How to warm concrete in the winter during construction?
How does construction work in winter?
Winter is a period of low temperatures, how is the construction of complexes of concrete structures at this time? After all, it is known that concrete is a mixture of gravel, sand, cement and water in a certain proportion. And the time for which the solution is gaining design strength is 28 days. We also know that water, when freezing, occupies a larger volume, and is capable of breaking monolithic structures.
There are several ways to get around the temperature limit, but they all come down to one thing, keeping the temperature of the solution above zero. If this norm is not observed, the constructed structure will not be strong enough and will collapse very quickly. Below we will provide some popular methods for heating concrete at a construction site in winter.
Shelter and heat guns
The technology is quite simple - a tent is built above the desired site and heat is pumped by heat guns. A fairly common grandfather's way of warming the foundation with hot air. Used on small construction sites, a laborious process associated with the construction of a heat-holding dome.
If you want to heat concrete with a heat gun, keep in mind that this will be a fairly costly option. The only advantage of this technique is the possibility of heating the concrete screed without electricity. There are autonomous heat guns, most often diesel. If there is no access to the 220 volt network, this heating option will be the most advantageous.
You can clearly see this method of heating in the video:
Thermomats
Special electric heaters in the form of mats surround the area filled with the prepared solution. Substances are added to the solution to accelerate the setting process and prevent the crystallization of water. This method is good for heating large, even horizontal surfaces in the winter.
Complex structures, columns you can’t heat. You can learn more about how to preheat a concrete structure with a mat, in the video below:
Formwork with heating elements and electrodes
For the heating of poured walls and concrete columns of the company, developers use heated formwork. The formwork is thermally insulated and heaters are installed on the concrete side.The design with the heater does not require additional complex equipment, the elements are easily replaceable.
The electrode formwork consists of rods or metal strips attached to the formwork at regular intervals. The electrodes are connected to a special transformer, and due to the water in the cement solution it is heated. As if the drawback of the heating formwork is the standard sizes, and if the customer has a non-standard project, other methods of concrete heating in the winter are used.
Electrodes
Most often used to warm concrete columns and walls. After pouring the frame elements in the formwork, insert the reinforcement into the solution, arranging and distributing them in groups, connecting to a transformer or welder, as shown in the diagram below:
It is also possible to arrange string electrodes in advance along the frame. The photo clearly shows the principle of the installation of electrodes in concrete:
Water in the solution plays the role of a conductor and gradually, as it hardens, the current through the electrodes drops. After solidification of the mixture, the wire rod remains part of the structure. The disadvantages of this method of heating include enormous energy costs and additional costs for the material of the electrodes.
PNSV wire
A universal and affordable way to heat concrete in winter using a high-resistance cable and a step-down transformer. During the linking of the frame from the reinforcement, a heating cable is laid, it does not matter the size and shape of the structure.
This method of heating is applicable both at the construction site and for home builders. We will tell you in more detail how to warm the concrete mixture with the PNSV wire at home.
After reinforcing the frame of the structure or laying the beacons under the bulk floor, the wire is laid by a snake no closer than 20 centimeters from each other (the optimal laying pitch). The length of one loop is from 28-36 meters. As a voltage source, you can use a welding machine. The connection diagram in this case will look like this:
The nuance of heating, PNSV can not be connected uncoated with a solution, because without heat absorption due to the high temperature in the open air, it will burn out. To avoid burnout, they make the transition to an aluminum cable, leaving the output ends of the PNSV heating wire 10 cm each from the solution. The manufacturer recommends a current in the cable of 11-17 amperes, which can be controlled by current clamps. About, how to use clamp meters, we told in a separate article.
For home construction, PNSV with a diameter of 1.2 mm is enough. Its characteristics:
- resistance 0.15 Ohm / m;
- operating current immersed in a solution of 14-16 amperes;
- laying temperature from -25 to 50 ° C.
The consumption of wire per cubic meter of concrete is 60 linear meters.The temperature to which the concrete is heated is 80 ° C; its control is carried out by any thermometer. The rate of temperature rise in the solution should not exceed 10 degrees per hour. To avoid meaningless spending on electricity bills, the heated area is covered with any material that prevents the heating of the atmosphere, for example, it is covered with sawdust. To obtain an excellent result, the concrete mixture is also heated before pouring, the temperature of the mixture should not be lower than +5 ° C. Here according to such instructions, you can warm concrete in the winter with your own hands. The technology is time-consuming, but even an inexperienced person can do it. About how to lay a heating cable in the foundation, is described in the video tutorial:
By the way, instead of the PNSV wire, you can also use a BET cable for heating concrete. The video below briefly describes the installation instructions for the heating conductor:
The article does not indicate all methods of heating concrete in winter. There are an induction, infrared method and others, but we do not consider them due to their low prevalence and complexity.We gave a general idea about the technology of building concrete structures, and the possibility of using home craftsmen to heat screeds and walls. By the way, the use of the PNSV wire is possible not only during the heating of the structure under construction, but already after that. It can be used as ready warm floor or anti ice on stairs or sidewalks. Short sections are connected via a step-down transformer from 400 to 1500 watts. To connect directly to the 220 volt network, the wire in length will be more than 120 meters.
That’s all I wanted to tell you about why concrete is warmed up in winter and how to implement it using heat guns, electrodes or PNSV wires. We hope our instructions were clear to you. You can get more information by watching the video tutorials in the article.
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