Temperature concrete mix Upon exit from the concrete mixer and its components when loading into the mixer should not exceed the following values \u200b\u200b(depending on the type of cement used), SS:

Mixture on Portland cement, SlagoporTland cement

those, Pozzolan portland cement class B45. . 35.

Mixture on fast-harden portland cement and

portland cement class B45 n above 30

To obtain such values, the temperature of the water when applying to the mixer should be, respectively, at least 80 and 60 ° C.

The order of loading the mixer components of the mat

the next. Simultaneously with the supply of half

put the portions of water into the mixer are loaded rubble (grams

they) and after several revolutions of the drum mixer

(When the water temperature drops slightly) add

sand and cement.

The above limitations of the temperatures of the constituents and the order of loading the latter are intended to prevent an overly rapid grasp of the cement test, I preventing it with a uniform distribution according to the mixture of the mixture and the worsening conditions of its hardening. OR- I Rajicing the temperature of the concrete mix is \u200b\u200bassociated with the necessary), firstly, reduce the thickening of the mixture and maintain its mobility for tight laying in the formwork, and secondly, to reduce heat losses contained in the mixture when transporting it to the place Styling (the higher the temperature of the mixture, those heat loss more).

In winter, it is most profitable to transport the mixture in a rapidly movable large capacity, as the mixture cools less. Especially effectively using concrete bridges adapted to transport the heated mixture with minimal heat lines. Body car dump trucks appropriate | Heat outgoing gases.

Gases are passed through I a specially arranged double bottom of the body or remove j through the pipes to the covered upper part of the body, giving them such a direction when the continuous thermal curtain is formed over the concrete mixture.

Heat losses with the most transportation less than losses in overload operations, so in winter it is necessary to maximize the oversight ways to deliver the concrete mix from the concrete mixer to the place of installation.

The container in which the concrete mixture is delivered immediately before the start of work and periodically in the process of warming them with steam. Overload and unloading places should be protected from wind. When applying a concrete mixture of concrete pumps? MI It is necessary to obtain a thorough insulation of the concouter (for example, walked) and the installation of a concrete pump in a warmed room, and with large frosts - also the heating of the conconsee located next to it with a steam tube. To clean the concrete and concrete pump should be used hot water. Freed from the concrete mixture of concouters are not washed from the concrete mix (in order to avoid the formation of a land), and they can be cleaned with scrapers and metal brushes on long handles and wipes with plows from burlap.

Conveyors and vibration cells, according to which the concrete mixture moves a thin layer, in winter conditions are unsuitable, since the mixture will quickly cool. Therefore, they are used limited, in small sections, with protection from cold and wind with removable boxes. The main line of the conveyor is placed in the heated gallery. | Laying the concrete mix outdoors shoulder! To be organized so that by the end of the installation, the mixture I had the desired temperature (not lower than 2 ° C, and with the thermos method - provided by the calculation). As already mentioned above, in some cases it is advisable to launch a concrete mixture with a high temperature in the formwork, subjected to its pre-electrical heating near the place of laying in special bunkers, badyes, car dump trucks. The widespread use of the electro-heating of the mixture in swivel baadyes, which is carried out on a planned area of \u200b\u200bat least 7x6 m with a mesh fencing with a height of 1.7 MI to the entry of vehicles with a concrete mixture. Access to the site to unauthorized persons is prohibited; Warming up the mixture leads with careful compliance with safety regulations.

The greatest permissible temperature of the warm-up mixture on Portland cement - 70 ° C, on SlagoporTland cement - 80 ° C. The temperature is specified in production from the conditions of the rate of thickening of the mixture, the possibility of tight laying in the formwork and consumed electrical power. A warm-up device gets power from a voltage of 120 ... 380 B, in connection with which there is a partial installation capacity of 25 ... 150 kV-A, and sometimes higher. In order to reduce the electric power consumption (up to 25 ... 50 kV - a), the heating leads at a voltage of 120 V, and a mustache housing system 1 1 ^% of the mass of Ttem-T; I is added to the mixture on a concrete plant. 1-temperature of the heating is prescribed depending on the temperature of the outer air (with an outer temperature -15 ...- 20 ° C, the mixture is heated to. 45 ... 55 ° C)

In cases where it is possible to unload the concrete mixture from the car directly in the design, the mixture is heated in the car body before its unloading, for which the body is equipped similarly to the Badyam.

Ensuring high quality concrete and reinforced concrete works performed at negative temperatures ambient air causes the need to comply with certain requirements.

At negative temperatures, free water is freezed in concrete, ice crystals are formed than water. Therefore, in the pores of concrete, a large pressure is developing, leading to the destruction of the structure of a non-hardened concrete and a decrease in its ultimate strength. The ultimate strength decreases the greater than in more early age Frozen concrete. The most dangerous freezing of concrete during the grasp of cement.

According to the requirements of SNiP 111-15-76 Concrete strength (without contamination additives) monolithic structures With unwired reinforcement and monolithic part of the collection and monolithic structures, at the time of false freezing should be at least 50% of the design strength in the design grade of concrete M150; 40% - for concrete brands M 200 and M 300; 30% for concrete M 400 and M500. Concrete strength for structures subjected to compromising freezing and thawing should be 70% regardless of the project brand; in pre-hard structures - 80%; For structures that are subjected immediately after the end of maintaining the action of the calculated water pressure, and to which special requirements for frost resistance and waterproof are 100% of the project strength.

Concrete strength with antiorrosal additives By the time it is cooling to a temperature, which calculated the number of additives, there should be no 30% of the design strength at the design grade of concrete - to M 200; 25% - for brand's concrete M 300 and - for brand concrete M 400. Concrete, frozen under the above strength, after thawing should be maintained under conditions that provide project strength to loading reinforced concrete structures by regulatory load. To ensure the required final strength of the concrete, it is necessary to perform appropriate preparation activities to make them and preparing a concrete mix. Special attention is paid to protecting concreted structures from the immediate effects of negative temperature and wind.

The most common way winter concrete It is a method of thermos, which involves providing in concrete during its hardening of the positive temperature due to heat, powered by heating the components of the concrete mixture, and heat released by cement when hardening. In order to accelerate the process of hardening in concrete, chemical additives-accelerators are introduced or it is additionally heated by electrical current, steam and warm air. In the production of concrete and reinforced concrete works in winter time The construction laboratory and engineering and technical staff of the buildings should be strictly controlled all the stages of work.

The preparation of concrete mix in winter is carried out on central concrete nodes in heated rooms under the supervision of laboratory staff, which are obliged to check the quality of the components and, assign and control the temperature of the components and the most concrete mixture, as well as the number of chemical additives entered.

First of all, it is necessary to pay attention to the storage of the components of the concrete mixture, since in winter conditions, the storage of materials is significantly complicated. Warehouses for storage of cement must have dense fences that do not allow snow. Sand, gravel and crushed stone To avoid mixing with snow, it is necessary to add on dry elevated places protected from snow-drifts. The form of stacks of materials should ensure the smallest surface at a given volume (round, dome-shaped). The altitude of them should be at least 5 m. Before laying in the stack, the filled fillers tear.

The temperature of the components of the concrete mix at the time of loading into the concrete mixer should provide a predetermined temperature of the concrete mix when leaving the concrete mixer. Therefore, in the preparation of a concrete mixture in winter, heated water is used, flawed or heated aggregates.

The concrete mix should have some heat supply, which is consumed from the moment of laying before the start of heating in the design, and with the thermos method - during its period withstanding concrete.

The temperature of the concrete mixture laid in the formwork, to the beginning of withstanding or heating, should not be lower than the temperature set by the calculation, when maintaining concrete using the thermos method; The freezing temperature of the indemnification solution increased by 5 ° C, when applying concrete with antiorrosal additives.

The heating temperature of water and aggregates when loading them into the concrete mixer and the temperature of the finished concrete mix when it outputs it from the concrete mixer is set by calculated by taking into account the heat loss during loading and mixing materials, transportation and laying the concrete mix in the design.

The concrete mix is \u200b\u200bprepared under the supervision of a duty laboratory assistant, which sets the temperature of the mixture and checks at least two times in shifting the temperature of the components and concrete mix after it is out of its concrete mixer. If necessary, it gives the indication to change the mode of heating materials.

When applying a heated water to avoid "brewing" cement, it should ensure that the following order is made to load the materials into the concrete mixer: simultaneously with the beginning of the water supply, rubble or gravel are loaded, and after pouring half of the required amount of water and multiple drum - sand and drum and cement.

The largest permissible temperature of the water and concrete mixture (Table 1).

Table 1

The duration of mixing of the concrete mix should be increased by no less than 25% against summer conditions (when used only heated water). The duration of mixing can not be increased if used to use heated water, flawed or heated aggregates.

Transportation of concrete mix. Controlling the transportation of concrete mixture, it is necessary to take into account that heat loss with the very transportation is less than loss during overload operations. Therefore, a concrete mixture from the plant to the place of installation should be delivered without overloads. In addition, it is necessary to ensure that the concrete mixture is transported without delays in loading, transportation and unloading, and the transport packaging was insulated and heated. When transporting a concrete mixture in body dump trucks, they are covered with tarpaulous (at low transportation distances) or heated by spent gases, which are passed through a specially arranged bottom of the body or remove through the pipe at the top of the body to create a thermal curtain over the concrete mixture. When transporting the mixture in the Badjah and bunkers, they are covered with wooden insulated lids, outside insulating felt, mineral wool mats and other materials, and then trim plywood.

Construction laboratory, carrying out control over the production of concrete work, prescribes the maximum allowable duration of transportation of a concrete mixture from the conditions for preserving its workability and temperature before laying, as well as a given temperature at the outlet of the concrete mixer.

Duration of transportation can be increased by using slowing or plasticizing additives, preparation of a low temperature mixture with subsequent heated in laying places, introducing into a concrete mixture of contamination additives. The time of transportation of a preheated concrete mixture and its laying should not exceed the start time of the concrete setting.

When transporting concrete, concrete pumps should develop and carefully perform special activities that ensure their work uninterrupted. It should also provide insulation of concrete pipelines and vibro-bobs.

Laying concrete mix. Concrete or Stone base, as well as frozen concrete and stone structures Before laying a heated concrete mixture, are thoroughly cleaned from snow, nondes, dirt and cement film, warm up to a positive temperature to a depth of at least 30 cm to ensure the adhesion of the newly laid concrete with the previously erected construction or reason.

The duty laboratory assistant, carrying out control over the laying of the concrete mix, should ensure that its temperature to the beginning of the maintenance in the formwork or heating is not lower than the temperature set by the calculation, when maintaining concrete using the thermos method; The freezing temperature of the indemnification solution increased by 5 ° C - when applying concrete with antiorrosal additives; O "C - in the cooled zones before the beginning of the pre-electromygerement of the concrete mixture or with a forced electro-herogery in structures and 2 ° C - when applying other methods of thermal treatment of concrete.

To prevent excessive heat loss by a concrete mixture, it is placed in small sections in length and width, while each laid layer is quickly overlapped by subsequently, not allowing the temperature drops in it below the calculated calculation. After laying the last or intermediate (in the case of a broken concreting), the layer of concrete is covered with shields or mats. The thickness of the stacked layers of concrete for better heat conservation when laying should be the maximum allowable to the conditions of vibration. The concrete mix should be laid around the clock until the end of the concreting of the entire array or part of the block.

The manufacturer must ensure that the top surface of the concrete after the end of concreting is immediately insulated. Otherwise, the upper layer of concrete can freeze. If concrete is freezing in the working seam, the simplifying area is heated by steam, then remove the imminent unloud layer, the surface of the old concrete is treated established rules. Only after that you can continue concreting.

Control of hardening concrete. Before proceeding to the production of concrete work in winter, it is necessary to choose the method of concreting. First of all, it is recommended to check the possibility of producing concrete work in the thermos method.

The method of thermos is the most simple in production and economical. It does not require special equipment for its implementation, concrete care is reduced to monitoring the condition of shelter and to control the temperature of the concrete. However, this method is applied only in concreting of massive structures, since thin-walled structures with a large cooled surface to insulate it difficult.

The massiveness of the structure is characterized by the ratio of the amount of cooled (outer) surfaces P (m2) to its volume V (m3). This ratio is called the MP surface module, which is determined by the formula: MP \u003d p / \\ /.

The thermosis method is used in concreting structures with MPs less than 6, if using rapid grades 500-600 grades and clamp cement, which not only gain strength, but also distinguish a large amount of heat, and when the chemical additives, hardening accelerators can be applied at MP equal to 6-10.

In the production of concrete works by the thermos method in last years Apply hot concrete mixes heated to a temperature of 70-80 "with electric shock in special bunkers.

During the electrically heating of the concrete mix in the bunkers, it is necessary to observe a certain mode of lifting the temperature of the mixture. First of all, the concrete mixture should be withstanding for 20-30 minutes at a temperature of 15-20 ° C, and then heated to a temperature of 70-80 ° C for 10-15 minutes. The heated concrete mixture is immediately laid into a warmed formwork, in which concrete hardens and dials strength. In this case, the concrete cools from a temperature of not 20-30 ° C, as usual with a thermos method, and from 60-70 ° C. In the production of concrete works by the thermos method, the building laboratory carefully monitors the temperature of each portion of the concrete mix, delivered to the construction site, compliance with the temperature and humidity regime, as well as timely and thorough insulation of concrete structures.

In the process of hardening concrete, laboratory technicians should measure the outdoor air temperature three times a day or ambient, concrete temperature and measurement results to enter concrete work. The temperature of the concrete should be controlled systematically, starting with the laying of concrete and ending with cooling to 2 "with. To measure the temperature of the hardening concrete, they use technical thermometers that are installed in wells. Wells are arranged in advance in places of the most unfavorable temperature regime. The depth of them in large-sized structures 10-15 cm, and in the plates - half the thickness of the plate. In each element there must be at least three wells, but at least one for every 2 m2 plates. In structures where MP is less than 3, it should be provided both superficial and deep wells. To measure concrete temperature at a depth of 75 cm and more in massive foundations, metal tubes with a diameter of 25 mm are installed.

Wells should be closed by traffic jams, numbered and applied to the scheme. During the temperature of the concrete temperature, thermometers should be isolated from the effect of the outdoor temperature and withstand them in a well for at least 3 minutes. The gap between the thermometer and the well wall is covered with felt or palauls.

When counting temperatures, it is desirable not to remove the thermometer from the well completely. Record the temperature on a separate sheet for each design and in the temperature log.

In the process of concreting, the design regularly select control specimens that are stored under the same conditions. In winter, in addition to the three main samples, six additional, three of which are experiencing on that day, when the temperature of concrete in the design falls to 1-2 "C, the remaining three are reserve and serve to obtain additional control data.

As a result of the test in the laboratory of control samples, cubes establish the strength of concrete, then the manufacturer of work with the representative of the author's supervision solves the possibility of the possibility of palabing the structures and their downloads. It is impossible to assume the formwork for concrete. After receiving the concrete, the concrete is covered (for example, a tarpaulter) to avoid its cracking.

The method of thermos, in which concrete acquires strength of at least 5 MPa, guarantees high quality concrete. If the method of thermos is not possible to obtain a concrete strength sufficient for its receipt within the time limit, it is recommended to use concrete with antiorrosal additives, pre-electric mixtures before laying it into the formwork, as well as artificial heating of concrete with electric current or steam.

Concrete with antiorrosal additives has the ability to solve under negative temperatures. As antiorrosal additives are used: sodium nitrite (NN); sodium chloride in combination with calcium chloride (XN + HC); compounds of calcium nitrite with urea (NKM); sodium nitrite, in combination with calcium chloride (NN + HC); Nitrite-nitrate chloride calcium (NNKK); nitrite nitrate-chloride calcium, in combination with urea (NNKK + M); calcium nitrite in combination with urea (NK + M); Potash (P).

Anti-corrosion complex additives are most effective: a mixture of calcium nitrite and urea in a ratio of 3: 1 (NKM) by mass; a mixture of nitrate and calcium nitrite and urea - 1.5: 1.5 (NNM); mixture of nitrite and calcium chloride - 1: 1 (NNKK); A mixture of nitrate and calcium nitrite, calcium chloride and urea -0.7: 0.75: 1.5: 1 (NNHKM). Concrete mixes with these additives are recognized as the most technologically.

Employees of the construction laboratory, assigning a kind of anti-corrosive additive, should take into account the scope of concrete applications with chemical additives, since for different designs, depending on the type of reinforcement and aggressiveness of the medium in which the designs will be in operation, there are restrictions on the use of one or another type of additives.

Concrete mixture with antiorrosal additives can be transported in a laptile container. The maximum duration of transportation and the allowable laying time of the concrete mixture depends on its mobility.

Concrete mixture with antiorrosal additives laid in the design and compact, observing general rules Styling. The surface of the concrete, not protected by formwork, is covered in order to avoid moisture freeing. Concrete is kept under the shelter until platforming strength. In the case when, after laying the concrete, the temperature of it was lower than the calculated, adopted when establishing the concentration of aqueous solutions of antiorrosal additives, laid concrete are insulated with dry sawdust, dry sand or combine the maintenance of concrete according to the method of thermosa with artificial heating until it dials the predetermined strength .

In the production of concrete work in the winter, artificial heating of concrete is carried out at the expense of electrothermood, steam-heat and heating with warm air.

The electrothermathing of concrete is carried out by the methods of electrode warm-up, electrical heating by various electric heating devices, induction heating. In the practice of winter concreting, the electrode heating of concrete was the highest voltage not higher than 60V. Warming up this way can be recommended for concrete structures with a surface module 5-20.

The electrical heating mode prescribes a laboratory based on the type of cement used, the massiveness of the structures, the required concrete strength and the possibility of accumulating it during the cooling of the heated structures. At the time of the electrical heating of reinforced concrete structures, the laboratory technicians, electrical installations and workers are specifically isolated, the duties of which are controlled by the concrete temperature heated according to a given design of the structures and the design of temperature sheets, the power on and off, the voltage measurement on the network, the shelter of the heated concrete with insulation materials.

Controlling the electrical heating, the laboratory technicians follow that the current at a concrete temperature is not lower than 3-5 ° C. The temperature of the concrete of structures with electrical heating is measured in the first 3 hours each hour, and during the rest of the warming time - three times in shift. The laboratory assistant is obliged to ensure that when heating structures with MP, less than 6, the temperature rise in the concrete body was carried out with an intensity of 8 ° C / h, and with a MP equal to 6-10 and more - 10 ° C / h, as well as in frame and thin-walled structures. up to 6 m - 15 ° C / h. The duration of isothermal heating depends on the type of cement, the heating temperature and the predetermined critical strength of the concrete.

table 2

Maximum allowable concrete temperature at electrical heating (Table 2)

Note. With peripheral electrical heating of structures with MP, less than 5, the temperature in the outer layers should not be more than 40 ° C.

The concrete temperature at electrical heating should be the same in all parts of the structure, and do not differ more than 15 ° C in length and cross section of the structure. In order to ensure a given electrical heating mode of concrete, it is necessary to adjust the voltage that causes the electrodes to turn off the electrodes from the network at the end of the temperature lift, periodically turn on and disconnect the voltage on the electrodes.

The duty laboratory assists that the cooler speed at the end of the electro-heating is minimal and did not exceed it for designs with MP more than 10-12 ° C / h and with MP equal to 6-10 - 5 "C / h. Cooling swells in the first Clock after turning off, then the intensity of the cooling is gradually slowed down. To create the same cooling conditions of parts of the structures of various thicknesses, thin elements, protruding angles and other parts that are cooled faster than the main structure, additionally warmed up. Formwork and warm-up structures are not previously removed than concrete Cools up to a temperature of 5 "C, but before the formwork will face concrete. In order to slow down the process of cooling the outer layers of concrete of the surface of the structures, after its receipt is covered with thermal insulating materials if the difference in the temperatures of concrete and outer air for structures with MP less than 5 is 20 "C, and for designs with MP, more than 5 is higher than ZO ° C.

Heated with infrared rays is carried out due to the transfer of heat concrete in the form of radiant energy, while the hardening is accelerated. As a source of infrared rays, metallic tubular electric heaters (TEN) and rod carboond emitters are used as a source of infrared rays.

Infrared emitters complete with reflectors and supporting devices are an infrared unit that is structurally spherical or trapezedal reflectors, inside which are placed emitters with supporting devices; The optimal distance between the infrared installation and heated surface should be 1-1.2 m. Due to the change in the power of generators of infrared rays and the distance from the surface of the heated concrete, it is possible to adjust the heating intensity of the concrete, the temperature of isothermal warming, as well as the intensity of concrete cooling by the end of the thermal processing .

It is possible to heat the infrared emitters open surfaces of concrete or through the formwork. For better absorption of infrared radiation, the formwork surface is covered with black matte varnish. The temperature on the surface of the concrete should not exceed 80-90 ° C.

This method of heating concrete is advisable to apply for thin-walled structures, as well as when laying concrete into trunks, joints, etc. During heating, infrared rays should carefully protect the concrete from evaporation from it. To eliminate the intensive evaporation of moisture from concrete, its open surfaces are closed with a polyethylene film, a pergamin or rubberoid.

Induction warming of concrete is carried out due to the energy of the variable magnetic fieldwhich is transformed into fittings or steel formwork to thermal and passed to concrete. This method is used to warm the concrete of reinforced concrete frame structures (columns, rheel, beams, runs, elements of frame structures, individual supports), as well as when the joints of the framework structures are deployed in winter conditions.

In case of induction heating along the outer surface of the formwork of the element, for example, the columns are placed by sequential turns insulated wire-inductor. The step and number of turns of the wire are determined by the calculation, according to which templates are manufactured with grooves for styling of the inductor turns.

After installing the inductor before the start of concreting heated armature carcass Or the junction to remove the land from it. Then the concrete mixture is then placed. The open surfaces of the design and formwork after the end of concreting should be covered with thermal insulation material and wells must be arranged for measuring the temperature, after which they begin to warm up. Stop it after reaching the concrete of the calculated temperature. The heating temperature should not exceed the calculated more than 5 ° C. After the warming is completed, it is necessary to monitor the cooling rate of concrete, which should be 5-15 ° C / h depending on the surface module of the warmed structures.

It is used in the construction of warm-up concrete structures in thermoactive formwork. Thermoactive is called a formwork consisting of steel panels mounted on them of heating elements and outer thermal insulation. To accelerate the turnover of thermoactive formwork, it is dismantled after the isothermal warming is completed. Cooling concrete is left under the sheeping of spike blankets, tarpaulin, polyethylene film. The rate of temperature lift is controlled, its maximum value and cooling rate.

A to avoid sharp cooling of the design, which causes large temperature stresses in the concrete and its cracking. The thermoactive formwork can be used to build a wide variety of structures at the outdoor air temperatures below -20 ° C.

Steamprogere and aircraft heating concrete are methods of additional warm-up laid in the construction of concrete. The use of them requires large additional costs and can only be recommended for thin-walled structures, for which there is a risk of cutting concrete during its electrical heating.

With steam-heating, high temperatures (80-95 ° C) are created in combination with favorable humidity conditions, significantly accelerating the hardening of concrete. Paroprogery concrete monolithic structures is made in steam shirts, in a capillary formwork, in a steam bath or by passing a steam along the pipes laid at concreting of this design. During steam-hearing, the maximum concrete temperature should not exceed 70 ° C, portland cement - 80 ° C, and Slagoportland cement and Pozzolant Portland cement - 90 ° C.

The duration of isothermal warming is prescribed (according to the results of inventive tests) and controls the construction laboratory, taking into account the type of cement used, the heating temperature and the required strength. The cooling of structures after isothermal warming occurs just as with electrical heating. The temperature of the laid concrete during its steamoprogere is controlled in the first 8 hours each 2 hours, in the next 16 h after 4 hours, and during the rest of the heating and cooling time - at least once in shift. When warming concrete with warm air, it is necessary to carefully ensure that the fence of the heated space does not pass the moisture evaporated from concrete. If air humidity in the heated space will be insufficient, the design must be sprayed with water.

In order to ensure the hardening of concrete in winter conditions, various flexible heaters are used, allowing to heat the concreting surface in a sliding formwork, individual elements of foundations, concrete training.

Table 3.

Temperature indicators when heating structures in thermoactive formwork (Table 3)