How to properly pour concrete in winter: the most effective techniques

It is better to stop the construction for the winter, as they say - to freeze it. But if it is "hot" and something needs to be concreted, then take note of several techniques on how to do it correctly at negative temperatures. Unfortunately, all of these technologies incur additional costs. But if you ignore them, then the consequences can be dire - improperly poured concrete in winter will not gain the design strength and will simply begin to crumble.

Influence of temperature on concrete hydration

The ideal conditions for concrete curing is an ambient temperature of +20 ˚C. At this temperature, it gains maximum strength in 28 days.

At +5 ˚C, the concrete hardening process doubles. That is, instead of 28 days, a full set of strength occurs in 56 days.

At zero or negative temperatures, hydration stops altogether, which means that in such conditions, concrete will not gain critical strength and after defrosting will collapse (peel off and crumbles).

During winter concreting, it is vital for concrete to gain critical strength, which, depending on the grade, equals 30-50% of the total grade strength. At a temperature of +20 ˚C, critical strength is gained in approximately three days; at +5 ˚C - in about 7 days.

If the concrete freezes without gaining critical strength, then after thawing it will collapse and we can safely say that all the work went down the drain. But if it freezes, gaining critical strength, then nothing terrible will happen - after thawing, the hydration process will be restored, and the concrete will pick up its own.

The conclusion follows from this: concrete should go into winter, gaining vital critical strength. If you are pouring the foundation without the use of heating technologies and the use of special frost-resistant additives, then rely on the weather forecast - at least a week the temperature should not fall below +5 ˚C. If during the day the temperature is higher than this value, and at night it drops slightly (but not below 0 ˚C) - it's okay. You just need to cover the concrete with straw, peat, styrofoam, old rags or other insulating materials.

Material in the topic - How to build a foundation in winter - recommendations from FORUMHOUSE experts.

Techniques for pouring concrete in winter

The most effective and relatively simple technology is the use of a heating cable. It's not cheap, of course, but it's better to spend some money in the winter than to do all the work over in the spring. For example, when using a heating cable 40 KDBS-35, about 4 thousand rubles will have to be spent additionally for each cubic meter of concrete solution. This includes the cost of the cable and the payment of electricity required for the complete and high-quality hardening of concrete.

It is quite simple to use the heating cable: you need to place it on the crate so that it is in the center of the concrete structure, connect it to the power supply and pour the concrete solution. After a complete cycle of solidification of the solution, the end of the cable must be cut off. And the wire remaining in the structure will serve as additional soft reinforcement.

The second effective technique is the installation of a hothouse over the concreting area. This is such an analogue of a greenhouse - it is built from boards and cellophane film. The temperature in the hothouse must be controlled - it must be higher than the cherished +5 ˚C. Ideally, it is better to catch her up to +12, +15 ˚C. For this, wood-burning stoves made from metal barrels or heat guns powered by electricity or gas / electricity can be used in the greenhouse.

The third method is the introduction into the composition of the concrete solution frost-resistant additives. They are of two types:

1. Some reduce the freezing point of water. That is, at frosts down to -25 ˚C, water does not crystallize and the hydration process continues. This group includes calcium / sodium salts and potash (medium potassium carbonic acid salt).
2. The second are set accelerators. They accelerate the hardening of the mortar and allow concrete to quickly gain critical strength at low temperatures. This group includes: calcium nitrite-nitrate; potash; calcium salts mixed with urea.

The dosage of these additives depends on the outside temperature:

• Up to -10 ˚C, 5–8% of the cement mass is introduced.
• Up to -15 ˚C, 10% of the mass of cement is introduced.
• Up to -25 ˚C, 15% of the mass of cement is introduced.

Another technology is heating the solution. Before kneading, fillers (crushed stone, sand, expanded clay) are heated to + 55–60 ˚C; cement up to +20 ˚C; water is converted into boiling water - served in a concrete mixer at +90 ˚C. This technology allows concrete to quickly gain strength, and builders can remove the formwork in a few days.

At the same time, the optimum pouring temperature, when concrete is fed into the formwork, is + 35–38 ˚C. If the temperature of the concrete solution exceeds +40 ˚C, then it will harden more slowly and in severe frosts it will not have time to gain critical strength.

Recommendations for winter concreting

For best results, follow these guidelines:

• Before pouring, the formwork should be free of ice.
• Before concreting, it is necessary to warm up the soil and the reinforcing cage. Heat guns or infrared emitters will help with this. As you already understood, this is very expensive.
• Any structure must be poured at one time - no breaks should be allowed.

Have you poured concrete in winter? Write what technology you used!

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