Concrete and frost: pouring mortar and operating structures
Ideally, information on how to pour concrete in a frost is only needed by professional builders. For us, it will be much easier to plan the work in such a way that the solution hardens during the warm season.
However, this is not always the case, therefore it will be useful for each master to study the features of building structures in the cold. Moreover, for this it is enough to master just a few techniques.
Cement mortar and low temperature
Processes occurring during solidification
Concrete work in frost is usually carried out only in exceptional cases. This is due to the fact that when the temperature drops below zero, cement hardening processes are disturbed. This can not only slow down the curing, but also completely stop it, and the mechanical characteristics of the structure will not be reached and 50% of the design value.
This happens for a number of reasons:
- First, all the water that is needed to hydrate the cement turns into ice.. Being in an inert form, it becomes inaccessible for reaction, and therefore the concrete in the cold simply does not harden.
- Secondly, the destructive effect of frost on concrete occurs due to the expansion of pores.: when freezing, the volume of liquid increases by 10-12%, and an irregularly shaped cavity is formed inside the concrete monolith. Even if we then warm up the material and melt the ice, the pore sizes will still be enlarged.
- Third, a thin ice crust on steel reinforcement lowers the connectivity of the metal with the solution by an order of magnitude.. After the ice melts, free moisture gets into this gap, so the appearance of rust and the destruction of the frame will be a matter of time.
- But the worst results are caused by repeated freezing and thawing of the solution.. In this case, its density becomes uneven, and the strength of the structure is seriously reduced.
To avoid such effects, when pouring mortar, the instruction recommends using different methods for heating it. Naturally, the cost of construction increases, but this is the only way to provide the necessary strength.
Methods of struggle
Laying concrete in frost is necessarily accompanied by a set of measures aimed at neutralizing the effects of low temperatures. To date, there are several techniques, the main of which are described in the table:
| Method | Features of the implementation |
| Chemical processing | Special concrete liquid from frost is introduced into the solution. When mixed with water, it prevents it from freezing, leaving it available for cement hydration. An additional advantage is the significant acceleration of the solution polymerization. |
| Thermal insulation | Here two aspects of the technique are implemented: · First, the solution is poured in a heated state. Mass temperature up to 70 0It is able to resist freezing for a long time, which contributes to a set of strength. · Secondly, to maintain the high temperature of the mortar, the formwork is carefully insulated. In addition, the top of the design is also covered with foil film reflecting heat waves. |
| Electrode heating | Reinforcement cuts are immersed in concrete, to which electrical wires are connected. With the passage of current through the solution, an electromagnetic field is formed, part of the energy of which is transferred to the moisture entering the concrete. |
| Cable heating | The method works according to the “warm floor” principle: the formwork contains conductors in polyethylene or polyvinyl chloride insulation, which are connected to a step-down transformer. When current is applied, the wires are heated, transferring heat to the surrounding material. Special cables are also used for this purpose, which can operate without a transformer. They cost a bit more expensive, but they are easier to assemble with your own hands. |
Note ! Analyzing what is added to the concrete in the cold, you can find both descriptions of branded compositions, and examples of homemade mixes. The most affordable will be the use of aqueous solutions of calcium chloride (from 3 to 4.5% depending on temperature) or sodium nitrate (from 4 to 10%).
Experts in the field of concrete work recommend the use of these methods in the complex, combining, for example, anti-frost additives with cable heating.
Cold resistance of concrete
However, pouring the solution and waiting until it hardens under heating is only half the battle. Cutting reinforced concrete with diamond circles clearly demonstrates that even very hard material under the influence of low temperatures loses strength over time. This happens due to the freezing of water falling into the surface pores.
Note! The more cycles of freezing / thawing takes place during a season, the greater the destruction will be.
There are several ways to deal with this:
- First, it is enough to simply close the pores on the surface with a special impregnation. True, this can disrupt the natural vapor permeability of concrete, because you need to act carefully, with an eye on the power of the ventilation system of the building.
- Secondly, it is possible to reduce the porosity by compacting the concrete. To do this, at the filling stage, a vibration treatment is applied, as a result of which practically all the air from the solution leaves.
Note! Another effect of vibrocompaction is to increase the strength of the material: if necessary, machining may require cutting with a special tool or diamond drilling of holes in concrete.
- Finally, there is a third, somewhat paradoxical way: the number of pores is not reduced, but increased to redundancy (about 20% more than the normal water absorption of concrete). This creates a reserve volume of air, which does not allow the freezing ice crystals to "tear" the material from the inside.
Conclusion
Using these methods, you can reliably protect the structure from the cold and provide it with a comfortable environment for curing. But it is still better to plan the construction for the period when the concrete is not terribly cold and we do not have to spend money on additional heating. And if it did not work out - then try to implement the techniques described in the text and shown in the video in this article.