Concreting of monolithic concrete and reinforced concrete structures. Technology of concreting monolithic structures. Mechanization of work

Monolithic structures are those that are erected directly on the pestle of their location. The erection of structures includes the installation of formwork, which recreates the outlines of the future structure in space, the installation of reinforcement, the concreting of the structure, and the maintenance of hardening concrete.

The formwork can be wooden from boards and plywood, metal from metal sheets or mesh, wooden with a polymer coating, reinforced concrete. Sometimes used as formwork reinforced concrete slabs, which are part of the future prefabricated monolithic structure

The fittings are installed in accordance with the project. Welding is used to connect it. In some cases, prefabricated reinforcing cages are used, which speeds up the work. For critical structures, the so-called rigid reinforcement is used in the form of I-beams, channels and rolled special profiles.

Concreting of large structures or structures is carried out in separate blocks, arranging working seams between them. The block is concreted continuously, in which case each subsequent portion of concrete must be placed and compacted before the previously laid concrete sets. The concrete mixture is usually prepared in centralized concrete mixing plants or factories and then transported to the place of laying.

Concrete transport, block placement and subsequent care determine the quality of concrete, structural properties and durability of the structure. Each step in the transport and placement of concrete must be carefully controlled to maintain the homogeneity of the concrete mixture within the batch and from batch to batch, so that the structure has the same quality. To do this, it is necessary to ensure that there is no separation of coarse aggregate from the solution or water from other components. Segregation at the point of discharge from the concrete mixer can be prevented by attaching a downward chute to the end of the discharge chute so that the concrete falls vertically into the center of the receiving bucket, hopper or cart Similar devices should be installed at the ends of all other chutes and conveyors

All bunkers must be provided with a vertical suspension under the discharge openings. When unloading at an angle, coarse aggregate is thrown to the far side of the loaded container, and the solution is thrown to the nearest side, resulting in delamination that cannot be eliminated during further transportation of concrete.

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Concreting of monolithic concrete and reinforced concrete structures

The erection of structures of buildings and structures from monolithic reinforced concrete consists of execution of formwork, reinforcing and concrete works.

Types and installation of formwork. Formwork is a form used for the manufacture of concrete and reinforced concrete structures and products. The formwork can be wooden, metal and reinforced concrete.

Wooden formwork is usually made in a special formwork yard or in the carpentry shop of a woodworking plant, where there is the necessary machine equipment for sawing and sharpening timber, as well as for assembling individual formwork elements. For its manufacture, softwood timber with a wood moisture content of up to 25% is used.

Wooden formwork has valuable qualities: lightness, low thermal conductivity, low adhesion forces with the concrete laid in it. The main disadvantages of this formwork are: hygroscopicity, low resistance to deformation, limited possibilities of turnover and service life. Despite these shortcomings, wooden formwork is widely used in the construction of monolithic concrete and reinforced concrete structures and structures.

Metal formwork and accessories for it are made in mechanical workshops or metal structures workshops. Details of the metal formwork are made of StZ steel. Formwork elements are processed with high precision. The metal formwork passes the control assembly. Parts in contact with concrete are coated with a special lubricant, and the rest are painted, after which all formwork elements are marked.

The main advantages of metal formwork are high turnover (at least 50 times), rigidity and exclusion of deformation under various humidity conditions. The disadvantages of this formwork include high cost and high thermal conductivity.

Reinforced concrete formwork during the concreting period acts as a formwork, and later, during the construction of hydraulic structures, it is a permanent structural element of the structure. The advantages of reinforced concrete formwork in these cases are the exclusion of the stripping process, ease of fastening and high rigidity. The disadvantages of this formwork are high thermal conductivity, weight and cost.

Metal and reinforced concrete formwork for monolithic structures they are rarely used in construction practice, and the need to install such formwork in each individual case is indicated in the working drawing.

The installation of formwork for monolithic structures is carried out along the axes placed on the cast-off, after preparing the place where it should be installed. Preparation consists in cleaning it of wood chips, dirt and debris. Formwork installation rules depend on the type of structure. So, the formwork of stepped foundations is made of ready-made wooden panels, tied with wire twists, with spacers made of bars or boards (Fig. 149). Formwork panels for each step are made in two sizes: the length of one pair of panels corresponds to the dimensions of the side walls of the foundation step. On the inside of these shields, straps are sewn, which serve as a support for short shields. The formwork of the subsequent steps is arranged in the same way as the first, and is supported on the formwork panels of the lower step.

Types and installation of fittings. Reinforcing steel is divided into hot-rolled rod steel and cold-rolled wire steel. Reinforcing bars and wire are made of smooth or periodic (changing) profile. Depending on the mechanical properties, reinforcing bars and wire are divided into classes, and classes into grades.

By appointment, the fittings are divided into working, distributive, mounting and clamps. According to the method of installation, the reinforcement is divided into piece, reinforcing mesh and frames.

Piece fittings can be bar (flexible) from round rods and rigid from profile rolled steel - I-beams, channels and corners.

Reinforcing mesh (Fig. 151) is a mutually intersecting rods connected at the intersections by welding

or viscous before laying it in the case. Grids are made in the form of separate flat panels of the required size or rolls of large length, from which pieces of the required size are cut. Reinforcing mesh is mainly used for reinforcing slabs.

Rice. 150. Reinforcing steel for reinforced concrete structures: a - round; b - hot-rolled periodic profile; c - cold flattened

Reinforcing cages can be flat and spatial (Fig. 152). Flat frames usually consist of longitudinal reinforcement interconnected by special mounting rods or clamps. Spatial frames are assembled from several flat frames or meshes by welding or knitting. Reinforcing cages are used to reinforce columns, beams, crossbars.

Rice. 151. Reinforcing mesh: a - separate; b - rolled

Rice. 152. Reinforcing cages: a - flat; b - spatial

Simultaneously with the grid, the lower part of the frame (reinforcement) of the column is installed - outlets that serve to connect the vertical rods of the frame of the columns. The outlets are installed using a wooden frame and their lower ends are welded to the grid.

Preparation and transportation of concrete mix. Concrete work consists of the following main technological processes: preparation of the concrete mixture, its transportation to the place of laying, laying in the formwork and care of the concrete during its hardening.

Rice. 153. Reinforcement of foundations:

All processes for the preparation of concrete mix are fully mechanized and automated. With small volumes of concrete and reinforced concrete work, the concrete mixture can be prepared in construction conditions. For this purpose, collapsible complex-mechanized concrete plants are used at construction sites. They are usually arranged as concrete-mortar Plants, producing concrete mix and mortar for various construction needs. Consequently, when performing a large amount of work, the concrete mixture is prepared in the factory (the so-called ready-mixed concrete) and centrally delivered to the construction site.

The methods of transporting the concrete mixture to the place of its laying depend on a number of factors: the distance of transportation, the time of year, the composition of the concrete mixture. Currently, the concrete mixture is delivered from the place of preparation to the place of its placement in the structure in dump trucks, in buckets (bunkers) on platforms or cars, conveyors, concrete pumps, and concrete mixer trucks.

During transportation, in order to maintain the homogeneity and mobility of the concrete mixture, it is protected from precipitation, the harmful effects of wind and sunlight, as well as from the leakage of cement laitance (mortar). AT winter time concrete mixture during transportation must be protected from freezing. For this, specially insulated modes of transport are used. In addition, the concrete mixture to the place of laying should be delivered without intermediate overloads.

With any method of transportation, the concrete mixture is protected from excessive shaking in order to avoid delamination. The duration of the transportation of the mixture from the place of its preparation to the place of laying should not exceed 1 hour (from the moment of unloading until the end of compaction).

Based on the conditions for maintaining the necessary qualities of the concrete mixture during its delivery to the place of laying, the mode of transport is chosen. Transportation of concrete mixture on dump trucks is advisable at a distance of up to 15-20 km.

Transportation in containers (buckets, bunkers, vibratory buckets), in the bodies of on-board vehicles and on railway platforms is used for the same distances as on dump trucks. Rail transport is used at large construction sites with a large flow of concrete mix. Concrete mixture is moved by belt conveyors during the construction of large foundation arrays and a significant intensity of concreting (150-200 m3 / shift). It can be applied horizontally over a distance of up to 2 km with an ascent of up to 18° and a descent of up to 12°. Transportation of the concrete mixture with the help of a concrete pump is also used for large volumes of concreting structures. The distance of the mixture supply horizontally and vertically is determined by calculation.

Concrete mixer trucks are most appropriate to use when the object under construction is at a considerable distance from a centralized concrete plant.

At the same time, the concrete mixture is prepared in a concrete mixer truck on the way immediately before it is placed in structures. The concrete mixture is laid in various ways, depending on the type of structure to be concreted.

Concrete laying and concrete maintenance. Upon receipt of a ready-mixed concrete mix, before laying it in the structure, it is necessary to check the passport, which is issued by the supplier plant for each batch of concrete mix, indicating the composition of the concrete and its grade. When laying the concrete mixture in the formwork, care must be taken to ensure that its separation does not occur. For this purpose, the height of the free fall of the mixture into the formwork, as a rule, should not exceed 3 m.
The concrete mixture should be placed into the formwork by mechanized compaction so that no air pockets remain. Vibrators of various TYPES are used for compaction.

The most widespread are electromechanical vibrators. According to the method of vibrating, vibrators are divided into surface and internal. Surface vibrators are used with a small thickness of concrete (up to 20 cm). With a greater thickness of the compacted concrete, internal (deep) vibrators are used. The duration of vibration depends on the type of construction, the quality of the concrete mixture, the type of vibrator. For example, the duration of vibration at one place of surface vibrators is about 1 minute. Increasing the set vibrating time of the concrete mixture can lead to its delamination. The main signs of the termination of vibration are as follows: noticeable settling of the concrete mixture; stopping the release of air bubbles; the appearance on the surface of the vibrated concrete of the so-called cement milk.

After laying the concrete mixture in the structure, the hardening process begins. To ensure normal hardening conditions for the concrete mixture in the early days, special care is required. The main goal of caring for summer time is to protect the mixture from drying out under the influence of wind and sun. For this purpose, after the end of the setting process, the concrete is poured with water and covered with matting, burlap, mats, etc. The watering time depends on the type of cement and the outside temperature. In dry weather, at an air temperature of more than + 15 °, concrete is recommended to be watered with Portland cement for at least 7 days, with aluminous cements - for at least 3 days. and with other cements - at least 14 days.

In winter, the concrete mixture must be provided with normal conditions for it to acquire a strength of at least 50% of the design grade. To this end, after the setting process, the concrete is usually covered thermal insulation materials: mats, sawdust, slag. In addition, freshly laid concrete should not be subjected to impacts and shocks. The movement of people and vehicles on concrete structures, the installation of scaffolding and formwork on them is allowed only after the concrete has acquired the necessary strength. The strength of concrete is determined by testing a series of samples in a building laboratory, as well as using ultrasound or a reference hammer.

Concreting and stripping of monolithic structures. Concreting of monolithic structures is carried out only after a thorough check of the condition of the formwork, compliance of the laid reinforcement with the working drawings and the implementation of all measures that guarantee high quality laying and compacting the concrete mix, as well as its uninterrupted delivery to the place of work. Concrete mix in various designs differs in some features depending on the type of these structures.

Rice. 156. Laying the concrete mixture in the foundations with a truck crane directly from the buckets

Concreting of foundations (Fig. 156) is carried out: by a truck crane (using buckets) or dump trucks.

The concrete mixture is placed in the formwork in layers of 20-40 cm thick, depending on the type of vibrator. The maximum thickness of the concrete mixture layer can be 1.25 times the length of the working part of the vibrator. With a deeper immersion of the vibrator, the structure of the concrete in the previously laid layer may be disturbed. The vibrator is immersed in the concrete mixture and kept there for an average of 20 s until the appearance of laitance on the surface, after which the vibrator is slowly, smoothly and without jerks removed from the layer of the concrete mixture. In order for the vibrator to not remain in the concrete mixture after removing the vibrator - leaks, it is removed with the motor turned on.

The step of moving the vibrators from parking to parking should not exceed one and a half vibrator ranges. The radius of action of the vibrator is the distance over which vibrations propagate, ensuring high-quality compaction of the concrete mixture. This distance is measured between the axes of the vibrators located in neighboring parking lots, and is approximately equal to 45-60 cm. The vibrators within the concreted sections are rearranged in an ordinary or staggered manner.

The increase in the strength of concrete in monolithic structures is controlled by the construction laboratory by testing samples (cubes) of concrete, as well as by non-destructive methods, as a result of which the terms for stripping concrete and reinforced concrete structures are set depending on the achieved concrete strength.

Stripping. Stripping is carried out in a certain sequence, established by the project for the production of works (PPR) for each type of structure. Before demoulding, open concrete surfaces(slabs, individual beams, crossbars) are inspected and tapped. Weak concrete, when tapped with a hammer, makes a dull sound, and with stronger blows, dents remain on it, the stripping of reinforced concrete structures is carried out on average after 10-12 days, depending on the strength achieved by the concrete, the purpose of the structures, its mass and loads. So, in summer, at an outside air temperature of 15-20 °, the load-bearing side panels of the formwork are removed 2-3 days after concreting, the load-bearing formwork of slabs, vaults, girders and beams with spans from 2 to 8 m - when the concrete reaches a strength of at least 70%. In all reinforced concrete structures with a span of 8 m or more, the supporting formwork is removed after the concrete has gained 100% design strength.

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Federal State Budgetary Educational Institution

higher professional education

"Ufa State Oil Technical University"

Department: "Building structures"

Field Practice Report

"Technology monolithic concrete and reinforced concrete"

Completed by: senior group BPGsz13-03

Sirazhetdinova A.M.

Checked by: Ryazanov A.N.

Ufa, 2017

Introduction

1. Composition of concrete and reinforced concrete works

2. Appointment and arrangement of formwork

3. Components of formwork and formwork systems

4. Formwork requirements

5. Materials for the manufacture of formwork

6. Main types of formwork

7. Technology of formwork processes

Conclusion

List of used literature

Introduction

Construction is one of the most important branches of material production, shaping the environment and activities of people, ensuring the creation, expansion and continuous improvement of the fixed assets of the state and enterprises, their material and technical base. The final building products are fully completed construction enterprises, start-up complexes and facilities prepared for the production of products and the provision of services. It is territorially fixed and has an individual character, is manufactured mainly for specific customers, is multi-part and material-intensive, is characterized by significant one-time costs and long service life. The rapid growth in the volume of use in the construction of recycled, i.e. repeatedly used, materials is associated not only and not so much with economic benefits, but with environmental reasons. It is necessary to reduce the number of landfills for waste after the mass demolition of morally and physically obsolete buildings and structures. In Denmark, for example, 100% of modern buildings are built from recycled materials. And in this regard, concrete, the most used building material in the world, is an architecturally attractive and environmentally friendly material. This is due to its strength, durability and fire resistance. In concrete, the bulk of the materials are aggregates, which are usually local materials and waste. industrial productions that do not require long-distance transportation. It is possible to manufacture structures and products of almost any shape and size from concrete using relatively simple technological methods. In addition to high construction and technical qualities, concrete compares favorably with environmental safety for environment. AT recent times these factors become decisive when choosing building materials for mass construction. Concrete production is the most resource-intensive human activity; no other product of industrial activity is produced in such volumes. In volume terms, the annual production of concrete in the world exceeds 2 billion cubic meters, in Europe it is about 580 million cubic meters, or 1.2 billion tons. For more than 150 years, reinforced concrete has been known with its amazing construction and technical capabilities. To develop new technologies for the production and use of this material, large international organizations have been created: the International Federation for Reinforced Concrete - FIB, the International Federation for Precast Concrete - BIBM, the American Concrete Institute - ACI, etc. For example, according to the calculations of Russian specialists (TsNIIEP housing ) monolithic housing construction in comparison with large-panel provides (per 1 m2 total area) reduction of one-time costs for the creation of a production base by an average of 40-45%, savings in reinforcing steel by an average of 7--25% (savings increase as the number of storeys increases), savings in energy costs for the manufacture of structures in the amount of 25--35%, reduction in construction costs by an average of 5%. Compared to brick housing construction with monolithic, labor costs are 25-30% less, construction time is 10-25% less, one-time costs for creating a production base are 35% less, energy costs are 25-35%. The technology of building from monolithic reinforced concrete has made a huge step forward in recent years. Over the past decade, outstanding structures with record technical performance have been built in monolithic reinforced concrete. These are high-rise buildings, and among them are the world record-breaking twin skyscraper "Petronas" with a height of more than 400 m in Kuala Lumpur (Malaysia), a frame-and-beam bridge made of high-strength lightweight concrete with a span of 300 m in Norway, a cable-stayed bridge with a span of more than 850 m in France, tunnels, places of worship, etc. The reinforced concrete TV towers in Toronto and Moscow are the tallest free-standing structures in the world.

1. Composition of concrete and reinforced concrete works

Wide application in modern construction concrete and reinforced concrete is due to high physical and mechanical properties, durability, good resistance to temperature and humidity influences, the possibility of obtaining specified structures by relatively simple technological methods, the use of local materials in the base (except steel), and relatively low cost. Expansion of the scope of concrete and reinforced concrete is facilitated by the existing advanced base for the production of prefabricated reinforced concrete. Plants of the building materials industry produce not only ready-made prefabricated reinforced concrete structures, but also formwork sets, reinforcing cages and meshes, ready-mix concrete, dry mixes for mortars and concretes, various additives to concrete mixtures and mortars, with which you can control their physical and mechanical properties. and technological properties.

According to the method of execution, concrete and reinforced concrete structures are divided into monolithic, prefabricated and precast-monolithic. Monolithic structures are erected at the facility under construction in the design position. Prefabricated structures are manufactured in advance at factories, combines and landfills, delivered to the facility under construction and assembled in finished form. In prefabricated monolithic structures, the prefabricated part is produced at factories and landfills, transported and installed at the facility, then the monolithic part of this structure is concreted in the design position. In industrial and civil construction, the use of monolithic and prefabricated monolithic reinforced concrete is effective in the construction of massive foundations, underground parts buildings and structures, massive walls, various spatial structures, walls and stiffening cores, high-rise buildings (including those in seismic regions), and many other structures. All types of engineering structures are erected from concrete and reinforced concrete, as well as bridges, dams, reservoirs, silos, pipes, cooling towers, etc. The construction of buildings in monolithic reinforced concrete allows you to optimize their design solutions, switch to continuous spatial systems, take into account the joint work of elements and thereby reduce their cross section. In monolithic structures, the problem of joints is easier to solve, their thermal engineering and insulating properties are increased, and operating costs are reduced. The erection of monolithic concrete and reinforced concrete structures includes the implementation of a complex interrelated processes formwork, reinforcement and concreting of structures, curing of concrete, its stripping and surface finishing of finished structures. According to the scope of work performed during the construction of monolithic concrete and reinforced concrete structures, they are divided into: formwork, including the manufacture and installation of formwork, stripping and repair of formwork; reinforcing, which consist in the manufacture and installation of reinforcement, with prestressing reinforcement, additionally in its tension; reinforcing works are an integral part in the manufacture of monolithic reinforced concrete structures and are absent in concrete structures; concrete, including the preparation, transportation and laying of the concrete mixture, the care of concrete in the process of its hardening. A complex technological process for the erection of monolithic concrete and reinforced concrete structures consists of procurement and assembly-laying (basic) processes interconnected by transport operations. The complex process of erection of monolithic structures includes: procurement processes for the manufacture of formwork elements and formwork forms, reinforcement and the preparation of concrete mixture in the factory and at landfills, in specialized workshops and workshops; 5 transport processes for the delivery of formwork, reinforcement and concrete mixture to the place of work ; the main processes (performed directly at the construction site) for setting the formwork and reinforcement into the design position, laying and compacting the concrete mixture, caring for the concrete during its hardening, tensioning the reinforcement (when concreting monolithic prestressed structures), stripping (dismantling) of the formwork structures after the concrete reaches the required strength.

2. Purpose and arrangement of formwork

Formwork - a temporary auxiliary structure that forms the shape of the product. The formwork is used to give the required shape, geometric dimensions and position in space of the erected structure by laying the concrete mixture in the volume limited by the formwork. The formwork consists of formwork panels (forms) that provide the shape, dimensions and surface quality of the structure; fastening devices necessary for fixing the design and invariable position of the formwork panels relative to each other during the production process; scaffolding (supporting and supporting devices), providing the design position of the formwork panels in space. The concrete mixture is placed in the installed formwork, compacted and kept in a static state. As a result of the ongoing chemical processes, the concrete mixture hardens and turns into concrete. After the concrete has acquired sufficient or required strength, the formwork is removed, i.e., stripping is carried out. The processes associated with the installation and fastening of the formwork are called formwork, and those associated with the laying of reinforcing cages and meshes in the formwork are called reinforcing. The processes for dismantling the formwork after the concrete has gained the required strength are called formwork stripping.

3. Components of formwork and formwork systems

At the heart of the effectiveness of any formwork system lies the possibility of its rapid modification in accordance with the requirements of the building site. The lightness of the panels and the ease of assembling the formwork can significantly increase the rate of production of the entire complex of concrete works and reduce the construction period. The manufactured formwork must guarantee the optimal dimensions of the panels, their high strength and rigidity, the quality of the concrete surface in contact with the formwork. The individual elements of the formwork system are as follows: formwork - a form for the manufacture of a monolithic concrete structure; shield - a forming element of the formwork, consisting of a frame and a deck; frame (frame) of the shield - Basic structure formwork shield, made of metal or wooden profile, made in a jig, which guarantees the accuracy of the outer dimensions of the manufactured structure; shield deck - the surface in direct contact with concrete; formwork panel - a large-sized planar formwork element with a flat or curved surface, assembled from several panels interconnected using special units and fasteners, and designed to create the required surface in the specified dimensions; formwork block - a three-dimensional, closed or open formwork element of several panels, intended for formworking corner sections of a concreted structure, made entirely and consisting of flat and corner panels or panels; formwork system - a concept that includes formwork and elements that ensure its rigidity and stability - fasteners, scaffolding supporting scaffolding; fastening elements - locks used to connect and securely fasten adjacent formwork panels to each other; couplers connecting opposing shields and other devices in the formwork, combining the elements of the formwork into a single unchanging structure; supporting elements - struts, posts, frames, spacers, supports, scaffolding, floor beams and other supporting devices used in the installation and fixing6 of wall and floor formwork, fixing the formwork in the design position and receiving loads during concreting. Auxiliary elements of formwork systems: hanging scaffolds - special scaffolds hung on the walls from the side of the facades using brackets fixed in the holes left during the concreting of the walls; roll-out scaffolds - designed to roll out tunnel formwork or ceiling formwork along them during their dismantling; opening formers - a special formwork designed to form window, door and other openings in monolithic structures; basement - the lower part of a monolithic wall 10 ... 20 cm high, which is concreted simultaneously with monolithic ceiling. The purpose of the plinth is to ensure the design thickness of the wall and fix the formwork relative to the center (coordinate) axes.

4. Formwork requirements

Any manufactured formwork must meet the following requirements: * a guarantee of the necessary dimensional accuracy of the future structure or structure; * strength, stability and invariability of shape under the action of loads arising in the process of work; all formwork elements count on strength and deformability; * the density and tightness of the formwork board deck, i.e. the absence of cracks that cause the formation of voids in the concrete, shells as a result of the outflow of cement mortar; * high quality surfaces, excluding the appearance of sagging, shells, curvature, etc.; * manufacturability - the ability to allow quick installation and disassembly, not to create difficulties in the installation of reinforcement, laying and compaction of the concrete mixture; * turnover - multiple use of formwork, which is usually achieved by making it inventory, unified and collapsible;

5. Materials for the manufacture of formwork

For the manufacture of formwork elements, a wide variety of materials are used. The supporting formwork elements are mainly made of steel and aluminum alloys, which allows them to achieve a high turnover. For formwork (deck), softwood (pine, spruce, larch), hardwood (birch and alder), waterproof plywood, steel, plastics, metal mesh, reinforced concrete and reinforced cement boards, chipboard (chipboard) and wood-fiber (Fibreboard) boards, polypropylene with fillers. Wood is used for the manufacture of decks in the form of edged and unedged boards with a width of not more than 15 cm, for scaffolding and fastenings - bars ranging in size from 8x10 to 8x14 cm, a bollard with a diameter of 10 ... 14 cm and round timber with a diameter of up to 20 cm. Advantages of wood - ease of processing , low weight, the possibility of making molds of any shape, relatively low cost. Disadvantages - warping, swelling, shrinkage, low turnover due to damage due to significant adhesion to concrete. After laying the concrete mixture in the formwork, the side in contact with it swells, and the other dries quickly under the influence of sunlight. As a result, the wood warps, bulges, cement mortar flows out through the cracks, voids and shells form in the concrete. Measures to counteract these processes are the use of sheet pile boards, coating the inner surface with various lubricants to reduce the adhesive force of the formwork with concrete. Waterproof plywood is used only for sheathing. It has a significant turnover, provides high-quality front surfaces of concrete. To increase turnover, it is necessary that the front surface of the formwork is flush with the framing elements of the frame and is constantly lubricated. Plywood laminated with phenol-formaldehyde coating is used as a sheathing (deck) for monolithic concrete works, formwork turnover is up to 100 times. Steel is used for the manufacture of all formwork elements. 7 Sheet steel with a thickness of 2 ... 6 mm is used for the manufacture of a deck (plating) of metal formwork. Profile steel, mainly channel and corners, is used for the frame and supporting devices, tubular steel - for the manufacture of inventory load-bearing scaffolding and struts. Bolts, wire and mostly hardware are used for all kinds of fastenings and connections. Steel formwork provides a smooth surface of the concreted structure, ease of stripping, rigidity, no deformation, significant turnover. It is advisable to use such formwork with at least 50-fold turnover. The disadvantages of metal formwork are high cost, significant weight and high thermal conductivity. However, currently metal formwork are increasingly being used due to their high turnover and the resulting smooth and even concrete surface. Plastics combine the advantages of steel (strength, repeated turnover, the ability not to change under various temperature and humidity conditions) and the advantages of wood (insignificant mass and ease of processing). The disadvantages of these materials are also excluded - the deformability of wood and the corrosion of steel. The low rigidity, increased flexibility, and relatively high cost of plastics make them still poorly competitive with other materials. Plastics are mainly used as thin protective films applied to wood and metal deck surfaces. Plastic formworks are used, especially those reinforced with fiberglass. They have high strength under static load, chemically compatible with concrete. Formworks made of polymeric materials are characterized by low weight, shape stability and resistance to corrosion. Possible damage can be easily repaired by applying a new coating. The disadvantage of plastic formwork is that their bearing capacity is sharply reduced during heat treatment of concrete with an increase in temperature up to 60 ºС. Metal meshes with cells up to 5×5 mm are used for the manufacture of mesh and vacuum formwork. Thin-walled reinforced cement and reinforced concrete slabs are slabs in which the outer side is smooth, and the inner side is uneven, with protruding reinforcement. This allows, when laying in-situ concrete in such a structure, to achieve a high degree of its connection with this type of formwork. This formwork is called non-removable, as it remains in the structure and works as an integral part of it. Chipboards (chipboards) and wood-fiber boards (MDFs) are located between wood and waterproof plywood in their characteristics, and they are used mainly for decking, less often for fixing the formwork frame. The turnover of inventory formwork with a deck of boards, chipboard and fiberboard is 5 ... 10 times, formwork made of waterproof plywood is 50 ... 100 times, steel formwork is 100 ... 700 times. The use of composites with conductive filler makes it possible to obtain heating coatings with controlled modes of thermal action on concrete.

6. Main types of formwork

The formwork is classified according to its functional purpose, depending on the type of concrete structures and, in general view, subdivided: for vertical surfaces, including walls; for horizontal and inclined surfaces, including ceilings; for simultaneous concreting of walls and ceilings; for curved surfaces (mainly pneumatic formwork is used). As a result of practical use in domestic and foreign mass industrial and civil construction, a number of structurally different formworks have been created and successfully used, depending on the characteristics of the structures being built, formwork material, conditions and methods of work, the most widespread of which are the following:

1. Collapsible small-panel formwork from small panels up to 2 m2 in area and weighing up to 50 kg, from which formwork can be assembled for concreting any structures, both horizontal and vertical, including arrays, foundations, walls, partitions, columns , beams, floor slabs and coatings.

2. Large-panel formwork made of large-sized panels with an area of ​​up to 20 m2, equipped with load-bearing or supporting elements, struts, adjusting and installation jacks, and scaffolding for concreting. It is intended for the construction of large-sized and massive structures, including extended or repeating walls, floors of buildings and structures for various purposes.

3. Horizontally movable formwork, the purpose of which is the construction of linear-extended structures with a length of 3 m or more, solved both in the form of a separate wall (retaining wall), two parallel walls (open collector), and a closed structure consisting of walls and covering the necessary specified length.

4. Volumetric-adjustable formwork, which has found application in the simultaneous construction of walls and ceilings of buildings. The formwork consists of L- and U-shaped block-sections, the design allows the sections to move inward. Formwork sections are interconnected along the length, forming several parallel rows at once with distances between blocks equal to the thickness of the walls. This allows, after the installation of the formwork, the laying of reinforcing cages, to simultaneously carry out concreting of the walls and the sections of floors adjacent to them.

5. Tunnel formwork is designed for the construction of a closed loop of tunnels built in a closed way. At present, tunnel formwork has found wide application for simultaneous concreting of buildings of the corridor system (hospitals, sanatoriums, rest homes, etc.), when using two sets of formwork, continuous installation of external and internal walls and ceilings immediately for the entire width of the floor of the building under construction.

6. Climbing formwork is used for the construction of high-rise structures of constant and varying cross-sectional geometry - pipes, cooling towers, bridge supports, etc.

7. Sliding formwork used in the construction of vertical structures of buildings and structures of great height. The formwork is a system consisting of boards, a working floor, scaffolds, jacks, jack rods fixed on the jack frames and a control station for lifting the formwork system. Formwork is used for the construction of external and internal walls of residential buildings, stiffening cores, as well as chimneys, silos, cooling towers and other structures with a height of more than 40 m and a wall thickness of at least 25 cm.

8. Block formwork can be used for formwork internal surfaces staircases, elevator shafts, closed cell walls of residential buildings, and external surfaces columnar foundations, grillages, arrays, etc.

9. Vertically movable formwork designed for the construction of structures (tower, cooling tower, residential building) or their parts (elevator shaft of a residential building) and individual parts of buildings and structures one floor high (section of an elevator shaft, a spatial closed cell of 4 walls of a building ).

10. Non-removable formwork used in the construction of structures without stripping, with the installation of waterproofing, cladding, insulation, etc. in the process of work. . Currently, fixed formwork is used not only for concreting individual structures, but also for the construction of complete buildings. This became possible when using expanded polystyrene plates 50...150 mm thick with a density of 20...25 kg/m3 as formwork, with high moisture resistance. Fixed formwork consists of factory-made formwork elements of walls and ceilings, which simultaneously perform the functions of formwork, insulation and sound insulation of walls and ceilings, as well as a base for applying finishing (textured) coatings. For fixed formwork, woven metal mesh, reinforced concrete, reinforced concrete and asbestos concrete slabs, foam plastic slabs, glass cement slabs, etc. can be used. This type of formwork can be used in cramped working conditions and when it is economically feasible to use it.

11. Special formworks do not fall into the nomenclature of the main types, although they often allow the construction of similar structures. This is a pneumatic formwork, consisting of an inflated rubberized fabric, which forms the formwork of the future spatial structure, supporting and load-bearing elements. In the working position, the pneumatic9 formwork is supported by excess air pressure and it serves for concreting thin-walled structures and structures of a curvilinear shape. One can also note the non-reversible (stationary) formwork, the purpose of which is to concrete individual places, sections and even structures, for the formwork of which the use of industrial formwork is uneconomical or technically irrational. This formwork is disposable, collected from production waste. Combined structures are rational, in which the bearing and supporting elements are made of metal, and those in contact with concrete are made of lumber, waterproof plywood, particle boards, plastic.

7. Technology of formwork processes

reinforced concrete construction formwork technology

The technological process of the formwork device is as follows. Formwork panels are installed manually or by crane and fixed in the design position. After concreting and reaching concrete strength, allowing stripping, formwork and supporting devices are removed and rearranged to a new position. There are two main types of formwork forms of collapsible formwork: small-panel and large-panel.

Small-panel formwork consists of inventory boards of various sizes with inventory supporting devices and fasteners. The dimensions of the main panels of the unified formwork are, as a rule, subject to one modular size (300 mm in width and 100 mm in height). In small-panel formwork, it is possible to assemble molds for almost any concrete and reinforced concrete structures - walls, foundations, columns, crossbars, flat, often ribbed and coffered floors and roofs, bunkers, towers, etc. The versatility of the formwork is achieved by the ability to connect panels along any edges. The main and fundamental feature of formwork panels are closed profiles of steel or aluminum frames, which, together with stiffening ribs, also made of closed profiles, create formwork connections that resist torsion loads and at the same time make it possible to simplify installation and horizontal alignment, and when forming high-rise structures improve work safety. The complete formwork system is designed for the formworking of all horizontal and vertical building structures, starting from the smallest structures. In addition to the closed profile of the shuttering board frames, a shuttering lock is proposed, which provides a quick (just a hammer blow) and high-quality connection of two adjacent boards horizontally or vertically anywhere in the structural frame. The deck is made of multi-layer waterproof plywood covered with a special powder or other coating that dramatically reduces adhesion to concrete. Bushings are welded into the profile of the formwork frames, which are provided for the passage and convenient insertion of tension rods, for the interconnection of opposing formwork panels. Flat panels of small-panel formwork have an area of ​​up to 1.5 ... 2.0 m2, a weight of not more than 50 kg for the possibility of their manual installation. If there is an assembly crane at the construction site, the panels can be pre-assembled into a formwork panel or a spatial formwork block with an area of ​​up to 15 m2. The technology of work with small-panel formwork is similar to work with large-panel formwork. Large-panel collapsible formwork includes boards with a size of 2...20 m2 of increased bearing capacity . The mass of such shields does not have strict restrictions, since they are mounted and dismantled only with the help of lifting mechanisms. In large-panel formwork, panels can be connected to each other along any edges and, if necessary, be completed with small panels of the same system. As in small-panel formwork, the deck can be made of steel sheet or water-resistant plywood. When constructing strip foundations, the formwork is formed from inventory boards, which are interconnected using locks of various designs. In the case of inserts between the panels of additional elements up to 15 cm wide, elongated locks can be used. The transverse dimension of the structure is fixed with temporary struts on the struts and end shields of the formwork. To absorb the lateral pressure of the concrete mixture, the opposite panels are connected with screw ties (strands).10 Formwork installation and dismantling should be mechanized as much as possible. Initially, formwork panels are assembled into a formwork panel to the full height of the strip foundation and an area of ​​about 20 m2. Shuttering panels are subject to increased requirements for their rigidity and load-bearing capacity. The panel formwork of stepped glass-type foundations for a column consists of separate boxes installed on top of each other. The boxes, in turn, are assembled from two pairs of shields - “mortgage” and “cover”, interconnected by screw ties. Wall formwork consists of modular panels that can be assembled into formwork panels of almost any size and configuration. The frame of the shuttering boards is made of a high-precision profile made of aluminum alloys, the cross section of which ensures the installation of a deck made of laminated plywood with a thickness of 18 and 21 mm, the ends of which are structurally protected by the aluminum profile itself and sealant. The formwork kit also includes struts for installing panels, hinged cantilevered platforms for concreting, locks for connecting panels and screw ties. Shield frames are made in conductors that provide non-flatness of surfaces no more than 1 mm, the difference in frame diagonals is no more than 3 mm. Cracks, burrs and local deviations with a depth of more than 2 mm are not allowed on the shield deck. When fastening a deck made of waterproof laminated plywood on the shield frames, the countersunk head of the screws can protrude onto the plywood plane by no more than 0.1 mm. Large-panel formwork provides formwork for monolithic structures with a module of 300 mm. The width of ordinary formwork panels is from 0.3 to 1.2 m in increments of 0.3 m, the standard height is 1.2, 2 and 3 m with a weight of panels from 42 to 110 kg. Large-panel wall formwork consists of formwork panels, scaffolds hung on these panels, bracing struts and bracing elements. Shields in shuttering panels are assembled by means of centering locks. To align the formwork panel in the design position, the formwork is equipped with struts, the screw couplers of which allow you to adjust the installation of the panel in a vertical plane. The formwork kit may include a compensation element 0.3 m wide and elongated locks, which are used if it is necessary to have inserts from bars up to 15 cm wide in the formwork when concreting non-modular structures. The formwork kit allows, if necessary, to make corner joints of panels, joints of wall junctions, arrangement of junctions-compensators and other options adjoining formwork panels to each other.

For the construction of the outer walls of the building, special scaffolds are provided, which are all-metal brackets with flooring boards and fences. The formwork panels are unfastened by means of screw ties and nuts that perceive the pressure of the concrete mixture. To organize workplaces at a height during the acceptance and placement of the concrete mix, scaffolds with railings are provided on the formwork, which are hung on the frame of the formwork panels. When installing and dismantling the formwork at a height along the perimeter and inside the building, the formwork shields must be protected by inventory protective devices. Formwork panels are made in accordance with a single module, they are universal and interchangeable, assembly, installation and connection of the panels to each other can be carried out in a vertical and horizontal position. There are holes in the frame ribs for attaching brackets and installing struts.

To connect the shields to each other, locks are used - at least three locks along the height of the shield: two locks - at a height of 250 mm from the bottom and top of the shield, and a third lock - in the central part of the shield. If, when forming the surface, it is planned to lay a horizontal shield on top of previously installed vertical shields, then three interlocks with vertical shields must be provided along the length of the horizontal shield. During the installation of the struts and hanging the brackets of the suspended scaffolds, they are fixed through the holes in the ribs of the formwork panels, regardless of the installation of the shield - vertically or horizontally. When installing the wall formwork with separate panels, two struts are installed for each panel, when mounted with panels - after 2 ... 4 m. during the installation of panels and wall formwork panels, according to the risks applied on the ceilings, they are pressed against the concrete base and brought to a vertical position with the help of strut couplers. The accuracy of the installation is checked by a level or a plumb line. After mounting the opposite panels of the wall formwork, the panels are fastened together with screw ties, placing at least three ties along the height of the shield. Screw ties installed between opposite shields are passed through steel bushings, bushings and cones made of plastic and plastic, the length of which must correspond to the thickness of the concreted wall. The cones protect the openings in the deck from concrete mixture getting into them, the bushings make it easier to pull out the screw ties after concreting during the stripping process. The shields are fastened by tightening the nuts of the screw ties. To exclude local deformations of the hollow section of the shield frame when tightening the nuts, wide-brimmed washers are used. After the formwork panels are installed, all unused through holes in the formwork must be plugged with special wooden or plastic plugs to prevent concrete from flowing out of these holes during the concreting process. Shields and panels of external walls are mounted from working scaffolds fixed on the walls of the previous floor. The scaffolding is carried out as follows. When concreting the walls, through holes remain in them from the screw ties of the formwork panels. When installing scaffolds using a mounting crane, bolts for fastening the bottom of the supports of the working scaffolds are passed through these holes, and these bolts are fixed from the inside of the walls with nuts. Thus, the scaffold is tightly pressed against the concreted wall of the underlying floor. First of all, the panels (panels) of the outer formwork are mounted, they are installed on the working scaffolds, aligned and fixed with the help of struts. Further, from the ceiling, the inner panels (panels) of the formwork are installed, which are sequentially attached to the outer panels during the installation process with the help of screw ties. Lifting and installation of boards and formwork panels is carried out with a special gripper, fixed on rope slings, at one point (for a separate board) or two points - for a formwork panel. Wall formwork can be mounted as separate panels or pre-assembled into panels. Assembly of panels from individual panels must be carried out on a specially prepared site in the area of ​​​​the assembly crane. The length of the panels assembled from the panels should not exceed 8 m in length. The dismantling of the wall formwork is carried out with enlarged panels of 5 ... On the panel to be dismantled, the nuts of the screw ties are unscrewed, the ties are pulled out. Then, with the help of struts, the shields are torn off from the concrete. The detached panel is carried by crane to the warehouse for inspection, repair, and, if necessary, lubrication. Formwork of columns with facets in the plan from 0.2 to 0.6 m is made of panels 0.8x3.0 m with holes for tie rods, which allows you to set the required size of the columns in the plan. The formwork of the columns is equipped with braces for installation, alignment and stripping, as well as suspended scaffolds with railings. When installing the column formwork, initially on concrete base(overlap) mark the place of its installation (risks of geometric axes, edges of the position of the columns). The reinforcing cage to be installed is initially connected to the frame of the underlying column, plastic rings are additionally installed or horizontal rods are welded to the frame at a height of 300 mm from the bottom and top of the columns to provide the necessary concrete protective layer during concreting. Initially, two adjacent shields are installed at risks and beacons and secured with struts. The lower supports of the struts are rigidly fixed to the floor and the shields are brought into a vertical position with the help of strut screws. Then the remaining two adjacent shields are installed, which are also brought to a vertical position. Opposite shields are fastened together with screw ties, they are installed four pieces along the height of the shield. Unused openings in the shields must be plugged with special plugs (wooden or plastic) to prevent leakage of the concrete mixture from the cavity. Cantilever scaffolds are installed from mobile towers. They arrange a working flooring from shields with a protective fence made of boards, which will allow you to safely perform work on concreting columns. 12 Before concreting, final alignment is carried out formwork and all its fixtures. The option of connecting the shields of the columns to each other provides for fastening by means of a clamp consisting of four brackets connected to each other by wedges. The brackets hold the shields in the required design position, providing the required geometric dimensions of the columns. Slab formwork can be made in two versions: 1) formwork, including a deck made of laminated plywood sheets, mounted on longitudinal and transverse load-bearing beams, mounted on frames with retractable jacks; 2) canteen prefabricated formwork, consisting of a table in the form of a set of frames with support jacks interconnected by longitudinal ties with roller bearings. Telescopic props up to 3.7 m high, which are a tubular structure consisting of a base part with a jack and a retractable rod, can be used as formwork load-bearing elements. Found the use of telescopic steel racks, consisting of two pipes included in one another. The initial position of the pipes among themselves is fixed thanks to special slots every 10 cm, the amplitude of changes is from 10 to 130 cm. passing into the slot of the upper part of the outer pipe. The pin rests on a nut screwed onto the thread at the top of the outer tube and holds the inner tube in position. For smooth lowering of the supports (circling) supporting the formwork panels, apply special devices. When using special inventory wood-metal racks, a screw jack is used, and steel telescopic racks - a nut on the screw thread of the outer pipe. Metal racks with jacking are used with three types of removable heads. The fork head is designed to install one or two main bearing beams in it. The drop head is convenient in that when the concreted floor structure is of sufficient strength, it becomes possible to remove some intermediate racks. When a special lever is pressed, the falling head drops up to 10 cm, while the remaining system of racks and beams supporting the ceiling maintains its position. The third type of head is the support head, which supports the formwork system until the formwork is removed. These heads, when the lever is pressed, lower by 1...2 cm, make it possible to visually assess the state of the system to be stripped, easily extend the posts and release the formwork-bearing beams. The formwork panels are detached from the concreted structure due to their own weight or using special crowbars. The large-panel formwork of the slabs consists of support frames equipped with sliding jacks, on which, through the supports available on them, longitudinal and transverse beams are mounted, carrying the deck of laminated plywood. load-bearing beams are interconnected by a special bolted connection. The laminated plywood deck is attached to the beams with countersunk screws. Mounting and dismantling of the formwork is carried out in accordance with the technological map (TC). The formwork may only be dismantled after the concrete has reached the required strength. Formwork is installed in accordance with technological maps in a sequence depending on its design; at the same time, the stability of its individual elements during installation must be ensured. The location of the load-bearing telescopic racks and frames on the concrete floor also depends on the location of the racks on the previously concrete floor. At the same time, it is necessary to take into account the rate of erection of structures, the rate of curing of concrete floors and walls, the loads acting on the structure at various stages of the construction of the structure, and other technological factors. The installation site of formwork and scaffolding must be cleared of debris, snow and ice. The surface of the earth should be planned by cutting off the top layer of soil. Pouring soil for these purposes is not allowed. When installing the formwork, special attention is paid to the verticality and horizontality of the elements, the rigidity and invariability of all structures in general, and the correct connections13 of the formwork elements in accordance with the working drawings. Permissible deviations during the installation of formwork and supporting scaffolding are standardized. The use of inventory formwork provides for mandatory lubrication of the board deck. The most common hydrophobic lubricants based on mineral oils or salts fatty acids, as well as combined lubricants. Lubricants reduce the adhesion of the deck to concrete, thus facilitating stripping and, as a result, increasing the durability of the formwork panels. Lubrication is restored after 1 ... 4 turns of the formwork.

Conclusion

Modern concrete has dozens of names. These are extra-strong, porous, waterproofing and many other concretes. According to some indicators, they approached natural stone and even metal. Using polymer resins as a binder, a more elastic material of increased strength (polymer concrete) is obtained. The variety of polymer resins, aggregates and fillers, as well as manufacturing technologies, makes it possible to obtain many varieties of polymer concrete with specific and, in some cases, unique properties. These are high strength characteristics, air and water resistance, high chemical and radiation resistance, damping, dielectric and other characteristics with an accelerated increase in strength, which is especially important for monolithic construction. Fiber-reinforced concrete compares favorably with traditional concrete, since it has several times higher tensile and shear strength, impact and fatigue strength, crack resistance, frost resistance, water resistance, cavitation resistance, heat resistance and fire resistance. The highest technical and economic indicators have fiber-reinforced concrete on fiber made of steel and alkali-resistant glass. The use of lightweight concrete is promising. For example, polystyrene concrete with a filler of foamed polystyrene granules can serve as a heat-insulating (for thermal insulation of coatings) and structural and heat-insulating (for the manufacture of wall blocks of low-rise residential buildings) material. In recent years, the technical level of construction of concrete and reinforced concrete structures has increased significantly. Multi-turn formwork is widely used. Concrete work is mechanized as much as possible. Our construction sites widely use concrete mixers and concrete mixing plants of various capacities, powerful concrete mixer trucks and concrete trucks, concrete pumps and pneumatic blowers, conveyors and cranes for the delivery and supply of concrete mix, different types vibrators for concrete mix compaction and other machines and equipment. In the production of concrete work, qualified workers are needed who are able to make the most full use of modern progressive concrete technologies, equipment, tools and mechanisms. Under the new conditions, the requirements for the qualifications and skills of a concrete worker, a representative of the most massive construction profession, have increased significantly (up to 20% of construction workers are employed in concrete work).

List of used literature

1. Terentiev O.M. "Technology of construction processes: Textbook for construction technical schools.", Moscow, 2002

2. " Construction Materials(Materials Science. Building Materials)» Under the general editorship of prof. V.G. Mikulsky and prof. V.V. Kozlov, Moscow, 2004

3. A.S. Statsenko "Technology of concrete works", Minsk, 2005

4. S.S. Ataev "Technology of industrial construction from monolithic concrete" Moscow, 198955

5. Magazine "Building materials" No. 11/2005, No. 12/2005, No. 1/2006

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Process technology for the installation of structures made of monolithic concrete and reinforced concrete

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Lecture #5
Topic 6: Technology of processes for the installation of structures made of monolithic concrete and reinforced concrete.

Study questions:
1. The composition of the complex process of concreting.
2. Formwork. Classifications. Formwork types.
3. Reinforcing products. Fittings installation. Stressed reinforcement.
4. Preparation, transportation, laying, compaction of concrete mixtures. Special methods of concrete mix processing.
5. Concreting structures. Curing. Stripping. Correction of defects.
Question 1. COMPOSITION OF THE INTEGRATED CONCRETING PROCESS.
According to the method of execution, concrete and reinforced concrete structures are divided into prefabricated, monolithic and precast-monolithic.
The erection of monolithic concrete and reinforced concrete structures requires a complex process , including: formwork, reinforcement of structures, concreting of structures, curing of concrete in concreted structures, stripping, correction of defects, surface finishing of finished structures.
Question 2. FORMWORK. CLASSIFICATIONS. TYPES OF FORMWORKS.
formwork- a temporary auxiliary structure that serves to give the required shape, geometric dimensions and position in space of the structure being erected (or part of it).
In accordance with the materials used in the construction of the formwork, it is customary to classify the formwork into: wooden; metal; polymer; reinforced concrete; reinforced cement; fabric, combined.
According to the frequency of application, they distinguish: individual formwork; wraparound formwork; fixed formwork.
Reversible formwork at least 50 concreting cycles can be used. In the group of reversible formworks, the following are the most widely used:
pneumatic.
Collapsible formwork consists of separate shields and their supporting elements: ribs, contractions, couplers, etc. At a height, formwork panels support scaffolding, consisting of racks, girders and braces.
Volumetric-adjustable (tunnel) formwork consists of spatial metal U-shaped sections, from which a formwork block is assembled to the width of the room. Side panels serve as internal formwork monolithic walls, and the upper one - the floor deck. The fully assembled formwork is installed in the design position using a crane. For extraction, the formwork is folded and pushed out on rollers to an adjacent position or on a scaffold.
sliding formwork. The main formwork elements are boards, jack frames, working floor, scaffolding, jacks and jack rods.
Shuttering panels cover the concreted structure along the outer and inner contours. The shields are given a taper. To lift the sliding formwork, hydraulic and electromechanical jacks are used.
The formwork is constantly moving; during breaks in concreting, the formwork is switched to the “step in place” mode.
Fixed formwork after concreting the main structure, it remains and works together with the structure. The formwork is made of reinforced concrete, reinforced cement slabs, metal sheets, and expanded polystyrene.
Question 3. REINFORCING PRODUCTS. INSTALLATION OF REINFORCEMENTS, PRETENSION REINFORCEMENT.
Reinforcing steel is divided into two main groups - rod reinforcement and wire.
Bar reinforcement is made of a smooth and periodic profile. Depending on the mechanical properties, rod reinforcement is divided into classes. The bars of steel of class A240 have a smooth profile, and of classes A300 and above - periodic. The industry supplies wire reinforcement in two classes: B-I and B-II. In addition to rods, the industry produces strands, ropes, wire bundles, reinforcing meshes, flat and spatial frames.
When installing reinforcement, reinforcing elements are connected into a single reinforcement structure by welding, overlapping or viscous.
When installing reinforcement, elements and rods must be installed in the design position, providing a protective layer of concrete of a given thickness. For this, special stops are provided in the designs of reinforcing elements. It is also possible to ensure the design dimensions of the concrete protective layer with the help of concrete, plastic and metal clamps, which are tied or put on reinforcing bars.
Stressed reinforcement.
Prestressing in structures is created by the method of tensioning reinforcement on hardened concrete with its linear arrangement. Prestressed reinforcing elements are used in the form of individual rods, strands, ropes and wire bundles.
Works with linear prestressing reinforcement include: preparation of prestressed reinforcing elements and the formation of channels for them; installation of reinforcing stressed elements with anchor devices; tension of reinforcement with subsequent injection of closed channels or concreting of open channels.
Channels for stressed reinforcing elements are formed by installing channel formers in the formwork, the diameter of which is greater than the diameter of the rod or reinforcing beam. Channel formers are removed 2...3 hours after concreting.
The tension of the reinforcement is carried out in several stages. Immediately after the reinforcement is tensioned, the final operation is started - the injection of channels. The solution is injected from one side of the channel. Injection is carried out continuously.
Question 4. PREPARATION, TRANSPORTATION, LAYING, COMPACTION OF CONCRETE MIXTURES. SPECIAL METHODS FOR PROCESSING CONCRETE MIXTURE.
Preparation of concrete mixes.
The concrete mixture is prepared according to the finished or dissected technology. With a finished technology, a ready-made concrete mixture is obtained as a product, with a dissected one - a dry concrete mixture.
The main technical means for the preparation of concrete mix are service hoppers with distribution devices, batchers, concrete mixers, vehicle and communication systems, a dispensing hopper. Technical means are assembled according to one-stage or two-stage schemes.
Transportation, laying and compaction of concrete mixtures.
Transportation of the concrete mix to the place of unloading into the concreting block or at the object being concreted is carried out by road, and transportation from the unloading point to the concreting block is carried out by cranes (in buckets), lifts, conveyors, concrete pavers, vibratory feeders, motor carts, concrete pumps and pneumatic blowers.
The main technological condition for the transportation of a concrete mixture is to maintain its uniformity and ensure the mobility required for laying.
Compaction of concrete mixtures.
The concrete mixture placed in monolithic structures is compacted by vibrating, bayoneting and tamping.
Special methods of concrete mix processing.
Vacuuming concrete. The essence of the process of vacuuming concrete is to remove part of the water and air from the freshly laid concrete mixture when the pressure is reduced. As a result, the final strength of concrete increases, water resistance, frost resistance and abrasion resistance increase.
Shotcrete. Shotcrete is a technological process of applying a cement-sand mortar or concrete mixture in a jet of compressed air to the surface of a structure or formwork.
Shotcrete is carried out by "dry" and "wet" methods.
Question 5. CONCRETING STRUCTURES. CURING. STRIPPING. CORRECTION OF DEFECTS.
Foundations and arrays. In stepped foundations up to 3 m high, the mixture is fed through the upper edge of the formwork. Internal vibrators are immersed through the open edges of the lower stage. The upper steps are concreted intermittently.
Massive foundations are continuously concreted. The concrete mixture is laid in massive foundations with dense reinforcement in horizontal layers, compacted with internal vibrators.
Preparations and floors. The area on which it is planned to arrange concrete preparation is divided into maps - strips 3 ... 4 m wide. Map strips are concreted through one. The concrete mixture is unloaded at the place of concreting from a concrete truck, leveled, and then compacted with a vibrating beam.
Walls and partitions. Walls with a thickness of more than 0.2 m with rare reinforcement are concreted, unloading the mixture directly into the formwork at a wall height of up to 3 m, and more than 3 m - feeding through funnels along the link trunks.
With a thickness of densely reinforced walls up to 0.15 m, concreting is carried out in tiers up to 1.5 m high. Formwork is erected on one side to the full height, and on the other, only to the height of the tier. The concrete mixture is fed and compacted with screws, less often with vibrators.
columns over 5 m high, they are concreted through funnels along the trunks. High and densely reinforced columns with intersecting clamps are concreted in tiers up to 2 m with the supply of concrete mixture through windows in the formwork or special pockets.
Beams and slabs, monolithically connected with columns and walls, are concreted 1 ... 2 hours after concrete is placed in vertical structures. Beams and slabs of ribbed floors are concreted simultaneously. Beams with a height of more than 80 cm are allowed to be concreted, regardless of the slab concreting, with the last layer laid 3 ... 5 cm below the bottom of the slab.
floor slabs they are concreted immediately to the full width with compaction by surface vibrators with their thickness up to 0.25 m and internal ones with a greater thickness.
The device of working seams.
Working joints should be arranged in sections where the joints of old and new concrete cannot adversely affect the strength of the structure.
The surface of the working seam must be perpendicular to the axis of the element, and in walls and slabs - their surfaces. To do this, install a mesh "chain-link" or guards-limiters with slots for reinforcing bars.
The surface of the previously laid concrete is carefully treated: it is cleaned of the cement film and a large aggregate is exposed; blow out with compressed air and rinse with a stream of water. The cleaned surface is covered with a cement mortar of the same composition as the concrete mix to be laid.
Curing.
In the process of aging, concrete is maintained with mandatory quality control. Freshly laid concrete is kept moist by periodic watering. In summer, it is protected from sunlight, and in winter, from frost - with protective coatings. In summer, concrete on ordinary Portland cements is watered for 7 days.
Freshly laid concrete must not be subjected to loads and shocks. The movement of people on concreted structures, as well as the installation of scaffolding and formwork on these structures, is allowed only after the concrete has reached a strength of at least 1.5 MPa.
Stripping.
When stripping structures, it is necessary to ensure the safety of the formwork for reuse, as well as to avoid damage to the concrete.
It is possible to remove side formwork elements that do not bear loads after the concrete has reached strength, ensuring the safety of corners, edges and surfaces. Side shields of foundations, columns, walls, beams and crossbars are removed after 48-72 hours.
The bearing elements of the formwork are removed after the concrete reaches strength, which ensures the safety of the structure.
Concrete defects and their correction.
After stripping, monolithic structures are inspected and defects in concreting are corrected. Small irregularities and influxes of concrete on the walls, columns and beams are cut down manually, followed by grouting the irregularities with cement mortar. Open concrete surfaces with small shells, after cleaning and wetting with water, are rubbed with cement mortar. Large shells are cleaned to the full depth. Loose concrete is cut down, followed by blowing with compressed air and washing with water. If the size of the sink allows, formwork is installed and concreted.
Cover large sinks with cement mortar categorically prohibited .
In case of gross violations of the technology, serious defects occur: low concrete strength, delamination, large through-holes, etc. It is almost impossible to correct such defects, respectively, the structures must be disassembled or reinforced.
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→ Building materials science

Monolithic reinforced concrete technology

The manufacture of monolithic concrete and reinforced concrete structures is economically feasible when using industrial methods of construction production and the widespread use of inventory metal or wooden formwork.

Distinctive feature the production of monolithic reinforced concrete lies in the fact that the main technological operations - installation of the formwork, laying reinforcement and concrete mixture into the formwork, compaction of the concrete mixture, hardening of molded products and concrete maintenance - are carried out at the construction site.

Depending on the configuration of the structure to be concreted, various types of formwork are used: stationary, collapsible-adjustable, sliding, moving in a horizontal direction, etc.

Reinforcement is prepared in the reinforcement and welding shops of reinforced concrete plants and delivered to the place of installation in the formwork. The concrete mixture is prepared at mechanized (automated) concrete plants and delivered in the form of “ready-mixed concrete” (concrete mixture) to the place of its laying. For most monolithic reinforced concrete products and structures, the workability of the concrete mixture, characterized by the draft of a standard cone, ranges from 1-3 cm (foundations, retaining walls, mass blocks, etc.) to 6-8 cm (structures saturated with reinforcement, thin walls, slabs, columns of small section, etc.).

The concrete mixture is transported to the place of work by dump trucks, and at considerable distances - by concrete mixer trucks. In truck mixers, ready-made concrete mixtures do not become contaminated and do not delaminate and remain homogeneous, as they can be mixed during transsorting. The concrete mixture is often prepared directly in the mixer truck drum. Dry components in predetermined quantities are loaded into the drum at the central dosing unit of the concrete plant and the concrete mixture is prepared on the way 5-8 minutes before arrival at the work site.

At the construction site, cranes, conveyors, pneumatic pumps and pneumatic blowers are used to transport and lay the concrete mix. The pneumatic method of supplying the concrete mixture to the place of laying is simple and allows it to be transported by compressed air through pipes over a distance of up to 150 m.

The concrete mixture is compacted in the formwork using mounted and portable surface or core vibrators.

Monolithic concrete and reinforced concrete structures are concreted continuously or in sections, blocks. Continuous laying of the concrete mixture is carried out when it is necessary to obtain increased solidity and uniformity of concrete in a structure or product. When concreting structures of a large area ( reinforced concrete floors) work is carried out in sections, providing for the construction of working seams in places of minimum stress.

The quality of the concreted structure largely depends on the favorable temperature and humidity conditions for cement hydration and the formation of the reinforced concrete structure. Therefore, immediately after laying and compacting the concrete mix, concrete care begins. During the summer period of concreting, the surface of the freshly laid concrete mixture is protected from drying out, and during the first hours of hardening - from rain. To do this, the open horizontal surfaces of the structure are covered with a layer of wet sand, sawdust or moistened coarse weave fabric (burlap). In hot weather, the protective coating is kept wet until the concrete acquires at least 70% of the design strength. The vertical surfaces of the structure to be concreted are moistened with water after the formwork has been removed.

When concreting structures with a large surface and length (aerodrome and road concrete pavements), various film-forming compounds that reflect the rays of the sun are used to preserve moisture. Laid concrete mixtures are often covered with polymer films (polyethylene, polyvinyl chloride, etc.), which retain moisture well and prevent the formation of temperature-shrinkage deformations. After the concrete reaches the design strength, the reinforced concrete structure is stripped and the actual (given) load is transferred to it.