Concrete heating in winter: targets, common methods and

Often the need for construction arises in the winter, and in this case, builders have to solve the problem of freezing concrete. Today, there are several effective technologies for heating concrete in the winter, and then we will introduce you to the main ones.

Why heat concrete

Pouring concrete in winter at temperatures below zero requires certain temperature conditions under which the mortar can harden normally. This need is related to the water content of the mixture.

The temperature of the structure should not fall below the technologically determined minimum. Otherwise, ice crystals of rather large size are formed in the mixture, which create great pressure in the pores of the cement.

As a result, the concrete structure is destroyed, and, as a result, the material loses its properties, in particular, this affects its strength. It is especially dangerous to allow the concrete to freeze during setting.

It should also be borne in mind that when the temperature of a substance decreases, the rate of interaction of cement with water decreases. With increasing temperature, respectively, the rate of interaction increases. However, it should be noted that with slow hardening, the strength of concrete is obtained higher.

Methods for heating concrete

Heating of monolithic concrete in winter conditions, as already mentioned above, can be carried out in several ways, depending on the type of construction and the ambient temperature.

Most often used:

• Heating formwork method;
• Electrodes;
• Induction or infrared method (heating with gas burners and other heaters);
• Heating wires.

Now consider the features of these methods of heating.

Electric heating

Perhaps the most common method of heating is passing electric current through concrete with the help of electrodes. The supply of current to the mixture is carried out in different ways and for each of them there is a certain connection scheme.

Note! Direct current causes the electrolysis of water in concrete, therefore, three-phase or single-phase alternating current can be used for heating.

Electrodes for heating can be of the following types:

• Rod - are made of reinforcement with a diameter of 6-12 mm. They are located in the thickness of the concrete with a certain design step. In this case, the extreme row of electrodes should be at a distance of 3 cm from the formwork.

With the help of such electrodes it is possible to warm up structures of any shape, even the most complex. Thanks to the simplicity of the method, you can do the connection yourself, however, for this you need to understand the electrics.

• Lamellar - hinged on the inside of the formwork. As a result of connecting plate-shaped opposite electrodes to different phases, an electric field is produced in a concrete solution, which heats the mass to the required temperature and maintains it throughout the mixture hardening.
• Strip electrodes - can be located on one or both sides of the structure.

Heating wires

Today, the winter heating of concrete with the help of heating wires is also widely used in practice, since this technology is well mastered. In particular, it is used by many major foreign and domestic construction companies.

It consists in the installation of a heating cable of a certain length on the reinforcement cage. The installation of the heating system is carried out immediately before pouring the solution into the formwork.

With this method of heating, a PNSV wire with a steel core of 1.2 mm is used. When a current is passed through such a wire, heat is generated, which due to the thermal conductivity of the material is evenly distributed throughout the concrete. This allows you to warm the concrete to +40 degrees Celsius.

As a rule, the power supply of PNSV cables is carried out through substations with several stages of reduced voltage. One substation of type KTP-63 / OB is sufficient for heating 20-30 meters of cubic concrete. At the same time, for warming up one cubic meter of concrete you need about 60 meters of a PNSV wire.

Among the advantages of this heating technology, it is possible to highlight the fact that it can be used for structures of any complexity. The minimum temperature at which it retains its effectiveness is -30 degrees Celsius.

Especially often this method is used when performing screed in the winter. At the same time, the installation manual for the cable is a lot like the installation of the “warm floor” system.

I must say that often builders use a combined method of heating.

The feasibility of applying a particular combination depends on factors such as:

• Required structural strength;
• Massive construction;
• Weather conditions;
• The presence of energy.

Note! After the concrete has gained a certain strength, it can resist frost without compromising strength. Those. after thawing, he will continue to gain strength.

Thermoactive formwork

Thermoactive formwork with plywood or steel decks is a great way to heat concrete during erection:

• Foundations;
• Not thick concrete walls;
• Overlaps, etc.

The minimum temperature at which this method can be used is -25 degrees. Cables, metal grids, etc. can serve as heaters.

Before pouring the formwork is heated to +18 degrees. Then, when feeding the mixture, its temperature is increased to +50 degrees. Heating formwork is often combined with electric heating of the mixture.

Fill without warming up

We considered the most common options for heating concrete, however, you can perform winter concreting without warming up. This method is good because it does not require electricity supply and installation of heating systems, which speeds up the construction process.

The principle of this technology is to use special additives that reduce the freezing point of water, as well as accelerate the process of hardening of concrete, so that the solution does not have time to freeze. At the same time, the strength of the material does not suffer at all.

Among other advantages of using this technology is to prevent the appearance of efflorescence.

Note! Before you pour concrete in the winter without warming up, you need to know at what minimum temperature you can perform this operation using one or another additive.

An example of such compositions is the additive "Frost". To ensure the frost resistance of the mixture with it, you just need to add the required amount of the substance, which is indicated on the package. The price of such an additive is quite affordable, so the cost of concrete practically does not increase.

Tip! After hardening, the concrete becomes so strong that its processing causes certain difficulties. For these purposes, diamond tools are used, in particular, cutting of reinforced concrete with diamond circles and diamond drilling of holes in concrete is often used.

Here, perhaps, are all the main nuances that you need to know about the heating of concrete and its pouring in the winter season, if you decide to engage in construction at minus temperatures.

Conclusion

To date, the technology of heating concrete is well mastered by builders, as they allow not to interrupt the process of building concrete structures, even in winter. The choice of a specific technology in a given situation must be made by an expert, depending on environmental conditions and the type of construction (also learn how to use a concrete preheating transformer when working in the winter).

From the video in this article, you can get more information on this topic.