At what temperature to lay the foundation

Pouring the foundation - important stage of construction.An important factor that contributes to the strength of the foundations at home is not only the quality of the concrete, but also weather conditions.At what temperature can be poured the foundation, so as not to disrupt the process of setting and hardening of concrete?This depends on the concrete quality, and also on the presence of additives which reduce the crystallization temperature of water.

concrete hardening process and its characteristics

After pouring the concrete foundation has two stages: setting and hardening.does not exceed the setting time of day, in this phase the concrete solution passes from the liquid to the solid phase.But its strength while still not high.After setting the curing process begins, it lasts much longer and is determined by many factors: the concrete brand, its composition, the presence of additives, temperature and humidity conditions.

optimal conditions for the setting and hardening of concrete is considered normal temperatures range from 3 ° to 25 ° C.In this process, the speed is directly dependent on temperature - warmer, the faster the concrete setting and strength development, it also increases with the grade of concrete.

concrete brand - it is characteristic of its compressive strength after soaking in normal conditions for 28 days.That is, after four weeks of any grade concrete acquires its design strength, after which the curing continues for several years with an extremely low velocity.

There is another characteristic of concrete - a critical strength.It is expressed as a percentage of the project and indicates the degree of hardening, in which exposure to low temperatures does not entail irreversible changes of the concrete structure and process of hardening.The share of different brands, this figure is different, its values ​​are given in the table.

speed hardening concrete changes non-linearly depends on the temperature and time.It can be defined by the graph shown in Fig.Charts are built for different ambient temperatures, thus it is necessary to take into account the daily fluctuations and to take the lowest temperature value.Concrete temperature above 35 ° C is achieved by heating the cast solution.

temperature falls below 3 ° C begin phase transformation into ice water, and the uncured concrete structure is broken, there are microcracks, which subsequently lead to its destruction.

Lowering the temperature below zero leads to a complete stop cement hydration process, the curing process is completely stopped.After raising the temperature and thawing process can be resumed, but the reverse recovery of destroyed relationships do not happen.However, if the concrete has reached a critical strength, the temperature drop will not cause irreversible changes in it, and after thawing the hardening process resumes.

example of determining the possibility of pouring the foundation

Condition: the foundation is poured at a temperature of 5 ° C, and the weather forecast promises cooling to sub-zero temperatures after 72 hours.Will this affect the strength characteristics of concrete and brand M300?

For concrete M300 critical strength is 40%.As seen from the graph, at a temperature of 5 ° C in the critical strength of the concrete is 40% dialed only after 130 hours.Conclusion - pouring of the foundation can not be performed.

How to pour the foundation of sub-zero temperatures?

To accelerate the setting time and hardening to a critical strength, you can resort to the following techniques:

1. provide increased temperature of the solution or poured foundation.
2. Choose a higher grade of concrete.
3. Use additives and plasticizers.

solution temperature increase is achieved by heating components to 30 ° C and using hot water with a temperature of 70 ° C.When mixed hot water solution is added to the particulate filler, and then introduced into cement mortar.

Flooded basement or insulated by covering film and insulating materials, or erect a temporary building heated.As a heat-insulating materials, you can use straw, sawdust, peat, snow.

Increase concrete brand can be by increasing the contained use of cement or dry cement a higher grade.Determine the contents of components is possible by means of calculation.

additives and plasticizers are used to impart various properties of concrete: accelerate the hardening process or lower the freezing point of water.Possible additives are given in the table.When using the additives are mixed with water.