Concrete work in the winter: current methods and features of

For any professional builder is not a secret the fact that concrete work in the winter period requires a special approach, which is fundamentally different from the methods of concreting in the warm season.

In this article we will look at how to work with cement-containing mortars at low temperatures and give effective recommendations on how to do this without compromising the quality and strength characteristics of the finished structures.

Reasons for applying special concreting methods in winter

Concrete work in winter conditions requires a special approach by chance. The fact is that the process of strength development by the majority of cement-containing solutions is based on chemical reactions that take place during the wetting of the grains of Portland cement.

According to statistics, the lower the ambient temperature, the less intensively the process of strength and hardening of concrete is carried out. At temperatures below 0 ° C, the curing process stops completely.

The situation is even worse at sub-zero temperatures. In this case, the water in the thickness of the cement-containing solution freezes completely and the material can be considered spoiled and unsuitable for further use.

Over the long history of the use of concretes, many different more or less effective ways of conducting construction work at low temperatures have been developed.

Features of concreting in the cold season

As already mentioned, the use of concrete for winter works is problematic, since the rate of hardening of the material is significantly reduced at low temperatures. It is connected with the freezing of water and, as a result, with the impossibility of interaction with the granules of cement. You can solve this problem without letting the water freeze.

It is possible to achieve non-freezing of water by heating the mixture to the optimum temperatures at the facility, or by maintaining the material temperature initially set at all times during construction.

The instruction to control the temperature of mortars involves the use of the following technologies:

• adding special ingredients (antifreeze additives) to the solution at the stage of its preparation;
• electric heating of the finished mixture;
• hiding the preheated mixture.

Consider the features of the implementation of the above methods in more detail.

Use of antifreeze additives

Based on the content of SNiP for the production of concrete work in the winter, the main problem for builders is a significant slowdown in the process of hydration of cement grains. Moreover, at a temperature of - 6 ° C, characteristic of warm domestic winters, the water that is part of the concrete freezes and the hydration process stops completely.

Important: Frozen warming water thaws, and the solution can be applied as intended. But, in this case, one does not have to hope that the finished structures and structures will be strong and durable.

In the event that, for organizational or technical reasons, it is impossible to warm the prepared solution at the facility, it is advisable to use special antifreeze additives, which are introduced into the mixture during the mixing stage.

Operation of building concrete with the use of antifreeze additives is allowed both during the construction of monolithic structures and in the formation of prefabricated reinforced concrete at a long-term ambient air temperature below 0 ° C.

At the moment, the most effective and at the same time tested in real conditions are electrolyte additives, which are characterized by an acceptable price and relative ease of use. These additives, along with the function of preventing freezing, simultaneously perform the function of a hardening and curing accelerator.

The most common additives include such fillers as:

• Ammonia water (NH4OH) is a solution of ammonia gas NH3 in an aqueous medium.
• Urea M (CO (NH2) 2) is a colorless, water-soluble crystals.
• Alcohol sodium formate is an aqueous solution of sulfuric and formic acids with sodium salts. This is a clear liquid that is injected by the user into the concrete mixture in the amount of 6% of the total volume of the solution in the mixer.
• UPDM (accelerating antifreeze additive) is a complex preparation, made on the basis of the waste obtained in the production of acetylacetone, acetoacetic ester and nitrochloroctinide. The additive is implemented as a dark brown solution with a liquid consistency. The dosage of the ingredient in relation to the finished mixture is determined empirically (on average, no more than half a liter of additive per 1 kg of cement). Concrete prepared with the addition of UPDM can be used in the temperature range from 0 ° C to -20 ° C.
• Sodium nitrite - yellowish-white NaNO2 crystals or aqueous solutions.
• Calcium nitrate in combination with urea NCM.
• Liquid antifreeze "Hydrozim" is presented in the form of a solution that is added to the solution at the stage of mixing. The introduction of this ingredient ensures hardening and intensive curing of concrete at -15 ° C.

Important: This is the only type of liquid antifreeze that, when dissolved in a concrete mix, prevents corrosion on the metal fittings.

• The antifrosty additive of S-ZM-15 "Gidrobeton" represents liquid of dark brown color. It is added to the solution at the mixing stage and prevents water in the concrete from freezing at ambient temperature up to –15 ° C.
• Asol-K is a complex of organic and inorganic ingredients, including an aqueous solution of potash, modifiers and corrosion inhibitors. At subzero temperatures, the additive eliminates the freezing of water in cement-containing solutions. At positive temperatures, the introduction of the complex provokes the accelerated hardening of concrete.
• WIN-Anti-frost is a complex additive that is introduced directly into the dry mix prior to the addition of water. The recommended concentration is not more than 8% of the total dry mix.

Of course, the list of antifrosty additives given in this article is incomplete, because, in addition to domestic products, a wide range of imported products is on the market. But, the above list is, first of all, available supplements that can be ordered and purchased in most specialized organizations.

Features of electric heating

SNiP on concrete work in the winter time allows the use of various technologies that prevent the freezing of water. One of the most effective methods are various methods of heating an already prepared mortar poured into the formwork.

Let us consider in more detail which types of electrical heating are on the market and can be applied both in industrial and in individual construction.

Warming up using the PNSV wire

This technique, with all its effectiveness, is considered one of the most simple and affordable. The instruction involves laying the heating wire directly during the pouring of the material.

The peculiarity of this type of wire is that the heating takes place through the undervoltage supplied from the transformer. Using a step-down transformer designed for 80 kW, we are able to warm up the solution up to 100m? Up to operating temperatures.

However, along with the advantages, there are some drawbacks, for example, the complex preparation of the object for heating. Experienced builders know how difficult it is to lay the heating cable in adverse weather conditions.

Electroheating by electrodes

This method is in many respects similar to the previous technology with only one difference: instead of PNSV, electrodes made from wire rod with a cross section of 10 mm are used here. The method is not suitable for the manufacture of floor slabs and most other concrete products, but is a good solution for casting vertical structures.

The instruction assumes immersion of the electrodes in the concrete poured into the formwork.

Voltage is supplied to the immersed metal rods from the step-down transformer. On average, the electrodes are laid with an interval of 50-60 cm. At temperatures below -10 ° C, the distance between the electrodes can be reduced.

The electrode warm-up method is especially effective when concreting columns, since in this case it is enough to stick one electrode into the solution. A characteristic advantage of the technology is the ease of implementation due to fast installation and intensive heating.

Important: The price of this method is high due to the large consumption of electricity and due to the fact that the electrodes remain in concrete after use.

Heating formwork application

In this case, heating elements are mounted to the folding formwork. The advantage of the method is the possibility of concreting, even in particularly cold weather, when the temperature drops below -25 ° C.

Among the shortcomings, we note the high cost of the solution and the impossibility of using it in the construction of objects with atypical sizes and non-standard configuration.

Conclusion

This article lists only a brief list of tools that can be used to control the temperature of concrete. But even among this small list, you will be able to find and choose a method suitable for your needs and possibilities.

You can find more useful information by watching the video in this article.