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Construction Materials

August 12, 2017 18:06

When removed after pouring concrete formwork

quite understandable desire hosts suburban area to speed up the processes with a troitelstva of their own home.However, the technology works with building materials - a "thing» serious , does not tolerate "free interpretations" and neglect in the style of - "and so come » ...

When removed after pouring concrete formwork ?

When removed after pouring concrete formwork?

Virtually none building not without concreting works.It can be construction belt or monolithic foundation under the house or fence, pouring slabs, floors with inspection pits in the garage, open areas and otmostki around buildings, construction subsidiary facilities, including hydro - septic tanks, swimming pools,wells and more. During active construction season you always want to get done as much as possible , so it is important for the amateur builders getting questions: when remove the formwork after the concrete is poured and, accordingly, when can proceed to further work to set up a concrete structure?

trick is that a clear answer to these questions

- terms stripping and resumption of work depends on several important factors.But with this and try to figure out in this publication.

How is the concrete maturation

Article Contents

  • 1 How is the maturation of concrete
  • 2 concrete ripening in a conventional construction
    • 2.1 Video: removal of the formwork from the strip foundation
  • 3 Creating optimal conditions for maturing concrete
  • 4 few recommendations for the process of removing the formwork
    • 4.1 Video: example of removing wooden formwork with foundation

maturation mortars based cement It can not be considered in terms of a simple water evaporation.This is not what happens, for example, a lump of clay - the evaporation of excessive moisture, and molded weight gains certain mechanical strength.Unbaked clay does not lose its properties and can be used repeatedly.

Maturation of the concrete - it is a complex and not completely reversible physico-chemical process, in which water plays a role not only and not so much solvent as one of the main agents.It is mixed with water drives the chemical reactions that take place with the main mineral components of the cement powder.

  • tricalcium silicate - probably the most important link in the process of recruiting his strength concrete.It was he when combined with water gives perceptible raising the temperature of the solution in the setting stage. action of this mineral will play a crucial role in the maturation of the cement stone in the first, the most decisive month.
  • Dicalcium silicate, on the contrary, "to intervene", as if taken over the baton from tricalcium.But its effect significantly over the years - concrete structures is constantly increasing its strength.
  • tricalcium aluminate - it is this component gives initial speed setting and set the strength in the first hours and days after the preparation of the solution and fill.
  • tetracalcium alumina ferrite - its effect is not so clearly expressed at the beginning, but it is necessary to set the strength of the concrete in the final stages of maturation.

In the process of formation of a stone structure concrete solution passes through two main stages:

A. first always comes grasping solution.This entire process can take several hours, especially in conditions of optimum temperature (about 20 ÷ 25 ° C ), and to one day.At this time, the concrete loses its mobility, acquires give it shape.There is a concept

thixotropic - until the liquid concrete is «stirring» impact processes with with hvatyvaniya not start (of course, to certain time limits).This is what allows you to deliver the finished solution from the production line at its manufacturing site to fill (which is sometimes at a considerable distance) in a slowly rotating containers truck mixer.

Property thixotropic concrete solution allows to transport it over long distances

property thixotropic concrete solution allows to transport it over long distances

Even bathed in the form of a concrete solution at this time still have the opportunity to exert any corrective action - for example, to correct sagging formwork.After setting all manipulations become useless.The solution goes into ripening stage - set strength.

B. curing process - much longer.To say more precisely - its upper limit at all sum is almost impossible.When they say that the concrete during the month of fully matured, more often refers to a set of grade strength at about 95 - 98 % .The remaining interest will be "slowly" to reach for years.

solution already adopted predetermined shape, and at the forefront of chemical reactions.Water served as the solvent, actively into contact with the components of cement, is associated with them, which leads to a rapid growth of the crystal structure of the cement stone.Intergranular communication envelop fillers - sand, gravel, fibrovolokno and etc, gradually transforming raw loose mass in the solid state..

The crystallization process of concrete under a powerful microscope

crystallization process of the concrete modes powerful microscope

more time you can emphasize the importance of water, which this case serves as an active participant in the physicochemical transition from one state of matter to another.Lack of water - is a direct prerequisite for shortage of concrete strength - he turns porous, covered with cracks, loose and etc .Therefore, it is important to maintain the wet condition of the curable solution.

second most important parameter for the concrete stone maturation is the temperature at which the reaction takes place crystallization.When creating certain conditions ( high temperature, humidity and the appropriate pressure, the timing of the initial setting of the concrete and the initial curing can be reduced to a minimum. It is used in concrete products plants where drenched in the form of billets prostrate high temperature steaming in a specially created. conditions

Industrial shakers with an automatic high-temperature steaming

Industrial shakers with an automatic high-temperature steaming

Joint impact on these stands high humidity, temperature and the desired vibration leads to the fact that the finished delati can be removed from the mold already 6 ÷ 10 hours - they this time gained sufficient strength for storage and transport, and formwork already not need.

why this is so is told in detail? Solely to the reader has developed a strong representation the relationship of external parameters and timingconcrete maturation.It is understood that under the conditions of the construction of a private house any special conditions we create just can not.So, let's focus on the real possibilities.

concrete ripening under normal construction

So, the speed set concrete strength, as we have specified, it depends on the grade of concrete, on the ambient temperature and moisture adequacy of the solution.Note, that there is no mention of the number of the cast solution - maturation at the other conditions being equal, will go the same way that an enormous monolithic slab, that in a single small unit.(This allows you to apply the experimental method to verify the strength of structures, where both large structures are cast from the same solution of the concrete blocks, which will serve as test samples) .

Cubes - the test samples of concrete batches

Cubes - the test samples of concrete batches

If dawdle in the old guidance documents for the construction, it is possible to find concrete standards of maturity at which it was officially allowed to conduct stripping filled structures ( SNIP 3.03.01 - 87). Despite the fact that this action SNIP has not been formally extended, it is possible to focus on these parameters - they are checked by many years of experience in industrial and residential construction.

Forms monolithic unloaded drenched designs minimum strength concrete typed, allowing to remove the formwork
vertical surface concrete strength not less than 0,2 ÷ 0,3 MPa
Reinforcedconcrete surfaces on porous fillers tape foundation concrete strength of at least 3.5 mPa, and wherein - at least 50% of the total grade strength
overlapping horizontal and inclined structures (ladders) with a total span of up to 6m not less than 70% of the overall grade strength concrete
horizontal overlap and inclined structure (stairs) with a total span of over 6 m not less than 80% of the overall grade strength concrete

In terms of private construction oftennecessary to resort to pouring belt or monolithic foundation, flooring unit.And in fact, in both cases the recommended concrete is scored to at least 50% of the projected grade strength.

For formwork foundation necessary set of not less than 50 % grade strength

for stripping the foundation requires a set of at least 50% grade strength

Less common, but still resort to casting slabs or inclined structures - stairs.There have to wait a little longer - until the concrete has pick up 70 to 80% strength, depending on the length of flight .

Flight of stairs - always loaded design .For stripping must be 70 - 80 % strength .

flight of stairs - always loaded design.For stripping must be 70 - 80% strength.

believed that with such strength typed unloaded cast construction without the risk can be without formwork - random shock effects are not afraid of it.The desired strength it would gather additionally already in place, and the material is removed the formwork can be used for further work.

But how long after pouring the concrete to reach the required strength values?

results of the survey and observation on the basis of practical construction works allow us to reduce options in a single concrete table maturation grade strength of M-200 M-300 ÷, zameshennogo on the basis of Portland cement M-400 or M-500.(Consider it a concrete, as the most as used across the private construction, in particular - for pouring foundations):

number of days after the concrete ambient temperature potting medium and the percentage of mature concrete
-3 ° C 0 ° C + 5 ° C + 10 ° C + 20 ° C + 30 ° C
1 0.03 0.05 0.09 0.12 0.23 0.35
2 0.06 0.12 0.19 0.25 0.4 55% *
3 0.08 0.18 0.27 0.37 50% * 0.65
5 0.12 0.28 0.38 50% * 0.65 80% **
7 0.15 0.35 48% * 0.58 75% ** 0.9
14 0.2 50% * 0.62 72% ** 0.9 about 1
28 0.25 0.65 77% ** 0.85 about 1 -

Several explanations to the table:

  • per unit (ie,100 % ) maturity taken conditional indicator of strength, which reaches concrete this brand in the "ideal" temperature conditions (+ 20 ° With ) for 28 days.As already mentioned, processes with a ozrevaniya does not end - it can last for years, albeit from a very slight increase in strength.
  • Emblem "asterisk" (*) marked values ​​typed strength, which allows fearlessly shoot formwork filled with design.
  • « double asterisk » (**) - at these rates of maturation can proceed to further construction work, such as masonry walls.Tensile strength yet been reached, but inherent in the structure of the same, for example, the foundation, the cut pB etc. ochnosti allow withstanding continuously increasing workload.A strength over time - will catch up .
  • By ambient temperature is meant its daily average for ripening.

This is important - accounted not peak day values ​​and averaged during the day.For example, the table has a column with a temperature of + 30 °.It would seem, according to values ​​in the table in the summer after 2 days can be carried out stripping, and after 2 weeks - concrete element reaches full maturity!However, to talk about such an average daily temperature in the Russian context, even in the height of summer - very difficult.Even day the thermometer rises to 30 - 32 degrees - at night it drops to 15 - 20. Thus, the average will be within 23 - 25 degrees.

Interesting fact - in the world so far there is no unity of opinion about evaluation criterion for the admissibility of formwork removal.For example, the European recommendations are very similar to the Russian - on the basis of 50% strength unloaded designs.But in the American standards comes a little bit easier - there is usually taken to remove the formwork after 7 days after filling provided the air temperature above + 10 ° C .

In general, if we in the construction of their own home will go a difference in 2 ÷ 3 days, it is best not to exercise anybody required haste.It is better to focus on what to create for concrete optimal conditions for maturation - its quality only benefit from this.

Video: removal of the formwork from the belt foundation

Creating optimal conditions for ripening concrete

naive to think that will be enough to pour concrete into the formwork, level the surface - and will onlyjust wait for the setting and curing, so that you can remove the formwork and move on. : Fresh concrete structure from the very first hours requires a certain care.And the main task here will be:

  • not prevent deformation under the weight of the formwork solution, to minimize shrinkage.
  • Try as much as possible to smooth out the possible temperature changes (daily).
  • Avoid drying the surface of the flooded parts, its rapid dehydration, which lead to cracking of the solidifying concrete.Create the optimal humid mode.
  • To protect the poured concrete structure from accidental mechanical damage.

After pouring should immediately check the strength of the entire casing and, if necessary, to carry out its strengthen weak points.Before setting all still possible to correct.

In some cases, it is advisable to cover the freshly poured the solution from possible rain

In some cases, it is advisable to cover the freshly poured the solution from possible rain

Summer sudden rain - business as usual, but for freshly poured it can be fatal solution.