The curing temperature of concrete and methods to control

At what temperature does concrete harden and how does the fluctuation of this factor affect the rate of strength development? We will answer these and other equally important questions within this article.

Despite the fact that the rate of drying of cement-containing mixtures depends on a number of factors, it is the temperature that is the most important parameter that should be taken into account both in construction using monolithic concrete and in the manufacture of various concrete goods.

Optimum conditions for curing and curing

The hardening of cement-containing mixtures is a complex physico-chemical phenomenon, during which Portland cement, interacting with water, forms new compounds.

This chemical reaction occurs gradually, as water penetrates the cement mass at a low speed. This observation explains the long periods of concrete hardening. Indeed, even after several months of hardening, a certain amount of cement grains only reacts with water.

Given that the rate of hardening of concrete depends on the temperature, it becomes possible to speed up the process at times. For this, it is necessary to create favorable conditions under which the process of setting and curing of the mixture will proceed more intensively.

The optimum temperature for the hardening of concrete is +22 ° C with a relative humidity of ambient air of about 90%. For example, such conditions are created during the chamber production of concrete goods, but in addition, these parameters of temperature and moisture content can be created by sprinkling the surface of concrete with moistened sand or during irrigation with water.

Under optimal conditions, the increase in the strength of hardening concrete proceeds quickly and already within 1 to 2 weeks after preparation, the material gains over 60% of the strength that could be achieved during 28-day hardening under normal conditions.

It is important to monitor this process in a timely manner and prevent further surface drying, periodically irrigating it with water. Thus, we will allow the cement-containing mortar to achieve a given strength throughout its thickness.

The effect of temperature and humidity on the hardening of concrete is indisputable. Moreover, the non-observance of technological regulations not only negatively affects the quality of the finished structures, but can also result in multiple destruction of concrete.

The fact is that in the process of solidification of the material, a large volume of liquid is released from its thickness and shrinkage occurs. If the optimum temperature and humidity parameters are not ensured, microcracks may appear on the surface of the material, and it will be necessary to cut the reinforced concrete with diamond circles for subsequent repair of the damage.

Control of the intensity of hardening of the material through special additives

As already mentioned, the increase in the strength of the cement-containing mortar during the drying process substantially depends on the temperature indices. For example, the hardening of concrete at low temperatures slows down, while increasing the temperature accelerates the process.

Since the duration of the process of strength building is of fundamental importance during construction work, this indicator is sometimes artificially accelerated.

How to accelerate the curing of concrete without negative consequences for its quality?

For these purposes, a number of additives accelerators are used, which are added by hand to the composition during the preparation of the mixture. Since the use of special additives is found mainly in industrial construction, their content in the composition is determined not by experiment, but by technological standards approved in the laboratory.

As a rule, the content of additives-accelerators for the normal hardening of concrete should be within the following limits:

• calcium nitrite nitrate-calcium chloride, calcium nitrate, sodium nitrate, calcium nitrite and sodium nitrite-nitrate-sulfate - 4%,
• sodium sulfate - 2%,
• calcium chloride — from 2 to 3%.

Important: A full list of recommendations on the use of additives that accelerate the hardening and curing in cement-containing solutions can be found in SNiP III-15-76.

Control of the intensity of hardening of the material through heating or the use of insulating formwork or shells

In the manufacture of precast concrete in the cold season, to speed up hardening, heat treatment of concrete by means of electricity, steam or insulated formwork is widely used.

Important: Significantly reduce the time required for hardening the mixture, without prejudice to the finished result, you can combine forced heating and the use of additives, accelerators.

The most popular today received methods of heating the concrete with the use of electricity. And this is not surprising, since such methods of controlling the temperature parameters of a concrete mix are simple to implement and, at the same time, quite effective.

The technologies of electric heating of the mixture include:

• electrode method;
• heating loop application;
• formwork heating method;
• induction heating;
• infrared heating;
• heating using liquid installations.

Since the schedule of hardening of concrete depending on temperature can undergo significant changes, consider the method of controlling the temperature of the solution by means of the electrode method and heating using heating loops.

Electrode method

By means of electrode heating, the rate of heating of concrete can be significantly accelerated even at sub-zero ambient temperatures. In the course of heating, electricity is passed through the material, as a result of which heat is generated.

As a rule, this technique is used in the manufacture of vertically arranged structures and concrete products, as well as for horizontal surfaces with a small area.

The advantages of this method include:

• simplicity of laying of the heating loops;
• operational safety;
• short time of hardening of the solution, even in adverse climatic conditions;
• low selling price of heating.

However, there are disadvantages, among which are:

• Significant energy consumption, since it is necessary to supply a current with a capacity of at least 1000 kW based on 3-5 m? concrete solution. Of course, not every construction site can boast such energy supply parameters.
• As the solution dries, the warm-up requires a higher voltage, or it becomes impossible at all.

Heating with heating loops

This method of controlling the temperature of concrete works on the principle of current limit on the cable and is used mainly in the formation of concrete floors and concrete screeds.

Among the advantages of the method it should be noted the possibility of effective heating of the mixture from the inside at all stages of its hardening. Among the drawbacks we note the complexity of the installation, and the possibility of destruction of the insulation of the wire during the drying of the mixture.

Conclusion

Now you know what factors can affect the parameters of concrete hardening and what is the instruction to ensure optimal conditions under which drying will take place not only quickly but also without prejudice to the performance of the finished object or structure. You can find more useful information by watching the video in this article.