Concreting is one of the main building processes. Freezing of uncured concrete mix leads to a significant loss of strength of the finished structure, since ice crystals cause expansion and destruction of the structure. Heating of concrete with electrodes makes it possible to carry out construction work in the winter without deteriorating the quality of the finished structure.
The electrode method does not require the use of sophisticated equipment. The principle of operation is based on the properties of an electric current - when passing through a humid environment, heat is released, which contributes to the heating of the concrete mixture and its uniform solidification.
Modes of heating concrete with electrodes
The mode is selected based on the massiveness and geometry of the structure, the grade of the concrete mix, weather conditions, and the operation of the structure being erected. Electrode heating of concrete is carried out according to one of the following schemes:
- two stages: heating the concrete mixture and subsequent isothermal exposure;
- two stages: heating and cooling with full thermal insulation or the construction of a heating formwork;
- three stages: heating, isothermal exposure, cooling.
When heating concrete with electrodes, it is critically important to observe the temperature parameters. The process starts at +5 degrees, then the temperature is increased at a rate of 8-15 degrees per hour. The maximum tolerances depend on the grade of concrete and are + 55 ... +75 degrees. For control, periodic temperature measurements are carried out.
Isothermal holding time is determined on the basis of laboratory studies of cubic compressive strength. Depends on the type of cement, heating temperature and the required strength of the finished concrete.
The permissible cooling rate is 5-10 degrees / hour. The exact parameter depends on the volume of the structure. Re-insulation after stripping is required if the temperature difference between the ambient air and concrete surfaces is more than 20 degrees.
Varieties of electrolytes for heating concrete
Depending on the type and geometry of the structure, different electrodes are used to heat the concrete. For each of them, its own connection diagram is developed:
- Strings.
- Rod.
- Lamellar.
- Striped.
Strings. They are made of reinforcement with a length of 2–3 m and a diameter of 10–15 mm. Used for columns and other similar vertical structures. Connect to different phases. A reinforcing element can be used as one of the electrodes.
Rod. They are pieces of reinforcement with a thickness of 6–12 mm. They are located in the solution in rows with a calculated step. The first and last electrode in a row is connected to one phase, the others to the 2nd and 3rd. They are used for a plot of any complex geometry.
Lamellar. They are suspended on the opposite edges of the formwork without being buried in the mortar and connected to different phases. The electrodes create an electric field that heats up the concrete.
Striped. They are made in the form of metal strips 20-50 mm wide. They are placed on the surface of the solution on one side of the structure and connected to different phases. Used for floor slabs and other elements in the horizontal plane.
Methods for installing electrodes into a structure
Electrode heating of concrete is used in the construction of walls, columns, diaphragms and other vertical elements. This method is not suitable for making slabs.
Electrodes are inserted into the filled solution with a calculated step (60–100 cm), depending on the geometry of the structure and weather conditions. Local overheating has a negative effect on the quality of concrete, so the placement of the electrodes must be uniform. The layout project is drawn up taking into account the basic norms:
- minimum distance between electrodes 200-400 mm;
- distance from electrodes to frame rods 50-150 mm;
- distance from the electrode to the technological seam of the structure- not less than 100 mm;
- distance from the outer row to the formwork- not less than 30 mm.
If these requirements cannot be met due to the size or design features of the heated surfaces, the electrodes in hazardous areas must be insulated with an ebonite tube.
After pouring concrete, you need to cover the heated area with roofing material, film or other heat-insulating material - without additional insulation, heating does not make sense.
A single-phase or three-phase alternating current is supplied to the electrodes through a step-down transformer connected according to the diagram. Direct current cannot be used, as it starts the electrolysis process. Control devices must be included in the electrical circuit - as it solidifies, it is required to adjust the parameters of the supplied current.
Safety rules for electrode heating
The use of technology for heating concrete with electrodes on a construction site requires increased attention to observing safety rules:
- The filling with a reinforcing structure is heated at a reduced voltage (60–127 V).
- The use of voltages up to 220 V is possible to warm up the local area, which does not contain any conductive elements (metal frame, reinforcement) and is not associated with neighboring structures.
- Warming up with voltage up to 380 V is permissible in exceptional cases for non-reinforced sections.
- The electrodes must be installed in places strictly defined by the project. It is strictly forbidden to allow them to come into contact with the reinforcing elements - this will lead to a short circuit and equipment failure.
Electrode heating of the concrete mixture must be carried out in strict accordance with the technology. Violation of the time or temperature regime, the electrode placement scheme can lead to local overheating and insufficient strength gain, which will subsequently lead to the appearance of cracks in the structure and possible destruction. If the work is done correctly, the solution hardens with uniform shrinkage, which ensures a homogeneous structure of the resulting material and the strength of the product during operation.
Concrete is a building material, without which it is impossible to build buildings, renovate apartments and houses. Concrete heating is a serious process, so it is important to know the entire manufacturing technology in order to end up with high-quality and durable, and most importantly, durable material.
- Heating up concrete with a wire.
- Heating of concrete with a cable.
- Heating of concrete with a welding machine.
Heating up concrete with a wire
Heating up concrete with a wire
A simple and relatively inexpensive PNSV heating wire is used to heat the concrete.
The wire consists of two elements:
- Single-wire steel conductor, round shape.
- Insulation - PVC compound or polyethylene.
The method of heating concrete with a wire is based on the transfer of heat to concrete from highly heated wires. Heating of the wires is carried out using step-down transformer substations, which have a regulation system. Such a system is very convenient, it allows you to adjust the heat output based on external temperature changes.
Concrete heating technology with wire:
- The wire is laid evenly in the structure, while it should not touch each other, not touch the formwork and not go beyond the concrete levels.
- The ends are taken out of the heating limits after connecting the heating wire and cold ends by soldering them. It is recommended to wrap the place of soldering with metal foil to preserve the thermal field.
- The number and length of the heating element is calculated based on the prepared technological documents and maps.
- A test check of the wire is carried out with a megohmmeter to ensure a uniform current load in phases.
- The current is supplied through a step-down transformer substation.
The number and length of the heating element is calculated based on: type of structure, heating area, concrete volume and the required electrical power.
When working with heating concrete with a wire, a separate and individual technological map is necessarily developed for each structure. Regular laboratory observations are carried out, the heating time and the time of concrete hardening are recorded.
Heating of concrete with a cable
The method of heating concrete with a cable does not require large energy consumption and does not require auxiliary equipment.
Concrete heating technology with cable:
- The cable is installed on the concrete base before grouting.
- Fixing with fasteners.
- The cable must not be damaged during installation and operation and must not cross each other.
- Connecting the cable to the low-voltage electrical cabinet.
When using a cable for heating concrete, a cable installation diagram is drawn up and temperature tests are carried out.
Heating up concrete with a welding machine
The method of heating concrete with a welding machine includes the use of: pieces of reinforcement, an incandescent lamp and a conventional thermometer. Pieces of fittings are installed in parallel to the circuit, with adjacent return and forward wires, an incandescent lamp is installed between them to measure the voltage, and a thermometer is used to measure the temperature. The concrete hardening time is very long and is more than a month. When heated in this way, the structure should not be exposed to cold and water flooding.
This method is used with small amounts of concrete and good weather conditions.
Warming up concrete in winter
In winter, concrete stops hardening, since water freezes and does not participate in chemical reactions. The quality and strength of concrete is also destroyed. Therefore, concrete heating in winter is very important and necessary.
Methods and methods of heating concrete:
- Adding antifreeze additives.
- Warming up by the "thermos" method.
- Other methods of heating concrete.
- Technological heating of concrete.
Adding antifreeze additives
Antifreeze additives withstand severe cold, even at a temperature of -30 C they fulfill their chemical indications. The composition of the additives is different, but the main component is antifreeze - a liquid that prevents water from freezing. For reinforced concrete structures and reinforcing floors, mixtures with the addition of Sodium nitrite and Sodium format are suitable. Their main feature is the preservation of physical, chemical and anti-corrosion properties at low temperatures.
For ready-mixed concrete, hollow reinforced concrete blocks, in the manufacture of curbs and paving slabs, mixtures with the addition of Calcium chloride are suitable. The properties of this substance are widely known throughout the world. Thanks to the speed of hardening, resistance to low temperatures and low cost, construction in the winter has become affordable for everyone.
The chemical is potash, an ideal antifreeze additive. It dissolves quickly even with a minimal amount of water, does not cause corrosion. The use of potash when heating concrete is a significant saving on building materials.
When using antifreeze additives, it is imperative to comply with all safety standards. For example: concrete with these additives cannot be used when the structure is under stress, monolithic chimneys are being erected, etc.
Warming up by the "thermos" method
The "thermos" method consists in placing concrete in the insulated formwork with a temperature equal to 20-25 degrees. Due to the outgoing heat, the structure gains strength. Another common method is additional heating of the concrete, and then placing it in the insulated formwork.
Other methods of heating concrete
The transformer heating method is similar to the “thermos” heating method, but instead of conventional heating, the formwork is heated by a transformer or wire.
Electrode heating takes place using strip, plate or string electrodes, which are immersed in concrete. The current is distributed to the electrodes through a step-down transformer.
Infrared heating of concrete does not occur immediately for the entire structure, but for individual zones. Infrared devices are placed in these zones, which consist of reflectors and directly from emitters. Infrared rays transmit thermal energy to the entire selected section of the structure. Thanks to the side radiation, all cold places are warmed up.
Technological heating of concrete
Technological heating of concrete is based on the transmission of current through a cable or wire, which are installed on the structure before pouring concrete. The ends of a wire or cable are connected to a transformer, then heat is applied. The voltage level is regulated in accordance with the established and developed project, and must be taken into account; construction area, weather conditions, concrete grade, wire length.
Warming up concrete in winter conditions is a necessary component for any construction work. There are many different schemes for heating concrete and the choice is made individually for each structure.
Construction work on the construction of facilities is carried out all year round. Often, builders make concreting to form solid structures in the winter. In this case, it is important to ensure the strength of the monolith and prevent water crystallization. While heating the concrete, it is important to maintain the required temperature of the mixture and create favorable conditions for the hydration of the cement. Let us dwell on the heating technology based on the use of infrared rays and electricity. Let's consider the pros and cons of each method.
What methods are used to heat concrete 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. What is the right thing to do? After all, moisture at a negative temperature 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 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 concrete mass. Panel elements of prefabricated formwork contain electric heaters;
- heating by infrared rays. Radiation in the infrared spectrum directed to the concrete mass increases its temperature;
- preliminary increase in the temperature of the solution. It heats up before concreting, maintaining the required temperature during pouring and solidification;
- construction of special structures of the tent type. They are covered with polyethylene or tarpaulin and heated with a heat gun.
To choose the optimal heating method, calculations should be made and all the nuances should be analyzed. It is necessary to take into account the possible level of costs and only after that give preference to a specific method. Let's consider the specifics of each method.
We connect the wire for heating concrete PNSV
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 with PNSV should be laid in the structure to be concreted and supplied with a supply voltage from a source of electrical energy.
This heating method is often preferred due to its serious advantages:
- increased efficiency. A correctly laid heating cable, which is chosen by calculation, can maintain the temperature necessary for the solidification of a significant volume of concrete;
As a rule, power supply of PNSV cables is carried out through substations with several stages of reduced voltage - profitability. Electricity consumption is acceptable. This allows you to invest in the estimate of construction activities and prevent cost overruns;
- 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 is excluded;
- versatility. Electric heating technology can be applied to solid building structures made from concrete or reinforced concrete.
Along with undeniable advantages, the technology also has weak points:
- needs preparatory work, during which the wire is laid. A flexible cable for heating concrete requires careful attention when placed 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 special design wire is used, which consists of the following elements:
- conductive core;
- protective insulation.
The selection of a cable 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 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 concrete mix has much in common with the method of forming a heated floor.
How concrete is heated with a welding machine
The technical characteristics of the welding transformer allow it to be used for heating concrete mixture. 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:
- support 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 passing an electric current through concrete using electrodes. Work technology:
- Stick the electrodes into the liquid mixture.
- Apply voltage and adjust the amperage.
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 a steel bar inserted into the solution.
To ensure 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;
- the possibility of using at various objects;
- quick 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, structures of any shape, even the most complex ones, can be heated. Electric heating of concrete using a special formwork
To ensure a positive temperature of the hardening concrete mixture, builders also use prefabricated panel formwork. Its feature is the equipping of unified panels with quick-detachable electric heaters.
Advantages of the application:
- accelerated dismantling of electric heaters. The design provides easy access for replacement and maintenance;
- versatility. The formwork is assembled from individual elements with standard dimensions and can be reused;
- efficiency. The formwork allows you to heat up an increased volume of concrete at temperatures down to -20 degrees;
- increased efficiency of use. Increased profitability and low cost levels are characteristic of this method;
- fast assembly of the structure. Accelerated assembly of formwork elements reduces installation time.
Along with the advantages, there are weaknesses:
- increased price of formwork;
- impossibility of use with a curvilinear shape of the object.
Shields with heaters are used in the construction of large facilities.
Installation of the heating system is carried out immediately before pouring the solution into the formwork Infrared heating of concrete
Infrared rays make it possible to perform directional heating of a concrete mass to a predetermined temperature. The radiation intensity and heating depth vary depending on the distance between the infrared heater and the surface of the concrete mass.
Heating technique with thermomats:
- Additives for accelerated hardening are added to the concrete mixture.
- Special infrared mats are laid on the surface of the array.
- The power cable is connected and the electrical voltage is applied.
The technology makes it possible to heat up concrete structures in a horizontal position.
The advantages of this method:
- low power consumption;
- ease of implementation;
- control of heating intensity;
- the possibility of heating the 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 warm up an increased space.
Despite its shortcomings, the infrared method is in demand in the construction industry.
This method is especially often used when performing screeds in the winter. Using a preheated solution
The method of heating the concrete mixture before 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 a 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 concrete poured;
- 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
Deciding on the best way to warm up requires a professional approach. It is important to study the technological features of each method and determine the economic feasibility of its application. Professional advice will help you understand the advantages and disadvantages of the applied heating technologies.
Construction work in the cold season is always inconvenient. Of course, sometimes you can wait until warm and fill the foundation in spring or summer, when the ambient temperature is more than 5 degrees Celsius. But this is not always the case, and often the work needs to be done as quickly as possible. In this case, it is very convenient to know the connection diagram of the welding machine for heating concrete.
Required tools
Construction work is troublesome, costly, but to some extent pleasant. Especially when the construction of a long-awaited home for your own family is underway. And if on an industrial scale a special transformer or cable is required for pouring concrete in the winter, then in conditions of small volumes, you can do this with a welding transformer, the power of which is from 150 to 200 watts. It is a mobile and economical device that is available to anyone and is often already in the builder's workshop. And if such a device is available, then why not use it.
It is worth paying attention to the connection method and the corresponding diagram when heating concrete with a welding machine. It will be slightly different from what you are used to.
In addition, to warm up concrete with a welding inverter, you will need:
Preparatory work
First of all, you need to check the availability of all the necessary tools and materials, because in the process of work there will be no time to be distracted. All the work performed, especially if it is carried out by the builder for the first time, is better thought out and broken down into sub-points: it will be easier and faster this way.
The plan for heating concrete with a welding machine should include such actions:
When the preparatory work has been completed, you can proceed to pouring concrete and connecting the welding machine to warm it up.
Warming up is done after pouring it. To warm up concrete with a welding machine, perform the following actions:
The warm-up process is not difficult, but it requires some skills in working with the welding machine. Therefore, before starting any construction activities, you should consult with a specialist about the feasibility and rules of work.
Experienced foremen advise:
All work should be carried out only in compliance with all safety rules. You should not neglect the purchase of high-quality electrodes and exceed the operating mode of the device. This can damage the inverter and suspend important construction work for a long time.
After all, heating concrete with a welding machine is a necessary process when pouring a foundation in the cold season.
Construction activities related to the concreting of 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 the water entering the solution from freezing. In order to maintain a positive temperature of the solution and ensure optimal setting conditions, the concrete is heated. Let us consider in detail the heating methods using electric energy and infrared rays.
How concrete is heated in winter
With the onset of winter cold weather, builders have to face serious problems associated with the characteristics of the concrete solution. It contains gravel, portland cement and sand with added water. The solution under normal conditions acquires operational characteristics within a month. However, the water increases when it freezes, which can destroy the monolith.
In the process of carrying out construction and repair work at low temperatures, to accelerate the hardening of concrete mortar, concrete heating should be used
The following techniques are used to maintain the 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 filled;
- electric heating using a welding transformer. A cable is connected to the power source for heating the concrete with the help of electrodes introduced into the array;
- heating with a special formwork. Quick-detachable electric heating elements are installed in standard elements of the formwork panel structure;
- infrared heating. It is based on the use of directional infrared radiation, due to which the temperature of the concrete rises;
- preheating the mixture. The mortar is heated before pouring in such a way that during hardening it maintains a positive temperature;
- arrangement of special tents. A frame structure with a tarpaulin or polyethylene overlap is being erected, inside which a heat gun works.
The decision to use a specific heating method is based on preliminary calculations. Having analyzed all the factors in a complex and evaluating the economic side of the issue, you can decide and make the right decision. Let's dwell on the features of each heating method.
Electric heating of concrete using PNSV cable
Using a wire for heating concrete PNSV, it is easy to ensure the temperature that is optimal for the solidification of the solution. This method is quite simple and involves laying a special PNSV wire, which heats up when a low voltage is supplied from a step-down transformer.
This method works on a fairly simple principle. Before pouring, a wire is laid to warm up the concrete.
Electric heating technology with a special wire has a number of advantages:
- provides high efficiency. Correctly selected and professionally laid heating wire is able to heat a concrete block of increased volume;
- guarantees economy. Insignificant consumption of electric energy allows avoiding significant financial costs and significantly reduces the estimated cost of work;
- preserves the structure of the monolith. When the supply voltage is applied, cracks are not formed in the zones of cable laying, as well as air bubbles in the concrete mass heated by the wire;
- is versatile. Electric heating can be used for monolithic structures made from ordinary concrete, as well as reinforced with steel reinforcement.
Despite its serious advantages, the method has certain disadvantages:
- requires preparatory measures, 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;
- needs a special transformer. The power of the step-down equipment must ensure the possibility of raising the temperature of the concrete mass to the required level.
A special cable is used, consisting of a conductive core and an insulating cover. The wire is selected based on calculations that take into account a number of factors:
- supply voltage of the transformer;
- conductor diameter;
- wire length.
It should be borne in mind that the laying of heating loops is usually carried out in unpleasant weather.
When laying the cable, it is important to observe the following requirements:
- ensure surface cleanliness and exclude the possibility of damage to the cable;
- avoid bending the conductors and lay the wire evenly over the entire area.
It is important to provide 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 during the entire warm-up period;
- the cooling rate of the heated massif should not exceed 5 degrees Celsius per hour.
Purchase a 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 arranging a warm floor.
Heating up concrete with a welding machine
You can warm up the solution using welding equipment and wire electrodes. The method has positively proved itself when pouring vertical structures in winter:
- columns;
- walls;
- fences.
Electric heating of concrete can be performed 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 stick electrodes into the concrete array;
- then, using a cable, supply the supply voltage from a step-down transformer.
When heating vertical columns of small cross-section, it is enough to use one electrode. In this case, the heating of the concrete mixture will be carried out by applying voltage to the reinforcing cage and the steel bar 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.