unit of measurement

According to calculation A

Schedule B

How much % is the indicator according to the graph more (+) or less (-) than according to the calculation

work hard bone works at 100 m 3 mixtures

people-h

15,6

Average rank of workers

Average week nevnaya wage one worker

rub.-kop

22. Technology for the preparation of concrete mix

The technological process of concreting structures includes the preparation of the concrete mixture and its transportation to the facility under construction, its supply, distribution, placement and compaction in the structure, the care of concrete during the hardening process.

Concrete mixture cannot be prepared in advance and transported to long distances. After preparation, it must be delivered and placed in the blocks of the structure before setting begins (usually 1 ... 3 hours). Therefore, the concrete mixture must be prepared near the places of its laying so that the time it takes to travel in the summer does not exceed 1 hour.

The concrete mixture is prepared on a mechanized or automated concrete plant in ready-made delivered to the construction site or prepared on-site inventory (mobile) concrete mixing plants.

Preparation of concrete mix consists of the following operations: reception and storage of constituent materials (cement, aggregates), weighing (dosing) and mixing them with water and issuing the finished concrete mixture to vehicles. IN winter conditions This technological process includes additional operations.

The concrete mixture is prepared according to the finished or dissected technology. With the finished technology, a ready-made concrete mixture is obtained as a product, with a dissected one, dosed components or a dry concrete mixture are obtained. The main technical means for the production of concrete mix are supply hoppers with distribution devices, batchers, concrete mixers, systems of internal vehicles and communications, a dispensing hopper.

Technological equipment of a stationary type for the preparation of a concrete mixture can be solved according to one-stage and two-stage schemes.

A single-stage (vertical) scheme (Fig. 6.1, a) is characterized by the fact that the constituent materials of the concrete mixture (binders, aggregates, water) rise to the top point of the technological process once and then move down under the action own strength gravity during the technological process. Advantages: compact, economical, and disadvantages - the complexity of installation (due to the considerable height, up to 35 m).

With a two-stage (parterre) scheme (Fig. 6.1, b), the rise of the constituent materials of the concrete mixture occurs twice, i.e. the components of the concrete mixture are first lifted into the feed bins, then they fall by gravity, passing through their own dispensers, fall into a common receiving funnel and rise again to be loaded into the concrete mixer. The advantage of this scheme is the lower cost of installation, and the disadvantage is a large building area.

When the need for a concrete mix is ​​not more than 20 m 3 / h, mobile mobile concrete mixers with gravity-type mixers are usually used.

Rice. 6.1. Layout diagrams of concrete mixing plants and installations: a - single-stage; b - two-stage; 1 - aggregate storage conveyor

in consumable bunkers; 3, 9, 10 - rotary guide and distribution; 4 - consumable bins; 5 - cement supply pipeline; 6 - cement dispenser; 7 – filler dispenser; 8 - water dispenser; 11 - concrete mixers; 12 - distributing hopper; 13 - concrete truck; 14 - cement truck; 15 - skip hoist.

The design of concrete mixing plants allows you to transfer from working to transport position during one work shift and transport them on a trailer to the next object. The use of such installations is expedient on large dispersed objects located from stationary concrete plants at distances exceeding technologically permissible.

Concrete plants usually produce two types of products - dosed components and ready-mixed concrete.

Cyclic and continuous mixers are used as equipment for the preparation of ordinary concrete mix.

Cyclic concrete mixers differ in the volume of the finished mixture dispensed in one batch.

The performance of the cyclic concrete mixer

P \u003d q n k in / 1000, m 3 / h

where q is the volume of the finished concrete mix for one batch, l; n is the number of batches per hour; k in - the coefficient of use of the concrete mixer in time (0.85 ... 0.93).

The loading of the cyclic concrete mixer is carried out in the following sequence: first, 20 ... 30% of the amount of water required for mixing is supplied to the mixer, then cement and aggregates are simultaneously loaded, without stopping the water supply to the required amount. The cement enters the mixer between the batches of aggregate, thereby eliminating its spraying. The duration of mixing the concrete mixture depends on the capacity of the mixer drum and the required mobility of the concrete mixture and ranges from 45 to 240 s.

Continuous concrete mixers are produced with a capacity of 5, 15, 30 and 60 m 3 / h, and gravity-type machines with a drum mixer - with a capacity of 120 m 3 / h. The duration of mixing in these concrete mixers is indicated in the passports of the machines.

When preparing a concrete mix using a separate technology, the following procedure must be observed: water, part of the sand, finely ground mineral filler (if used) and cement are dosed into the mixer. All these components are thoroughly mixed, the resulting mixture is fed into a concrete mixer, pre-loaded with the rest of the sand and water, coarse aggregate, and once again the whole mixture is mixed.

The composition of the concrete mixture must provide the properties specified for it, as well as the properties of the hardened concrete.

There are certain requirements for concrete mix:

1) it must maintain uniformity (during transportation, reloading and laying in the formwork), which is ensured by cohesion (non-separation) and water-holding capacity. All this is achieved by the correct selection of the composition of the mixture, the accuracy of the dosage of the components and the thorough mixing of all components;

2) be workable. Workability is the ability of a concrete mixture to spread and fill a mold under the action of vibration. It depends on grain composition mixture, the amount of water, the degree of reinforcement, methods of transportation and compaction of the mixture.

Dry mortar(ССС) - a mixture of binder, aggregates, additives, pigments, dosed and mixed at the factory, and mixed with water before use. Accurate dosing of components allows obtaining higher technical characteristics of the finished product compared to mixtures obtained, prepared at the construction site. An important advantage of dry mixes is the possibility of adding chemical additives and microfillers to them, both improving their structure and prepared for use in the cold season.

Concrete Mix Transportation Technology

Transportation of concrete mix includes its delivery from the place of preparation to the construction site, the supply of the mixture directly to the place of laying, or its reloading onto other vehicles or devices, with the help of which the mixture is delivered to the concreting unit. A concreting block is a structure prepared for laying a concrete mix or a part of it with an installed formwork and mounted reinforcement.

In practice, the process of delivering the concrete mixture to the concreting blocks is carried out according to two schemes:

From the place of preparation to direct unloading into the concrete block;

From the place of preparation to the place of unloading at the concrete object, with the subsequent supply of concrete to the concreting unit. This scheme provides for intermediate unloading of the concrete mix.

Transportation and laying of the concrete mixture must be carried out by specialized means that ensure the preservation of the specified properties of the concrete mixture.

Transportation of the concrete mix from the place of preparation to the place of unloading or directly to the concreting unit is carried out mainly by road, and transportation from the place of unloading to the concreting unit is carried out in buckets by cranes, lifts, conveyors, concrete pavers, vibratory feeders, motor carts, concrete pumps and pneumatic blowers.

The method of transporting the concrete mixture to the place of its laying is chosen depending on the nature of the structure, the total volume of the laid concrete mixture, the daily requirement, the transportation distance and the lifting height. With any method of transportation, the mixture must be protected from atmospheric precipitation, freezing, drying, and also from the leakage of cement laitance.

The permissible duration of transportation depends on the temperature of the mixture at the outlet of the mixer: it should not exceed 1 hour at a temperature of 20-30°C; 1.5 h - 19-10°C; 2 h - 9-5°С. Long-term transportation on bad roads leads to its delamination. Therefore, in vehicles without stirring the mixture along the way, it is not recommended to transport a distance of more than 10 km along good roads and more than 3 km - on the bad ones.

Choice of vehicles carried out on the basis of the conditions of the facility under construction: the volume of concrete work; the period of their production; travel distances; the size of the building in plan and in height; TEP (productivity, speed of movement, unit cost of transportation). In addition, it is also necessary to take into account the requirements for maintaining the properties of the concrete mixture - preventing decay, changes in uniformity and consistency.

To transport the mixture to the site, road transport is widely used - general-purpose dump trucks, concrete trucks and concrete mixer trucks (mixers).

Transportation of the mixture by dump trucks. Disadvantages: there are difficulties in protecting the mixture from freezing, drying, leakage of cement milk through the cracks in the bodies, the need for manual cleaning of the body.

Transportation of concrete mix by concrete trucks , equipped with sealed dump-shaped tipping bodies. Advantages: transportation of the mixture is possible at a distance of up to 25-30 km, and without splashing it and leaking cement laitance.

Transportation of the mixture by truck mixers (mixers). It is the most efficient means of transportation. Concrete mixer trucks are loaded at the factory with dry components and prepare the concrete mix en route or at the construction site. The capacity of truck mixers for the finished mix is ​​from 3 to 10 m 3 . Mixing of components with water usually starts 30-40 minutes before arrival at the site. In truck mixers (mixers) it is also advantageous to transport ready-made concrete mixtures due to the possibility of inducing them along the way due to the rotation of the drum. Advantages: the range of transportation of dry mix components in truck mixers is not technologically limited.

The concrete mixture delivered to the facility can be unloaded directly into the structure (when concreting structures located at ground level or shallow) or reloaded into intermediate containers for subsequent delivery to the concreting site.

The mixture is fed into the structures to be concreted by cranes in fixed or rotary buckets or by belt conveyors (conveyors), concrete pumps and pneumatic blowers (through pipes), link arms and vibrating arms, belt concrete pavers. Rotary tubs with a capacity of 0.5 - 8 m 3 are loaded directly from dump trucks or concrete trucks. Belt mobile conveyors are used when it is difficult or impossible to supply the mixture to the place of laying by means of delivery or in tubs. Conveyors up to 15 m long serve the mixture to a height of up to 5.5 m. To reduce the height of free fall of the mixture during unloading, guide shields or funnels are used. Disadvantage: The conveyors need to be changed frequently during the concreting process.

Therefore, self-propelled belt trucks are more effective in this regard. pavers mounted on the base of a tractor, equipped with a skip hoist and a belt conveyor up to 20 m long. To supply the mixture in structures located in cramped conditions and in places not accessible to other means of transport, concrete pumps. They supply the mixture through a steel detachable pipeline (concrete pipe) to a horizontal distance of up to 300 m and vertically up to 50 m. Also, for non-overload supply of the mixture and its laying, pneumatic superchargers. The maximum range of transportation by them is 200 m horizontally or up to 35 m vertically when supplying up to 20 m 3 / h. To supply and distribute the mixture directly at the installation site at a height of 2 - 10 m, apply trunks, representing a pipeline of conical metal links and an upper funnel; vibration robots, representing a link trunk with a vibrator. On the loading funnel with a capacity of 1.6 m 3 and sections of the vibro-shoe with a diameter of 350 mm, vibrators-stimulators, as well as dampers, are installed every 4-8 m.

The supply and distribution of the concrete mixture in the structure at a distance of up to 20 m with a slope of 5-20 ° to the horizon is ensured by vibration chutes in conjunction with vibration feeder with a capacity of 1.6 m 3. They can lay mixtures up to 5 m 3 /h at an angle of inclination of 5 °, and at an angle of 15 ° - up to 43 m 3 / h.

I approve:

______________________

______________________

______________________

"____" __________ 200 g.

ROUTING

TECHNOLOGICAL CARD FOR CONCRETING STRUCTURES

REINFORCING, FORMWORKING AND CONCRETE WORKS

4. Preparatory, formwork and reinforcing work

4.1. Prior to the start of formwork and reinforcement work on the erection of concrete structures, geodetic marking work should be fully completed with fixing the axes of concrete structures in place. Particular attention should be paid to geodetic work when constructing formwork and installing reinforcing cages.

4.2. In the course of work, special attention should be paid to ensuring the rigidity of the installed formwork and to the inadmissibility of its deformation and separation under the pressure of the column of the laid concrete mixture, as well as to determine the rate of erection of all support elements, taking into account the setting time of the concrete mixture.

4.3. Prior to the start of reinforcement work, the base should be cleaned of debris and dirt.

4.4. When preparing concrete bases and working joints to remove the cement film, surface treatment is carried out with a water and air jet, metal brushes or sandblasting installations.

For reinforcement, reinforcement with a diameter of 32 mm, 22 mm, 20 mm, 16 mm, 14 mm, 12 mm class AIII, reinforcement steel grade 25G2S, reinforcement with a diameter of 10 mm, 8 mm class AI steel grade St5 sp. GOST 5781-82.

The order of storage of reinforcement and angle.

Steel reinforcement is stored in a specially designated area. Reinforcement packages are laid on wooden linings and covered with waterproof material. Rough handling of reinforcement, its fall from a height, exposure to shock loads, mechanical damage is not allowed.

Inspection.

Reinforcing bars should be checked for defects, such as cracks, local thinning, pores, peeling, dents, bends, rust, local or general distortions, deviations from the specified cut length of the bar.

Armature cleanliness.

By the time the reinforcement cage is assembled, the reinforcement must be clean, free of dirt, oil, grease, paint, rust, mill scale and similar materials.

The fittings are connected into spatial frames using a knitting wire D = 1.6 mm. Reinforcing reinforcement is overlapped using a knitting wire, the overlap of reinforcement bars is at least 30 diameters of the reinforcement. No more than 50% of bar joints should be located in one section.

4.7. Prior to the start of work on concreting structures, it is necessary to produce the required number of spacers-"crackers" that provide the required thickness of the protective layer and the design position of the reinforcing cages in all sections of the concreted structural elements. The quality of concrete spacers-"crackers" for the design of the protective layer of concrete should not be lower than the quality of concrete structures.

It is allowed to use plastic spacers - "crackers" made in the factory.

4.8. Distance pads should be made of fine-grained concrete with the inclusion of crushed stone screenings. The dimensions and configuration of concrete spacers-"crackers" must correspond to the design of the reinforcing cage and the design values ​​of the concrete protective layer, ensure their stable position in the formwork and on the reinforcing bars of the cage.

To eliminate the possibility of staining and subsequent destruction of the surface layer of concrete at the locations of the “crackers” gaskets, the outer (supporting) surface of the gasket made of fine-grained concrete in contact with the formwork should have a curvilinear outline (radius of curvature 30 - 50 m).

4.9. During the execution of reinforcing work, it is necessary to install embedded parts in accordance with the project.

4.10. Preparation of reinforcing cages (separate items) and embedded parts, their installation and installation in the formwork and other work related to design features reinforcement of the concreted elements is performed in accordance with the working drawings.

4.11. Reinforcing bars laid in the formwork of the frame elements are fixed with the required number of spacers - "crackers", reliably ensuring the design location of the reinforcing cage in the formwork and the size of the protective layer of concrete in all sections.

4.12. Reinforcement installed in place with all embedded elements (parts) must be a rigid frame that cannot be upset during concreting.

4.13. Plastic or metal tubes should be fixed to the reinforcing cages in the surface layer and in the central zones in order to form wells for measuring the temperature of the concrete during its curing.

4.14. Formwork panels are installed in accordance with the project. For concreting, an inventory formwork made in accordance with TU is used. Additional sections of the formwork are made on site. For additional formwork, a wooden frame is used. It is necessary to ensure a good tightness of the mutual adjoining of the edges of the formwork panels. If leaks are found that can lead to leakage of cement mortar during concreting, all detected places should be securely sealed before applying lubricant by gluing with adhesive tape (construction plaster) 30 - 40 mm wide or smeared with sealant. The joints of formwork panels are sealed with silicone or other sealants. Formwork panels must be fastened and fixed (uprights, stops, braces, tie rods, etc.) in such a way as to create a rigid, geometrically unchanging structure.

4.15. Before installation, the forming surfaces of the formwork panels should be wiped with burlap impregnated with grease or other grease. The lubricant should be applied in an extremely thin layer, which excludes the ingress of lubricant on the reinforcement during the installation of formwork panels.

4.16. After an instrumental check of the position of the reinforcing cages, installed formwork panels, the reinforcing cages and the installed formwork are examined and an act is drawn up for covert work with the participation of representatives of the Customer, the general contractor and supervisory services.

5. Concreting

5.1 Before starting work on laying concrete, the equipment for concrete supply should be prepared for operation and its serviceability should be checked.

5.2 Prior to the start of work, the site manager must clarify: the time of delivery of concrete from the plant to the facility, the availability of documentation confirming the compliance of the indicators of the concrete mix and concrete with the requirements of this "Technological map". A representative of the construction laboratory must check the availability of a standard cone for determining the mobility of the concrete mixture, thermometers for measuring the temperature of the concrete mixture and outside air, a device for determining the amount of entrained air in the concrete mixture and the sufficiency of molds for making control concrete cubes.

5.3 An effective operational connection must be established between the concrete plant and the facility under construction, ensuring the delivery of the concrete mixture in full compliance with the requirements of the project and this "Technological map".

5.4 Delivery of the concrete mixture to the construction site must be carried out by truck mixers. The number of truck mixers must be assigned from the conditions of the volume of concreted structural elements, the intensity of laying the concrete mixture, the distance of its delivery, the concrete setting time. The total time of delivery of the concrete mix to the construction site, its laying in structural elements should not exceed its setting time.

5.5 Descent The supply of concrete mixture to the place of laying can be carried out through link, easily assembled disassembled trunks, concrete pipelines and the end hose of the concrete pump.

5.6 Before supplying the concrete mixture directly into the body of the structure, the concrete pump must be tested by a test hydraulic pressure, the value of which.

The assigned composition and mobility of the concrete mixture must be checked, refined on the basis of test pumping of the concrete mixture.

The internal surfaces of the concrete pipeline before concreting must be moistened and lubricated with lime or cement mortar.

5.7 During production concrete work it must be taken into account that in cases of interruptions in the pumping of the mixture from 20 to 60 minutes, it is necessary to pump the concrete mixture through the system every 10 minutes for 10 - 15 seconds. at low operating modes of the concrete pump. For breaks exceeding the specified time, the concrete pipeline must be emptied and flushed.

5.8 The intensity of concreting should be determined by the construction laboratory, taking into account the properties of the concrete mixture, the distance of delivery of concrete.

5.9 When performing work in the winter period, before concreting each element, the base and upper zone of the previously concreted elements should be warmed up to a temperature of at least plus 5 °C to a depth of at least 0.5 m.

5.10 To prevent the appearance of thermal cracks in structures, the value of the heating temperatures of previously concreted elements is linked to the temperature of the incoming concrete mixture in accordance with the table.

Table 1

TYPICAL TECHNOLOGICAL CHART (TTK)

APPLICATION OF CONCRETE WITH ANTI-FROST ADDITIVES

1 area of ​​use

1.1. The technological map has been developed for concreting structures in winter conditions with the use of antifreeze additives.

1.2. Winter conditions are conditions under which the average daily outdoor temperature is below 5°C and the minimum daily temperature is below 0°C.

1.3. The essence of the method of introducing antifreeze additives into the concrete mixture consists in introducing into the concrete mixture during its manufacture additives that lower the freezing point of water, ensure the hydration reaction of cement and its delayed hardening at low temperatures.

1.4. Antifreeze additives are used in the case of a device during the construction in winter conditions of monolithic concrete and reinforced concrete structures, monolithic parts of prefabricated monolithic structures, monolithic joints of prefabricated structures.

1.5. The scope of works considered by the technological map includes:

Laying of concrete mix with antifreeze additives;

1.6. Concreting in winter conditions with the use of antifreeze additives is carried out in accordance with the requirements of federal and departmental regulations, including:

SNiP 3.03.01-87. Bearing and enclosing structures;

SNiP 12-03-2001. Labor safety in construction. Part 1. General requirements;

SNiP 12-04-2002. Labor safety in construction. Part 2. Construction production.

- "Guidelines for the production of concrete work in winter conditions, areas Far East, Siberia and the Far North". Moscow, Stroyizdat, 1982;

- "Manual for the production of concrete work." Moscow, Stroyizdat, 1975;

- “Guidelines for quality control of construction and installation works”, St. Petersburg, 1998.

2. Organization and technology of work performance

2.1. Prior to the start of the installation of a robot for the use of concrete mixtures with antifreeze additives in winter conditions, it is necessary:

Execute and accept the underlying structures;

Prepare tools, fixtures, inventory;

Deliver to workplace materials and products,

Instruct workers on labor protection;

Familiarize the performers with the technology and organization of work.

2.2. The use of concrete mixtures with antifreeze additives includes:

Selection of antifreeze additives;

Preparation of concrete mix with antifreeze additives;

Transportation of concrete mix with antifreeze additives;

Laying concrete mix with antifreeze additives;

Curing of concrete with antifreeze additives;

Quality control and acceptance of works.

2.3. As antifreeze additives, it is possible to use chemicals, the characteristics of which are given in Table. 2.1. It is recommended to use complex additives containing compatible plasticizing and antifreeze (simultaneously accelerating hardening) components.

2.4. The scope of concrete with antifreeze additives and hardening accelerators are given in table. 2.2.

2.5. The antifreeze additives listed above have a different mechanism of influence on the process of concrete structure formation. Some of them only reduce the freezing point of water and do not affect the rate of setting and hardening of concrete (for example, HH, M).

Other additives, along with effective antifreeze properties, are simultaneously setting accelerators (P) and hardening accelerators (NK, NNK). Approximate strength of concrete with antifreeze additives is given in Table 2.3.

2.6. The optimal amount of antifreeze additive depends on the minimum temperature of the concrete mixture. When curing concrete with antifreeze additives, it is necessary to create such conditions that during the period of transportation and laying the concrete mixture does not cool below 0°C. In this case, the optimal amount of antifreeze additives should correspond to the data in Table. 2.4.

2.7. Concrete mixtures with NK, NNKi, especially P additives are characterized by accelerated setting times, which makes it difficult to lay the concrete mixture and degrades the structure. cement stone. Therefore, simultaneously with the indicated antifreeze components, it is recommended to introduce plasticizing agents into the composition of the concrete mixture. As a plasticizing component of the complex additive, which increases the mobility and reduces the water demand of the concrete mixture, it is recommended to use the additives given in Table. 2.5.

Concrete with the addition of potash during setting and initial hardening must have negative temperature.

2.6. The most effective complex additives are compositions that include surface-active substances (surfactants) and electrolytes. With properly selected dosages of electrolyte and surfactant additives, it is possible to use the plasticizing properties of the latter and at the same time obtain a high hardening rate. The list of the most effective complex antifreeze additives and their reduced amount is given in Table. 2.5.

2.7. The recommended amount of chemical additives for complex curing of concrete is given in Table 2.6. The use of concrete with antifreeze additives should be preceded by laboratory tests of the effect of additives on the strength and hardening rate of concrete.

2.8. The final choice of the type of chemical additives is made taking into account the prices of manufacturers and suppliers of chemical additives.

2.9. The preparation of the concrete mixture is organized at a concrete plant. The selection of the concrete composition for winter laying is carried out in accordance with GOST 27006-86. The selection of the composition is carried out by a calculation-experimental method, which includes the solution of the following issues:

Determination of all requirements for the quality of the concrete mix and concrete;

Quality assessment and selection of materials for the preparation of concrete mix;

Calculation of the nominal composition of concrete;

Experimental verification of the design composition;

Adjustment of the composition and calculation of the production composition of concrete.

2.10. When preparing a concrete mixture, it is possible to heat the mixing water, warm or heat the components, as well as heat the concrete mixing unit, batching and bunker compartments.

2.11. To obtain the maximum temperature of the concrete mixture at the outlet of the concrete mixer, water is heated up to the maximum possible temperature of + 80 ° C.

2.12. The mixing time of the concrete mixture in the concrete mixer should be 25% longer than in summer conditions, and not less than the values ​​given in Table 2.7.

2.13. The amount of chemical additives established in accordance with the recommendations is introduced during the preparation of concrete mixtures in the form of aqueous solutions of a working concentration. Salt solutions are prepared on water heated to 40 ° C in mixers. The main indicators of aqueous solutions of antifreeze and plasticizing additives are given in table. 2.8, table 2.9.

2.15. Transportation of the prepared concrete mix is ​​carried out by truck mixers. To minimize heat loss, the open parts of the mixer truck drum are covered with moisture-proof materials and insulated. The neck of the mixer truck drum is insulated and covered with a heat-insulating cover or the neck is heated with exhaust gases from the engine. When using only potash, it is recommended to add it at the facility by introducing an aqueous solution of potash with mixing of all components in the mixer truck drum. protected from wind and precipitation. The bunker for supplying the concrete mixture must also be insulated.

2.16. When using concrete pumping plants to supply the concrete mixture, all components and parts in contact with the concrete mixture are insulated. At the same time, the pipelines and the main components of the concrete pump should be especially carefully insulated in order to maintain the initial temperature of the concrete. At extreme temperatures down to -40°C, in addition to the insulation of the main components of the concrete pump, additional heating of the insulated concrete pipeline is required with flexible heating elements. It should also provide for hot water in insulated tanks for flushing concrete pipelines after concreting.

2.17. Maintaining monolithic concrete and reinforced concrete structures erected from concrete with antifreeze additives is carried out in compliance with the following guidelines:

Concrete surfaces that are not protected by formwork, in order to avoid moisture loss or increased moisture due to precipitation, should be immediately covered with a layer after concreting. waterproofing material(polyethylene film, rubberized fabric, roofing material, etc.);

Concrete surfaces that are not intended in the future for a monolithic connection with concrete or mortar can be coated with film-forming compounds or protective films (bitumen-ethinol, etinol varnish, etc.);

In the event of an unexpected decrease in the temperature of concrete below the design structure, it is necessary to insulate or heat it until the concrete reaches critical strength.

2.18. Demoulding of load-bearing concrete and reinforced concrete structures should be carried out after the concrete reaches the strength given in Table. 2.9.

2.31. If it is impossible to provide the required strength of concrete by the time the structure is loaded with a standard load, it is allowed, with an appropriate feasibility study, to use a concrete class increased by one step.

2.32. It is allowed to remove the formwork, which perceives the mass of concrete of structures reinforced with load-bearing welded frames, as well as side elements that do not bear the load from the mass of structures, after the concrete reaches critical strength.

2.33. The strength of concrete before stripping must be confirmed by tests.

2.34. Removal of thermal protection and formwork from structures, when using concrete with antifreeze additives - upon reaching the strength specified in section 3.

3. Requirements for the quality and acceptance of work

3.1. When curing concrete with antifreeze additives in winter conditions, production control quality which includes:

Input control of materials for the preparation of concrete mix, reinforcement and embedded parts, thermal insulation materials;

Operational control of the performance of reinforced concrete works;

Acceptance control of work performed.

At all stages of work, inspection control is carried out by representatives of the technical supervision of the customer.

3.2. Input quality control of materials, semi-finished products, products and parts consists in checking external inspection their compliance with GOSTs, TUs, project requirements, passports, certificates confirming the quality of their manufacture, completeness and compliance with their working drawings. During the input control, compliance with the rules for unloading and storage is also checked. Input control is performed by line personnel when materials, structures, products arrive at the construction site.

3.3. Operational control should be carried out during the performance of reinforced concrete work and ensure the timely detection of defects and the adoption of measures to eliminate and prevent them. During operational control, they check the compliance of the work performed with the working project and regulatory requirements. The main tasks of operational control:

Compliance with the technology of performing reinforced concrete works;

Ensuring compliance of the work performed with the project and the requirements of regulatory documents;

Timely detection of defects, their causes and taking measures to eliminate them;

Performing subsequent operations after the elimination of all defects made in previous processes;

Increasing the responsibility of direct executors for the quality of their work.

3.4. When laying the concrete mixture, it is necessary to control:

The quality of the concrete mixture;

Rules for unloading and distribution of concrete mix;

The temperature of the concrete mixture;

Concrete compaction mode;

The order of concreting and ensuring the solidity of the structure;

Timeliness and correctness of sampling for the manufacture of control samples of concrete.

3.4. When laying and compacting a concrete mixture with antifreeze additives, laid in winter conditions, the requirements given in Table. 3.1.

3.5. When curing concrete with antifreeze additives, the following is controlled:

Maintenance of temperature and humidity conditions;

Protection of hardening concrete from mechanical damage;

curing time of concrete.

3.6. Technical requirements when curing concrete with antifreeze additives are given in table. 3.2.

3.6. Concrete quality control provides for checking the compliance of the actual compressive strength of concrete in the design with the design and specified in the terms of the intermediate control. The compressive strength of concrete should be checked by testing control cubes with dimensions of 100x100x100 mm in accordance with GOST 10180-90. Test specimens are made from samples of the applied concrete mix. Samples are taken at the place of preparation of the concrete mixture and directly at the place of concreting.

At least two samples should be taken at the concreting site. From each sample, one series of control samples is made (at least three samples in a series). Control samples are concreted in detachable steel molds corresponding to GOST 22685-89. Before concreting, the inner surfaces of the molds are lubricated. The concrete mixture is placed in the molds immediately after sampling with compaction by bayoneting or vibrating. Control samples are stored under the conditions of hardening of the concrete structure. Demoulding the samples after keeping the structure.

The terms for testing control samples are assigned by the construction laboratory, taking into account the achievement of design strength by the time of testing. Samples stored in frost must be kept for 2 ... 4 hours at a temperature of 15 ... 20 degrees C before testing. Intermediate control is carried out after the temperature has dropped to the calculated final temperature.

3.7. When accepting a sustained design, check:

Compliance of the design with working drawings;

Conformity of concrete quality to the project;

The quality of the materials used in the construction, semi-finished products and products.

3.8. The requirements for the finished design are given in Table. 3.3.

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