The minimum pour point of concrete - features of concreting

When working with concrete, it is extremely important to take into account the effect of ambient temperature on its hardening rate and strength. Ignoring this point can lead to a decrease in the quality of the material, which in some cases is simply unacceptable. Therefore, we will consider below what is the optimal temperature for concrete hardening, and what to do if the ambient temperature is significantly lower than this figure.

General information

So, the best temperature for concrete hardening is considered to be about + 20 degrees Celsius. However, it is not always possible to withstand such conditions. There are cases when it is necessary to perform concreting in the cold season.

For example, the need for winter works may arise in the following cases:

• Concreting in crumbling soils, which is difficult to perform in the warm season.
• Winter discounts on cement. Sometimes the price of the material can be really very low, but, at the same time, it does not make sense to keep it before the onset of warming, since the quality of the cement will decrease. In such a situation, the best option would be to work in low temperature conditions.
• With private construction. Often, it is easier to get a vacation in winter than in summer.

Note! In winter, more expensive to dig trenches, in addition, it is necessary to provide a place for heating people. Therefore, building is not always profitable.

Features of concrete pouring at low temperatures

First of all it is necessary to figure out what temperature, when working with concrete, should be considered low. It is considered to be cold weather among builders if the average daily temperature falls below + 4 degrees Celsius. In this case, for the success of this construction operation with your own hands, you must take special precautions that will protect the solution from the negative effects of cold.

The fact is that the freezing of concrete at low temperatures occurs in a special way. The speed of this process and the quality of the final result depends largely on the temperature of the water in the composition.

The higher it is, the, respectively, faster freezing occurs. Its optimal rate is 7-15 degrees.

However, low ambient temperature in any case has a critical effect on the rate of cement hydration. As a result, the curing and hardening occurs much slower.

To calculate how much concrete hardens at sub-zero temperatures, you need to consider that its fall by 10 degrees reduces the curing rate twice. Such calculations are important in the planning of construction works and the removal of formwork.

Note! If the temperature drops below -4 degrees Celsius, the mortar will simply freeze, and, in this case, the solidification process will stop altogether, and the concrete will lose up to 50 percent of its strength.

However, there are positive aspects of pouring at low temperature - with proper organization of the process, there is a chance to get a better result, since a lower initial temperature ultimately gives greater strength. The only thing you need to remember at what temperature freezes the concrete solution, i.e. make sure that it does not fall below -4 degrees.

Artificial increase in the rate of hardening

Since concrete freezes at sub-zero temperatures very slowly, and construction times are often limited, builders have come up with several ways to speed up this process.

The most common ones are the following:

• Adding special additives to the solution;
• Concrete heating электрическим кабелем;
• Using more cement in the composition.

Now let's take a closer look at the features of each of these methods.

Using modifiers

Most often, when carrying out construction works in the winter, modifiers of the following types are used:

• Type C Additives - accelerators of hardening of concrete;
• Type E supplements - water displacing boosters.

The most effective and common is potassium chloride. However, its share in the total mass should not exceed 2%.

It must be said that the hardening accelerators do not affect the quality of concrete, however, at the same time they do not protect it from freezing. In addition, their use does not cancel the requirements for the solution temperature and the implementation of measures to protect it from freezing.

Note! When performing a screed or foundation, you need to immediately consider the presence of openings and channels for communication, since the subsequent processing will be very time consuming. In addition, it will require a special tool, for example, cutting reinforced concrete with diamond circles implies the presence of a powerful grinder.

Concrete heating

For heating concrete often use a special cable. This method can be called the most natural. The only thing to achieve a positive result should be strictly followed certain instructions for heating (find out also how the concrete is heated by the welding machine).

Unlike the previous method, heating allows you to protect the concrete from freezing. Accordingly, there is no need to calculate at what temperature the concrete hardens and how long this process lasts, since it is possible to ensure quite normal conditions.

Increased cement dosage

This method can be used with a slight decrease in temperature. Increasing the dosage should be small, otherwise the quality of concrete and its durability may be significantly reduced.

Tip! If after hardening the mortar it was necessary to drill it, then the most effective method is diamond drilling of holes in concrete.

Conclusion

Бетонирование при минимальных температурах имеет ряд особенностей и требует особого подхода к выполнению работ. Самое главное – не допустить цикл замораживания и размораживания раствора. Но, в то же время, если выполнить операцию правильно, то в итоге вы получите более прочный материал, чем при заливке в нормальных условиях (см.также статью «Перегородки из газобетона – основные нюансы возведения»).

From the video in this article you can get some additional information on this topic.