Concrete heating with electrodes: work scheme, types of

Heated concrete in winter is a prerequisite for a set of design of sufficient strength. A variety of technologies are used to ensure the optimum temperature of the solidifying solution, and one of them is the use of electric current.

We will talk about the features of the implementation of this scheme in this article.

Winter problems

As you know, it is better to work with cement mortar at positive temperatures — then, after solidification, the structure is quite durable. However, in some cases there is a need to arrange concrete foundations or walls in the cold.

And here the problems begin:

• First of allThe liquid in the mortar freezes and stops reacting with the cement. Accordingly, the activity of the hydration process is greatly reduced, and the curing practically stops.
• Secondly, ice crystals expand the pores inside the concrete, which leads to a decrease in its density. If, during drying, several freezing-thawing cycles take place, then the pores will become very unstable and the monolith will begin to crumble.
• Thirdly, the stress zone is formed in the areas of contact between the concrete solution and the reinforcement. A thin ice film forms on the metal, and after it melts, the bond strength decreases by an order of magnitude.

Note! An additional disadvantage is the activation of corrosion processes due to oxidation of the metal in the presence of water.

There are two ways to avoid these effects:

• First of all, in the composition of the liquid for hydration add special anti-frost components. They prevent water from freezing, so hydration takes place under normal conditions.
• Secondly, electric heating of concrete is used. By optimizing the temperature conditions inside the mortar, favorable conditions are created, and the cement gains strength just as actively as when it dries with a positive air temperature.

For best results, the instruction recommends using both methods in parallel. However, many experts are limited only by active heating: so the price of work is somewhat reduced, and the quality practically does not suffer.

Features of the technique

General scheme of work

The very method of heating the concrete mass using electrodes is quite simple.

It is implemented according to the following algorithm:

• Inside the formwork mounted conductive elements connected to the power source. The arrangement configuration and the type of electrodes are selected separately depending on the design features.
• After the electrodes are placed, the solution is poured into the formwork. Being in a liquid state, it turns into one of the elements of an electrical circuit that conducts current well enough.
• Voltage is applied to the electrodes, due to which an electric field is created in the concrete body. It gradually gives its energy to the surrounding substance, heating it.
• By changing the current parameters (force, voltage), you can adjust the degree of heating with your own hands.

Note! The effectiveness of this process is reduced simultaneously with the loss of a solution of a significant part of the water. The drier concrete becomes, the higher the voltage required for effective heating will be.

As a result, during the set of cement strength it maintains the optimum temperature. Such processing is quite enough to ensure a homogeneous structure of the frozen material. Cutting reinforced concrete with diamond circles confirms this - on test specimens, voids and loose areas are practically not detected.

Warm-up time depends on many factors, among which the most important are the volume of the concrete structure to be concreted and the outdoor temperature. In some cases, heating the solution takes up to 4-5 weeks, i.e. to the full set of strength. However, more often, additional heat is required only in the initial stages.

Electrode Types

To implement this method, current-carrying elements of various configurations are used. You can study their design features by analyzing the table given here:

Note! The use of composite reinforcement fragments as conductive rods is not allowed!

 Depending on the type of parts involved, the following methods of temperature increase are distinguished:

• Surface (peripheral) processing - electrodes are superimposed on the surface of the solution without immersion, often using special conductive substrates. After finishing work can be dismantled and reused on another object.
• Submersible (through) electrical heating of concrete - the electrodes are inside the material, and after its solidification are not removed. So that the strength of the structure does not decrease, we place the conductive elements no closer than 30 mm from the surface.

Note! The position of metal conductors must be taken into account when diamond drilling of holes in concrete without reinforcement or other work associated with the violation of the integrity of the product.

Use of welding machines

Мастера, которые пытаются реализовать данную методику самостоятельно, часто интересуются, как греть бетон электродами с применением сварочного аппарата (см.также статью «Как осуществляется прогрев бетона сварочным аппаратом»).

Indeed, it is quite possible:

• Conventional welding machine includes two units - the engine and the welding generator itself. At the same time, the capacity of the latter is enough to provide heating of about 50m.³ concrete solution.
• Before starting work, we lower the electrodes into the cement. For most tasks, a step of 20-30 cm is enough.
• The electrodes are connected in series, forming several parallel circuits.
• To monitor the voltage between the circuits, experts recommend installing an incandescent lamp.
• We connect the circuits to the device and apply voltage. Heating control is carried out in special wells.

Tip! So that when heating water from the surface layers evaporates more slowly, it is necessary to fill the solution with a layer of sawdust about 50 mm thick. Naturally, this should be done after the cement grabs.

Implementation Tips

When arranging an electrode heating system, the following points should be considered:

• When the solution dries out, it is necessary to gradually increase the strength of the current in the network. To do this, we must integrate a regulating device into the circuit (at least a primitive rheostat).
• The use of direct current sources is not allowed, as this results in electrolysis of the fluid inside the structure.

• In order for the treatment to be as effective as possible, it is necessary to reduce surface heat losses. To do this, we cover the solution with roofing material, insulation mats, several layers of plastic film, etc.
• When laying the core conductors need to strictly control the step between them. Deviations of more than 5 cm can lead to uneven loading due to different resistance of the sections.
• To save electricity, you can speed up the process of cement hydration. To do this, we introduce special additives into the solution, due to which hardening is faster.
• The optimum voltage when laying the electrodes is not more than 127 volts. If reinforcing rods are used to supply voltage, the allowable value is reduced to 60 volts.

In any case, the organization of this process should be handled by a specialist who has the appropriate approval and is familiar with the safety regulations.

Conclusion

Если вам необходимо залить фундамент или возвести стены, но при этом на улице установилась отрицательная температура, ждать весны совсем не обязательно. Подогрев бетона электродами позволяет сформировать приемлемые условия для гидратации раствора и набора цементом прочности (читайте также статью «Прогрев бетона проводом ПНСВ: цели и технология»).

Naturally, the cost of electricity will be substantial, but the design will meet all the requirements. More information on this topic can be found by studying the video in this article.