Hardening of concrete: autoclave treatment, the use of

The main feature of concrete is compressive strength - it is this property that is displayed in the brand. However, brand strength is not achieved immediately, but in the process of gradual solidification. Next, we take a closer look at how concrete hardens, what factors influence this process and how the strength of the material depends on it.

Hardening features

What is concrete hardening and how does it occur?

As is known, cement is used as a binder in concrete. When it interacts with water, a chemical reaction occurs, which leads to the appearance of rocky growths, which fasten together the filler, crushed stone and sand.

The length of time during which the initial bonds between the filler are formed is called seizure. However, immediately after the formation of these bonds, the hardness of the concrete is very low. Therefore, to build strength, they need some more time.

Since the process of solidification is quite long, during this time the water, without which the curing is impossible, has time to evaporate. In order to prevent the solution from drying out prematurely, after pouring, it is covered with plastic wrap or roofing material, and periodically moistened with water.

Note! It is imperative that the mass dries out evenly and moderately. Otherwise, this will lead to a decrease in the strength of the material and its cracking.

Solidification time

Home craftsmen who are engaged in concrete work for the first time are always interested in how much concrete hardens? This process depends on a number of factors, such as ambient temperature, air humidity, etc. However, under normal conditions, this period is 28-30 days.

After the end of the curing period, the structure can be subjected to design loads. It must be said that even after the final hardening, the material continues to gain strength. This increase gives a guarantee of reliability of concrete structures.

The most active curing occurs in the first 5-7 days after casting. During this period, the material gains up to 70 percent strength.

I must say that with an increase in the duration of the solidification of the solution, the characteristics of the material are improved. Therefore, in some cases, the time of hardening of concrete is specially slowed down. As a rule, this occurs during the construction of structures, which will subsequently be exposed to moisture.

These include:

• Piers;
• Dams;
• Dams, etc.

Acceleration of curing

In some cases, the rate of hardening of the solution is necessary to increase, for example, when carrying out construction work in the winter or in the production of building materials from concrete.

To date, there are two ways to accelerate the solidification of the solution:

• Using autoclave treatment;
• With a special hardener.

Autoclaving

Thermo-moisture treatment, which is also called zaparka or autoclave treatment, allows you to shorten the process of solidification dozens of times. For this purpose, special furnaces (autoclaves) are used, in which concrete products are placed for a certain time.

Thanks to steaming under high pressure, the solution gains strength in 12-16 hours.

The disadvantages of this technology include the following points:

• After steaming the material ceases to gain strength. However, at the moment this method is so improved that autoclaved concrete is almost as good as usual.
• It is impossible to handle large structures. Therefore, in the conditions of construction, this technology is not applicable.

Use hardener

The hardener for concrete is a liquid additive that allows you to accelerate the setting time of the solution. This is the only effective way to influence this process at the construction site.

I must say that similar additives improve some other properties of concrete:

• Increase early frost resistance and early strength of the material.
• Plasticize solution.
• Increase the compressive strength of the material at low temperatures.
• Allow you to engage in construction work at low temperatures. The permissible temperature limit may be different, depending on the type of composition. This information contains instructions on the packaging.

As a result of all these properties, the use of hardeners has recently become widespread.

Hardening of concrete at low temperatures

To ensure the normal setting of the concrete solution, the ambient temperature should not fall below +5 degrees, especially during the setting stage. If concrete freezes during solidification, the consequences will be irreversible.

This is due to the fact that there is water in the composition, which crystallizes when it freezes. Moreover, these crystals are capable of destroying the structure of concrete, therefore, after the freeze / thaw cycle, the strength of the material will seriously decrease, and its other properties will deteriorate. Accordingly, it is impossible to continue construction in this case.

To date, builders have come up with many ways to prevent freezing. We have considered one of them above - quick-hardening concrete can be used so that it does not have time to freeze in the cold. In addition, they add special additives that lower the freezing point of water.

Some additives allow you to engage in construction work at temperatures up to -25 degrees Celsius. It should also be noted that the price of such compositions is quite affordable, so that the cost of construction does not increase.

In addition, the mixture is often heated directly in the formwork. For this, external heaters for concrete or heating wires that are mounted with their hands on the reinforcement can be used. Also common is the method of passing electricity through concrete.

Tip! After the final solidification, the concrete becomes so strong that its mechanical treatment causes certain difficulties, especially if it is reinforced. Therefore, the only effective option is to use a tool with diamond nozzles, an example of this is diamond drilling of holes in concrete or cutting of reinforced concrete with diamond circles.

After the mortar sets, the low temperatures will not be scary, so the most important thing is to protect it from freezing in the first stages of hardening.

Conclusion

Concrete hardening is an important process, as the final quality of the material, and hence the strength of the entire structure, depends on it. Therefore, when performing concrete work, it is necessary to ensure optimal conditions for the hardening of the composition, as well as to wait for a set of its brand strength.

From the video in this article, you can get more information on this topic.