Laying concrete at low temperatures: how to ensure the

The need for concrete work exists all year round. The climate in most regions of Russia is severe. Negative laying temperature of concrete has a negative effect on the strength and hardening of the mortar.

As a result, in winter, you should additionally create a humid and warm environment around the poured concrete, to ensure the preservation of all its design characteristics.

Problem solving methods

The water present in the solution freezes at negative temperatures. The pieces of ice that are formed have a larger volume than liquid water.

Note! They create voids after the mixture thaws. This leads to a significant loss of concrete strength. If the mortar freezes at the initial stage of setting of the cement contained in it, then the concrete structure or structure in the spring simply collapses.

During Soviet times, effective methods were developed for pouring concrete in the winter.

They provided the opportunity to work at low temperatures.

1. Then the most popular method of winter laying concrete was that the components included in it were heated. Further, their temperature was kept constant. In addition, the positive temperature of the concrete was created when the concrete was laid (the structure itself), until it gained regulatory strength.
2. Now new methods have been developed that make it possible to carry out work in the winter, without the need to heat the components of the mixture or its own, after installation.

      Laying the mixture using the principle of "thermos"

1. The instruction says that a simple method to create acceptable conditions for the hardening of concrete in winter is the arrangement of a “thermos”. It will isolate the structure from the action of the environment. This technology was developed 50 years ago by Professor I. A. Kiriyenko.
2. When applied, the surface of a concrete structure is covered with a layer of insulation (sawdust, slag, straw mats, reeds, etc.). The “thermos” method is optimal for creating massive structures with a relatively small cooling surface. The air temperature should not be lower than -15 degrees, and the ratio of the surface of the structure to its volume should be less than 6.
3. The heat released by the cement during curing heats the entire structure from the inside. Insulation does not allow him to go into the atmosphere.

Concrete heating

1. In order to increase the curing of the solution in small structures, special accelerator additives are added to it.
2. For structures with relatively small dimensions, additional heating is also used. This is done with the help of wood houses made of wood, hot steam or air (a special casing is made for it around the formwork).
3. The positive temperature of the concrete during laying in the winter is maintained by means of electric current. For this, manufacturers produce special thermal mats for concrete.

Alternative to conventional concrete

When working with concrete in the winter, another method has gained wide popularity.

Cold resistant additives

It is based on the addition to concrete of special additives that increase the frost resistance of the solution. They lower its freezing temperature and accelerate hardening and strength gaining.

These are, as a rule, salts, the price of which is low - sodium chloride or calcium.

1. This method is optimal for the construction of any critical structures, if there are frosts or light frosts. In this case, additional heating of the concrete is not needed. After the mixture is completely hardened, diamond drilling of holes in the concrete can be performed.
2. When the object being built is not responsible, a larger amount of modifier can be applied. Then the work can be done at -20 degrees.

During the construction of monolithic concrete structures not reinforced, SNiP No. 111/1/76 requires to ensure that the strength of the solution is gained, to the freezing point, not less than:

• 50% if M-150 concrete is used;
• 40% when works are performed with a mixture of M-200 or M-300;
• 30%, when choosing a solution of M-400 or M-500.

When constructing objects that after the completion of construction will freeze and thaw, the strength of the mixture should be at least 70% (for any classes of concrete). If the design was prestressed - 80%.

The strength of the solution with additives

Antifreeze additives are added to the solution, taking into account the atmospheric temperature.

The strength characteristics of the mixture, by the time it has cooled to the design temperature, should be equal to:

• 30% if concrete is used up to M-200;
• 25% when the choice falls on the solution M-300 / M-400.

Note! Solutions of voiced brands, having gained a preliminary strength of 25/30%, can freeze without negative consequences. However, after their spring thawing, they must reach the strength characteristics up to 100% until they are fully loaded. The same statement is true if reinforced concrete is cut with diamond circles.

Preparation of the mixture in the winter

1. In winter, the solution is produced in heated workshops of concrete plants.. The process is monitored by laboratory technicians who test and test the mixture for strength. Determining at what temperature you can put aerated concrete or other types of material, they control the addition of modifiers to the mixture.
2. Fillers (gravel, crushed stone, sand) before filling them into concrete mixers, are heated without fail (like the water used) and are loosened. This is necessary to ensure that the temperature of the finished concrete meets the permissible standards.

1. Determining the temperature at which the concrete is laid, designers should understand that it should be poured in winter with a store of heat.. It is spent during transportation of the mixture to the construction site and during the work, before the building starts to warm up (if this method is used).
2. Concrete laid with your own hands in the formwork should have a temperature not less than the design, calculated for the application of the "thermos" method.
3. In the manufacture of winter mortar, the temperature of the fillers and water (when they are fed into the concrete mixer), as well as the temperature of the finished concrete, are determined using. This takes into account the heat loss during mixing of the components of the mixture, delivery and laying of the material.
4. The use of excessively heated water may result in steaming of the binder.. To avoid this process, it is necessary to strictly regulate the order in which the concrete components are placed in the mixer. So, crushed stone / gravel at the same time with water poured into the mixer. Only after filling the unit with half the volume of water needed can sand and cement be poured.
5. The mixing time of the components of the solution should be increased in winter, at least 25 percent, compared to the process of preparing concrete in summer (if only hot water is used). When all components of the mixture are heated, the duration of the process can not be increased.

Conclusion

At the moment there is the possibility of high-quality concrete work under the most severe winter conditions.

There are several important factors to consider:

• temperature regime associated with the work;
• optimal concrete mix for these conditions;
• and exact following of the chosen technology.

The video in this article will help you understand the topic presented today more clearly.