Concrete is one of the most characteristic artificial building materials in the construction industry, the setting of which will be “delicate” as winter approaches. It is often the case that we sometimes want / need to concretize even when the weather conditions are not really favorable. What can be done to prevent the construction process from getting stuck in this case? The critical properties of the concrete for use (setting time, water retention, compactness) can be changed by adding additives. In addition, precautions taken during the construction process can help ensure that the bonding process proceeds properly.
One of the most important factors influencing the hardening of concrete is temperature. Ideal conditions for concreting are when the ambient temperature is + 20 ± 2 ° C. Thus, very low or high temperatures can be detrimental to the solidification of concrete.
Concreting in warm weather
Although cold weather is typically a more serious barrier to concreting, for the sake of completeness, we mention the effect of particularly warm weather on concreting.
During the hot summer months (above 25 ° C), it can be a problem to lose the water needed for the concrete to harden properly too soon. In addition to cracks on the surface, this can also lead to a loss of strength. In such cases, it is usually sufficient to keep the concrete in the formwork for a longer period of time, or to spray and water it regularly. In this case, the additional cost is only the shutter rental caused by an increase in its duration, which must be undertaken to ensure the stability of the building.
Concreting in cold weather
Concreting in cold weather is when the average daily ambient temperature is lower than + 15 ° C. In this case, we must take precautions to ensure that the concrete structure being prepared is properly solidified. In this case, it is advisable to produce concrete with a higher strength than planned (for example by increasing the strength class of the cement) and / or to schedule the concreting in the morning, as well as to increase the service life of the formwork.
Between + 2-15 ° C, the temperature of the applied concrete mix must reach + 5 ° C (this can be achieved, for example, by adding warmer mixing water) or the use of various antifreeze or setting accelerators. Consider that, by default, mixing water is the cheapest ingredient in concrete. While heating the mixing water increases the cost of concreting by only a few forints per liter, the addition of antifreeze or setting accelerator additives costs in the order of 50-100 forints / liter, which significantly affects the price of concreting. In order to ensure the right quality, instead of mixing the concrete on site, it is advisable to order the concrete from a concrete mixing plant, where the mixture is prepared under controlled conditions.
At an average temperature below + 2 ° C In addition to the fact that the embedded concrete must be preheated to at least + 10 ° C, but even 30 ° C, depending on the ambient temperature, it is also necessary to use additives and to protect the formwork with thermal insulation (because in this case it is already the temperature drops below 0 ° C in the evening) and a longer shuttering time must be calculated. It is important that it is not enough to post-treat the concrete wet below 0 ° C, or to cover it with foil without thermal insulation, as this will not prevent frost damage.
In colder weather than the average daily temperature of + 2 ° C, concreting should be postponed if possible. If the daily average ambient temperature is lower than -10 ° C, concreting is not permitted. (Of course, concreting in a heated room is an exception to the rule).
If concreting work is completed before the arrival of more severe colds, further construction processes are typically less sensitive to weather. Sometimes it is necessary to for the correction of concreting works by concrete cutting, which is a weather – independent workflow.
Thermal protection of concrete structures
With regard to foundations, it can be said that most of them can be done well even in cold weather, because in the case of the often used salt base, the grown soil is able to provide sufficient thermal insulation, so post – treatment is only necessary in the upper plane of the foundation. Until the subsoil of the load-bearing subsoil and the trenches have been frozen, concreting can be started with relative safety, even at an average temperature of less than + 2 ° C (but not more than -10 ° C), in accordance with the rules mentioned above. Care must be taken to ensure that there is no ice or snow in the working trench and on the hardware. If this is the case, concreting should be postponed.
The most sensitive structural elements to cold and the most exposed to cooling are free-standing structures such as pillars and columns. In the case of these elements, thermal protection is of paramount importance and it is therefore often justified to provide them with thermally insulated formwork.
Preparation of prefabricated concrete and sidewalks and plinths, shutter fence if possible, start concreting only above freezing point, for their protection is usually uneconomical and can only be effected with great care.
Prefabricated structures, especially stairs, wall and ceiling panels can be installed in cold weather. At the same time, the fist rules detailed earlier apply to the concreting of semi-monolithic (ie partly prefabricated, partly locally concreted) structures, the remaining formwork and bark panels. However, for this type of building material, manufacturers’ construction guidelines can usually be found in their product catalogs, which should be taken into account (even for warranty purposes only).
Source: Ingatlanhírek by ingatlanhirek.hu.
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