Concrete screed is poured not only in summer, when it is warm weather, but also in winter, when the temperature rarely rises above zero. As you know from a school physics course, water at sub-zero air temperatures transforms from a liquid state into a solid state, and therefore In winter you will need to warm up the concrete welding machine, since the composition of this material water comes in.
Today, methods of heating concrete are actively used, such as heating using a PNSV cable specializing in this procedure, heating using specialized thermomats, but the welding machine continues to be the most popular, the action of which we will consider.
The welding machine is standalone installation for carrying out welding work on metal parts, cutting materials using electric arc welding. Welding units have, in addition to the main elements for welding work, additional elements.
Many people believe that concrete hardens in just a few days, but this widespread 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, concrete does not harden completely, since the hardening process can continue for years.
It has been proven that concrete after 28 days receives the main quality characteristics: strength, frost resistance, water resistance. That is why it is not recommended to subject the concrete screed of the foundation or floor to any loads during the above-mentioned time.
To warm up concrete base on construction site Builders often use special devices, but ordinary welding machines can get in the way of realizing this need. The primary issue in solving the problem is additional electrodes, the role of which can be perfectly fulfilled by segments of reinforcement.
The reinforcement, in turn, is installed evenly throughout the entire work area, which is covered with sawdust. Sawdust serves as an excellent addition to the thermal insulation layer concrete surface. In addition, sawdust will reduce moisture evaporation to a minimum. Next, the fittings are connected to each other by wire in such a way that parallel circuits emerge.
The forward and return welding wires are connected to the circuits, but you should pay attention to the fact that they are connected to each other. Using an incandescent light bulb, we find out about the presence of voltage, and the light bulb must be installed between the circuits. When heating the reinforcement, it is necessary to diligently monitor the heating temperature of the concrete itself so that overheating does not occur. Temperature control is done by using any thermometer.
The above method of heating a concrete surface promotes excellent heating of the material, without requiring the use of any additional complex equipment during the procedure. Despite everything, it is preferable to use a welding machine for small concrete working surfaces.
Close the welding circuit to concrete reinforcement strongly not recommended because this method will not bring the expected result, and the electricity bill will not be very attractive. There are several ways to warm up.
The method of heating a concrete surface using electrodes is based on the passage of electric current. In turn, there are several types of electrodes that can provide excellent service during heating of the concrete surface.
Heating of concrete should be carried out taking into account the area of the working surface, safety regulations and safe handling of the welding machine specifically. Before using the welding fixture to warm up the working surface, whether concrete screed floors, foundation or anything else, it is necessary to consult with competent and experienced professionals.
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 in this case the power of the unit will be less. This method is acceptable for small objects and is almost ideal at home, given that you do not have to look for additional power. For example, we use a 250A device when pouring a small 4x5m slab, and as additional material We will show you a video in this article on this topic.
Note. According to SNiP 13.03.01-87 for load-bearing structures, if the average daily temperature outside drops below 5⁰ C, the concrete should be electrically heated. This is used to prevent an ice film from forming in the fresh mortar around the reinforcement.
At home, you can heat concrete with a welding transformer.
Schematic diagram - how to heat concrete with a welding machine
Note. In addition to the loops, heating fresh concrete structures can be carried out by electrode method, in heating formwork, liquid installations, induction method and infrared radiation.
If the solution does not harden properly temperature conditions(the mixture freezes), then the strength sharply decreases and the surface turns out to be crumbling - this is immediately visible when cutting reinforced concrete with diamond wheels or diamond drilling holes in concrete.
Heating of reinforced concrete structures with heating loops based on the principle of supplying limiting current to the cable is needed mainly for platforms ( slab foundations) 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 them to maintain the required thermal power depending on changes in air temperature outside. This method is more economical than electrode ().
And, of course, such work can be carried out only in those areas where there is a 220V power source - this can be a power line, but also (this happens at the beginning of construction) you can use a carburetor or diesel (more economical) generator.
Let's get started
We have a 250A welding machine, now we need PNSV, the quantity 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 =0.88ohm.
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) - for a 4x5 m slab this will be enough. Strip the ends of the PNSV 40-50 mm each and connect to each of them aluminum wire
(you can, of course, use copper, 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 the distance at which you can install the welding machine - it would be more advisable to bring it as close as possible. If these ends turn out to be short, don’t be upset - they can be extended at any time to the required length, just isolate the twist carefully (). Now we need to lay the PNSV, distributing it evenly over the entire area so that the twists with aluminum are inside the slab being poured, but in no case touch metal frame
! It’s best if you can thread the PNSV between two sheathings - inside the frame - so the cable will end up inside right in the middle of the slab, like butter in a sandwich between two pieces of bread of the same thickness.
You can also cut the PNSV into pieces, one loop at a time, and remove the aluminum ends from each, so it will be much easier to thread the wire between the reinforcement bars in the frame, but here you need to be careful not to mix up the ends. It is best to mark them with an insulation marker (use 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 quickly as possible after filling and turn the voltage regulator to 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 hardens, it will drop, and you can gradually increase it as needed.
Since you need to heat concrete with a welding machine gradually, check the voltage every 2 hours, gradually increasing it (
When working with concrete in low temperature conditions, there is always a need to warm up this building material. If the volume of such work is not too high, low-power two-phase welding machines can be used to heat the concrete. Moreover, the concrete mixture can be heated efficiently even with low-power models of welding machines that are used by ordinary homeowners. We will tell you about how such heating of concrete is carried out using a welding machine.
Most of the currently common varieties of this building material require operation at temperatures above 5 degrees Celsius. Only at such positive temperatures is high-quality hardening of the material ensured, which quickly gains strength and is free of cracks and other defects. If such work is carried out at sub-zero temperatures, the concrete hardens unevenly, cracks appear, the material begins to crumble, which subsequently leads to the need for expensive repair work. The use of special equipment for heating concrete allows us to ensure proper hardening and solidification of this material, while all such construction works can be carried out even at sub-zero temperatures. If special oil and electric heaters are used for large volumes of work, then when small volume For concreting, it is much easier and more convenient to use compact portable welding machines for heating.
Low-power amateur models are better suited for this job than powerful ones professional equipment. Such welding inverters are portable, they are more economical and allow you to smoothly regulate the welding current. Such a welding machine can easily be found in the household of every homeowner, and if necessary, it can be rented and carried out correct filling concrete with heating of the building material used.
To heat up concrete using a PNSV wire, you will need the following:
The PNSV cable used must be cut into strips about 15-20 meters long. Each such segment must withstand a welding current of 25 Amps. If you use the maximum power of the welding machine, you will need to use about 10 pieces of PNSV. On both sides of each such PNSV wire it is necessary to screw aluminum cables of the same length. The twist should be in heated concrete, and the other end of the wire is subsequently connected to welding inverter. The twist in concrete should be insulated with electrical tape.
Wire scraps should be tied to the fittings using plastic fasteners and the connection should be insulated with high-quality wire. This will avoid short circuit. Don't forget to label the wires with plus and minus.
We pour concrete into the reinforcement with tied PNSV wires, and then connect the cable terminals to the outputs of the welding machine. We set the minimum current, after which we measure the welding current on the main and conductive sections. In our particular case, the welding current on the main wire should be 250 Amps, and on each segment 20 Amps. Remember that as the concrete warms up, the current drops, so using the device manually, the current will need to be increased stepwise. At the same time, try not to let sharp increase tension on the cables, and the hardening material itself is best covered with insulation and plastic film. This eliminates heat loss, and the material will dry evenly, which will prevent the appearance of cracks on its surface.
It is recommended to warm up the concrete before the poured slab acquires the required strength. Typically, concrete takes about 30-40 hours to harden and gain strength. All this time, the cement should be warmed up, avoiding its sudden cooling.
The technology of heating with a welding machine using electrodes implanted directly into concrete as heating elements has also gained popularity. In this case, current flows through the solidifying solution, heating the electrodes and heating construction material. The disadvantage of this concrete heating technology is the risk of injury electric shock people and pets who are in close proximity to the flooded area concrete mixture. That is why it is necessary to limit the voltage to 36 V.
Reinforcement rods can be used as electrodes, which are placed in the structure and connected in series, which makes it possible to obtain isolated sections. These insulated sections are used to connect the forward and return wires. You can control the current power by connecting an incandescent lamp between two electrodes.
When performing heating using electrodes, it is necessary to constantly monitor the temperature of the concrete, preventing it from cracking and dehydration. It is recommended to cover the poured structure with insulation or film, which will avoid loss of heat and moisture.
Low-power welding machines are excellent for heating building materials. The most popular currently are two technologies for heating concrete using welding machines using special heating cables or reinforcing electrodes. Regardless of which method of heating the material you choose, it is necessary to carefully and efficiently connect the wires and fittings, which will be the key to the safety of such heating of the material.
When electrically heating concrete in temperature conditions below +5°C, special oil or air ones are used to reduce the voltage of the 200 or 380 V network. But in the case of small volumes when pouring the foundation at 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.
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 will need a 150-250 A welder, an aluminum cold-end cable, an ammeter (pliers) and fabric-based electrical tape.
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 fastenings 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 strength will drop, and it 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. At particularly low temperatures, a layer of insulation can be placed on top of the film.
A video on laying PNSV wire can be viewed below:
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 warming up the welding machine together with the electrodes: 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. 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.
