Concrete at sub-zero temperatures: the main methods of

It can be said without a hitch that concreting at minus temperatures is by no means something common in construction, therefore, any foreman or site manager tries to do this before winter to avoid unnecessary problems and unnecessary expenses.

Nevertheless, there are certain deadlines laid down in the project and adopted by the contractor, therefore, if such a need arises, then this is a completely solvable problem, especially since there are enough ways to do this. Below we will talk about what methods of heating exist in general, and we will analyze one of them more specifically and as a supplement we will show you a video in this article on our topic.

Concrete pouring in winter

Possible methods

• So, to the question whether it is possible to concrete at a sub-zero temperature, we have already answered positively and this is possible with the help of electrical heating of the concrete solution to be poured. (sometimes chemical hardening accelerators are used additionally). One of the methods provides for an anode method - this is when an armature is installed in the solution at a distance of 80-100 cm from each other (depending on the weather) or, in extreme cases, wire rod with a cross section of at least 8-10 mm, which is connected to a step-down transformer.
• Here, the cement at subzero temperature is heated due to the moisture in the solution between the electrodes, which, in turn, create polarity (the principle of the kettle of blades), only the transformer is used, as a rule, three-phase. The disadvantage of this method can be called the high cost of electricity - one electrode is able to consume from 45A to 50A.

• In this case, everything is very simple - the heating elements are pre-assembled in the shields, and the assembly is carried out in the same way as the instructions for conventional formwork (supports, clamps). This method of heating is perhaps the most cost-effective - it allows you to carry out monolithic construction of virtually any heights and it is very quick to assemble and dismantle, and if necessary, it is very easy to replace heating elements. The main and, probably, the only drawback of the heating formwork is its high cost, but it quickly pays off.

• Enough convenient and effective can be called concrete heating using an infrared emitter - the advantage is that you can warm, both through the formwork, and an open area, for example, slab foundation. The intensity of the radiation is controlled by changing the distance between the object and the emitter, which is quite simple and does not require special skills. The main disadvantage is the high price of equipment, so this heating is most likely applicable at small facilities.

Note. IR heating of concrete causes intensive evaporation of moisture, therefore, when using such equipment, the solution is covered with cellophane film.

• You can also use the old-fashioned method - arrangement of a heat tentOnly nowadays thermomats for concrete are used as a bedspread, so practically any frost is not terrible here. Only here before they made a tent from the mat and kindled a gas or gasoline burner inside, which is possible only in small areas. But with hot mats, as in the photo above, you can cover almost any fill area.

Warming up by welding machine and PNSV

Resistance PNSV depending on the cross section

Since it is necessary to concrete at minus temperatures not only at industrial facilities, but also at home, we will consider separately the method of heating up concrete with the help of a PNSV cable (Steel Heating Wire Vinyl insulation).

It is connected to a step-down transformer, and in private, instead of a transformer, a 250A welding machine is used, which is enough for small volumes. Calculation of the wire should be made according to the formula R = U / I, where U = 220V, I = 250A, therefore, R = U / I = 220/250 = 0.88 ohm.

Try to distribute the hinges in such a way that their resistance does not exceed the capabilities of the welding unit, but on the contrary, it is slightly less than what is required (in reserve). Laying PNSV on the reinforcement cage, you will achieve that when the air temperature is below -4? C, the cable will heat up to 80? C, and the solution will be up to 40? C-50? C. H

o When installing, you should be careful not to damage the insulation and do not ground the wire to the frame - so the loop will fail - it will burn out.

You need to put the PNSV loops with your own hands so that the entire wire is in solution (otherwise it will burn out), and for connection, output some AR with a similar cross section, besides aluminum, you can build it up to any length, if necessary, but still It is desirable to put as close as possible.

Pay attention to the fact that the twist was sufficiently dense, otherwise they will spark and, as a result, will burn out. When connecting the welding transformer, the automatic reclosing device is screwed either directly to the terminals, or connect it to the ground and holder cables.

Note. When concrete is heated (especially if chemical accelerators are added there), a more intensive setting and hardening of the mortar occurs, but its technical characteristics do not change. Therefore, cutting of reinforced concrete with diamond circles and diamond drilling of holes in concrete occurs in the usual way, according to the instructions.

Conclusion

As you can see, it is quite possible to pour concrete into sub-zero temperature, only this requires carrying out certain additional measures for its heating, among which the most frequently encountered method is with loops from the PNSV. Despite all the troublesome such an installation, this is probably the cheapest and most effective way to warm up, moreover, it can be applied at home without any particular complications.