Concrete pouring in frost: features of work with cement

In this article we will discuss the actual question whether it is possible to pour concrete in a frost and how to do it with the least damage to the quality of the final result. It is no secret that the use of cement-containing solutions in the winter is practiced in industrial construction, since the construction of individual low-rise buildings can be preserved before the onset of the warm season.

However, there are exceptions to this rule, and you have to pour concrete into the formwork at sub-zero temperatures. Consider how this can turn around and how to avoid such consequences.

Low temperatures are a negative factor during concreting.

Instructions for the winter use of cement-containing solutions are significantly complicated by two features that negatively affect the rate of setting and hardening of the material:

• slowing down the hydration of cement particles and, as a consequence, an increase in the duration of the time required for curing;
• freezing of water in the concrete composition, as a result of which the curing process stops.

Let's try to figure out how many days after pouring the concrete is afraid of frost and how the above factors affect the pace of curing.

Low temperatures in the range of 0 to +10 degrees inhibit the hydration of cement. That is, the cement particles are more slowly soaked with water and the chemical reactions that are responsible for the intensity of the strength increase more slowly. As a result, the material not only dries slowly, but even after complete drying, it is characterized by insufficient strength characteristics.

For example, under normal temperature conditions (+ 20 ° C), concrete gains at least 70% of the optimum strength indicators during the week. Similar strength characteristics, under which reinforced concrete can be cut with diamond circles, at a temperature of + 5 ° C, the material acquires within 4 weeks.

Temperature parameters are a catalyst for most of the various chemical processes and the hydration of cement is no exception. Therefore, in the process of manufacturing concrete products, various technologies for heating cement-based mixtures are commonly used.

For example, the previously mentioned 70% of grade strength, at which diamond drilling of holes in concrete can be carried out, the material gains within 12 hours at a temperature of 70 ° C and humidity above 80%.

While the temperature below 10 degrees of heat slows down the curing and setting of concrete, the negative temperature completely stops these processes. Since the water in the composition of the solution partially or completely freezes, the flow of chemical reactions becomes impossible.

In accordance with the technology of concreting cement particles must be in contact with water during the entire period of the set of strength. The average time required for this process to take place under normal climatic conditions is 28 days. But as already mentioned, the lack of heat can adversely affect the course of the process, and therefore a special approach to construction in the winter will be required.

Features of work with cement mortars at low temperatures

Since we are considering winter concreting, we will agree that it takes place at sub-zero temperatures. Therefore, our main task is to prevent the freezing of water, which is part of the solution.

Currently, there are several popular and effective ways to save water in cement mortars from crystallization.

Among these methods, we note:

• the use of antifreeze additives (PMD);
• electric heating application
• sealing the solution with polyethylene films and insulants;
• the use of temporary teams shelters around the formwork with infrared heaters or heat guns.

We will tell about each of these methods in more detail.

Antifreeze additives (PMD) and their use

This method of ensuring optimal hardening parameters of the solution has become widespread. Practically all domestic specialized enterprises have mastered the production of winter concrete with the addition of mineral wool.

At the moment, several variants of winter-type solutions have been developed, differing from each other by the percentage of additives in relation to the volume of the material used.

Importantly, the content of PMD can be determined by the air temperature at the construction site and the grade of concrete used.

Among the advantages of the method we note the following:

• Ease of use in the manufacture of concrete with their own hands, as additives are poured into the mixer at the same time as other components;
• Full safety, in comparison with the same electric heating;
• Affordable PMD, which has a positive effect on the cost of the finished object.

Important: The use of additives in individual construction has one major drawback. To ensure optimal strength indicators, PMD must be applied in strict accordance with laboratory tests, to which most contractors prefer to close their eyes.

Electric heating application

On large construction sites, before pouring concrete into the frost, special electric heating systems are equipped. For these purposes, a powerful transformer equipment with a capacity of over 30 kW and a system of heat cables are used.

The method has the following advantages:

• the possibility of effective heating throughout the thickness of the layer and, as a result, ensuring uniform setting of the mixture;
• the possibility of accelerated curing of concrete in large areas at temperatures up to - 20 ° C;
• suitability of the method for combining with thermally insulated formwork.

Among the drawbacks, we note the high energy consumption and high cost of concreting.

Sealing solution with plastic films and insulation

Sealing and insulation of the mixture using materials with low thermal conductivity today seems to be the most rational method of working with concrete at negative temperatures down to -3 ° C.

The process of hardening and drying of cement mortars isothermal. In other words, when cement particles interact with water, a chemical reaction occurs and a certain amount of heat is released into the external environment. Thus, by covering the formwork and its contents with cellophane or peat-insulating material, this heat can be saved and used to provide curing strength.

Of course, this method is not the best solution for severe frosts. But if necessary, the solution can be preheated, and then covered, and then it can be built at temperatures up to -10 ° C.

The use of heat guns and infrared heaters

If the air temperature drops below -15 ° C, instead of the previously listed methods, it is advisable to apply more efficient methods of heating. For example, in the construction of small objects around structures made of monolithic concrete, temporary collapsible shelters are lined up, within which heat guns are used.

In some cases, the formwork may turn thermomat with infrared heating function. This technique is quite effective, but the road to implement.

Conclusion

So, we reviewed the features of concreting in the winter and found that the sub-zero air temperature is not a reason to refuse to build. But if there is such an opportunity, it would be better to postpone the planned work for warmer days.

If you have any questions that require comprehensive explanations, you will find interesting answers by watching the video in this article.