Why and how is the concrete heated by electrodes

The weather in our country is not always conducive to construction, and in some regions the conditions are altogether extreme. However, this is not a reason to interrupt work or completely abandon it. In particular, there are several methods for concreting, which make it possible to complete the task even under special conditions, for example, in cold weather or when creating massive structures.

Construction temperature

This parameter has a great influence on the set of concrete of final strength. It should also be noted that the fresh solution may freeze through when its temperature was at + 10 ° C for 3 days. Therefore, electrode heating of the concrete is necessary in winter. Be aware that when laying concrete at 5 ° C, you will have to wait 2 times longer to achieve their strength, which can be compared with a temperature of 20 ° C.

When the thermometer drops below freezing, hydration may simply stop. We must not forget the following: unbound water in a concrete solution during freezing will begin to increase in volume.

If the freezing and thawing processes are repeated many times, this will cause:

• loosening of the structure;
• moisture reduction;
• weathered concrete;
• the price of works will increase.

But when the mixture gained strength greater than 5 N / mm², it becomes resistant to a single freezing. In this case, the stripping period must be increased for the period when the concrete was below 0 ° C.

In this case, it is necessary to ensure that it quickly gain strength, so that freezing does not disrupt the process.

For example:

• during the month, the concrete should be protected from precipitation in the form of snow and rain;
• it should not come into contact with the loose salt used for anti-icing the first winter.

The temperature of the fresh composition relative to DIN 1045 should not be lower than the parameters that are taken depending on the ambient temperature and the type and amount of cement.

Tip: if measures are taken to heat a fresh concrete mortar, with the exception of supplying steam, its temperature should not exceed + 30 ° C and be below + 5 ° C.

In the first case, this will lead to rapid hardening and a decrease in the plasticity of the material, which makes it difficult to work with it.

It will also cause:

• large shrinkage;
• premature curing;
• low final strength of the concrete material.

To prevent this from happening, in each particular case, for example, a technological map of concrete warming up with electrodes is being developed.

How to protect

To do this, follow these steps:

• heat the mixing water and the aggregate, never use the last component that has been frozen;
• use cements of high grade. They harden faster and produce more heat during this process than lower-grade cements;

Advice: if you need to carry out communications work after hardening of the composition of the structure, diamond drilling of holes in concrete with professional crowns necessary for diameter will help you.

• increase the cement content to speed up the curing;
• lower the ratio between cement and water, this will allow the solution to harden faster and gain strength, while releasing a high level of heat;
• add your own hands in special cases and after conducting tests for compliance with a hardening accelerator. Do not use chlorine-containing hardening accelerators in prestressed concrete.

What should be done when transporting the solution and laying it:

• protect vehicles from heat loss. Do not use open trays or conveyor belts;
• if possible, pre-heated concrete should be laid in pre-heated formwork and immediately compact;
• keep the reinforcement and formwork planes free of snow; you can use heated air or flame burners to warm up. Never use a jet of hot water;
• do not lay concrete on frozen structures and on frozen ground;
• Maintain the temperature of the concrete, if possible for the first 3 days, not lower than + 10 ° С, and also heat the adjoining premises.

How to warm concrete

In winter, electrodes are often used to heat concrete. This makes it possible to eliminate the conversion of water into ice, so that it normally enters into a chemical reaction with cement. Let's take a closer look at how this process happens.

What is it for

Above in the article we reviewed general information on the effect of temperature on the quality of a concrete mortar. It's time to explain it with an example.

Since it is necessary to concrete not only in the warm season, but also in cold weather, it is necessary not to forget about the physical transformation of water into ice. It should be understood that this should not be allowed in any case, since it is necessary for a chemical reaction with the main component of the solution - cement.

Tip: if you need to dismantle concrete goods or make technological grooves in them, cutting of reinforced concrete with diamond circles will help you.

When freezing hydration will stop, and the processes of hardening of the concrete will stop, causing a violation of the structure of the material. Even after the ice is thawed and hydration is resumed, it cannot be restored.

The same can be said about reinforced concrete, when an “ice crust” is formed on the reinforcement, which takes water from a zone of not so cooled sections. These processes adversely affect the structure of the material.

That is why the instruction requires you to warm up the concrete, so that its hardening is as successful as possible.

Currently, there are several methods to achieve the desired results, in particular, they use heating:

• electrodes;
• welding machine;
• infrared waves.

Electrode heating - types

One of the most popular ways in the construction industry. The basis of the method is the passage of electric current through the thickness of concrete.

Consider which electrodes for heating concrete are used in this case:

1. Lamellar, resembling plates, are installed from the inside of the formwork, so that there is better contact with the mixture. Concrete begins to heat up to the desired temperature due to the appearance of an electric field. In a warm state, the concrete mixture may be for some time.

   

1. Banding (in the form of plates) have a total width of 400-450 mm. Such electrodes can be mounted from two sides. After connecting the current, the electric field is created in the layer of concrete adjacent to the plates.
2. Strings are usually used for heating the mixture in cylindrical structures, in particular, columns. The technology of heating the concrete with electrodes in this case is as follows: the string electrode is placed in the center of the structure, and the formwork is wrapped around a special conductive sheet.

   

1. The rod variant resembles rod fittings O 7-11 mm. Place it inside the concrete with the appropriate design step. In this case, the extreme electrodes are mounted at a distance of 40 mm from the formwork. Very often, this method is carried out by electric heating of concrete in complex structures.

Tip: Select the electrodes based on the conditions of work.

Work with the welding machine

Application for heating the concrete welding machine is a very real idea. But, for a good heating of the mixture it is necessary to use auxiliary electrodes in the process of work. Do not worry about the reliability of the equipment, modern units are reliable and do not pose a danger to humans, subject to the rules of TB.

The design of many devices is simple and easy to use. Thanks to such stations, it is possible to warm up 30-100 m³ mixture, and the work can be carried out almost at -45 ° C.

The welding machine is designed as an autonomous unit consisting of a welding unit and an engine.

In addition to the basic functions, it can be equipped with auxiliary, in particular, have:

• block of heating of frozen soil;
• electrode dryer unit;
• voltage reduction unit;
• current generator.

With its help, it is possible to regulate the heating, since it has several voltage levels. We can safely say that this unit has everything necessary for normal operation.

The correct heating process is as follows:

1. Electrodes (reinforcement segments) are evenly laid across the concrete pad.
2. Connect them to 2 parallel circuits.
3. An incandescent lamp is placed between them to monitor the voltage.
4. Direct and feedback wires are connected to the circuits.

Tip: so that the moisture does not evaporate quickly from the surface of the concrete, cover it with a layer of sawdust, and to control the overheating of the material, use an ordinary thermometer.

Work only according to the technical documentation for a specific object.

Conclusion

It became clear from the article that it is possible to work with concrete not only in summer, but also during the cold season. To do this, there are many ways to help avoid the transformation of water into ice and preserve the structure of the material. One of the most popular methods for today is concrete heating by electrodes. The video in this article will help you find additional information on this topic.

A diagram of the connection of concrete heating by electrodes is given in another article on our website.