Temperature for concrete work: optimal values ​​for quality

The main problem accompanying work on concreting in winter is low temperature. As a way out, you can consider the use of special-grade material, the use of antifreeze additives, electric heating and other modern tricks.

Each of the options is good in its own way. But only properly selected technology will help to carry out concrete work at low temperatures without loss of quality.

Temperature conditions

Concreted surface sets and hardens the faster, the warmer and drier around.

What prevents the cold

In winter, it is not only cold that interferes, but also excessive moisture, which slows down the process of hardening.

Here are the main factors negatively affecting the process.

1. Cement hydration slows down, up to a full stop of hardening and curing of a concrete product.
2. Water, necessarily present in the mixture, freezes, destroying the structure of the material.
3. Moisture contained in ambient air in high concentrationslows down freezing. The time to build strength in this case is significantly increased.

Optimal conditions

With the onset of the winter season, construction work does not stop.

Depending on the conditions, the temperature during concrete work may contribute, not to interfere with or interfere with the process.

1. When the mode is from 0? up to +10? hydration noticeably slows down. On average, the process of curing up to 70% is up to 4 weeks.
2. Is the temperature above +11? slightly speeds up the hardening, but in this case it is far from the norm.
3. Favorable is the temperature of +20 ?, then you can not carry out additional operations to accelerate the set of strength.

Note! The standard established by regulatory documents, it is considered to be the full hydration of the material within 28 days. To achieve 70 percent strength with favorable factors, 10–12 days are sufficient.

Water as a necessity

Cement hydration without the presence of water is impossible. It acts as a necessary component that helps the formation of cement stone. Throughout the maturation period, water must be in contact with the cement.

Temperature mark below 0? considered critical.

At this time, the liquid begins to freeze, expanding and destroying the structure of the material. Especially undesirable several cycles of freezing and thawing. In this case, structural bonds are broken more intensively, ultimately completely destroying the finished structure.

Features of work in the winter

Consider all the nuances and possible problems arising from a negative ambient temperature. The main task is to keep the water in the solution from freezing. The problem is even more urgent if you work with your own hands, equipping your life.

Let the summer wait for a long time, it is necessary to adapt to not the most comfortable conditions.

1. You can apply antifreeze additives (PMD) for concrete.
2. In some cases, it helps to cover the poured surface of PVC with a film or rolled insulation.

1. Electric heating of concrete structures works well.
2. Temporary structures are erected over the concreted areas and provide heating with a heat gun.
3. Often, the cement mixture is prepared on heated water. A positive temperature maintained with mixing will give a good result. Especially if the laid concrete is isolated from frost by one of the above methods.

Note! During large-scale installation work, expensive techniques are not always used due to the high cost. Often the instruction prohibits the use of electric heaters. So you have to choose the best option for your case.

Basic rules and regulations

1. With a well-chosen heat balance of the finished mixture, dry fillers that do not contain icing, they are loaded into a concrete mixer in an unheated condition.
2. The temperature of the mixture at the exit from the mixer for Portland cement (including pozzolanic), slag Portland cement below 600 grade should be +35?
3. For grades above 600 and fast-hardening analogs, a temperature strip of +30 ?, for alumina cement +25 ?.
4. The time of transportation and laying of the heated cement mixture should not exceed the time before the concrete begins to set.
5. The temperature of the concrete mixture laid in the formwork at the beginning of heating or aging should not be below +5 (when using concrete with antifreeze components). At heat treatment the mode not below +2? Is observed.
6. The concrete is poured continuously, during forced breaks it is covered with a film or heated.

Note! Regulatory conditions are considered when concrete work is carried out and the air temperature around is not below +5? Temporary warming over the structure will help to raise it to the desired level.

1. Concrete without antifreeze additives at the time of freezing should acquire the strength of 50%, 40% and 30% for grades B-12.5; B-15 / B-22.5 and B-30 / B-40 respectively. For those susceptible to periodic freezing and thawing after keeping the structures, the limit of strength, regardless of the concrete grade, is 80%.
2. The solution with antifreeze additives should reach a strength of 30%, 25% and 20% for grades B-15, B-22.5 and B-30, respectively, at the time of freezing.
3. When the temperature difference between the laid concrete and ambient air is more than 25 ?, the structure with the removed formwork is covered.

Works on permafrost soils

It should be particularly noted that the handling of concrete mixtures on soils in regions with permafrost is recommended to be carried out in strict accordance with the norms.

The effect on the cooling of the cast of the harsh effects of wind and temperature is also taken into account.

1. When selecting the composition of the mixture will have to take into account the effect of related components on the behavior of cement. The season of delivery, storage time in warehouses is also important.
2. Installation of concrete structures in specific regions produced when the soil conditions correspond to the design.
3. The base prepared for pouring is protected from thawing in the summer and frost penetration in the winter.

1. When laying directly on permafrost, the temperature of the concrete solution should not be above +10 ?. This is calculated by heat engineering calculations that prevent the soil from thawing.
2. If necessary, laying the mixture with a temperature in excess of +10? with keeping in the way of a thermos or electro-heating, the pillow becomes.

It is a thermally insulating sandy layer with a positive temperature. Sand rammed and wait for freezing.

Then another layer of sand is poured on it, a waterproofing is laid and it is poured with concrete. The thickness of the insulating cushion depends on the production project.

1. To speed up the hardening of the solution, antifreeze components and hardening accelerators are often used. Their number should not provoke the defrosting of the soil base.
2. Present formwork and waterproofing layer exclude the transfer of salts from the concrete structure to permafrost soil. It is allowed to use concreting with a large percentage of antifreeze components.

Probable consequences of concreting in winter

It happens that the developer began work in the early autumn, hoping to finish it before frost. But the cold came earlier than planned, and concrete structures are already poured, but have not reached the required strength.

The owner, having carefully studied the information at what temperature it is possible to work with concrete, is experiencing light shock and confusion. But you should not worry, as the curing only stops. When the thaw occurs, the freezing process will resume in standard mode.

Experts explain that with a temporary decrease in air temperature only a thin surface layer of concrete freezes. A powerful base plate or ceiling will not be damaged, the design will not suffer irreversible damage. The worst thing that awaits the builder is the shedding of a thin upper layer that can be restored at any time.

Why only the outer shell suffers

1. Fresh concrete mixture undergoes isothermal process. That is, the stages of the reaction of the interaction of water with cement and other components. As a result, heat is released, which warms most of the structure.
2. The presence of formwork also plays an important, insulating role. The surface layer, though it freezes, protects everything else.
3. Of all the components of the concrete mass of water is the most lightweight. Therefore, it rushes into the upper layer of the block, concentrating there in surplus. As a result - crystallization, expansion and destruction of the shell of the basement, slabs and other things.

If the concrete froze

It happened, and your creation, nevertheless, was subjected to inadvertently sudden early frosts, not having time to harden properly.

1. Buy in the hardware store PVC film. The material is an affordable price, but you get a lot of benefit. Cover it with concrete elements, pressing on the edges of the stones. If there is no hope for a thaw, leave the construction until spring. So you will save everything by donating only a thin top layer.
2. Uncovered concrete collapses by spring more. Snow accumulating on it will accelerate the process of crystallization of water, destroying the material. Several cycles of thawing and freezing adversely affect the fruits of your work.
3. If in the spring you find flaking fragments, carefully brush them with a broom or brush. For the main part do not worry, she is fine. But just restore the surface by plastering them. Concrete will reach the “mind” the faster, the warmer it will be on the street.

Cold concrete method

This method is now widely used in the construction of large areas, airfields, roads. The principle is to add sodium chloride and calcium chloride to the antifreeze mixture.

Supplements greatly lower the freezing threshold of water.

1. Calcium chloride reduces the time it takes to set the composition, while other components plasticize the mixture, making it easier to lay.
2. Salt is admixed to the concrete mass in the form of aqueous solutions. Their concentration is calculated according to the tables.
3. The design gains the necessary strength for the month by 50%, for three months - by 100%.

1. At positive temperatures, it is not recommended to work with such a mixture due to too fast setting. It is advisable to use the material in the winter, but it is undesirable to work with frosts below -20 ?.
2. Unlike conventional formulations, this type is less durable and durable, technical characteristics are slightly inferior, but satisfactory.

Conclusion

Severe climate or forced construction work at low temperatures should not be alarming. Competent calculation, properly selected supplements and technologies will help to cope with the task. More topic will reveal the video in this article.