Drying time of concrete: factors affecting the process of

24-01-2018

Building

The drying time of concrete (or to be precise, the time for gaining strength) is precisely the factor that significantly slows down any construction. And the main difficulty in this case is the fact that the reduction of this time can be achieved only when carrying out quite complex and costly activities.

Below we describe what happens to the solution when it dries, and also give a number of recommendations for optimizing this process.

Material moisture control is an important factor in ensuring its performance.

Dry concrete correctly

Main stages

While the solution is not seized, it can be leveled

To understand how to dry the concrete as quickly as possible and without loss of quality, you need to figure out what happens inside the solution itself after pouring. If you do not take into account the chemical component (it is interesting only for professionals), then we can conventionally distinguish several stages. For convenience of analysis, we have brought them into a single table:

Stage	What's happening?
Grasping	As soon as we poured the solution into the formwork or form (if we were not sufficiently agile, then still in the trough or container of the concrete mixer), the cement begins to react with water. When this happens, primary hydration of the most active components occurs, and a part of the material is polymerized. As a rule, this process takes from 30 minutes to several hours. During this time, the concrete retains its fluidity and lends itself to fairly simple processing.
Strength up to design value	After the initial hardening, the rate of cement hydration is markedly reduced, but still remains at an acceptable level. During this time, the poured concrete hardens, gradually "assimilating" the liquid inside it. In optimal conditions (humidity about 90%, temperature + 15-20 ⁰C) The process takes 28 days. During this period, the material should gain from 60 to 70% of the strength of the potential value.
Ripening	This stage is typical only for piece materials that are used in the manufacture of prefabricated structures. The instruction recommends that, after the completion of the technological cycle, it is necessary to withstand the products for some time in the warehouse, and only then let them go into operation. This is a period of rest, in which there is a smooth completion of all internal processes, and is called ripening.
Changes during operation	It should be noted that even after the start of the use of completely dried construction, the process of cement hydration does not stop completely. If the material receives a sufficient amount of natural moisture from the air, then it gradually becomes more durable. However, this is typical only for those structures that are not exposed to the damaging effects of the external environment.

Note! Artificially accelerating the course of these stages is not worth it: if the solution loses moisture earlier than the cement reacts with it, some of the material will remain without hydration. As a result, areas of uneven structure are formed in the thickness of the monolith, seriously reducing the strength of the concrete structure.

The dependence of the strength of time and temperature

Factors affecting the process

So, we have characterized the main stages of the process. However, as we know from practice, the time required for drying the solution may vary.

What does it depend on?

The first parameter to consider is the composition of the material.. If necessary, various means are added to the solution, which can accelerate the hardening without compromising quality. Naturally, the cost of construction in this case increases significantly, because hardeners are not used in large quantities.

Note! The additive can work both in natural conditions and during heating. In the second case, the use of finely ground slag will be the most economical (approximately 25% of the total mass of Portland cement).

The next factor is the humidity of the surrounding air.. Of course, in a dry climate, the dehydration of the solution will be faster, but as we know, this will lead to the removal of water, which is necessary for the hydration of cement. Consequently, the acceleration of the process can lead to a deterioration in the quality of the product or structure.

Dusting and cracking the surface when dried in the sun

Finally, temperature is important.. With additional heating, the polymerization rate increases due to the increased activity of the reaction between cement and water. Due to this, you can either speed up construction or compensate for the decrease in temperature during the cold season.

In the cold, the material practically does not dry: need additional heating

Speaking of temperature, we can not forget about the cold. When the liquid freezes, the drying process of the concrete practically stops. Moreover, the resulting internal ice expands the pores in the material by increasing the volume, which leads to its premature destruction.

Recommendations for accelerating the drying of concrete

Erecting a building with our own hands, we are often limited in time, but we don’t want to sacrifice quality. That is why the question of how to quickly dry concrete without losing strength, interests many.

Here you can make such recommendations:

The less moisture was originally - the faster it goes out of solution. It is for this reason that a very thick solution is used for irresponsible concreting (leveling the base under the foundation, pouring unloaded screeds, garden paths, etc.).
The reaction rate depends on the size of the particles: the smaller they are, the greater the area of contact with water. So, using fine binders and fillers, we can reduce the time spent on concreting.

Composition with a high rate of solidification

Note! Fine grinding cement is somewhat more expensive than the standard, and it is more difficult to find it.

If we are ready for financial investments, then it is possible to modify the material at the stage of solution preparation. To do this, we either prepare it on the basis of quick-hardening cement, or add chemical modifiers (soda, potash, potassium chloride, sodium nitrite, etc.).

A separate group consists of thermal methods:

First, to prepare the solution, you can use preheated to + 60–80⁰With water. This will facilitate rapid setting and shorten the period of initial curing.
Secondly, formwork for concrete with high thermal insulation values should be used. So the heat accumulated in the concrete will last much longer.

Steaming in autoclaves (in the photo - mass production of aerated concrete)

Finally, in the industrial production of building concrete blocks, a heat and moisture treatment is applied. 8-12 hours in an autoclave with hot steam can effectively replace several weeks of drying in the open air.

Conclusion

Accelerate the drying of concrete to reduce the time of construction work is necessary only if you know how to compensate for the loss of strength of the material. It should be very careful here, because the lack of water in the cement can have a very negative effect on the reliability of the building and its service life. In more detail this problem is covered in the video in this article.