Time runs fast, we also want to build quickly, and our climatic conditions from positive temperatures gradually go to negative. Not so long ago on the construction of the foundation at negative temperatures there could be no question. But modern achievements in construction lead to continuous construction at any time of the year. An important role is played by quality cement from a reliable company, for example pargrupp.ru and various modifying additives to create high-quality concrete in the winter. There are new ways, using which creates a solid monolithic base in the winter.
Content
- 1 Preparation of concrete, how concrete works and what is the hydration of concrete
- 2 Methods of concreting
- 3 Heated concrete
- 4 The foundation is frozen
- 5 Additives for concrete in the form of modifiers of concrete, plasticizers for mortar
- 6 Methods of winter concreting or artificial heating
- 7 Important Tips
Preparation of concrete, how concrete works and what is the hydration of concrete
At negative temperatures, water crystallizes, and water, along with cement, is the main component for the preparation of concrete.
Hydration is the process of binding particles of a water-soluble substance to water molecules, and as water turns into ice, formation of reliable molecular bonds is broken, porosity is obtained and the strength of the foundation is reduced.
At positive temperatures, the process of concrete formation goes as follows:
- a thin shell of sodium hydrosilicate is created on the surface of the mixed cement mixture with sand and crushed stone;
- solid inclusions of cement suck in moisture and get bonded all the components of the solution;
- the outer shell loses water and begins to contract;
- gradually, the same thing happens in the deeper layers of concrete;
- after 28 days, concrete is gaining maximum strength.
At positive temperatures, during a hot time, the hydration process accelerates, and low temperatures can slow the hydration process due to the fact that the water turns into ice crystals and unfilled pores are created in the concrete.
That is why, in order to prevent the creation of voids in concrete, the foundation must be filled in winter in accordance with special rules.
The process of hydration is able to arbitrarily increase the temperature of the concrete pouring.
Based on this, the practitioners came to the conclusion that the larger the concrete structure, the more heat this concrete releases and the slower its cooling.
Important! In cold weather, it is better to pour a tape or monolithic foundation and do not make a foundation of pillars. And if you install a heat-saving formwork around a tape or monolithic foundation, at low minus temperatures, you can get quality concrete without additional efforts.
Methods of concreting
The quality of a concrete structure in the winter depends on various conditions:
- from the dimensions of the concrete structure;
- from the composition of concrete and its components;
- on the quality of cement and the fineness of its grinding;
- from climate change;
- from heating water and aggregate.
At low temperatures, there is not always enough heat, which is released during hydration, to obtain high-quality concrete.
Important! To the aid will come the fine grinding of cement, it quickly reacts and emits more heat. Heating water and aggregate are also capable of raising the temperature.
Important! Cement can not be heated, since it will lose its binding properties. Only water and aggregate can be heated.
Usually builders heat water up to 32 * C and this is enough.
But, if the water temperature is higher, then first it is mixed with the aggregate and only then cement is added.
In addition, builders advise to increase the time for mixing concrete components by 25% and use only fine cement.
Heated concrete
The option of heating water, filler is quite suitable for the time of foundation flooding with small night frosts and plus temperatures during the day.
Next to the concrete mixer, you can install a brazier, a heat gun or a gas burner.
But in doing so, you must strictly follow certain rules:
- water heating is not higher than up to 80 * C;
- hot water is first mixed with the aggregate and only then, gradual cement is introduced from M400 to M500;
- it is necessary to use additives that increase the speed of hardening;
- it is desirable to use a vibratory device, thereby reducing the porosity;
- after pouring concrete, the foundation is completely covered with sacks, blankets or straw;
- around the base set the braziers or heat guns for heating;
- after the strength of concrete is set, the heating stops and the formwork is dismantled.
Important! Formwork can be removed only after the foundation will gain 70% strength.
The foundation is frozen
In the case where the concrete is not completely cured, it is allowed to freeze.
The process must be mothballed, and after defrosting at plus temperatures, the solidification reaction will go its course.
If the water-cement ratio in the mixture of concrete was not more than 0.6, such unfrozen foundations will not lose their strength properties by more than 5%.
Since it is difficult to produce the correct mixture of concrete in the frosty time, it is better to purchase it in ready-made form with various additives at the factory.
Additives for concrete in the form of modifiers of concrete, plasticizers for mortar
By incorporating various additives into concrete, concrete is capable of increasing thermal energy and reducing the temperature of water transfer to ice.
Adding calcium chloride or a common salt to the concrete, and it can be introduced no more than 2% of the total mass of concrete, anti-frost properties are formed in concrete, concreting can be carried out at a temperature of -15 * C. And yet, once again, we advise you to use the ready-made concrete compound made at the factory.
The formwork can be removed if the strength is set:
- concrete M200 - 40% strength;
- concrete M300 - 30% strength;
- concrete M400 and more - 20% strength.
And even using concrete with various modifiers - use artificial heating.
Methods of winter concreting or artificial heating
When winter concreting, in the building organization you can order different types of concreting:
- thermos method. On the foundation is put an insulation covering in the form of a metal casing with electric, steam or water heating;
- steam heating. Such a method is more costly and complex, since a number of pipes are installed in the formwork, which will then remain in the foundation body, steam will be supplied through these pipes and concrete will be heated;
- installation of a greenhouse around a flooded foundation. A tarpaulin or polyethylene tent is placed on the foundation, a portable stove, a heat gun, etc., which maintain a constant temperature and humidity, are in the firebox. This option is also expensive;
- electric heating of the foundation. One of the more economical and simple ways. The electric wire entangles the formwork or the reinforcement structure, the current heats the concrete. It is possible simply to lay the heating cable in concrete.
Important! These jobs must be performed by qualified employees.
Important Tips
- The foundation in winter conditions is poured completely, without stopping, if necessary, it will be necessary to work around the clock.
- Laying of concrete is done in small, in height and length, portions, the layer is superimposed on the layer, this will reduce the loss of concrete temperature.
- If a gel shell forms on the surface of the filled concrete, it must be removed by physical methods. Before pouring the foundation, it is necessary to clean the trench from snow and ice. Before the concreting, the bottom warms up, approximately 30 cm.
Important! On the frozen ground it is impossible to pour concrete, otherwise, the ground will melt, under the concrete, and there may be a sediment, and uneven.
Observing all the above conditions, you can make a quality foundation in the winter.
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