 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 for heating an increased space.

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

Using a preheated solution

The method of heating the concrete mixture before performing concreting work 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 aimed at determining the operating temperature.

This takes into account:

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

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

Conclusion

Deciding on the optimal heating method requires professional approach. It's important to study technological features each method and determine the economic feasibility of its use. Recommendations from professionals will help you understand the advantages and disadvantages of the heating technologies used.

When electrically heating concrete in temperature conditions below +5°C use special oil or air to reduce the voltage of the network 200 or 380 V. But in the case of small volumes when pouring the foundation on summer cottage with your own hands, for example, sometimes it is 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 does exist, although it is associated with certain difficulties. Let's try to understand them for the types of heating elements PNSV wires and electrodes.

Warming up concrete with a welding machine and PNSV wire

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

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

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

We lay the pieces of wire, tying them to the fittings plastic fasteners or insulated wire to avoid 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 to different parties designs. 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 the concrete, we immediately connect our terminals to the forward 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 it heats up, the current will drop and will need to be increased on the device.

As a result, a slab of these dimensions acquired the required strength in 40 hours. Also, after pouring concrete, it is recommended to cover it protective film to prevent drying out. When especially low temperatures ah, you can put a layer of insulation on top of the film.

A video on laying PNSV wire can be viewed below:

Warming up concrete with a welding machine and electrodes

With this method, the heating elements are implanted into the concrete. And the current flows directly through the solution. It follows from this main drawback heating the welding machine together with the electrodes: danger of injury electric shock 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. There is also an opinion that such reinforcing electrodes quickly wear out the welding transformer.

Electrodes (reinforcement rods) are laid in the structure, connected in series so that two segments isolated from each other are obtained. I connect the direct wire to one of them, and the reverse wire to the other. To control the current, an incandescent lamp (optional) is connected between the two electrodes. It is very important to measure the temperature of concrete to prevent dehydration and cracking. Do not forget to cover the poured structure with film and insulation to avoid loss of heat and moisture.

• 1 Why heat the solution
• 2 Basic heating methods
• 3 Heating calculation
• 4 Heating the solution with wire
  • 4.1 Technology for heating the solution with wire
• 5 Heating with cable
  • 5.1 Technology for heating the solution with cable
• 6 Heating the solution using a welding machine
• 7 Heating concrete in winter
  • 7.1 Antifreeze additives
  • 7.2 Thermos method
• 8 In conclusion

Concrete is a popular, inexpensive and widely used material, without which processes such as construction and repair of buildings and structures become impossible. In order for a solution of this kind to make it possible to create high-quality, strong, and most importantly, durable structures, it is important to know not only the recipe and technology for its preparation, but also to have information about how to heat concrete and at what temperature heating of concrete is mandatory and necessary.

Heating of concrete for construction work V winter period

Why heat the solution?

Thermal heating mats

Negative temperature has Negative influence on the process of hydration or hardening of the concrete mixture. This type of mortar consists of cement, sand, water and crushed stone.

In this mixture, it is water that catalyzes the solidification process of the solution. But at negative temperatures, moisture freezes, which jeopardizes not only the process of strengthening the solution, but also further construction work.

The main task of developing a connection diagram is how to warm up concrete during concreting in winter to ensure optimal temperature conditions for the hardening process.

Note! If the moisture in the solution still manages to crystallize, the solution will no longer save anything. You should not wait for a thaw, mistakenly assuming that the solution will acquire the necessary characteristics when the water in it melts.

• The optimal temperature regime for setting concrete without additives and heating is +10…+20 degrees;
• Concreting at temperatures from -20 to +10 degrees will make you think about how to properly heat concrete;
• If the temperature is below -20 degrees, all work with the solution is prohibited.

Basic heating methods

Laying the heating cable

There are three main methods for heating a solution at low temperatures:

Heating calculation

Now that you know at what temperature the concrete needs to be heated, you need to figure out how to calculate the heating.

Calculations of this kind for each method must take into account following parameters:

• View concrete structure;
• total area products requiring heating;
• Volume of solution;
• Required electrical power.

Heating the solution with wire

The photo shows an example of wire laying

For implementation this method For heating, you will need a PNSV wire, the price of which is low.

This wire consists of only two structural elements:

This method is based on the transfer of heat to the concrete mass from a heated wire. The heating of the wires themselves is realized using transformer substations with a control system. This system allows you to adjust the heating temperature while working with the solution depending on the ambient temperature.

Wire solution heating technology

The instructions stipulating how to connect the heating of concrete provide for the execution next stages works:

Advice. To preserve the thermal field, solder joints should be wrapped with metal foil.

Heating wire location

To implement this method, it is necessary to compile technological map individual for each design.

Heating with cable

The advantage of heating by this method is that there is no need to use additional equipment. In addition, the presented method does not require large amounts of electricity.

Cable solution heating technology

Cable layout

The process answering the question of how to heat concrete at home with a cable consists of the following steps:

• The cable is located at the base of the concrete structure just before the mortar is poured;
• The cable is fixed with fasteners;
• During the installation process, the cable should not be damaged, and its individual sections should not touch;
• The cable is connected through an electrical low-voltage cabinet.

Cable heating diagram

Note! When implementing this method, it is necessary to develop a cable layout and conduct temperature tests.

Heating the solution using a welding machine

Implementation of the method using welding equipment

Knowing at what temperature concrete is heated, you can use a welding machine for heating.

To implement this method, you will need the following equipment and materials:

• Several pieces of reinforcement;
• Incandescent lamps;
• Thermometer.

In this case, the fittings are located parallel to the circuit consisting of forward and return wires. Between them there are incandescent lamps, with the help of which voltage measurements will be made. To measure temperature, a very ordinary thermometer is used.

The hardening process of the solution is quite long and can take about a month. During the process of heating and hardening of the solution, the structure should under no circumstances be flooded with water or exposed to cold.

This method is applicable when it is necessary to heat small concrete poured structures and in acceptable weather conditions.

Heating concrete in winter

In winter, the most pressing question becomes how and at what temperature the concrete is heated. This is due to the fact that at this time the phenomenon of water crystallization in solution can most often be observed, which excludes its participation in chemical reaction associated with mass hardening.

That is why heating concrete in winter is very important procedure, which can be implemented using the following methods:

• Introduction of antifreeze additives into the solution;
• Heating using the “Thermos” method.

Antifreeze additives

Antifreeze based additives

Antifreeze additives can withstand extreme cold even at temperatures of -30 degrees. The composition of such additives may vary, but the main component is antifreeze - a substance that prevents water from freezing.

Any builder can add antifreeze agents to the solution with his own hands.

For reinforced concrete products or reinforced floors, it is better to use additives containing nitrite or sodium format. It is these additives that will ensure the design also preserves the physical and chemical properties and they will become anti-corrosion protection for reinforced concrete at low temperatures.

Advice. If after hardening such monolithic structures You will need to drill a hole or trim the edges, you can use methods such as diamond drilling holes in concrete or cutting reinforced concrete with diamond wheels.

Thermos method

The essence of this method lies in laying concrete in a warm heated formwork, which will maintain a temperature of 20-25 degrees throughout the hardening period. Due to such heating, the structure will maintain its strength.

Advice. To speed up the hardening process, you can pour a heated solution into the heated formwork.

Finally

Pouring concrete in winter

Heating the concrete solution in winter is a necessary component of construction work. There can be quite a lot of methods for heating the concrete mass, and the choice of one or another scheme should be made individually for each structure in accordance with its main parameters.

And the video in this article will reveal to you even more features and nuances of the process of heating the solution to create monolithic concrete products.

Heating concrete with a welding transformer

This heating method is suitable for small volumes of pouring and if you have a welding transformer, it is ideal for home use. Warming up with a welding machine is the same as heating with a special step-down transformer. The principle remains the same, only the power is noticeably reduced.

For example, let's take a DC welding machine with a power of 250 amps.

I will not go into calculations for winter concreting, but will describe the heating process itself, based on personal experience when pouring concrete slab 4 by 5 meters. The article contains explanatory photographs; I don’t have my own, but I tried to select the most suitable ones so that they would clearly explain the principle of concrete heating.

We need: a welding machine 150-250 amperes, heating wire PNSV, single aluminum wire 2.5-4 sq., current clamps, HB electrical tape.

1. The heating wire must be cut into pieces of 18 meters, I calculated the length empirically. The number of such segments must be calculated based on the power of the existing welding machine. Let's take a 250 ampere device as a basis. At maximum load, our loop will withstand 25 amperes and this is the ceiling. So you need to build on this figure. Let's not force the welding transformer, 8 loops will be just right. To warm up a concrete slab 4 by 5 meters and 19 cm thick, this amount will be normal.

2. It is necessary to attach 2 aluminum wires to the cut pieces of PNSV wire; we connect them using a twist of 3-5 cm. The length of the aluminum end is selected locally. See for yourself, these aluminum ends will need to be attached to the welding cable. There is no need to worry too much, since it is always possible to increase the required length. We carefully isolate the twist.

3. Next we need to lay out the heating loops. We arrange it wisely so that the heating cable is located just above the middle of the slab, but below the top layer of reinforcement. We tie the loops with an insulating cable so that when they warm up they do not short out to the ground. The twist of PNSV and aluminum wire must be in concrete, otherwise it will burn. We remove the aluminum ends from the pouring area. When laying loops, mark the aluminum outlets from the loops so as not to get confused when connecting. Most best option this is to make an exit on one side of the slab + and on the other side of the exit plate to - .

4. After pouring, we need to assemble the entire heating circuit as quickly as possible. There are two cables coming out of the welder; to put it simply, this is our power supply for the warm-up loops.

We connect all the positive outputs of the loops to the positive welding cable and, accordingly, we throw the other ends of the loops to the minus. Choose the connection method yourself, I personally made a so-called “guitar”; I attached two textolite plates to the welding cables, on which bolts were welded to clamp the aluminum ends of the heating loops. In general, see for yourself what is convenient for you, in the end we get eight ends on each welding cable.

5. We turn on the welding machine and begin to heat the concrete. Before turning on, set the current regulator to minimum. Having turned it on, we measure the amperage on the welding cables with a current clamp. If it is approximately 240 amps, do not be alarmed because as the concrete heats up, the amps will begin to drop. We check the performance of each loop with pliers; to begin with, there should be 14-18 amperes on each loop. After about two hours we measure again, if the amperes have dropped, we add current to the welding. Add gradually minimum - middle - maximum, if you reach the maximum in 8 hours, this is already a good result. Be sure to check the load on the loops, remembering that they will not withstand more than 25 amperes. Depending on the temperature, the heating time of the concrete may increase or decrease. Based on my experience, I will say that at -12C I heated and dried the above-described concrete slab for 38 hours.

More articles on heating concrete

In order for the electric heating of concrete to be as effective as possible, cover the slab with insulation or sawdust. Electrical heating of concrete with a welding transformer must be carried out by appropriate personnel, as there may be a threat to human life. Please do not take this article as a guide for winter concreting., I just described what I did myself, not being able to do normal heating of concrete.

Construction activities related to concreting monolithic structures are carried out throughout the year. In winter, builders have to solve a number of problems to ensure the strength of concrete and prevent freezing of the water entering the solution. In order to maintain a positive temperature of the solution and ensure optimal conditions During setting, the concrete is heated. Let us consider in detail heating methods using electrical energy and infrared rays.

How concrete is heated in winter

With the onset of winter cold, builders have to face serious problems associated with the characteristics of the concrete solution. It contains gravel, Portland cement and sand with added water. Solution at normal conditions acquires performance characteristics for a month. However, water increases when it freezes, which can destroy the monolith.

In the process of carrying out construction and repair work in low temperature conditions, concrete heating should be used to accelerate the hardening of the concrete solution

The following techniques are used to maintain temperature:

• electric heating with a special cable. To increase the temperature, a PNSV wire is used, which is laid in advance along the structure to be poured;
• electric heating using a welding transformer. A cable is connected to the power source to heat the concrete using electrodes inserted into the array;
• heating using special formwork. Quick-detachable electric heating elements are installed in the standard elements of the panel formwork structure;
• infrared heating It is based on the use of directional infrared radiation, due to which the temperature of the concrete increases;
• preheating the mixture. The solution is heated before pouring in such a way that during hardening it maintains a positive temperature;
• arrangement of special tents. Under construction frame construction with a tarpaulin or polyethylene covering, inside which a heat gun operates.

The decision to use a specific heating method is made on the basis of preliminary calculations. Having comprehensively analyzed all the factors and assessed the economic side of the issue, you can decide and accept correct solution. Let's look at the features of each heating method.

Electrical heating of concrete using PNSV cable

Using a wire for heating PNSV concrete, it is easy to ensure the optimal temperature for the solution to harden. This method is quite simple and involves laying a special PNSV wire, which heats up when low voltage is supplied from the step-down transformer.

This method works quite well simple principle. Before pouring, a wire is laid to warm up the concrete.

The technology of electric heating with a special wire has a number of advantages:

• provides high efficiency. A correctly selected and professionally laid heating wire can heat a concrete mass of increased volume;
• guarantees economy. Insignificant consumption of electrical energy allows you to avoid significant financial expenses and significantly reduces the estimated cost of work;
• preserves the structure of the monolith. When supply voltage is applied, cracks do not form in the cable laying areas, as well as air bubbles in the concrete mass heated by the wire;
• is universal. Electric heating can be used for monolithic structures made of ordinary concrete, as well as reinforced with steel reinforcement.

Despite serious advantages, the method has certain disadvantages:

• requires preparatory activities, during which a heating cable for concrete is laid. It is important to be careful when laying wire loops and adhere to the working diagram;
• requires the use of a special transformer. The power of the reducing equipment must ensure the ability to increase the temperature of the concrete mass to the required level.

A special cable is used, consisting of a conductive core and insulating coating. The wire is selected based on calculations that take into account a number of factors:

• transformer supply voltage;
• diameter of the conductor;
• wire length.

It should be taken into account that the laying of warm-up loops is usually carried out in unpleasant weather

When laying the cable, it is important to comply with the following requirements:

• ensure the surface is clean and eliminate the possibility of damage to the cable;
• Avoid bending the cores and lay the wire evenly over the entire area.

It is important to ensure the required heating intensity:

• during the first two hours of heating, the speed should not increase by more than 10 degrees per hour;
• the operating temperature must be stable throughout the entire warm-up period;
• the cooling rate of the heated mass should not exceed 5 degrees Celsius per hour.

Purchase wire for heating concrete only from trusted manufacturers, and check for a certificate. The method of using a cable to heat a concrete solution is similar to the process of installing a heated floor.

Warming up concrete with a welding machine

You can heat the solution using welding equipment and wire electrodes. The method has proven itself positively when pouring vertical structures in winter:

• column;
• walls;
• fencing.

Electrical heating of concrete can be carried out using electrodes that replace PNSV wires

The following can be used as conductive elements:

• steel reinforcement;
• wire with a diameter of 8–10 mm;
• metal plates.

The practical implementation of this method is simple:

• after concreting vertical structures, it is necessary to insert electrodes into the concrete mass;
• then you should use a cable to supply the supply voltage from the step-down transformer.

When heating vertical columns of small cross-section, it is sufficient to use one electrode. In this case, the concrete mixture will be heated by applying voltage to the reinforcement frame and a steel rod installed in the solution.

When performing work, it is important to comply with the following requirements:

• select the distance between the rods, which should be at least 60 cm depending on climatic conditions;
• regulate the supply voltage to achieve the required heating temperature of the concrete mass.