Excerpts from SNiP related to concrete work in winter: transportation, laying concrete mix, how to pour concrete in winter at subzero temperatures.

SNiP. PRODUCTION OF CONCRETE WORK AT NEGATIVE AIR TEMPERATURES

2.53. These rules are followed during the period of concrete work when the expected average daily outside air temperature is below 5 °C and the minimum daily temperature is below 0 °C.

2.54. The preparation of the concrete mixture should be carried out in heated concrete mixing plants, using heated water, thawed or heated aggregates, ensuring the production of a concrete mixture with a temperature not lower than that required by calculation. It is allowed to use unheated dry aggregates that do not contain ice on the grains and frozen lumps. In this case, the duration of mixing the concrete mixture should be increased by at least 25% compared to summer conditions.

2.55. Methods and means of transportation must ensure the prevention of a decrease in the temperature of the concrete mixture below that required by calculation.

2.56. The condition of the base on which the concrete mixture is laid, as well as the temperature of the base and the method of laying must exclude the possibility of the mixture freezing in the area of ​​contact with the base. When curing concrete in a structure using a thermos method, when preheating the concrete mixture, as well as when using concrete with antifreeze additives It is allowed to lay the mixture on an unheated, non-heaving base or old concrete, if, according to calculations, freezing does not occur in the contact zone during the estimated period of curing the concrete.

At air temperatures below minus 10 °C, concreting of densely reinforced structures with reinforcement with a diameter greater than 24 mm, reinforcement made of rigid rolled sections or with large metal embedded parts should be carried out with preliminary heating of the metal to a positive temperature or local vibration of the mixture in the reinforcement and formwork areas, with the exception of cases of laying preheated concrete mixtures (at a mixture temperature above 45 ° C). The duration of vibration of the concrete mixture should be increased by at least 25% compared to summer conditions.

2.57. When concreting elements of frame and frame structures in structures with rigid coupling of nodes (supports), the need to create gaps in the spans depending on the heat treatment temperature, taking into account the resulting temperature stresses, should be agreed upon with the design organization. Unformed surfaces of structures should be covered with steam and heat insulating materials immediately after concreting is completed.

Reinforcement outlets of concrete structures must be covered or insulated to a height (length) of at least 0.5 m.

2.58. Before laying the concrete (mortar) mixture The surfaces of the joint cavities of precast reinforced concrete elements must be cleared of snow and ice.

2.59. Concreting of structures on permafrost soils should be carried out in accordance with SNiP II-18-76.

Acceleration of concrete hardening when concreting monolithic bored piles and embedding bored piles should be achieved by introducing complex antifreeze additives into the concrete mixture that do not reduce the freezing strength of concrete with permafrost soil.

2.60. Choosing a concrete curing method for winter concreting monolithic structures should be carried out in accordance with recommended Appendix 9.

2.61. Concrete strength control should be carried out, as a rule, by testing samples made at the place where the concrete mixture is laid. Samples stored in the cold must be kept for 2-4 hours at a temperature of 15-20 °C before testing.

It is allowed to control the strength by the temperature of the concrete during its curing.

2.62. The requirements for work at subzero air temperatures are set out in the table. 6

Methods for heating concrete in winter period at sub-zero temperatures today they are numerous. They are distinguished by their compliance with specific rules and requirements when using technology. The choice depends on local conditions, air temperature during the period of the year when the work is carried out.

Whatever method is chosen, when heating concrete in winter, the conditions of the process should be thoroughly observed, combining a set of measures used in the construction of monolithic and any other type of structures.

The main requirement for winter concreting work is to complete the process at a given pace and in strict sequence. Thanks to the error-free actions in compliance technological regulations are seeking guaranteed quality structures and foundations poured at sub-zero temperatures. The conditions for professional concrete work are regulated by:

• norms and rules SNiP 3.03.01-87;
• SNiP 3.06.04-91;
• several other documents on the basis of which building standards for areas with cold climates have been developed.

It is prohibited to warm up concrete in winter without deviating from the construction project.

Basic methods of heating concrete

There are several methods for heating concrete in winter. It should be understood that when using technology, price is not always the leading parameter. Often, with a slight increase in costs, the results obtained are many times more technologically advanced and stronger than analogues.

Thermos method

One of the old and inexpensive methods of concreting in the cold is the thermos method. It is based on the effect of hydration. It is based on the fact that the exothermic heat released during the hardening process of concrete is added to the heat added to the mixture during the production of concrete at the factory.

• Concrete brought from the factory is delivered to the site at the highest possible temperature.
• In this case, the solution should be quickly placed in the formwork prepared in advance and covered with thermal insulation.
• During the hydration process, 1 kg of the mixture releases approximately 80 kilocalories of heat, which contributes to the production of concrete products with critical strength, acquired by the time of freezing.

Method based on complex antifreeze additives

When choosing antifreeze additives, you must strictly follow the technology and adhere to the following requirements:

• the thermal resistance of the formwork must be higher than the calculated value (only in this case is the concrete able to reach the critical strength level);
• thin structural elements, protrusions and other parts that cool/harden faster than the base must be additionally heated (this ensures uniform hardening of the concrete);
• the surface of the structure that is not protected by formwork to prevent loss of moisture or, conversely, to prevent waterlogging due to excessive snow falling during hardening, must be covered with waterproofing (use polyethylene or other dense materials);
• if there is a clear threat of the temperature falling below the calculated value (follow the forecasts for the area), the structure must either be insulated or heated.

Electric heating of concrete

Most economical way heat treatment of concrete - electrical heating, namely electrode heating of concrete. An electric current passes through a conductor, which is concrete, and heats the entire volume of the solution from the inside. The method has proven itself well in reinforced and lightly reinforced blocks and foundation grillages.

Important: the use of electrodes for structures with a large amount of reinforcement is extremely undesirable.

Peripheral heating is carried out using strip electrodes made of wide strips of roofing steel, fixed to the formwork. Smooth steel reinforcement with a thickness of 5 mm or more is used as rod electrodes.

The electrodes are connected using taps. The connection between the tap and the electrode is done by twisting, using loops, a ring or a clamp. To connect, you must use a step-down transformer or welding machine. After the concrete has hardened, the electrodes remain inside, the contacts that look out are cut off.

An alternative to the electrode heating method is the innovative FlexiHIT thermoelectromats. They reduce energy costs by 4.4 times.

• When using a thermomat, infrared rays evenly heat the structure. Branded concrete gains the strength in 11 hours that it would acquire in 28 days under natural conditions.
• With their help, they get rid of unnecessary structures. An important characteristic of a thermomat is the speed of laying. By equipping foundations and grillages with thermomats for heating bored concrete piles, the hydration rate increases.
• The master will need only half an hour to install the thermomats, and when connecting the electrodes, at least half a day will be spent assembling the circuit and connecting it to the voltage source.

Heating concrete in formwork

The method of heating formwork involves transferring heat from it to the outer layers concrete structure. From there, heating occurs in the thickness of the concrete due to thermal conductivity. An alternative to heating formwork is the installation of the same FlexiHIT thermomats with similar benefits.

• Both methods are used for thin-walled and average size concrete walls with and without reinforcement.
• Heat from formwork or IR heating by thermomat compensates heat losses wall layers of concrete in large monolithic blocks of large mass and volume. It is based on the “adjustable thermos” principle for the foundation.
• However, if heating wires and carbon-graphite fiberglass-insulated tapes 10 cm in size are used in the form of heating formwork for concrete, then the use of a thermomat consists of a tight fit of the product to the surface of the grillage.

In both cases, to maintain an isothermal process, it is necessary to avoid the appearance air gaps, if possible, insulate the structure. Installation of heating equipment occurs with outside formwork.

Application for heating a heating wire, 2-segment or one-piece thermomat

At the core traditional way— heat release from the conductor located in the structure. Heating occurs by conductive heat generation.

The newest method used for the manufacture of columns in winter is based on the use of solid thermomats or 2-segment infrared heaters to warm up concrete columns. The devices are equipped with a built-in thermostat in each segment of the heating device.

A one-piece thermomat is used if the size of the column is known in advance. When producing floors and beams, thermoelectromatic mats are placed in the lower part of the concrete product.

Air heating method

The method of air heating of concrete is of the convective type and consists in uniform heating of the structure from warm air supplied from outside. A flexible hose or rubberized sleeve is used for this. The air is produced by a heat generator powered from the mains AC voltage or running on diesel fuel.

Air heating is used to pour concrete into formwork in a closed space with air circulation enhanced by a fan to heat the concrete evenly. When heating with air, it is recommended to use insulated tarpaulin airtight materials to create a greenhouse over a concrete structure.

Control over concrete work in winter

According to SNiP 152-01-2003, the quality of concrete products is confirmed after carrying out control measures. Control used:

• input (the mixture is checked for compliance with the presence of all components);
• operational control (performed during installation and other work);
• acceptance control (checking the quality of the design as a whole).

Thus, the correctness of the principle of concreting the foundation and erecting monolithic structures in winter is checked.

There are many ways of concreting in winter. They are widely used in cold climate areas. Modern methods using infrared heating more effective and safe, which is why they are increasingly chosen by qualified craftsmen.

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IN modern conditions There are many technologies that make it possible to continue the construction process even in winter. If the temperature drops, it is necessary to maintain a certain level of heating of the concrete mixture. In this case, the construction of houses and various objects does not stop for a minute.

The main condition for carrying out such work is to maintain a technological minimum at which the solution will not freeze. Electric heating of concrete is a factor that ensures compliance with technological standards even in winter. This process is quite complicated. But nevertheless, it is actively used everywhere at various construction sites.

Electric heating

Electrical heating of concrete is a rather complex and expensive process. However, to prevent the influence of low temperatures on the solidifying cement mixture it needs to provide a number of conditions. In winter, cement hardens unevenly. To prevent such deviation from the norm, electric heating technology should be used. It promotes a constant process of hardening of the mixture over the entire area.

Concrete is able to harden evenly at a temperature that will be close to +20 ºС. Forced electric heating is becoming an effective tool in the preparation of mortars.

Most often, electric heating technology is used for such purposes. If simple insulation the object becomes insufficient, such an alternative can solve the problem with unevenly hardening concrete.

Construction companies can choose from several approaches. For example, electrical heating can be carried out using a conductor such as a PNSV cable, or using electrodes. Also, some companies resort to the principle of heating the formwork itself. Currently, an induction approach or infrared rays can also be used for similar purposes.

Regardless of which method the management chooses, the heated object must be insulated. Otherwise, it will be impossible to achieve uniform heating.

Warming up with electrodes

The most popular method of heating concrete is the use of electrodes. This method is relatively inexpensive, because there is no need to purchase expensive equipment and devices (for example, wire type PNSV 1.2; 2; 3, etc.). The technology for its implementation also does not present any great difficulties.

The fundamental principle of the presented technology is the physical properties and characteristics of electric current. As it passes through concrete, it releases some thermal energy.

When using this technology, you should not apply voltage to the electrode system higher than 127 V if there is metal structure(frame). The instructions for electrical heating of concrete in monolithic structures allow the use of a current of 220 V or 380 V. However, it is not recommended to use a higher voltage.

The heating process is carried out using alternating current. If in this process participates D.C., it passes through water in solution and forms electrolysis. This process of chemical decomposition of water will prevent it from performing the functions that the substance has during the hardening process.

Types of Electrolytes

Electrical heating of concrete in winter can be carried out using one of the main ones. They can be string, rod or made in the form of a plate.

Rod electrolytes are installed in concrete at a short distance from each other. To create the presented product, scientists use metal reinforcement. Its diameter can range from 8 to 12 mm. The rods are connected to different phases. The presented devices are especially indispensable in the presence of complex structures.

Electrolytes, which are in the form of plates, are characterized by a fairly simple connection diagram. Their devices must be located on opposite sides of the formwork. These plates are connected to different phases. The current passing between them will heat the concrete. The plates can be wide or narrow.

String electrodes are necessary in the manufacture of other elongated products. After installation, both ends of the material are connected to different phases. This is how heating occurs.

Heating with PNSV cable

Electrical heating of concrete using PNSV wire, which will be discussed a little further, is considered one of the most effective technologies. In this case, the heater is a wire, not a concrete mass.

When laying the presented wire in concrete, it is possible to evenly heat the concrete, ensuring its quality when drying. The advantage of such a system is the predictability of the operating period. For high-quality heating of concrete in conditions of decreasing temperature, it is very important that it rises smoothly and evenly over the entire area of ​​the cement mortar.

The abbreviation PNVS means that the conductor has a steel core, which is packaged in PVC insulation. The cross-section of the wire when carrying out the presented procedure is selected in a certain way (PNSV 1,2; 2; 3). This characteristic is taken into account when calculating the amount of wire per 1 cubic meter of cement mixture.

The technology for heating concrete with wire is relatively simple. Electrical communications are allowed along the reinforcement frame. The wire should be secured in accordance with the manufacturer's recommendations. In this case, when feeding the mixture into the trench, formwork or mixture, the conductor will not be damaged by the pouring and operation of the hardened substance.

The wire should not touch the ground when laid out. After pouring, it is completely immersed in the concrete environment. The length of the wire will be influenced by its thickness, sub-zero temperatures in this climate zone, and resistance. The supplied voltage will be 50 V.

Cable application method

Electrical heating of concrete using PNSV wire, the technological map of which involves placing the product in a container immediately before pouring, is considered a reliable system. The wire must have a certain length (depending on its operating conditions). Due to good heating, the heat is smoothly distributed throughout the entire thickness of the material. Thanks to this feature, it is possible to increase the temperature of the concrete mixture to 40 ºС, and sometimes higher.

The PNSV cable can be powered into a network whose electricity is supplied by either 80/86. They have several levels of reduced voltage. One substation of the presented type is capable of heating up to 30 m³ of material.

To increase the temperature of the solution, it is necessary to spend about 60 m of PNSV 1.2 wire per 1 m³. In this case, the ambient temperature can be down to -30 ºС. Heating methods can be combined. This depends on the massiveness of the structure, weather conditions, and specified strength indicators. Also an important factor for creating a combination of methods is the availability of resources at the construction site.

If concrete can gain the required strength, it can resist destruction due to low temperatures.

Other wired heating options

Warm-up technology concrete PNSV cable is effective provided that all instructions and requirements of the manufacturer are followed. If the wire extends beyond the concrete, it is likely to overheat and fail. Also, the wire should not touch the formwork or the ground.

The length of the wire shown will depend on the conditions in which the wire is used. They require the operation of a transformer to operate. If, using PNSV wire, the use of such a system is not very convenient, there are other types of conductor products.

There are cables that do not require power supply to operate. This makes it possible to save a little money on servicing the presented system. Ordinary wire has a wide range of applications. However, the PNSV wire, which was discussed above, has wider capabilities and scope of application.

Scheme of using a heat gun

Heating concrete with wire is considered one of the newest and most effective technologies. However, just recently no one knew about it. Therefore, a rather expensive but simple method was used. A shelter was built above the surface of the cement. For this method, the concrete base had to have a small area.

They brought it to the constructed tent heat guns. They pumped up the required temperature. This method was not without certain disadvantages. It is considered one of the most labor-intensive. Workers need to erect a tent and then monitor the operation of the equipment.

If we compare heating of concrete with wire and the method of using thermal units, it becomes clear that the old approach will require more costs. Most often certain equipment is purchased autonomous type work. They work for diesel fuel. If there is no access to a regular fixed network on the site, this option will be the most advantageous.

Thermomat

The heating wire or can serve as the basis for creating special thermomats. They are quite effective. The only condition is a flat surface of the concrete base. Some types of heaters presented can work as a winding on columns, elongated blocks, poles, etc.

When using matte technology, a plasticizer is added to the solution itself, which speeds up the drying process. At the same time, they can also prevent the formation of water crystallization.

When using the presented technologies, it should be remembered that there are special documents regulating the electrical heating of concrete in winter. SNiP draws the attention of construction organizations to the need for constant monitoring temperature indicators of this substance.

The cement mixture should not overheat above +50 ºС. This is just as unacceptable for its production technology as severe frosts. In this case, the rate of cooling and heating should not be faster than 10 ºС per hour. To avoid mistakes, the calculation of electrical heating of concrete is carried out in accordance with current standards and sanitary requirements.

Infrared mats can replace cable counterparts. They can be used for wrapping figured columns and other elongated objects. This approach is characterized by low energy consumption. Concrete structures exposed to infrared rays begin to quickly lose moisture. To prevent this from happening, you need to cover the surfaces with regular plastic film.

Heated formwork

Electric heating of concrete in winter can be carried out immediately in the formwork. This is one of the new ways that is very effective. Heating elements are installed in the formwork panels. If one or more of them fails, the faulty equipment is dismantled. It is replaced with a new one.

Equipping the mold in which the concrete hardens with infrared heaters was one of the successful decisions made by managers construction companies. This system is able to provide the required conditions to the concrete product located in the formwork, even at a temperature of -25 ºС.

In addition to high efficiency, the presented systems have a high efficiency rate. Very little time is spent preparing for heating. This is extremely important in conditions severe frosts. The profitability of heating formwork is determined to be higher than that of conventional wired systems. They can be used repeatedly.

However, the cost of this type of electric heating is quite high. It is considered unprofitable if you need to heat a building of non-standard dimensions.

Principle of induction and infrared heating

In the above systems of thermomats and heated formwork, the principle can be used infrared heating. To better understand the operating principle of these systems, it is necessary to delve into the question of what infrared waves are.

Electrical heating of concrete using the presented technology takes as its basis the ability sun rays heat opaque, dark objects. After heating the surface of the substance, the heat is evenly distributed throughout its entire volume. If the concrete structure is wrapped in a transparent film in this case, when heated it will transmit rays into the concrete. In this case, heat will be retained inside the material.

The advantage of infrared systems is that there are no requirements for the use of transformers. Experts say that the disadvantage is the inability of the presented heating to evenly distribute heat throughout the entire structure. Therefore, it is used only for relatively thin products.

Inductive approach in modern construction used quite rarely. It is more suitable for structures such as purlins and beams. This is influenced by the complexity of the presented equipment.

The principle of induction heating is based on the fact that a wire is wound around a steel rod. It has a layer of insulation. When an electric current is connected, the system produces an inductive disturbance. This is how the concrete mixture is heated.

Having considered the electrical heating of concrete, as well as its basic methods and technologies, we can conclude that it is advisable to use one or another method in production conditions. Depending on the type of manufactured structures and production conditions, technologists choose the appropriate option. A meticulous approach to the technology of hardening the concrete mixture allows us to produce high-quality products, screeds, foundations, etc. Every builder should know the rules for working with cement in winter.

2.1. The selection of cements for preparing concrete mixtures should be made in accordance with these rules (recommended Appendix 6) and GOST 23464-79. Acceptance of cements should be carried out in accordance with GOST 22236-85, transportation and storage of cements - in accordance with GOST 22237-85 and SNiP 3.09.01-85.

2.2. Fillers for concrete are used fractionated and washed. It is prohibited to use a natural mixture of sand and gravel without sifting into fractions (mandatory appendix 7). When choosing aggregates for concrete, materials from local raw materials should be used predominantly. To obtain the required technological properties of concrete mixtures and operational properties of concrete, chemical additives or their complexes should be used in accordance with mandatory Appendix 7 and recommended Appendix 8.

CONCRETE MIXTURES

2.3. Dosing of concrete mixture components should be done by weight. It is allowed to dose additives introduced into the concrete mixture in the form of aqueous solutions by volume of water. The ratio of components is determined for each batch of cement and aggregates when preparing concrete of the required strength and mobility. The dosage of components should be adjusted during the preparation of the concrete mixture, taking into account data from monitoring indicators of cement properties, humidity, granulometry of aggregates and strength control.

2.4. The order of loading components and the duration of mixing the concrete mixture must be established for specific materials and conditions of the concrete mixing equipment used by assessing the mobility, uniformity and strength of concrete in a specific batch. When entering segments fibrous materials(fibers), a method of their introduction should be provided so that they do not form lumps and inhomogeneities.

When preparing a concrete mixture using separate technology, the following procedure must be observed:

• water and part of the finely ground sand are dosed into the operating high-speed mixer mineral filler(if used) and cement, where everything is mixed;
• the resulting mixture is fed into a concrete mixer, pre-loaded with the remainder of the aggregates and water, and everything is mixed again.

2.5. Transportation and supply of concrete mixtures should be carried out using specialized means that ensure the preservation of the specified properties of the concrete mixture. It is prohibited to add water at the site of laying the concrete mixture to increase its mobility.

2.6. The composition of the concrete mixture, preparation, acceptance rules, control methods and transportation must comply with GOST 7473-85.

2.7. Requirements for the composition, preparation and transportation of concrete mixtures are given in table. 1.

Table 1

LAYING CONCRETE MIXTURES

2.8. Before concreting, rock foundations, horizontal and inclined concrete surfaces of working joints must be cleaned of debris, dirt, oil, snow and ice, cement film, etc. Immediately before laying the concrete mixture, the cleaned surfaces must be washed with water and dried with a stream of air.

2.9. All structures and their elements that are covered during subsequent work (prepared structural foundations, reinforcement, embedded products, etc.), as well as the correct installation and fastening of the formwork and its supporting elements must be accepted in accordance with SNiP 3.01.01-85.

2.10. Concrete mixtures should be laid in concrete structures in horizontal layers of equal thickness without breaks, with a consistent direction of laying in one direction in all layers.

2.11. When compacting the concrete mixture, it is not allowed to rest vibrators on reinforcement and embedded products, ties and other formwork fastening elements. The depth of immersion of the deep vibrator into the concrete mixture should ensure its deepening into the previously laid layer by 5 - 10 cm. The step of rearrangement of deep vibrators should not exceed one and a half radius of their action, surface vibrators should ensure that the vibrator platform overlaps the border of the already vibrated area by 100 mm.

2.12. Laying the next layer of concrete mixture is allowed before the concrete of the previous layer begins to set. The duration of the break between laying adjacent layers of concrete mixture without forming a working joint is established by the construction laboratory. The top level of the laid concrete mixture should be 50 - 70 mm below the top of the formwork panels.

2.13. The surface of the working joints, arranged when laying the concrete mixture intermittently, must be perpendicular to the axis of the columns and beams being concreted, the surface of the slabs and walls. Concreting may be resumed once the concrete reaches a strength of at least 1.5 MPa. Working joints, in agreement with the design organization, may be installed during concreting:

• columns - at the level of the top of the foundation, the bottom of purlins, beams and crane consoles, the top of crane beams, the bottom of column capitals;
• beams large sizes, monolithically connected to the slabs - 20 - 30 mm below the mark of the bottom surface of the slab, and if there are haunches in the slab - at the mark of the bottom of the haunch of the slab;
• flat slabs - anywhere parallel to the smaller side of the slab;
• ribbed floors - in a direction parallel to the secondary beams;
• individual beams - within the middle third of the span of beams, in a direction parallel to the main beams (purlins) within the two middle quarters of the span of purlins and slabs;
• arrays, arches, vaults, tanks, bunkers, hydraulic structures, bridges and other complex engineering structures and structures - in the places specified in the projects.

2.14. Requirements for laying and compacting concrete mixtures are given in table. 2.

table 2

CURTINING AND CARE OF CONCRETE

2.15. During the initial period of hardening, concrete must be protected from precipitation or moisture loss, and subsequently maintain temperature and humidity conditions to create conditions that ensure an increase in its strength.

2.16. Measures for the care of concrete, the order and timing of their implementation, control over their implementation and the timing of stripping of structures must be established by the PPR.

2.17. Movement of people on concreted structures and installation of formwork on overlying structures is allowed after the concrete reaches a strength of at least 1.5 MPa.

TESTING OF CONCRETE DURING ACCEPTANCE OF STRUCTURES

2.18. Strength, frost resistance, density, water resistance, deformability, as well as other indicators established by the project, should be determined in accordance with the requirements of current state standards.

CONCRETE ON POROUS AGGREGATES

2.19. Concrete must meet the requirements of GOST 25820-83.

2.20. Materials for concrete should be selected in accordance with the mandatory Appendix 7, and chemical additives - with the recommended Appendix 8.

2.21. The selection of concrete composition should be made in accordance with GOST 27006-86.

2.22. Concrete mixtures, their preparation, delivery, laying and maintenance of concrete must meet the requirements of GOST 7473-85.

2.23. The main quality indicators of the concrete mixture and concrete must be controlled in accordance with Table. 3.

Table 3

ACID-RESISTANT AND ALKALI-RESISTANT CONCRETE

2.24. Acid-resistant and alkali-resistant concrete must meet the requirements of GOST 25192-82. The compositions of acid-resistant concrete and the requirements for materials are given in Table. 4

Table 4

2.25. The preparation of concrete mixtures using liquid glass should be carried out in the following order. First, in a closed mixer, the hardening initiator, filler and other powdered components sifted through sieve No. 03 are mixed dry. Liquid glass is mixed with modifying additives. First, crushed stone of all fractions and sand are loaded into the mixer, then a mixture of powdered materials is added and mixed for 1 minute, then liquid glass is added and mixed for 1-2 minutes. In gravity mixers, the mixing time for dry materials is increased to 2 minutes, and after loading all components - to 3 minutes. Adding liquid glass or water to the finished mixture is not allowed. The viability of the concrete mixture is no more than 50 minutes at 20 °C; it decreases with increasing temperature. Requirements for the mobility of concrete mixtures are given in table. 5.

2.26. Transportation, laying and compaction of the concrete mixture should be carried out at an air temperature of at least 10°C within a time period not exceeding its viability. Laying must be carried out continuously. When constructing a working joint, the surface of the hardened acid-resistant concrete is incised, dust-free and primed with liquid glass.

2.27. The surface moisture of concrete or brick protected with acid-resistant concrete should be no more than 5% by weight, at a depth of up to 10 mm.

2.28. The surface of reinforced concrete structures made of Portland cement concrete before laying acid-resistant concrete on them must be prepared in accordance with the design instructions or treated with a hot solution of magnesium fluoride (3-5% solution at a temperature of 60 ° C) or oxalic acid (5-10% - nal solution) or primed with polyisocyanate or a 50% solution of polyisocyanate in acetone.

Table 5

2.29. The concrete mixture on liquid glass should be compacted by vibrating each layer no more than 200 mm thick for 1-2 minutes.

2.30. Concrete hardening for 28 days should occur at a temperature not lower than 15 °C. Drying using air heaters at a temperature of 60-80 ° C during the day is allowed. The rate of temperature rise is no more than 20-30 °C/h.

2.31. The acid permeability of acid-resistant concrete is ensured by the introduction of 3-5 % of the mass of liquid glass into the concrete of polymer additives: Furil alcohol, Furfurol, Futorol, Acetonomaldehyd Smole of ACF-3M, Tetrafurfuril ester of TFS orthcore acid with phenolformaldehytic resilo FRV- 4.

2.32. The water resistance of acid-resistant concrete is ensured by the introduction into the concrete composition of finely ground additives containing active silica (diatomaceous earth, tripolite, aerosil, flint, chalcedony, etc.), 5-10% of the mass of liquid glass or polymer additives up to 10-12% of the mass of liquid glass: polyisocyanate, urea resin KFZh or KFMT, organosilicon hydrophobizing liquid GKZh-10 or GKZh-11, paraffin emulsion.

2.33. The protective properties of acid-resistant concrete in relation to steel reinforcement are ensured by the introduction of corrosion inhibitors 0.1-0.3% of the mass of liquid glass into the concrete composition: lead oxide, complex additive of catapine and sulfonol, sodium phenylanthranilate.

2.34. Stripping of structures and subsequent processing of concrete is allowed when the concrete reaches 70% of its design strength.

2.35. Increasing the chemical resistance of structures made of acid-resistant concrete is ensured by twice treating the surface with a solution of sulfuric acid of 25-40% concentration.

2.36. Materials for alkali-resistant concrete in contact with alkali solutions at temperatures up to 50 ° C must meet the requirements of GOST 10178-85. The use of cements with active mineral additives is not allowed. The content of granular or electrothermophosphorus slags must be no less than 10 and no more than 20%. The content of mineral C 3 A in Portland cement and Portland slag cement should not exceed 8%. The use of aluminous binders is prohibited.

2.37. Fine aggregate (sand) for alkali-resistant concrete, operated at temperatures up to 30 ° C, should be used in accordance with the requirements of GOST 10268-80, above 30 ° C - crushed from alkali-resistant rocks - limestone, dolomite, magnesite, etc. should be used. Coarse aggregate (crushed stone) for alkali-resistant concrete operating at temperatures up to 30 ° C should be used from dense igneous rocks - granite, diabase, basalt, etc.

2.38. Crushed stone for alkali-resistant concrete operated at temperatures above 30 ° C should be used from dense carbonate sedimentary or metamorphic rocks - limestone, dolomite, magnesite, etc. The water saturation of crushed stone should be no more than 5%.

HEAT-RESISTANT CONCRETE

2.39. Materials for the preparation of ordinary concrete operated at temperatures up to 200 °C and heat-resistant concrete should be used in accordance with recommended Appendix 6 and mandatory Appendix 7.

2.40. Dosing of materials, preparation and transportation of concrete mixtures must meet the requirements of GOST 7473-85 and GOST 20910-82.

2.41. Increasing the mobility of concrete mixtures for ordinary concrete, operated at temperatures up to 200 °C, is allowed through the use of plasticizers and superplasticizers.

2.42. The use of chemical hardening accelerators in concrete operated at temperatures above 150°C is not allowed.

2.43. Concrete mixtures should be laid at a temperature not lower than 15°C, and this process should be continuous. Breaks are allowed in places where working or expansion joints are installed, provided for by the project.

2.44. Hardening of cement-based concrete must occur under conditions that ensure a wet state of the concrete surface.

Hardening of concrete on liquid glass should occur in an air-dry environment. When hardening these concretes, good air ventilation must be provided to remove water vapor.

2.45. Drying and heating of heat-resistant concrete should be carried out in accordance with the PPR.

CONCRETE IS ESPECIALLY HEAVY AND FOR RADIATION PROTECTION

2.46. Work using especially heavy concrete and concrete for radiation protection should be carried out using conventional technology. In cases where usual ways concreting is not applicable due to the stratification of the mixture, the complex configuration of the structure, the saturation of reinforcement, embedded parts and communication penetrations, the method of separate concreting should be used (the method of ascending solution or the method of embedding coarse aggregate into the solution). The choice of concreting method should be determined by the PPR.

2.47. The materials used for radiation protection concrete must comply with the requirements of the project.

2.48. Requirements for particle size distribution, physical and mechanical characteristics mineral, ore and metal fillers must meet the requirements for fillers for heavy concrete. Metal fillers must be degreased before use: Metal fillers may have non-flaking rust.

2.49. Passports for materials used for the manufacture of radiation protection concrete must indicate complete data chemical analysis these materials.

2.50. Work using concrete with metal fillers is allowed only at positive ambient temperatures.

2.51. When laying concrete mixtures, the use of belt and vibrating conveyors, vibrating hoppers, and vibrating robots is prohibited; dropping particularly heavy concrete mixtures is allowed from a height of no more than 1 m.

2.52. Concrete testing should be carried out in accordance with 18">clause 2.18.

PRODUCTION OF CONCRETE WORK AT NEGATIVE AIR TEMPERATURES

2.53. These rules are followed during the period of concrete work when the expected average daily outside air temperature is below 5°C and the minimum daily temperature is below 0°C.

2.54. The preparation of the concrete mixture should be carried out in heated concrete mixing plants, using heated water, thawed or heated aggregates, ensuring the production of a concrete mixture with a temperature not lower than that required by calculation. It is allowed to use unheated dry aggregates that do not contain ice on the grains and frozen lumps. In this case, the duration of mixing the concrete mixture should be increased by at least 25% compared to summer conditions.

2.55. Methods and means of transportation must ensure that the temperature of the concrete mixture does not decrease below that required by calculation.

2.56. The condition of the base on which the concrete mixture is laid, as well as the temperature of the base and the method of laying must exclude the possibility of the mixture freezing in the area of ​​contact with the base. When curing concrete in a structure using the thermos method, when preheating the concrete mixture, as well as when using concrete with antifreeze additives, it is allowed to lay the mixture on an unheated, non-heaving base or old concrete, if, according to calculations, freezing will not occur in the contact zone during the estimated period of curing the concrete. At air temperatures below minus 10 °C, concreting of densely reinforced structures with reinforcement with a diameter greater than 24 mm, reinforcement made of rigid rolled sections or with large metal embedded parts should be carried out with preliminary heating of the metal to a positive temperature or local vibration of the mixture in the reinforcement and formwork areas, with the exception of cases of laying preheated concrete mixtures (at a mixture temperature above 45°C). The duration of vibration of the concrete mixture should be increased by at least 25% compared to summer conditions.

2.57. When concreting elements of frame and frame structures in structures with rigid coupling of nodes (supports), the need to create gaps in the spans depending on the heat treatment temperature, taking into account the resulting temperature stresses, should be agreed upon with the design organization. Unformed surfaces of structures should be covered with steam and heat insulating materials immediately after concreting is completed.

Reinforcement outlets of concrete structures must be covered or insulated to a height (length) of at least 0.5 m.

2.58. Before laying the concrete (mortar) mixture, the surfaces of the joint cavities of precast reinforced concrete elements must be cleared of snow and ice.

2.59. Concreting of structures on permafrost soils should be carried out in accordance with SNiP II-18-76.

Acceleration of concrete hardening when concreting monolithic bored piles and embedding bored piles should be achieved by introducing complex antifreeze additives into the concrete mixture that do not reduce the freezing strength of concrete with permafrost soil.

2.60. The choice of concrete curing method for winter concreting of monolithic structures should be made in accordance with the recommended Appendix 9.

2.61. The strength of concrete should be monitored, as a rule, by testing samples made at the site where the concrete mixture is laid. Samples stored in the cold must be kept for 2-4 hours at a temperature of 15-20°C before testing.

It is allowed to control the strength by the temperature of the concrete during its curing.

2.62. Requirements for work at subzero air temperatures are set out in Table. 6

Table 6

PRODUCTION OF CONCRETE WORK AT AIR TEMPERATURES ABOVE 25°C

2.63. When carrying out concrete work at air temperatures above 25 ° C and relative humidity less than 50% should use quick-hardening Portland cement, the grade of which should exceed the grade strength of concrete by at least 1.5 times. For concrete of class B22.5 and higher, it is allowed to use cements whose grade exceeds the grade strength of concrete by less than 1.5 times, provided that plasticized Portland cements are used or plasticizing additives are introduced.

The use of pozzolanic Portland cement, slag Portland cement below M400 and aluminous cement for concreting above-ground structures is not allowed, except for cases provided for by the design. Cements should not have false set, have a temperature above 50°C, normal thickness cement paste should not exceed 27%.

2.64. The temperature of the concrete mixture when concreting structures with a surface modulus of more than 3 should not exceed 30-35 °C, and for massive structures with a surface modulus of less than 3-20 °C.

2.65. If cracks appear on the surface of the laid concrete due to plastic shrinkage, repeated surface vibration is allowed no later than 0.5-1 hour after the end of its laying.

2.66. Maintenance of freshly laid concrete should begin immediately after the completion of laying the concrete mixture and should be carried out until, as a rule, 70% of the design strength is achieved, and with appropriate justification - 50%.

During the initial period of maintenance, freshly laid concrete mixture must be protected from dehydration.

When concrete reaches a strength of 0.5 MPa, subsequent care should consist of ensuring a wet surface condition by installing a moisture-intensive coating and moistening it, keeping exposed concrete surfaces under a layer of water, and continuously spraying moisture over the surface of structures. At the same time, periodic watering of open surfaces of hardening concrete and reinforced concrete structures with water is not allowed.

2.67. To intensify the hardening of concrete, solar radiation should be used by covering structures with rolls or sheets of translucent moisture-proof material, covering them with film-forming compounds, or laying a concrete mixture at a temperature of 50-60 ° C.

2.68. To avoid the possible occurrence of a thermally stressed state in monolithic structures when directly exposed to sunlight, freshly laid concrete should be protected with self-destructive polymer foams, inventory heat-moisture insulating coatings, polymer film with a reflection coefficient of more than 50% or any other thermal insulation material.

SPECIAL CONCRETE METHODS

2.69. Based on specific engineering-geological and production conditions, in accordance with the project, the use of the following special concreting methods is allowed:

• vertically moved pipe (VPT);
• ascending solution (AS);
• injection;
• vibration-injection;
• laying concrete mixture in bunkers;
• compacting the concrete mixture;
• pressure concreting;
• rolling concrete mixtures;
• cementation using drill-mixing method.

2.70. The VPT method should be used when constructing buried structures with a depth of 1.5 m or more; in this case, concrete of design class up to B25 is used.

2.71. Concreting using the VR method with pouring outlines from large stone cement-sand mortar should be used when laying concrete under water at a depth of up to 20 m to obtain concrete strength corresponding to the strength of rubble masonry.

The VR method with filling crushed stone fill with cement-sand mortar can be used at depths of up to 20 m for the construction of structures made of concrete of class up to B25.

At a concreting depth of 20 to 50 m, as well as during repair work, pouring crushed stone aggregate with cement mortar without sand should be used to strengthen structures and reconstructive construction.

2.72. Injection and vibration injection methods should be used for concreting underground structures, mainly thin-walled concrete of class B25 on aggregate maximum fraction 10-20 mm.

2.73. The method of laying concrete mixture in bunkers should be used when concreting structures made of class B20 concrete at a depth of more than 20 m.

2.74. Concreting by compacting the concrete mixture should be used at a depth of less than 1.5 m for structures of large areas, concreted to a level located above the water level, with concrete class up to B25.

2.75. Pressure concreting by continuous injection of a concrete mixture at excess pressure should be used when constructing underground structures in water-logged soils and difficult hydrogeological conditions when constructing underwater structures at a depth of more than 10 m and constructing critical heavily reinforced structures, as well as with increased requirements for the quality of concrete.

2.76. Concreting by rolling a low-cement rigid concrete mixture should be used for the construction of flat extended structures made of concrete of class up to B20. The thickness of the rolled layer should be within 20-50 cm.

2.77. For the construction of zero-cycle cement-soil structures at a laying depth of up to 0.5 m, it is allowed to use drill-mixing concreting technology by mixing the calculated amount of cement, soil and water in the well using drilling equipment.

2.78. When underwater (including under clay mortar) concreting, it is necessary to ensure:

isolation of the concrete mixture from water during its transportation under water and placement in the concrete structure;

density of formwork (or other fencing);

continuity of concreting within an element (block, grip);

monitoring the condition of the formwork (fencing) during the process of laying the concrete mixture (if necessary, by divers or using underwater television installations).

2.79. The timing of stripping and loading of underwater concrete and reinforced concrete structures should be established based on the results of testing control samples that hardened under conditions similar to the conditions for hardening concrete in the structure.

2.80. Concreting using the VPT method after an emergency break may be resumed only if:

• concrete in a shell achieves a strength of 2.0-2.5 MPa;
• removing sludge and weak concrete from the surface of underwater concrete;

ensuring reliable connection of newly laid concrete with hardened concrete (fines, anchors, etc.).

When concreting under clay mortar, breaks lasting longer than the setting time of the concrete mixture are not allowed; if the specified limit is exceeded, the structure should be considered defective and cannot be repaired using the VPT method.

2.81. When supplying concrete mixture under water with bunkers, it is not allowed to freely drop the mixture through a layer of water, as well as leveling the laid concrete by horizontal movement of the bunker.

2.82. When concreting using the method of compacting the concrete mixture from an island, it is necessary to compact the newly arriving portions of the concrete mixture no closer than 200-300 mm from the water's edge, preventing the mixture from floating over the slope into the water.

During the setting and hardening period, the surface surface of the laid concrete mixture must be protected from erosion and mechanical damage.

2.83. When constructing structures of the “wall in the ground” type, concreting trenches should be carried out in sections no more than 6 m long using inventory intersection dividers.

Table 7

If there is a clay solution in the trench, the section is concreted no later than 6 hours after pouring the solution into the trench; otherwise, the clay solution must be replaced with the simultaneous production of sludge that has settled to the bottom of the trench.

The reinforcement frame should be moistened with water before immersing in the clay solution. The duration of immersion from the moment the reinforcement frame is lowered into the clay solution until the moment the section begins to be concreted should not exceed 4 hours.

The distance from the concrete pipe to the intersection separator should be no more than 1.5 m for a wall thickness of up to 40 cm and no more than 3 m for a wall thickness of more than 40 cm.

2.84. Requirements for concrete mixtures when laying them special methods are given in table. 7.

CUTTING EXPANSION JOINTS, TECHNOLOGICAL FROWS, OPENINGS, HOLES AND SURFACE TREATMENT OF MONOLITHIC STRUCTURES

2.85. Tool for machining should be selected depending on the physical and mechanical properties of the processed concrete and reinforced concrete, taking into account the requirements for the quality of processing by the current GOST for diamond tools, and the recommended Appendix 10.

2.86. Cooling of the tool should be provided with water under pressure of 0.15-0.2 MPa, to reduce the energy intensity of processing - with solutions of surfactants with a concentration of 0.01-1%.

2.87. Requirements for mechanical processing modes of concrete and reinforced concrete are given in table. 8.

Table 8

CEMENTATION OF SEAMS. WORKS ON SHOTCREATING AND APPLICATION OF SPRAYED CONCRETE

2.88. For cementation of shrinkage, temperature, expansion and construction joints, Portland cement of at least M400 should be used. When cementing joints with an opening of less than 0.5 mm, plasticized cement mortars. Before the start of cementation work, the seam is washed and hydraulically tested to determine its bandwidth and tightness of the card (seam).

2.89. The temperature of the joint surface during cementation of the concrete mass must be positive. For cementation of joints at subzero temperatures, solutions with antifreeze additives should be used. Cementation should be carried out before the water level in front of the hydraulic structure rises after the main part of the temperature-shrinkage deformations has died down.

2.90. The quality of cementation of joints is checked: by examining the concrete by drilling control wells and hydraulic testing of them and cores taken from the intersections of the joints; measuring water filtration through seams; ultrasonic tests.

2.91. Aggregates for shotcrete and sprayed concrete devices must meet the requirements of GOST 10268-80.

The size of the aggregates should not exceed half the thickness of each shotcreted layer and half the mesh size of the reinforcing mesh.

2.92. The surface for shotcrete must be cleaned and blown compressed air and washed with a jet of water under pressure. Sagging heights of more than 1/2 the thickness of the gunite layer are not allowed. The installed fittings must be cleaned and secured against displacement and vibrations.

2.93. Shotcrete is carried out in one or several layers 3-5 mm thick on unreinforced or reinforced surface according to the project.

2.94. When constructing critical structures, control samples should be cut from specially shotcrete slabs with a size of at least 50´50 cm or from structures. For other structures, quality control and assessment are carried out using non-destructive methods.

REINFORCEMENT WORK

2.95. Reinforcing steel (bar, wire) and rolled products, reinforcing products and embedded elements must comply with the design and the requirements of the relevant standards. The dismemberment of large-sized spatial reinforcement products, as well as the replacement of reinforcing steel provided for by the project must be agreed upon with the customer and the design organization.

2.96. Transportation and storage of reinforcing steel should be carried out in accordance with GOST 7566-81.

2.97. The preparation of rods of measured length from rod and wire reinforcement and the manufacture of non-prestressed reinforcement products should be carried out in accordance with the requirements of SNiP 3.09.01-85, and the manufacture of load-bearing reinforcing frames from rods with a diameter of more than 32 mm of rolled profiles - in accordance with Section. 8.

2.98. The production of spatial large-sized reinforcement products should be carried out in assembly jigs.

2.99. Preparation (cutting, welding, formation of anchor devices), installation and tension of prestressing reinforcement should be carried out according to the project in accordance with SNiP 3.09.01-85.

(Clarification, BST 10-88)

2.100. Installation of reinforcement structures should be carried out mainly from large-sized blocks or standardized factory-made meshes, ensuring fixation of the protective layer according to Table. 9.

2.101. Installation of pedestrian, transport or installation devices on reinforced structures should be carried out in accordance with the PPR, in agreement with the design organization.

2.102. Non-welding connections of rods should be made:

butt joints - with an overlap or with crimp sleeves and screw couplings, ensuring equal strength of the joint;

cross-shaped - with viscous annealed wire. The use of special connecting elements (plastic and wire fasteners) is allowed.

2.103. Butt and cross-shaped welded joints should be carried out according to the design in accordance with GOST 14098-85.

2.104. When constructing reinforcement structures, the requirements of Table. 9.

Table 9

FORMWORK

The section was declared invalid by Resolution of the State Construction Committee of Russia dated May 22, 2003 No. 42.

2.105. Types of formwork should be used in accordance with GOST 23478-79. Loads on the formwork should be calculated in accordance with the requirements of these codes and regulations (mandatory appendix 11).

2.106. Wood, metal, plastic and other materials for formwork must meet the requirements of GOST 23478-79; wooden laminated structures - GOST 20850-84 or TU; laminated plywood - TU 18-649-82; pneumatic formwork fabrics - to approved technical specifications. Permanent formwork materials must meet the project requirements depending on functional purpose(cladding, insulation, insulation, corrosion protection, etc.). When using formwork as cladding, it must meet the requirements of the corresponding cladding surfaces.

2.107. Completeness is determined by the consumer's order.

2.108. The formwork manufacturer must perform control assembly of the fragment at the factory. The fragment layout is determined by the customer in agreement with the manufacturer.

Tests of formwork elements and assembled fragments for strength and deformation are carried out during the manufacture of the first sets of formwork, as well as when replacing materials and profiles. The testing program is developed by the organization - the formwork developer, the manufacturer and the customer.

2.109. Installation and acceptance of formwork, stripping of monolithic structures, cleaning and lubrication are carried out according to PPR.

2.110. The permissible strength of concrete during formwork is given in table. 10. When installing intermediate supports in the floor span with partial or sequential removal of the formwork, the strength of concrete may be reduced. In this case, the strength of concrete, the free span of the floor, the number, location and method of installation of supports are determined by the PPR and agreed upon with the design organization. Removal of all types of formwork should be done after preliminary separation from the concrete.

Table 10

ACCEPTANCE OF CONCRETE AND REINFORCED CONCRETE STRUCTURES OR PARTS OF STRUCTURES

2.111. When accepting completed concrete and reinforced concrete structures or parts of structures, the following should be checked:

• compliance of designs with working drawings;
• quality of concrete in terms of strength, and, if necessary, frost resistance, water resistance and other indicators specified in the project;
• quality of materials, semi-finished products and products used in construction.

2.112. Acceptance of completed concrete and reinforced concrete structures or parts of structures should be formalized in in the prescribed manner an act of inspection of hidden work or an act of acceptance of critical structures.

2.113. The requirements for finished concrete and reinforced concrete structures or parts of structures are given in Table. eleven.

Table 11

Methodological documentation in construction

JSC "TSNIIOMTP"

WINTER CONCRECTING
USING HEATING CABLES

MDS 12-48.2009

Moscow 2009

This methodological document contains information about winter concreting using heating wires: technical requirements for heating wires and power electrical equipment, methodological provisions for the calculation and selection of parameters for the heat treatment of concrete, recommendations for organizing work, rules and techniques for performing technological operations, standards and assessment procedures quality of work. Examples of concreting typical structural elements of a building are given: columns, walls and ceilings.

The information contained in the document can be used to draw up technological documents for winter concreting: work plans, technological maps, technical regulations and so on.

The methodological document is intended for design and construction organizations and construction specialists involved in the production of concrete work in winter conditions.

The methodological document was developed by employees of CJSC "TsNIIOMTP" - candidates of technical sciences. Sciences V.P. Volodin and Yu.A. Korytov.

INTRODUCTION

Winter concreting includes work performed when the average daily outside air temperature is below 5°C and the minimum daily temperature is below 0°C. It is believed that winter concreting can be carried out at air temperatures down to minus 40°C. In practice, winter concreting has been mastered down to temperatures of minus 15-20°C.

To ensure that concrete gains the required strength, special measures are taken to prepare and carry out concrete work in winter.

For winter concreting special concretes with chemical antifreeze and plasticizing additives are used.

When performing work, freshly laid concrete is heated in various ways using steam, heated water or electricity.

Freshly laid concrete is protected from heat loss (thermos method) by covering it with various insulation materials (mats, blankets, panels).

Special measures, in particular for the insulation of working bodies and concrete pipes, are carried out when preparing machines and technological equipment for winter concreting.

The main requirement when performing winter concreting is to create favorable conditions for concrete to acquire the required design strength in a short time.

Massive monolithic structures (base slabs and blocks) with cooling surface module M p from 2 to 4 are concreted using the thermos method using quick-hardening cements, hardening accelerators and anti-frost and plasticizing additives.

Structures (columns, blocks, walls) with a cooling surface module of 4-6 are concreted using the thermos method using preheating of the concrete mixture, heating wires and heating formwork.

Relatively thin-walled structures (partitions, ceilings, walls) with a cooling surface module of 6-12 are concreted using the methods mentioned above using heating wires, thermoactive flexible coatings (TAGC), and heating flat elements (HEP).

This document discusses the method of winter concreting using heating wires. This method has a number of advantages compared to heating with steam, hot water, and infrared irradiation. The effectiveness of the method increases in combination with the other measures and techniques of winter concreting mentioned above: the use of high-quality concrete with chemical additives, insulation materials, preparation of machines and technological equipment.

The use of heating wires makes it possible to erect buildings and structures that are no different in strength from those erected in the summer.

This document contains methodological recommendations and examples that allow you to select work methods (modes, techniques) and materials for winter concreting for a specific construction project, taking into account local conditions and the characteristics of the construction organization. The choice of method of work and materials is made at the stage of developing a work project (technological maps), agreed with the customer and approved in the prescribed manner.

This document is necessary not only for the development of the technological documentation mentioned above, but may be useful for licensing construction organization(firms) for the production of this type of work, when certifying the quality management system, when certifying the quality of winter concreting,

The document is based on research work carried out at TsNIIOMTP and other institutes of the construction industry, as well as a generalization of the experience of winter concreting of Russian construction organizations.

When developing the document, regulatory and methodological documents were used, the main ones of which are given in section 2.

1 AREA OF USE

The document applies to winter concreting using heating wires of monolithic reinforced concrete building structures (slabs, walls, floors, columns, etc.) with a cooling surface module of 4-10, during the construction and repair of residential, public and industrial buildings and structures.

Winter concreting using heating wires is carried out at ambient temperatures, usually down to minus 20°C.

The document is used for the development of work projects (technological maps), for the certification of monolithic reinforced concrete structures and for licensing organizations performing winter concreting.

The use of the document helps ensure the design strength of monolithic reinforced concrete structures erected in winter conditions.

2 REGULATORY AND METHODOLOGICAL DOCUMENTS

4.3.2 As insulation for open concrete surfaces In addition to those given in Table 5, expanded clay, perlite, sovelite slabs, peat slabs, reeds and other heat-insulating materials are also used.

To insulate formwork panels, poured thermal insulation based on, for example, polyurethane foam and phenolic can be used.

The same thermal insulation materials are used to cover the metal frame of the formwork and ribs, which are, as is known, “cold bridges”.

4.4 Truck-mounted concrete pump and concrete pipeline

4.4.1 Preparation of the working parts of the concrete pump (hopper, other components) and the concrete pipeline consists, first of all, of insulating them with heat-insulating materials. Insulation must be such that the heat loss of the concrete mixture when loading it into a bunker, transporting it and laying it in formwork is minimal and ensures the temperature of the mixture specified by the project during laying.

The concrete pump hopper is regularly cleaned and protected from snow and wind.

In a number of cases (for example, when the outside air temperature is down to minus 5°C, when concreting secondary structures), a truck-mounted concrete pump can be used without winter preparation, that is, in a summer version.

4.4.2 Preparation for winter of other organs, components and assemblies of the concrete pump is carried out during the seasonal Maintenance, which includes routine operations for replacing oils and working fluids, adjustment and other operations to ensure uninterrupted operation of the concrete pump in winter.

4.4.3 Before the concrete pump starts operating (transporting and laying the concrete mixture), the concrete pipeline is heated with warm air, steam or hot water.

The concrete pump hopper and concrete pipeline are cleaned after use with warm water. The water remaining after cleaning is completely removed.

4.4.4 At the initial moment of operation of the concrete pump, the temperature of the starting solution and the concrete mixture filling the concrete pipeline must be at least 30°C.

The temperature of the concrete mixture during the laying process must correspond to the temperature specified by the project.

With an insulated concrete pipeline, unintentional stopping of the concrete pump is allowed for up to 30 minutes. In case of a longer stop, it is necessary to remove the concrete mixture from the concrete pipeline.

5 CONCRETE HEAT TREATMENT TECHNOLOGY

5.1 Before starting work on laying heating wires, as a rule, formwork and reinforcement work must be completed. In some cases, it is advisable to lay heating wires simultaneously with reinforcement and formwork work.

As part of winter concreting, the following preparatory and basic work is performed.

Carry out preparatory work to organize the workplace and equip it with labor tools and technological equipment, to create safe conditions labor. Fencing the workplace, installing alarms and lighting. The power equipment is installed on a flat, solid area and electrical distribution sections are installed along the grip. Connect the heating wires to the electrical distribution sections, and the sections to the transformer.

The main work of winter concreting (heat treatment of concrete) is carried out after completion of concrete laying work. The exposed concrete surfaces are covered with a waterproofing film, thermal insulation material, and voltage is applied to the heating wires.

The cooling rate of concrete is usually taken to be 2.0-3.0°C/h.

5.3 To ensure, at a given outside air temperature and wind speed, a given heat treatment regime for a reinforced concrete structure, characterized by the surface modulus, the class of concrete with a known cement consumption, the temperature of the concrete laid in the formwork, the electrical parameters of concrete heating are determined based on the parameters of the existing formwork and insulation, wires and power equipment: heat transfer coefficient, specific heating power of the concrete structure, linear electrical load, pitch and length of wires.

5.4 Heat transfer coefficientKdetermined by (including using linear interpolation or extrapolation) or by the formula

Where

α λ = 2.1 - 3.2 W/(m 2 °C) - coefficient of heat transfer from the formwork by radiation;

δ i = 0.015 - 0.1 m - thickness of the layer of thermal insulation material;

λ i = 0.02 - 0.8 W/(m 2 °C) - thermal conductivity coefficient of the insulating material;

α To = 20.0 - 43.0 W/(m 2 °C) - heat transfer coefficient by convection:

at wind speeds up to 5 m/s α k = 20.0 W/ /(m 2 °C),

at 10 m/s α k = 30.0 W/(m 2 °C),

at 15 m/s α k = 43.0 W/(m 2 °C).

Calculation examples TO shown in .

5.5 Specific heating power of a concrete structure R ud is determined by the ratio total power R heating to the heated area of ​​the concrete structure. The specific power required to heat the concrete to a given temperature is determined. Specific power depends on the difference in heating temperature of concrete and outside air ∆T, °C, massiveness of the heated structure, characterized by the module of the cooled surface M p, from the heat transfer coefficientKand cement content in the concrete mixture C.

Theoretically, the difference in heating temperature between concrete and outside air ∆T, °C, can range from minus 40 to plus 80, that is, 120 °C; practically it ranges from minus 20 to plus 50, that is, 70°C. The module of the cooled surface has a practical value in the range from 4 to 10 m -1 ; This range includes typical foundation slabs, columns, floors, walls and ceilings. The heat transfer coefficient, depending on the type of heat-insulating materials used, as well as the thickness and design of insulation, and wind speed, varies widely: from 0.2 to 6.0 W/(m 2 °C); for insulated formwork panels it does not exceed 3.0 W/(m 2 °C). Since hardening of concrete is an exothermic process, the more cement, the less electrical power is required to heat the concrete. Thus, when the cement content in the winter concrete mixture is doubled (from 200 to 400 kg/m3), the required specific heating power is reduced, all other things being equal, from 960 to 600 W/m2, that is, by 37%. The dependence of the specific heating power of concrete on the considered parameters was established experimentally and presented in the form of a nomogram (Fig. 1).

5.6 with a diameter of a steel current-carrying core of 0.6-3.0 mm is specified experimentally from the range: for reinforced structures 30-35 W/m, for unreinforced ones 35-40 W/m. With a linear electrical load of more than 40 W/m, the wire temperature exceeds 100°C, which leads to structural damage in concrete and a decrease in its strength. In addition, the electrical insulation of the wire may be damaged and short circuit for fittings and embedded parts.

5.7 The pitch and length of the wires must create such a density of their laying that ensures the necessary uniformity of heating of the concrete in the structure.

Wire pitch bdetermined by the formula

The length of the wires, depending on the linear electrical load, the diameter of the wires (current-carrying core) and operating voltage, can be approximately determined using the nomogram in Fig. 2 and specified in terms of the shape and dimensions of the structure.

The wire pitch is selected from the range 50-150 mm. For structures in contact with the ground, the pitch can be 150-200 mm. At the joints of elements, in grouts for columns and equipment, and in local seals, the wire pitch is reduced to 25-70 mm.

The length of the wires must be a multiple of the height of walls, columns, foundations and the width of the floors.

Examples of determining the pitch and length of wires are given in.

Between straight lines 2 and 4 heat transfer coefficientsK, W/(m 2 °C), visually draw a straight line equal to 3.6 W/(m 2 °C).

∆ T= 60°С with ordinate M n = 8.0 m -1 module of the column surface. From this point we draw a horizontal line until it intersects with the mentioned straight line, equal toK= 3.6 W/(m 2 °C).

C= 350 kg/m3.

The projection of the resulting point onto the ordinate of the specific heating power of the wire indicates R beat = 320 W/m2.

Heating wire pitch (b) determined by

b= 1/(R beat/ R+1) = 1/(320/33 + 1) = 0.09 = 0.1 m,

Where R= 33 W/m - specific load on the wire from the recommended interval R= 30-35 W/m for reinforced structures.

Wire length L, necessary for winding according to the scheme, G on the reinforcing frame with a step of 10 cm, is

L = 2(A + B)WITH/ b= 2(0.5 + 0.5)7.5/0.1 = 150 m.

dd= 1.2 mm.

R= 33 W/m draw the ordinate to the point of intersection with the curve, then from this point horizontally we find the point of intersection with the curvedU, B. Projections of the intersection points onto the ordinate of the heater length allow us to select the length of the heaterl, m. The closest value is the length of the heater 25 m at operating voltageU= 55 V. Thus, 6 heaters of 25 m each are placed on the cooling surfaces of the column.

The specific wire consumption (per 1 m 3 of concrete) will be 150.0/1.87 ≈ 80.0 m.

We will determine the heat treatment regime for concrete taking into account the recommendations and provided that the strength of the concrete is at least 70%R 28 . The duration of heating at a heating rate of 4.0°C/h is at least 6 hours, isothermal holding at +40°C according to the schedule (see) is 60 hours and cooling to zero at a cooling rate of 2.0°C/h is not less than 20 hours

Similar calculations were performed at air temperatures of -10 and -15°C.

The main parameters of heat treatment of concrete in a column are summarized in the following table 6.

Table 6

6.2 Wall

Concreting (class B15 concrete, cement consumption 350 kg/m 3) walls with dimensions A´ IN ´ C (3000 ´ 500 ´ 6000 mm) is produced in inventory steel formwork with panel dimensions of 2000´ 1000 mm, insulated mineral wool slabs 60 mm thick. For heat treatment of concrete, heating wire PNSV 1 is provided´ 1.4 and transformer substation type KTPTO-80-86 VI

The temperature of the concrete mixture placed in the formwork is +5°C;

The average outside air temperature during the day is -15°C;

Wind speed 3 m/s;

The temperature of isothermal curing of concrete is +45°C.

It is assumed that heat losses through the upper and lower surfaces of the wall are insignificant (the upper open surface is reliably covered with heat-insulating material) and therefore are not taken into account.

Wall cooling surface module M n is equal to

M n = F/ V= 39.0/9.0 = 4.3 m -1.

Heat transfer coefficient TO formwork is determined by formula (1)

K = 1/(1/ α λ + å δ i/ λ i + 1/ α To ) = 1/(1/2.8 + 0.06/0.6 + 1/25) = 2.0 W/(m 2 °C),

Where

α λ

δ i = 0.06 m - thickness of the layer of thermal insulation material;

λ i = 0.6 W/(m 2 °C) - thermal conductivity coefficient of the insulating material;

α To = 25.0 W/(m 2 °C) - heat transfer coefficient by convection at a wind speed of 3 m/s.

Finding the difference in temperature between heated concrete and outside air ∆ T, which is

∆ T= 45 - (-15) = 60°C.

R the beat is determined according to the nomogram in Fig. 1.

Finding the point of intersection of the line ∆ T= 60°С with ordinate M n = 4.3 m -1 module of the wall surface. From this point we draw a horizontal line until it intersects with the straight line of the heat transfer coefficient equal toK= 2.0 W/(m 2 °C).

We lower the perpendicular from this point to the cement consumption line C= 350 kg/m3.

R beat = 250 W/m2.

Heating wire pitchbdetermined by formula (2)

b= 1/(R beat/ R + 1) = 1/(250/34 + 1) = 0.12 m,

Where d= 1.1-1.4 of the recommended interval R= 30-35 W/m for reinforced structures.

Wire length L, required for winding according to the diagram in Fig. 3, V on the reinforcement frame with a step of 12 cm, is

L = 2A(WITH + IN)/ b= 2 3(6 + 0.5)/0.12 ≈ 324 m.

From the abscissa point of the specific load Rd= 1.4 mm. We lower the perpendicular from this point to the operating voltage curvesU, B. Projections of the intersection points onto the ordinate of the heater length allow us to select the length of the heater. The closest value is the heater length is 27 m at operating voltageU= 58 V. Thus, 12 heaters of 27 m each are placed on the cooling surfaces of the wall.

The specific wire consumption (per 1 m 3 of concrete) will be 324.0/9.0 = 36.0 m.

We will determine the heat treatment mode for concrete taking into account the recommendations of section 5.2 and provided that the strength of concrete is at least 70%R 28 . The heating duration at a heating rate of 4.0°C/h is at least 10 hours, isothermal exposure at +45°C according to the schedule in Fig. 7 - 48 hours and cooling to zero at a cooling rate of 2.0°C/h - at least 22 hours.

Similar calculations were performed at air temperatures of -10 and -20°C.

Table 7

The main parameters of heat treatment of concrete in the wall are summarized in the following table 7.

6.3 Overlapping

Concreting (class B25 concrete, cement consumption 400 kg/m 3) floors with dimensions A´ IN ´ C (6000 ´ 6000 ´ 200 mm) is produced in formwork made of laminated plywood with a thickness of 21 mm. The open surface of the ceiling is insulated with 80 mm thick mineral wool slabs, thermoactive flexible coatings (TAGP) or flat heating elements (GEP).

For heat treatment of concrete, heating wire PNSV 1 is provided´ 1,2 and transformer substation type KTPTO-80-86.

The concreting conditions are as follows:

The temperature of the concrete mixture placed in the formwork is +10°C;

Temperature of isothermal curing of concrete +45°С;

Outdoor temperature: during the day -16°С, at night -20°С;

Wind speed 1.5 m/s.

The parameters of the concrete heat treatment mode are determined in the following sequence.

It is assumed that heat losses through the open upper surface of the ceiling are insignificant (reliably covered with heat-insulating material) and therefore are not taken into account.

Floor cooling surface module M p is equal to

M n = F/ V= 40.8/7.2 ≈ 6.0 m -1 .

Heat transfer coefficientKformwork made of laminated plywood is determined by formula (1)

K = 1/(1/ α λ + å δ i/ λ i + 1/ α To ) = 1/(1/2.8 + 0.021/0.4 + 1/20) = 2.2 W/(m 2 °C),

Where

α λ = 2.8 W/(m 2 °C) - coefficient of heat transfer from formwork by radiation;

δ i = 0.021 m - thickness of laminated plywood;

λ i = 0.4 W/(m 2 °C) - thermal conductivity coefficient of laminated plywood;

α To = 20.0 W/(m 2 °C) - heat transfer coefficient by convection at a wind speed of 1.5 m/s.

Finding the temperature difference ∆ T heated concrete and the average outside air temperature during the day (equal to -18°C), which is

∆ T= 45 - (-18) = 63°C.

Required specific heating power of concrete R BP is determined using a nomogram.

Finding the point of intersection of the line ∆ T= 63°С with ordinate M n = 6.0 m -1 module of the floor surface. From this point we draw a horizontal line until it intersects with the straight line of the heat transfer coefficient equal toK= 2.2 W/ (m 2 °C).

We lower the perpendicular from this point to the cement consumption line C= 400 kg/m3.

The projection of the resulting point onto the ordinate of the specific heating power indicates R beat = 300 W/m2.

Heating wire pitchb determined by

b = 1/( P beat/ R + 1 = 1/(300/34 + 1) = 0.10 m,

Where d= 1.1-1.4 from the recommended interval p = 30-35 W/m for reinforced structures.

Wire length Lrequired for laying reinforcement in the lower level according to the diagram, b in increments of 10 cm, is

L = B(A/b + 1) + A= 6(6/0.1 + 1) + 6 ≈ 372 m.

Between curves 1.4 and 1.1 mm wire diameterdvisually draw a curve equal tod= 1.2 mm.

From the abscissa point of the specific load R= 34 W/m draw the ordinate to the point of intersection with the curve, then from this point horizontally we find the point of intersection with the curved= 1.2 mm. We lower the perpendicular from this point to the operating voltage curvesU, IN . Projections of the intersection points onto the ordinate of the heater length allow us to select the length of the heater. The closest value is the heater length is 25 m at operating voltageU= 55 V. Thus, 15 heaters of 25 m each are placed in the ceiling.

The specific wire consumption (per 1 m 3 of concrete) will be 372.0/7.2 ≈ 52.0 m.

We will determine the heat treatment regime for concrete taking into account the recommendations and provided that the strength of the concrete is at least 70%R 28 . The duration of heating at a heating rate of 4.0°C/h is at least 9 hours, isothermal exposure at +45°C according to the schedule is 48 hours, and cooling to zero at a cooling rate of 2.0°C/h is at least 22 hours.

Similar calculations were performed at an air temperature of -10°C.

The main parameters of heat treatment of concrete in the ceiling are summarized in the following table 8.

Table 8