formwork is called a formative temporary structure designed for molding monolithic concrete and reinforced concrete structures and consisting of the actual form, supporting scaffolding and fastening devices. The formwork must be stable and durable, ensure the correctness and invariability of the structure, the quality of the concrete surface, quickly assemble and disassemble, not create difficulties when installing reinforcement, laying and compacting the concrete mix. When calculating the formwork, vertical and horizontal loads from the self-weight of the formwork and scaffolding, concrete mixture and reinforcement, working people and vehicles, vibration and dynamic loads that occur when the concrete mixture is unloaded into the formwork, as well as the lateral pressure of the concrete mixture are taken into account. The side elements of the formwork are calculated on the pressure of the concrete mixture, based on the fact that the pressure of this mass extends deep into the concrete by no more than 1 m.

Depending on the material used, formwork can be wood, metal, wood-metal, reinforced concrete, reinforced cement, synthetic or rubberized fabrics.

wooden formwork made of wood with a moisture content of not more than 25%. For the manufacture of wooden formwork elements, boards, chipboards and fibreboards are used. Timber and wood-based materials can be made from softwood and hardwood. Scaffolding racks with a height of more than 3 m used for formwork, as well as girders supporting the formwork, are made only from coniferous wood. For other formwork elements and fasteners, hardwood is used - aspen, alder. In the manufacture of wood-metal shields, birch is used for sheathing. For the shield deck, water-resistant bakelized plywood or sheet fiberglass is used. To reduce adhesion with concrete and improve the quality of front concrete surfaces, coating of the shield deck with films based on polymers is also used.

For more see "Carpentry"

metal formwork made from steel sheets 1.5-2 mm thick and rolled profiles; it must have quick connectors. The metal parts of the wood-metal formwork are also made from steel sheets. Cell size metal mesh used as mesh formwork should not exceed 5x5 mm.

Reinforced concrete formwork is a reinforced concrete slab-shell; these slabs are installed as formwork slabs before the start of concreting and are the outer part of the structure being erected, monolithically connected with it.

Armored cement formwork It is used in the form of reinforced cement slabs with a thickness of 15-20 mm. Such slabs are made from fine-grained concrete reinforced with wire mesh. The mesh can be bent before applying the concrete layer, giving the required curvilinear profile to the concreted slab.

Pneumatic structures are formed by forcing air into the inner closed space of the shell of an airtight fabric; in this case, the shell can be given almost any shape. Materials for the manufacture of inflatable formwork are technical textiles, synthetic materials, single-layer and multi-layer rubberized fabrics.

An important problem is to reduce the adhesion of concrete to the formwork. This adhesion depends on the adhesion (sticking) and cohesion (tensile strength of the boundary layers at the "formwork-concrete" contact) of the concrete, its shrinkage and the nature of the forming surface of the formwork. Adhesion lies in the fact that during laying and vibrocompaction, the concrete mixture acquires the properties of plasticity and therefore the continuity of contact between it and the formwork increases. If the deck is made of slightly wetted (hydrophobic) materials, such as plastics, textolite, etc., and has a smooth surface, adhesion to the deck is negligible. If the deck is made of highly wettable (hydrophilic) materials, such as steel, wood, etc., has a rough surface or a porous structure, the continuity and contact strength increase and, consequently, adhesion increases. If the adhesion is low and the cohesion is high, when stripping the formwork, the detachment occurs along the contact plane and the forming surface of the formwork remains clean, and the front surfaces of the concreted structure are of good quality.

Adhesion forces can be reduced by using hydrophobic materials for forming formwork surfaces, applying special lubricants and anti-adhesive hydrophobic coatings to the deck surface. The most practical are combined lubricants in the form of so-called inverse emulsions. In addition to water repellents and setting retarders, plasticizing additives are introduced into them, which plasticize the concrete in the zone of contact with the formwork and facilitate its separation.

The formwork design should provide sufficient strength, reliability and ease of installation and dismantling of its elements, the possibility of an enlarged assembly and a wide layout variability with their minimum range. By turnover, non-inventory formwork, used only for one structure, and inventory formwork, that is, reusable formwork, are distinguished. Inventory formwork can be collapsible and movable.

Inventory collapsible formwork assembled from shields, boxes, large inventory racks and other elements. The collapsible formwork is designed so that it is possible to strip the side surfaces, beams, girders and columns, regardless of the bottoms of the boxes of beams and girders, which are stripped only after the concrete reaches the stripping strength provided for by the project. After dismantling, the formwork is cleaned, if necessary, repaired and reused. The main elements of a wooden or combined collapsible formwork are frame structure boards made of boards 25-30 mm thick upholstered with waterproof plywood or boards upholstered on the forming side with roofing steel, plastic, etc. The dimensions and weight of the formwork elements must allow their manual installation .

Formwork of foundations for columns arrange from rectangular boxes, which are assembled from external and internal shields. The outer shields are 20-25 cm longer than the inner ones and have special thrust bars to which the inner shields are attached; wire ties are attached to the outer shields, which perceive the spacer pressure of the freshly laid concrete mix. The formwork of the columns consists of panels fastened in the form of a box with metal or wooden clamps installed every 0.4-0.7 m.

Wooden formwork for girders and beams consists of a bottom, which rests on the heads of the supporting posts, and side shields. The slab formwork boards are installed on the circles, which are supported on the boards under the circles, nailed to the side boards' stitching strips.

To maintain formwork forms, scaffolding is arranged. With a formwork height of up to 6 m, telescopic inventory wood-metal or metal racks are used. To increase the bearing capacity, telescopic racks are grouped using inventory links of 3 or 4 pcs.

When constructing walls up to 15 cm thick, ribs are installed on one side of the partition and one wall is assembled from shields, after which the partition is reinforced to the full height. Then, rack ribs are installed from the side of the work front, which are shuttered with shields to a height of 1 m. As the concreting progresses, the shields are increased.

The unified collapsible formwork differs from the usual inventory one by the large interchangeability of elements, it has increased rigidity and inventory devices (battles, interlock connections etc.) facilitating installation. Such formwork can be wooden, wood-metal (combined) or steel. Steel formwork is made of corners, channels and sheet steel 2 mm thick. With good operation, it can be used up to 200 times, while the turnover of wooden inventory formwork is no more than 10-15 cycles. The design of a unified formwork makes it possible to assemble large-sized panels up to 35 m 2 in area, as well as rigid formwork or reinforcement-formwork blocks. The use of panel or block formwork for large-sized structures and for large volumes of work makes it possible to approximately halve labor intensity and significantly reduce the time of formwork.

Sliding and rolling formwork belong to the so-called mobile formwork systems.

sliding The (movable) formwork system is used for concreting high structures with a compact perimeter and a plan shape that does not change in height. Sliding formwork consists of formwork panels suspended from a jacking U-shaped frame, jacks, oil lines, a working platform and suspended scaffolds. Jacking frames are the main bearing element; formwork, scaffolding, work table are suspended on them. Sliding formwork usually has a height of 1.1-1.2 m and covers the structure to be concreted along the outer and inner contours. With a circular section of the structure, the sliding formwork consists of two concentrically located walls attached to the inner and outer circles. The formwork has a taper (the width of the form at the top is 6 ^ -8 mm less than at the bottom), which facilitates its lifting, and is usually made of all-metal, which gives it greater rigidity and increases turnover. The formwork is lifted with the help of jacks resting on jack support rods installed inside the formwork of the structure under construction. Jacks, climbing the jack rods, carry the formwork with them. The working flooring of the mold block is wooden, it is laid on lightweight metal girders and fixed to the uprights of the U-shaped frames. If necessary, scaffolds are suspended from them, from which the concrete surface is rubbed or other work is performed. For the safety of work along the outer contour of the movable formwork, fences of the working floor with a height of 1 m are arranged, and for the protection of workers located on the external suspended scaffolds, visors. The lifting speed depends on the strength acquired by the concrete, which allows stripping and excludes the possibility of adhesion of concrete to the formwork. The walls of small-block formwork have greater flexibility than large block. The boards of this formwork at a height of 1.1 m have a width of 0.5-0.65 m. They are hung on circles assembled into frames. In stacks of large-block formwork, the circles are one with the shield skin. A steel shield 2 mm thick is welded by intermittent welding to the upper side corner and to the vertical stiffeners - corners. The upper and lower circles of angle steel are welded to the stiffeners. The shields are interconnected with the help of pads and bolts. The length of the shields is from 0.5 to 2.5 m, the height is 1.1 m.

Roll formwork is a formwork form with a mechanical device for demoulding and folding into transport position. The formwork is installed on shields or trolleys and moved along the rail track. Depending on the design of the scaffolds supporting the formwork, all types of rolling (horizontally movable) formwork can be divided into two groups: with scaffolds that are unchanged in height, and with lifting and lowering scaffolds. The former are used for concreting smooth surfaces without ribs and diaphragms, and the latter, if any. Then, in the first case, the formwork is moved with its slight separation from the concrete or lowering with the help of jacks, wedges or other devices, and in the second case, with the help of a winch and chain hoists or hoists. The correctness of the position of the formwork axes is checked after each rearrangement. The following requirements are imposed on the rolling formwork:

the structural elements that make up each section of the formwork must be securely connected to each other so that the design section of the concreted structure is not distorted during rearrangements;

formwork structures should provide the possibility of its quick separation from the concreted parts of the structure, unhindered movement to a new position of a precise installation for re-concreting.

Climbing formwork consists of two conical shells - outer and inner - suspended from radial guides, which are attached to an annular frame, hinged to the mine hoist. The shells are assembled from panels made of 2 mm thick sheet steel, which are bolted together. The outer shell panels are of two types - rectangular and trapezoidal, due to which the shell takes the form of a cone. The panels of the inner shell are half the height, they are hung in two tiers. All panels of the inner shell and formwork are rectangular. On the inside of these panels, "lugs" are welded into which reinforcing bars with a diameter of 14 mm are laid, forming four rows of closed elastic horizontal rings. The structure is concreted in layers. After the concrete in the next tier reaches the required strength, the formwork is moved to the higher tier. In this case, the formwork is adjusted in the radial direction. As the rearrangement upwards, in the course of concreting the formwork, the circumferential length of the form decreases due to the removal of the shell panels after each rise of the formwork.

Climbing formwork can be used instead of movable (sliding) formwork, if it is difficult to organize concreting of structures in the latter due to the small amount of work or for other reasons.

Climbing formwork structures should provide:

the possibility of changing the cross-section of the concrete structure in accordance with the project when moving the formwork along the height;

strictly specified position of the formwork and reliable fastening of its elements during rearrangements;

the possibility of unhindered lifting of people and the supply of materials to the working area during the construction of the structure.

When moving the climbing formwork, the displacement of its longitudinal axis relative to the axis of the structure is allowed no more than 10 mm.

block form is a large-sized spatial frame structure, consisting of shields and fasteners, designed for mechanized installation and dismantling. According to the design of the block molds, there are one-piece from rigid one-piece molds and detachable. The first ones are removed with the help of jacks from the concreted foundation without dismantling due to the taper of the forming surfaces, the second ones - with the help of special corner locks connecting the formwork panels and detachable devices, which, when stripping, ensure the separation of the forming planes from the concrete.

Fixed formwork(formwork-shell) is a thin-walled form that serves as a formwork during concreting, and then its cladding. Fixed formwork works together with cast-in-situ concrete and is included in the calculated section of the structure. Depending on the purpose, fixed formwork is made from heat-insulating reinforced concrete and reinforcing slabs, asbestos-cement plastic sheets, expanded polystyrene, etc. It is most economical to use fixed formwork when it also plays the role of waterproofing and insulation.

Pneumatic (inflatable) formwork is a kind of collapsible-adjustable. It is made from rubberized and other special fabrics. Pneumatic formwork in the form of a shell is spread and fixed. When air is injected into a closed space, the shell takes a given shape. After reaching the stripping strength, air is released from the shell, and the structure is released from the formwork.

Stripping of structures is carried out with the preservation of the formwork. Support posts should only be removed after the side formwork has been removed and the stripped structures have been inspected. Stripping of load-bearing reinforced concrete structures is allowed after the concrete reaches at least 70% strength. It is allowed to load the stripped structure with the full design load only after the concrete reaches the design strength. Structures concreted in winter should be stripped after confirming the required strength by testing control samples; after removing the thermal protection, not earlier than the concrete has cooled down to a temperature of +5 °C.

Formwork care and formwork lubrication ensure formwork turnover. Inventory formwork panels, as well as supporting elements - scrambles, racks, crossbars, girders and similar fasteners - clamps, clamps, locks, etc. after each turn must be cleaned of cement mortar using metal brushes and scrapers. The use of hammers or other percussive tools to clean the formwork elements from mortar is strictly prohibited. The use of inventory formwork provides for the obligatory lubrication of the shield deck and its thorough cleaning from cement mortar residues after each turn. The lubricant must not leave oily spots (in some cases, when concreting foundations and structures covered with soil or protected by waterproofing, this requirement may not be observed), the lubricant must not impair the strength properties of the surface layers of reinforced concrete structures, the lubricant components must not be volatile and harmful to health substances. When using lubricants for formwork on vertical surfaces, they must have sufficient viscosity and adhesive properties to remain on the vertical surface for 24 hours at a temperature of +30 °C.

Formwork works are carried out in strict accordance with the working drawings. The formwork project is part of the overall construction project and consists of:

marking drawings of the most characteristic, frequently repeated or complex formwork designs. The drawings show the location of individual formwork elements in plan, section, facade or in a development;

technological maps of works;

schemes for organizing formwork work, interconnected with other types of work, in which it is necessary to provide for: breakdown into grips, the direction of movement of the formwork sets, the rate of turnover of the set on separate grips or blocks when concreting complex structures and structures; specifications of the elements and the total volume of the formwork set.

On the formwork organization scheme, in addition to the image of concreted structures and structures with an indication of the amount of formwork work, a list of lifting mechanisms is placed, storage areas are indicated, as well as linear work schedules.

Formwork quality control consists in determining:

conformity of forms and geometric dimensions of the formwork with working drawings;

coincidence of the formwork axes with the alignment axes of structures and structures;

the accuracy of the marks of individual formwork planes or callouts on the formwork areas;

verticality and horizontality of formwork planes;

correct installation of embedded parts, plugs, etc.;

density of joints and joints of formwork elements with extensions in place, with previously laid concrete or preparation.

Adhesion (sticking) and shrinkage of concrete, surface roughness and porosity affect the adhesion force of concrete with formwork. With a high adhesion force between concrete and formwork, work on formwork becomes more difficult, the labor intensity of work increases, the quality of concrete surfaces deteriorates, and formwork panels wear out prematurely.

Concrete adheres to wood and steel formwork surfaces much stronger than to plastic ones. This is due to the properties of the material. Wood, plywood, steel and fiberglass are well wetted, therefore the adhesion of concrete with them is quite high, with poorly wetted materials (for example, textolite, getinax, polypropylene), the adhesion of concrete is several times lower.

The strength (N) of adhesion of some formwork materials to concrete is as follows:

Therefore, to obtain high quality surfaces, one should use linings made of textolite, getinax, polypropylene or use waterproof plywood treated with special compounds. When the adhesion is low, the concrete surface is not disturbed and the formwork can be easily removed. With an increase in adhesion, the concrete layer adjacent to the formwork is destroyed. This does not affect the strength characteristics of the structure, but the quality of the surfaces is significantly reduced. Adhesion can be reduced by applying aqueous suspensions, hydrophobizing lubricants, combined lubricants, lubricants - concrete setting retarders to the surface of the formwork. The principle of action of aqueous suspensions and water-repellent lubricants is based on the fact that a protective film is formed on the surface of the formwork, which reduces the adhesion of concrete to the formwork.

Combined lubricants are a mixture of concrete setting retarders and water-repellent emulsions. In the manufacture of lubricants, they add sulfite-yeast stillage (SDB), soap naphtha. Such lubricants plasticize the concrete of the adjacent zone, and it does not collapse.

Lubricants - concrete setting retarders - are used to obtain a good surface texture. By the time of stripping, the strength of these layers is somewhat lower than that of the main mass of concrete. Immediately after stripping, the structure of the concrete is exposed by washing it with a jet of water. After such washing, a beautiful surface is obtained with a uniform exposure of coarse aggregate. Lubricants are applied to the formwork panels before installation in the design position by pneumatic spraying. This method of application ensures uniformity and constant thickness of the applied layer, and also reduces lubricant consumption.

For pneumatic application, sprayers or spray rods are used. More viscous lubricants are applied with rollers or brushes.

Adhesion (sticking) and shrinkage of concrete, surface roughness and porosity affect the adhesion force of concrete with formwork. With a high adhesion force between concrete and formwork, work on formwork becomes more difficult, the labor intensity of work increases, the quality of concrete surfaces deteriorates, and formwork panels wear out prematurely.

Concrete adheres to wood and steel formwork surfaces much stronger than to plastic ones. This is due to the properties of the material. Wood, plywood, steel and fiberglass are well wetted, therefore the adhesion of concrete with them is quite high, with poorly wetted materials (for example, textolite, getinax, polypropylene), the adhesion of concrete is several times lower.

Therefore, to obtain high quality surfaces, one should use linings made of textolite, getinax, polypropylene or use waterproof plywood treated with special compounds. When the adhesion is low, the concrete surface is not disturbed and the formwork can be easily removed. With an increase in adhesion, the concrete layer adjacent to the formwork is destroyed. This does not affect the strength characteristics of the structure, but the quality of the surfaces is significantly reduced. Adhesion can be reduced by applying aqueous suspensions, water-repellent lubricants, combined lubricants, lubricants - concrete setting retarders to the surface of the formwork. The principle of action of aqueous suspensions and water-repellent lubricants is based on the fact that a protective film is formed on the surface of the formwork, which reduces the adhesion of concrete to the formwork.

Combined lubricants are a mixture of concrete setting retarders and water-repellent emulsions. In the manufacture of lubricants, they add sulfite-yeast stillage (SDB), soap naphtha. Such lubricants plasticize the concrete of the adjacent zone, and it does not collapse.

Lubricants - concrete setting retarders - are used to obtain a good surface texture. By the time of stripping, the strength of these layers is somewhat lower than that of the main mass of concrete. Immediately after stripping, the structure of the concrete is exposed by washing it with a jet of water. After such washing, a beautiful surface is obtained with a uniform exposure of coarse aggregate. Lubricants are applied to the formwork panels before installation in the design position by pneumatic spraying. This method of application ensures uniformity and constant thickness of the applied layer, and also reduces lubricant consumption.

For pneumatic application, sprayers or spray rods are used. More viscous lubricants are applied with rollers or brushes.

Tech Candidates. Ya. P. BONDAR (TsNIIEP housing) Yu. S. OSTRINSKY (NIIES)

To find ways of concreting in the sliding formwork of walls with a thickness of less than 12-15 ohms, the forces of interaction between the formwork and concrete mixtures prepared on dense aggregates, expanded clay and slag pumice were studied. With the existing technology of concreting in sliding formwork, this is the minimum allowable wall thickness. For molding concrete, expanded clay gravel from the Beskudnikovsky plant with crushed sand from the same expanded clay and slag pumice made from melts of the Novo-Lipetsk Metallurgical Plant with a fishing line obtained by crushing slag lemza were used.

Claydite concrete grade 100 had vibrocompaction, measured on N. Ya. Spivak's device, 12-15 s; structural factor 0.45; bulk density 1170 kg/m3. Slag-pumice concrete grade 200 had a vibrocompaction of 15-20 s, a structural factor of 0.5, and a bulk density of 2170 kg/m3. Heavy concrete grade 200 with a bulk density of 2400 kg/m3 was characterized by a draft of a standard cone of 7 cm.

The forces of interaction of the sliding formwork with concrete mixtures were measured on a test rig, which is a modification of the Casa-Rande device for measuring single-plane shear forces. The installation is made in the form of a horizontal tray filled with concrete mix. Across the tray, test rails were laid from wooden bars, sheathed on the surface of contact with the concrete mixture with strips of roofing steel. Thus, the test rails simulated a steel sliding formwork. The slats were kept on the concrete mixture under weights of various sizes, simulating the pressure of concrete on the formwork, after which the forces causing the horizontal movement of the slats along the concrete were recorded. The general view of the installation is given in Fig. one.

According to the results of the tests, the dependence of the forces of interaction between the steel sliding formwork and the concrete mix m on the pressure of concrete on the formwork a (Fig. 2), which is linear, was obtained. The angle of inclination of the graph line with respect to the abscissa axis characterizes the angle of friction of the formwork on concrete, which makes it possible to calculate the friction forces. The value cut off by the graph line on the y-axis characterizes the adhesion forces of the concrete mixture and the formwork m, which do not depend on pressure. The angle of friction of the formwork on concrete does not change with an increase in the duration of the fixed contact from 15 to 60 minutes, the value of the adhesion forces increases by 1.5-2 times. The main increase in adhesion forces occurs during the first 30-40 minutes with a rapid decrease in the increment over the next 50-60 minutes.

The adhesion force of heavy concrete and steel formwork 15 minutes after compaction of the mixture does not exceed 2.5 g/ohm2, or 25 kg/m2 of the contact surface. This is 15-20% of the generally accepted value of the total interaction force of heavy concrete and steel formwork (120-150 kg/m2). The main part of the effort falls on the friction forces.

The slow growth of adhesion forces during the first 1.5 hours after concrete compaction is explained by an insignificant number of neoplasms in the process of concrete mixture setting. According to research, in the period from the beginning to the end of the setting of the concrete mix, the mixing water is redistributed in it between the binder and aggregates. Neoplasms develop mainly after the end of setting. The rapid growth of adhesion of the sliding formwork with the concrete mixture begins 2-2.5 hours after the compaction of the concrete mixture.

The share of cohesive forces in the total interaction forces of heavy concrete and steel sliding formwork is about 35%. The main part of the efforts falls on the friction forces determined by the pressure of the mixture, which, under concreting conditions, changes with time. To test this assumption, the shrinkage or swelling of freshly molded concrete specimens was measured immediately after vibration compaction. During the formation of concrete cubes with an edge size of 150 mm, a textolite plate was placed on one of its vertical faces, the smooth surface of which was in the same plane with the vertical face. After the concrete was compacted and the sample was removed from the vibrating table, the vertical faces of the cube were freed from the side walls of the mold, and within 60–70 min, the distances between the opposite vertical faces were measured using a messureur. The measurement results showed that freshly molded concrete shrinks immediately after compaction, the value of which is the higher, the greater the mobility of the mix. The total value of bilateral upset reaches 0.6 mm, i.e. 0.4% of the sample thickness. AT initial period after molding, there is no swelling of freshly laid concrete. This is explained by contraction in the initial stage of concrete setting during the redistribution of water, accompanied by the formation of hydrated films that create high surface tension forces.

The principle of operation of this device is similar to the principle of operation of a conical plastometer. However, the wedge-shaped shape of the indenter makes it possible to use the calculation scheme of a viscous-flowing mass. The results of experiments with a wedge-shaped indenter showed that To varies from 37 to 120 g/cm2 depending on the type of concrete.

Analytical calculations of the pressure of a layer of concrete mixture with a thickness of 25 ohm in a sliding formwork showed that the mixtures of the adopted compositions after their compaction by vibration do not exert active pressure on the formwork skin. The pressure in the "sliding formwork - concrete mixture" system is due to the elastic deformation of the panels under the influence of the hydrostatic head of the mixture in the process of its compaction by vibration.

The interaction of sliding formwork panels and compacted concrete at the stage of their joint operation is quite well modeled by the passive repulsion of a viscoplastic body under pressure from a vertical retaining wall. Calculations have shown that with a one-sided action of the formwork shield on the concrete mass, in order to shift a part of the array along the main sliding planes, an increase in pressure is required, significantly exceeding the pressure that occurs with the most unfavorable combination of conditions for laying and compacting the mixture. With double-sided pressure of formwork panels on a vertical layer of concrete of limited thickness, the pressure forces necessary to shift the compacted concrete along the main sliding planes acquire the opposite sign and significantly exceed the pressure required to change the compression characteristics of the mixture. The reverse loosening of the compacted mixture under the action of bilateral compression requires such high pressure, which is unattainable when concreting in sliding formwork.

Thus, the concrete mixture, laid according to the rules of concreting in a sliding formwork in layers of 25-30 cm thick, does not exert pressure on the formwork panels and is able to perceive from their side the elastic pressure that occurs during compaction by vibration.

To determine the interaction forces that occur during the concreting process, measurements were carried out on a life-size sliding formwork model. A sensor with a high-strength phosphor bronze membrane was installed in the molding cavity. The pressures and forces on the lifting rods in the static position of the installation were measured by an automatic pressure gauge (AID-6M) in the process of vibration and lifting of the formwork - an N-700 photooscilloscope with an 8-ANCH amplifier. The actual characteristics of the interaction of steel sliding formwork with different types of concrete are given in the table.

In the period between the end of the vibration and the first lifting of the formwork, a spontaneous decrease in pressure occurred. which was held unchanged until the formwork began to move upward. This is due to the intense shrinkage of the freshly molded mixture.

To reduce the forces of interaction of the sliding formwork with the concrete mixture, it is necessary to reduce or completely eliminate the pressure between the formwork panels and the compacted concrete. This problem is solved by the proposed concreting technology using intermediate removable shields ("liners") made of thin (up to 2 mm) sheet material. The height of the liners is greater than the height of the molding cavity (30-35 ohms). The liners are installed in the molding cavity close to the sliding formwork panels (Fig. 5) and, immediately after laying and compaction, the concrete is removed from it one by one.

The gap (2 mm) remaining between the concrete and the formwork, after removing the shields, protects the formwork shield, straightening after elastic deflection (usually not exceeding 1-1.5 mm) from contact with the vertical surface of the concrete. Therefore, the vertical edges of the walls, freed from the liners, retain the shape given to them. This allows thin walls to be concreted in sliding formwork.

The fundamental possibility of forming thin walls with the help of liners was tested during the construction of full-scale fragments of walls 7 cm thick, made of expanded clay concrete, slag-pumice concrete and heavy concrete. The results of test moldings showed that lightweight concrete mixes correspond better to the features of the proposed technology than mixes based on dense aggregates. This is due to the high sorption properties of porous aggregates, as well as the continuous structure of light concretes and the presence of a hydraulically active dispersed component in light sand.

Heavy concrete (although to a lesser extent) also shows the ability to maintain the verticality of freshly molded surfaces with its mobility not exceeding 8 cm. 1.6 m, providing concreting of walls with a length of 150-200 m. This will significantly reduce the consumption of concrete compared to buildings erected according to the accepted technology, and increase economic efficiency their construction.

a. Filling the formwork with concrete mix

For concreting structures in sliding formwork, concrete mixes are used on Portland cement grades of at least 400 with the onset of setting no earlier than 3 hours and the end of setting no later than 6 hours. Based on the cement test data, the speed of concreting and lifting of the sliding formwork should be determined.

The draft of the cone of the applied concrete mixture should be: when compacted with a vibrator 6-8 and manual compaction 8-10 cm, and W / C - no more than 0.5. The grain size of coarse aggregate should be no more than /6 of the smallest cross-sectional size of the concreted structure, and for densely reinforced structures - no more than 20 mm.

The thickness of walls and beams erected in sliding formwork, as a rule, should not be less than 150 mm (the weight of concrete should be greater than the friction forces), and the volume of concrete per 1 linear meter. m of their height should not exceed 60 x3.

Initially, the formwork is filled with concrete mixture in two or three layers to a height equal to half the formwork, for a period of not more than 3;6 hours. The second and third layers are laid only after the previous layer is laid along the entire perimeter of the formwork. Further filling of the formwork resumes only after the start of its lifting and ends no later than 6 hours later.

Until the formwork is filled with concrete mixture to its full height, it is lifted at a speed of 60-70 mm/h.

b. The process of compacting the mixture

After the initial filling of the formwork to its full height, with its further lifting, the concrete mixture is laid continuously in layers up to 200 mm thick in thin walls (up to 200 mm) and no more than 250 mm in other structures. Laying a new layer is carried out only after the completion of laying the previous layer before its setting begins.

During the concreting process, the upper level of the mixture to be laid must be more than 50 mm below the top of the formwork panels.

The concrete mixture is compacted with rod vibrators with a flexible shaft or manually - with screws. The diameter of the vibrator tip should be 35 mm for wall thicknesses up to 200 mm and 50 mm for thicker walls.

During the compaction of the mixture, it is recommended to raise and lower the vibrator by 50-100 mm within the layer being laid, while the tip of the vibrator should not rest against the formwork or reinforcement, and should not reach the previously laid setting layer of concrete.

The rate of laying the concrete mixture and lifting the formwork should exclude the possibility of adhesion of the laid concrete to the formwork and ensure the strength of the concrete coming out of the formwork, sufficient to maintain the shape of the structure and at the same time make it easy to rub the traces of the formwork on its surface with a grater.

c. Breaks in concreting

The intervals between formwork lifts should not exceed 8 minutes when using vibrators and 10 minutes when manually compacting the concrete mixture. The rate of formwork lifting at an outside air temperature of +15, +20 ° C and the use of Portland cement M 500 reaches 150-200 mm per hour.

In the process of concreting walls in a sliding formwork, there may be "failures" of concrete: the formwork carries along a part of the weak concrete of the wall, as a result, shells are formed, reinforcement is exposed. The main causes of "failures" are as follows: contamination of the formwork; non-observance of the formwork taper; large breaks during concreting.

In cases of a forced break in concreting, measures should be taken to prevent adhesion of the laid concrete to the formwork; the formwork is slowly raised until there is a visible gap between the formwork and the concrete, or it is periodically raised and lowered within one step of the jack (“step in place”). When resuming concreting, it is necessary to clean the formwork, remove the cement film from the concrete surface and rinse them with water.

During the concreting process, traces of formwork movement and small shells on the outer surface of the buildings being concreted and inside silos, bunkers and rooms are rubbed with a 1: 2 cement mortar immediately after the concrete leaves the formwork.

d. Mix supply

Mats or tarpaulins are attached to the lower edges of the formwork to protect fresh concrete from drying out (hypothermia) and in summer it is regularly watered with water using an annular pipeline.

Window and door blocks in buildings and structures are installed in place during the movement of the formwork, for which they are pre-prepared (antiseptic, sheathed with roofing paper) in accordance with the requirements of the project. To reduce the gaps between the formwork walls and the block box to 10 mm, rails are sewn to the box, which are subsequently removed. The reinforcement around the block is installed in accordance with the project.

Laying of concrete near the installed blocks is carried out simultaneously from two sides. After the formwork rises above the installed blocks, the temporary rails are removed.

Tower cranes, mine hoists, self-elevating cranes are used to supply concrete mix, reinforcement, jacking rods and other goods to the formwork.

Concrete pumps and pneumatic blowers are also used to supply the mixture. Upon completion of the erection of the structure, the sliding formwork and all structures and equipment fixed on it are dismantled in a manner in which, after the removal of individual parts, the stability and safety of the remaining elements are ensured.

The channels in the concrete formed by the movement of the protective tubes must be carefully sealed after the removal of the jacking rods.

e. Prefabricated floors

During the construction of structures in winter conditions, concrete is heated in specially constructed greenhouses above the working floor and on external scaffolds using steam or electric heaters or infrared radiation.

Multi-storey floor slabs, flights of stairs and sites are concreted using additional inventory formwork or assembled from prefabricated elements. In the latter case, during the construction of a building or structure, the need for alterations and additional devices in the sliding formwork is eliminated.

Prefabricated ceilings can be mounted with a tower crane after the walls have been erected in a "well" to the entire height of the building. In this case, the slabs are supported on special inventory, removable brackets fixed on the walls slightly below a number of small openings in the wall. Reinforcing bars are passed through the openings, butted with outlets from floor slabs. Docking of external walls with floor slabs is carried out with the help of grooves in the walls. This technology ensures the continuity of concreting, fast and high-quality construction of walls.

Monolithic ceilings can be concreted after the walls of the building are erected with a “well”. Inventory formwork panels and supporting devices (metal telescopic racks and sliding crossbars) are transferred from floor to floor by a tower crane or manually.

Monolithic slabs can also be concreted using drop formwork mounted on a special platform. This method is especially effective if concrete pumps or pneumatic blowers are used to supply the concrete mixture.

f. Floor concreting

Concreting of floors with a lag of 1-2 floors from the concrete of walls, the process of erecting buildings is complicated by the need for frequent stops when lifting the sliding formwork.

The method of combined cyclic concreting of walls and ceilings is that the concreting of walls in a sliding formwork stops each time at the level of the next ceiling. The empty formwork of the walls is brought out above this mark so that between the bottom of the sliding formwork and the mark of the bottom of the slab there is a gap equal to the thickness of the future slab. At the same time, the formwork panels of the outer walls, as well as the formwork forming inner surface elevator shafts and other cells that do not have overlaps are made larger in height than the panels of the rest of the formwork. Concreting of floors is carried out on panel or sectional formwork with the working floor panels removed after stopping and aligning the sliding formwork.

The construction of buildings and structures with a height of 40-50 m in monolithic reinforced concrete using the sliding formwork method, according to the main technical and economic indicators, is at the level of construction from prefabricated reinforced concrete structures, and the construction of high-rise civil buildings has a number of advantages: reduction of construction time; reduction of labor intensity and estimated cost of construction, including by reducing specific capital investments in the base of the construction industry; increasing the reliability, durability and rigidity of structures due to solidity and the absence of joints, which is especially valuable in construction in seismic areas, in mine workings and subsiding soils.

g. Construction of high-rise structures

In recent years, a new method for erecting high-rise structures from monolithic reinforced concrete in a sliding formwork of a rodless system, consisting of hydraulic or pneumatic support-lifting devices, has been developed and implemented in our country, providing reliable support by compressing the erected part of the walls with special grips and creating friction support forces.

On the basis of the proposals of the Donetsk PromstroyNIIproekt, a pilot production sample of a mobile formwork was created, consisting of two (lower and upper) support-lifting sections of walking action with support on the walls of the structure under construction, electromechanical worm-and-screw lifts, sliding formwork forms and frames for fastening. With the help of this formwork, the tower supports of the transport galleries of the blast-furnace ore warehouse were erected at the construction site of the Zaporozhye iron ore plant.

The erected tower supports have outside diameter 6 m and a height of 14 m, the thickness of the walls is 300 mm. The construction of one tower was carried out by a team of five people. The average speed of concreting reached 0.3 m/h with the machine speed of raising the formwork in the process of laying and compacting the concrete mix 0.6. m/h At the same time, the lower section of the lifting device rested on concrete of 10-12 hour strength. A step of lifting sections of 2 m made it possible to conduct continuous concreting for 6-6.5 hours.

h. Climbing formwork

Climbing formwork is used in the construction of structures of variable cross-section in height, including chimneys, hyperbolic cooling towers, television towers and other tall objects. The main element of this formwork is a mine hoist with a working platform, to which a set of adjustable external and internal formwork is attached.

The design of the lift allows you to periodically increase it from above or grow it from below. After each cycle of installation of formwork panels, reinforcement and laying of the concrete mixture, the next lifting of the working platform and rearrangement of the formwork is carried out.

The formwork of chimneys up to 320 m high consists of external and internal panels, bearing rings, a framing (support) frame, radial movement mechanisms, a working platform, suspended scaffolding, as well as a post mine lift with a lifting head, assembled from 2.5-meter tubular sections and equipped with a cargo cage and a passenger-and-freight elevator.

The lifting head mounted on a lift with a lifting capacity of 25 and 50 tons, when the formwork is moved to the next tier, rises at a speed of up to 3 mm / s. The working step of lifting the formwork is 2.5 m.

i. Pipe shaft concreting

The formwork consists of two shells - outer and inner, which are assembled from panels made of 2 mm thick sheet steel, bolted together.

The outer formwork of the chimneys consists of rectangular and trapezoidal panels 2.5 m high. The combination of these panels will make it possible to obtain a cone-shaped surface of the pipe.

The outer formwork is suspended from the carrier ring, which, when the pipe perimeter is reduced, is replaced with a new one of smaller diameter.

For the convenience of laying concrete, the inner formwork is assembled from panels measuring 1250x550 mm.

Pipe shaft concreting: work organization scheme; development of the outer climbing formwork of the conical chimney; rectangular panels; trapezoidal panels; c - panel of the inner shell of the formwork; covered canopy; protective cover; mine lift; lining platform; clip; work site; distributing bunker; ladle of a cargo cage; lifting head; passenger-and-freight elevator; hoist; cargo cage; Cathead; strip overlay; lugs made of strip steel; steel strips; steel sheet 2 mm thick.

To give rigidity to the panels, overlays are welded to their upper and lower edges, with the help of which the panels are assembled in height. From the outer side of the shields, lugs are welded into which reinforcing bars 10-14 mm are laid, forming a series of elastic horizontal rings.

j. Construction of cooling tower shells

Shields are installed in two (sometimes three) tiers. The formwork of the second tier is installed after the concrete is placed in the formwork of the first tier. After 8-12 hours after concrete is placed in the second tier, the outer formwork is removed and installed in the next highest position. After installing the reinforcement of the third tier, the lower tier of the inner formwork is removed and rearranged higher. Then the cycle repeats. Reinforcement is installed by individual rods manually.

The concrete mixture is fed by a bucket of a cargo stand into a receiving hopper located on the working site, then into the movable hopper of the concrete paver and from there - along the trunk into the formwork. The concrete mixture is compacted with deep vibrators with a flexible shaft.

The speed of concreting the shafts of chimneys at an outdoor temperature of 15-20 ° C reaches 1-1.5 m / day.

The construction of cooling tower shells is carried out using a unit, which is a lattice (increasable) tower, on the rotary head of which rotating booms are mounted, to which climbing formwork shields are attached, as well as working cradles.

The concrete mixture is fed to the upper platform of the cradle in a vibrating bucket by a hoist moving along the boom. Concreting is carried out in tiers by analogy with concreting chimneys.

2. Methods of concreting structures

a. Concreting in sliding formwork

Special methods of concreting structures. Sliding formwork concreting is used in the construction of chimney walls, working towers of elevators and silos, shaft headframes, water towers, as well as frames of multi-storey buildings. Structural elements of buildings and structures erected in sliding formwork must be vertical, which is dictated by the main feature of sliding formwork.

The method of concreting monolithic reinforced concrete buildings and structures in sliding formwork is a highly organized and complex-mechanized, flow-speed construction process. Formwork installation, reinforcement, laying and compaction of the concrete mixture, concrete stripping are carried out in combination and continuously in the process of formwork lifting (SNiP N1-B.1-70).

Sliding formwork includes: formwork panels, jacking frames, a working floor with a canopy along the outer contour of the formwork, suspended platforms, formwork lifting equipment.

Formwork panels are made inventory 1100-1200 mm high from the following materials: steel sheet not less than 1.5 mm thick; planed wooden planks not less than 22 mm thick; waterproof plywood 8 mm thick; baked plywood 7 mm thick or fiberglass 3 mm thick. In some cases, wood-metal shields are made, in which the frame is made of rolled steel profiles, and the sheathing is made of planed boards or plywood. Circles for fixing formwork panels, as a rule, are made of rolled steel profiles.

b. Erection of non-standard structures

Metal formwork panels are used in the construction of a number of structures of the same type (silos, chimneys, tanks), when the side walls perceive the high pressure of the freshly laid concrete mixture and, in addition, multiple turnover of the formwork panels is ensured.

Wooden and wood-metal shields have less rigidity and turnover, but at the same time, lower cost compared to metal ones. They are used in the construction of residential and civil buildings, where the wall thickness does not exceed 200 mm, as well as in dry and hot climates to protect concrete from overheating.

Promising are formwork panels made of waterproof plywood and fiberglass. They are durable and lighter than shields made of other materials, but still more expensive than them.

For the construction of non-standard structures, non-inventory wooden formwork is used. By design, sliding formwork inventory boards are used in two types: large-block and small-block.

In large-block shields, metal circles are rigidly fastened to the skin. These shields are strong, durable and relatively easy to assemble.

In small-block shields, only metal circles are rigidly connected to each other, forming the frame of the walls, and the formwork panels are hung on the circles without fastening to each other.

3. Concreting of bases and floors

a. Concrete preparation

Concrete floors and bases (preparations) are widely used in industrial and civil buildings.

Concrete preparations are arranged mainly in one-story industrial workshops for cement and asphalt floors, floors made of cast-iron slabs, end wooden checkers and other types of floors 100-300 mm thick on prepared and leveled soil. For concrete bases, rigid concrete mixes of grades 100, 200 and 300 are usually used.

Concrete and cement-sand floor coverings are made up to 40 mm thick from concrete or mortar according to preparation. In multi-storey buildings, reinforced concrete floors usually serve as the foundation.

The scope of work on the installation of single-layer concrete floors in one-story buildings includes: preparation of soil bases; installation of lighthouse boards; reception, leveling of the concrete mixture; surface grouting or ironing.

Prior to the start of the concrete preparation, all underground work on the installation of foundations, channels, tunnels, etc. must be completed, backfilling of the sinuses of the pits, leveling and compaction of the soil must be completed.

Soil preparation. With dense soils, the concrete mixture is laid directly on the planned soil. Bulk and disturbed soils in the foundations must be compacted mechanized way. In places inaccessible to compacting mechanisms, the thickness of the soil layer compacted by manual rammers should not exceed 0.1 m.

b. Floor concreting techniques

Soils subject to significant settlement are replaced or strengthened. In the latter case, the concrete preparation is reinforced with mesh.

A layer of crushed stone or gravel 60-150 mm thick is rammed or rolled into the base surface of weak soils before laying concrete preparation on it. Before installing floors on water-saturated clay, loamy and dusty soils, it is necessary to lower the groundwater level and dry the base until the design bearing capacity is restored. On heaving soils, the installation of floors should be carried out in compliance with the instructions of the project.

Planning and compacting soil with an admixture of frozen soil, as well as with snow and ice, is prohibited. It is also not allowed to install concrete floors on frozen soils.

Techniques for concreting floors and foundations. Before concreting, beacon boards are installed along the level so that their upper edge is at the level of the surface of the concrete preparation (Fig. 14, a). The distance between the boards depends on the length of the vibrating rail and is usually 3-4 m. Lighthouse boards are fixed with wooden stakes driven into the ground. Floors and bases are concreted in strips through one, starting from the places most remote from the passage.

c. Concreting preparations

Intermediate strips are concreted after the concrete of adjacent strips has hardened. Before concreting the intermediate lanes, the lighthouse boards are removed. The length of the strips is taken as large as possible. The layer of concrete mixture in preparation before its leveling and compaction should exceed the level of lighthouse boards by 2-3 cm.

The concrete mixture is compacted with a vibrating rail, which is a metal beam (channel, I-beam), on which one or two electric motors from a surface vibrator are mounted.

When concreting preparations and floor coverings, each vibrated section must be covered with a vibrating screed, respectively, by 150 mm and half of its width.

Techniques for concreting floors and bases: scheme for concreting the base under the floors; hand tool for smoothing concrete surfaces; laid base; foundation preparation; stakes; side formwork; scraper with a rubber band to remove laitance; trowel; trowel; ironing board; rubber band.

Depending on the conditions of work, the laying of the concrete mixture by concrete pavers into the bases is carried out in two ways: “away from you”, when the unit moves behind the concreting front, and the concrete in the area of ​​the unit’s action has time to gain the strength necessary for its movement, and “on itself”, when the mechanism moves ahead of the concreting front, since the concrete does not have time to gain the necessary strength.

d. Production of concrete mix

The first method is preferable, since it creates a wide front of work to prepare the foundation. In the second method, the preparatory work precedes the laying of the concrete mixture by one plot, the length of which is equal to the radius of the mechanism.

In unheated premises in concrete preparation, every two strips arrange longitudinal and after 9-12 m along the length of the strips, transverse temperature-shrinkage seams, which break the area to be concreted into separate slabs with dimensions of 6X9-9X12 m.

Longitudinal seams are made by installing planed boards coated with hot bitumen, or boards wrapped with roofing paper. After the concrete has set, the boards are removed and the seams are filled with bitumen. Seams are also arranged by coating with bitumen a layer of 1.5-2.0 mm of the side faces of the strips before laying the concrete mixture in adjacent spaces.

For the formation of transverse expansion joints(half-joints) use metal strips 60-180 wide and 5-7 mm thick, which, during the concreting process, are laid in preparation for 73 of their width and then removed after 30-40 minutes. The resulting recesses after the final hardening of the concrete are cleaned and filled with grade III bitumen or cement mortar.

e. Surface of concrete bases

In places where there is a break in the concreting of foundations and floors, it is not allowed to install a vibrating screed at the edge of the laid layer, as this will cause slipping and delamination of the concrete mixture. Therefore, at the end of the work shift, in places of the planned break in concreting, a partition of boards is installed and the last portion of the concrete mixture is leveled and vibrated along it.

The surface of concrete bases before laying on it continuous floor coverings on a cement binder or from piece materials on a cement-sand mortar must be cleaned of debris and cement film.

In the early age of concrete, mechanical steel brushes are used for this purpose. With a high strength of concrete, with the help of a pneumatic tool, grooves with a depth of 5-8 mm are applied to its surface every 30-50 mm. This makes it possible to obtain a rough surface of the underlying layer and to ensure its better adhesion to the upper layer.

Concrete or cement-sand floor coverings consist of a 20-40 mm layer of concrete or mortar and are concreted similarly to preparation in strips 2-3 m wide through one.

Before concreting the coating, beacon wooden slats or metal frame corners are fixed on the surface of the concrete base. The concrete mixture is compacted with vibrating screeds, and the concrete surface is leveled with a wooden slat moved across the strip.

f. cement milk

Cement laitance, which has come to the surface during compaction of concrete bases and floor coverings, is removed using a scraper with a rubber band.

For small volumes of work, the surface of the concrete floor is finally finished with an ironing board or a tarpaulin rubberized tape, the length of which should be 1-1.5 m longer than the width of the concreted strip. The ends of the tape are attached to the rollers that serve as handles, the width of the tape is 300-400 mm. The compacted concrete mixture is smoothed 25-30 minutes after laying. When the tape is moved alternately across and along the strip, the protruding thin film of water is removed from the concrete surface and the concrete floor is pre-smoothed. The final leveling of the surface is carried out after 15-20 minutes with shorter movements of the tape.

To give concrete floor high abrasion strength, its surface is treated with a metal trowel approximately 30 minutes after the final leveling, exposing crushed stone grains. If high abrasion resistance is not required, then a cement mortar floor is laid on the concrete preparation.

If it is necessary to immediately install a two-layer floor, first the bottom layer is laid between the lighthouse boards and compacted with a site vibrator or an obliquely installed vibrating rail, then with a break of no more than 1.5-2 hours (for better connection of the lower layer with the upper one), a clean floor is made.

e. Iron surface of concrete

For large volumes of work, the surface of a clean concrete floor in the initial period of hardening is rubbed with a SO-64 (or OM-700) machine, consisting of a trowel disc with a diameter of 600 mm, an electric motor and a control handle. Rotating at a speed of 140 rpm, the trowel disc levels and smoothes the concrete floor surface. The productivity of the machine is 30 m2/h.

Ironing of the concrete surface is used to give the floor an increased density. It lies in the fact that dry and sifted cement is rubbed into the surface of wet concrete until an even sheen appears on it. Dry concrete surfaces are moistened with water before ironing. Ironing can be done manually using steel trowels or with a CO-64 trowel.

A variety of concrete floors are mosaic, made from a mixture that includes: white or colored Portland cement, marble, granite or basalt chips and mineral dye. A mosaic layer 1.5-2 cm thick is laid, as a rule, on an underlying layer of cement mortar of approximately the same thickness. The limitation of single-color fields and the implementation of the patterns provided for by the project is carried out with the help of strips-veins made of glass, copper or brass, embedded in the underlying layer of the solution. These strips are placed in such a way that their upper ribs serve as beacons when laying and leveling the mosaic layer.

Finishing the surfaces of mosaic floors electrical machines after hardening of concrete (after 2-3 or more days). After the first grinding, the flaws found on the floor surface are puttied with a colored cement-sand mortar. Then the floor is sanded with finer abrasives, treated with polishing powders and glossed with a buffing machine.

4. Concreting of columns

a. Formwork for rectangular columns

Columns as an element of the frame of buildings and structures are rectangular, polygonal and circular. The height of the columns reaches 6-8 m or more.

The formwork of rectangular columns is a box of two pairs of panels (wooden, metal or combined). The lateral pressure of the concrete mixture is perceived by the clamps that compress the box. Clamps are made of inventory metal with a large turnover of formwork and wooden - with a small number of revolutions. Holes in the straps of the metal clamp for fastening wedges allow them to be used for columns of various sections. To clean the box, a temporary hole is made in the lower part of one of the shields. Block forms are also used for concreting columns.

Typical unified shields and formwork panels are attached to the reinforcing blocks with tie bolts and pulled together with tie rods. The formwork of low columns is fixed in two mutually perpendicular directions with inclined jointing (braces). With a column height of more than 6 m, the formwork boxes are attached to specially arranged scaffolding.

After installing the formwork of the column, holes of 500x500 mm in size and work platforms for concrete work are arranged every 2-3 m in height. The formwork of high columns can only be mounted on three sides, and on the fourth side it can be built up during the concreting process.

b. Column concreting

For round columns, special metal block forms are made.

Compliance with the thickness of the protective layer in the columns is ensured by special cement gaskets, which, before concreting, are attached to the reinforcement bars with a knitting wire embedded in the gaskets during their manufacture.

Concreting of columns with transverse dimensions from 400 to 800 mm in the absence of crossing clamps is carried out from above without interruption in sections up to 5 m high. Columns with sides of a section of less than 400 mm and columns of any section with crossing clamps, which contribute to the separation of the concrete mixture when it falls, are concreted from the side plots with a height of no more than 2 m.

Column formwork: assembled box; inventory metal collar; wooden clamp on wedges; detail of a wooden clamp knot; box; inventory metal clamp; wedges fastening clamps; frame for column formwork; cleaning hole door; cover shields; holes for wedges embedded shields; hard plates.

With a higher height of sections of columns concreted without working joints, it is necessary to arrange breaks for the concrete mixture to settle. The duration of the break should be at least 40 minutes and not more than 2 hours.

c. Frame structures

In cases where the columns are part of the frame structure and above them, there are beams or girders with thick reinforcement, it is allowed to first concrete the columns, and then, after the installation of the reinforcement, the beams and girders.

The lower part of the formwork of the columns when concreting them from above is recommended to be initially filled to a height of 100-200 mm with a cement mortar of the composition 1: 2-1 = 3 to prevent the accumulation of coarse aggregate without mortar at the base of the column. When a portion of the concrete mixture is dropped from above, large aggregate particles are embedded in this solution, forming a mixture of normal composition.

The concrete mixture in the columns is compacted by internal vibrators with a flexible or rigid shaft. Compaction with external vibrators attached to the formwork of small-section columns is less effective and is practically not used.

In order to avoid the formation of shells during the concreting of columns (especially corners), it is very useful to tap with a wooden mallet from the outside at or slightly below the concrete layer being laid.

Concreting of columns in accordance with SNiP III-B.1-70 is carried out to the full height without working joints. It is allowed to arrange working joints: at the level of the top of the foundation, at the bottom of the girders and beams or crane consoles and the top of the crane beams.

d. Concreting of frame structures

In columns of beamless ceilings, it is allowed to arrange seams either at the very bottom of the columns, or at the bottom of the capitals. The capitals are concreted simultaneously with the floor slab.

The surface of the working joints, arranged when laying the concrete mixture intermittently, must be perpendicular to the axis of the columns to be concreted.

Concreting of frame structures should be carried out with a break between the placement of the concrete mixture in the columns (racks) and crossbars of the frames. Working seams are arranged a few centimeters below or above the junction of the frame crossbar to the rack.

Walls (including partitions) are of constant and variable cross-section, vertical and inclined, in terms of round, curvilinear, polygonal and straight.

When concreting walls and partitions, the following types of formwork are used: standard unified panels and panels of collapsible-climbing formwork, block-forms, rolling climbing-climbing, sliding-climbing and sliding formwork.

The collapsible small-panel formwork is installed in two steps: first, on one side, to the entire height of the wall or partition, and after installing the reinforcement, on the other. If the wall thickness is more than 250 mm, the formwork of the second side is installed with special inventory.

They are installed on the entire height of the wall, otherwise - in tiers in the process of concreting. In the formwork installed to the entire height of the wall, holes are provided for supplying the concrete mixture through them into the structure.

5. Concrete walls

a. Design wall thickness

Wall formwork up to 6 m high is mounted from mobile platforms or light scaffolds. At higher altitudes, forests are arranged. The formwork of the walls is fastened with struts or braces, tie bolts or wire ties.

To comply with the design thickness of the walls, concrete or wooden spacers are installed in the places where the screeds pass. The latter are removed during the concreting process.

Collapsible large-block formwork is installed in tiers in the process of concreting the walls. This allows you to limit yourself to a set of formwork of only two tiers. All work of the full cycle of concreting walls in this formwork is carried out in the following sequence: first, scaffolding (scaffolding) is installed or increased, then the working seam of concreting is processed and reinforcement is installed, after which the formwork is rearranged from the lower tier to the upper one. The concreting cycle of one tier ends with the laying and compaction of the concrete mixture and the subsequent curing of the concrete in the formwork.

Block form for formwork: fixing clamp No. 1; reinforced concrete tape; bedding; screw jack; formwork block; fencing element for the 1st tier of concreting; formwork panel; fixing clamp No. 2; working floor; fencing element for the 2nd tier of concreting; inventory insert; sliding rack; double wooden wedge.

b. Block formwork

Formwork block forms are used when concreting walls of considerable height and length, i.e., when their repeated use is ensured. The block-form of the design of the Kharkovorgtekhstroy trust consists of blocks, panels, additional and fasteners.

The rigidity of the blocks is ensured by horizontal braces and supporting trusses, which also serve as scaffolds. For the installation, alignment and dismantling of the formwork, the supporting trusses are equipped with jacking devices. The dimensions of ordinary blocks are 3X8,3X2 and 1.5x3 m.

Rolling formwork designed by Donetsk PromstroyNIIproekt: trolley; Column; beam; shield lifting winch; formwork board; clamps; stairs; sliders; clamping device; flooring; fencing; bunker.

The deck of blocks, panels and extensions is assembled from small-sized shields made of 45X45x5 mm corners and 3 mm thick sheet steel. In the ribs of the shield frame there are holes with a diameter of 13 mm for attaching the shields to each other.

The assembled formwork blocks, if necessary, can be disassembled into separate panels. The block form of the formwork is rearranged by tiers during the concreting process. When concreting walls of constant and variable cross-section, rolling formwork is used (including horizontally moved on skids).

c. wall construction

The concreting of structures can be carried out in tiers with continuous or cyclic movement of the formwork, as well as by grips to the entire height of the wall. Rolling formwork designed by the Donetsk PromstroyNIIproekt consists of two metal panels 6-8 m long and 1.3 m high. The frame of the panels is made of an angle, and the deck is made of sheet steel 6 mm thick. Formwork size 6700X X 5400X3900 mm, weight 800 kg. With the help of special devices - sliders - the shields are attached to the guide columns of the portal.

The columns of the portal at the bottom rest on the trolley, and at the top they are connected by a beam, which allows you to spread the columns to the required width (up to 600 mm). The movement of the shields perpendicular to the surface of the structure being concreted is carried out by a screw device, and the rise is carried out on cables through fixed blocks attached to connecting beams. Moving the formwork along the concreted wall is carried out with the help of double-sided winches.

The construction of walls in sliding and climbing formwork is discussed below, among the special construction methods.

When concreting walls, the height of sections erected without interruption should not exceed 3 m, and for walls less than 15 cm thick - 2 m.

d. Concrete supply

With a higher height of wall sections concreted without working joints, it is necessary to arrange breaks lasting at least 40 minutes, but not more than 2 hours to settling the concrete mixture and preventing the formation of sedimentary cracks.

If there is a window or door opening in the wall to be concreted, the concreting should be interrupted at the level of the upper edge of the opening or, if possible, a working seam should be arranged in this place. Otherwise, sedimentary cracks form near the corners of the mold. When supplying a concrete mixture from a height of more than 2 m, link trunks are used.

The lower part of the wall formwork during concreting from above is first filled with a layer of cement mortar of composition 112-1: 3 in order to avoid the formation of porous concrete at the base of the walls with accumulation of coarse aggregate.

When concreting the walls of tanks for storing liquids, the concrete mixture should be laid continuously over the entire height in layers with a thickness of not more than 0.8 of the length of the working part of the vibrators. In exceptional cases, the formed working joints must be very carefully processed before concreting.

The walls of large tanks are allowed to be concreted in vertical sections, followed by processing and filling with concrete mixture of vertical working joints. The joints of the walls and the bottom of the tanks are made in accordance with the working drawings.

6. Concreting beams, slabs, vaults

a. Concreting of ribbed slabs

Concreting beams, slabs, vaults, arches and tunnels. Beams and slabs, ceilings are usually concreted in collapsible formwork from standard unified panels and panels. Beams and girders are also concreted in block forms.

The formwork of the ribbed floor is made of small-piece wooden panels supported by wood-metal sliding racks at a height of up to 6 m and specially arranged scaffolding at a height of more than 6 m.

The formwork of the beam is made of three shields, one of which serves as the bottom, and the other two - as side railings of the surfaces. The side panels of the formwork are fixed at the bottom with pressure boards sewn to the head of the rack, and at the top - with the formwork of the slab.

Concreting of ribbed slabs: general form scaffolding and ribbed formwork; the location of the working seams when concreting ribbed slabs in a direction parallel to the secondary beams; the same, the main beams; beam formwork; slab formwork; circled; run formwork; column formwork; sliding racks; pressure boards; stands; frieze boards; slab formwork boards; circled; circumferential boards; side shields; bottom: rack head; working position of the seam (arrows show the direction of concreting).

b. Beamless slab formwork

The slab formwork decking boards are laid edgewise on the boards circles, which in turn rest on the boards under the circles, nailed to the seam planks of the beam side boards and supported by supports.

To fix the circles and side panels, frieze boards are laid along the perimeter of the slab, which also facilitates the stripping of the slab. With a beam height of more than 500 mm, the side panels of the formwork are additionally reinforced with wire ties and temporary braces.

The distance between the racks and circles is determined by calculation. The supporting racks are unfastened in mutually perpendicular directions with inventory strands or braces.

Beamless slab formwork consists of column formwork, capitals and slabs. The formwork of the slab consists of two types of panels laid in circles between frieze boards sewn onto the tops of the racks. To support the circles, paired runs are arranged from boards resting on racks. The shields of the capitals rest on the formwork of the columns on one side, and are supported by circles along the outer contour.

When mounting the suspended formwork of floor slabs along precast concrete or metal beams, metal suspension loops are arranged, laid out along the beams with a given step. These loops are used to install the circumferential boards, on which the circumferential boards and boards of the slab formwork rest.

c. protective layer

Concreting of ceilings (beams, purlins and slabs) is usually carried out simultaneously. Beams, arches and similar structures with a height of more than 800 mm are concreted separately from the slabs, arranging working seams 2-3 cm below the level of the lower surface, and if there are haunches in the slab, at the level of the bottom of the slab haunch (SNiP Sh-V.1-70 ).

In order to prevent sedimentary cracks, the concreting of beams and slabs monolithically connected with columns and walls should be carried out 1-2 hours after the concreting of these columns and walls.

The concrete mixture is placed in beams and girders in horizontal layers, followed by compaction with flexible or rigid shaft vibrators - in strong or weakly reinforced beams. The concrete mixture is placed into the floor slabs along the lighthouse rails, which are installed on the formwork with the help of linings in rows of 1.5-2 m. After concreting, the rails are removed, and the resulting depressions are smoothed out. With double reinforcement of floor slabs, the leveling and compaction of the concrete mixture is carried out from the adjustable deck so as not to bend the upper reinforcement.

Floor slabs are concreted in the direction of secondary beams. The protective layer in slabs, beams and girders is formed with the help of special gaskets from cement mortar or clamps. As the structures are being concreted, the reinforcement is slightly shaken with metal hooks, making sure that a protective layer of the required thickness forms under the reinforcement.

d. Floor concreting

Concrete mixture in slabs up to 250 mm thick with single reinforcement and up to 120 mm thick with double reinforcement is compacted by surface vibrators, in slabs of greater thickness - deep.

Working joints when concreting flat joints can be arranged anywhere parallel to the smaller side of the slab. In ribbed slabs, when concreting parallel to the direction of the main beams, the working seam should be arranged within two middle quarters of the span of the run and slabs, and when concreting parallel to secondary beams, as well as individual beams, within the middle third of the beam span.

The surface of working joints in beams and slabs must be perpendicular to the direction of concreting. Therefore, in the planned places for a break in the concreting of the slabs, boards are installed on the edge, and in the beams - shields with holes for reinforcement.

Expansion joints in the ceilings are arranged on the consoles of the columns or by installing paired columns, ensuring free movement in the joint of the beams in the horizontal plane along the metal base sheet.

When concreting floors in multi-storey frame buildings, receiving platforms are arranged at the level of each floor, and conveyors and vibration chutes are installed inside the building to supply the concrete mixture after it has been lifted by a crane to the place of installation.

e. Vaults and arches

In the process of concreting coatings, ceilings and individual beams, it is not allowed to load them with concentrated loads exceeding the allowable ones specified in the project for the production of works.

Vaults and arches of small length are concreted in a collapsible small-piece or large-panel formwork supported by racks. For concreting arches and arches of great length, inventory rolling formwork mounted on a trolley is used. On the lower part of the formwork, lifting and lowering circles are installed, carrying a two-layer sheathing, consisting of boards laid with a gap of 10 mm, and waterproof plywood. The gap between the boards reduces the risk of formwork jamming in the vault when it swells. Raising and lowering the circles is carried out with the help of hoists and blocks, and the entire formwork moves along the rails with the help of a winch.

Vaults and arches of a small span should be concreted without: breaks simultaneously from both sides of the supports (heels) to the middle of the vault (castle), which ensures the preservation of the design form of the formwork. If there is a danger of formwork bulging at the vault lock during the concreting of the side parts, it is temporarily loaded.

Rolling formwork of the vault-shell: cross section; lengthwise cut; tightening the arch-diaphragm; retractable racks; hand hoists.

7. The process of concreting complex structures

a. Massive arches and vaults

Arches of great length are divided along the length into limited areas of concreting by working seams located perpendicular to the generatrix of the arch. Concrete is laid in limited areas in the same way as in vaults of short length, i.e. symmetrically from the heels to the castle.

Massive arches and vaults with a span of more than 15 m are concreted in strips parallel to the longitudinal axis of the vault. The laying of the concrete mixture in strips is also carried out symmetrically on both sides from the heels to the vault lock.

The gaps between the strips and sections of arches of great length are left approximately 300-500 mm wide and concreted with a rigid concrete mixture 5-7 days after the concreting of the strips and sections is completed, i.e. when the main concrete laying occurs.

With steep arches, the sections at the supports are concreted in a double-sided formwork, and the second (upper) formwork is installed with separate panels along the concreting.

The concrete mixture is compacted in massive arches and vaults with internal vibrators with a flexible or rigid shaft, depending on the degree of reinforcement, in thin-walled vaults - with surface vibrators. The tightening of vaults and arches with tensioners should be concreted after tightening these devices and turning the coatings around. Rigid puffs without tensioning devices are allowed to be concreted simultaneously with the concreting of the coating.

b. Tunnels and pipes

Tunnels and pipes are concreted in open trenches and underground in collapsible and retractable mobile formwork. The movable wooden formwork of the curvilinear walk-through tunnel with a cross section of up to 3 m consists of shields in the form of curved circles, sheathed with planed boards, waterproof plywood or sheet steel on a boardwalk. Racks supporting the working flooring are sewn to the circles of the outer shields. The internal formwork consists of two shields, the bottom of which rests on paired wedges, and the top is bolted in the vault lock.

The outer and inner formwork are connected to each other by tie bolts. The length of the shields is usually taken equal to 3 m, the weight of the formwork reaches 1.5 tons. The outer and inner formwork is moved using a winch along wooden rails. The outer formwork can also be moved to a new location by a crane. Rolling timber formwork, designed by Eng. V. B. Duba for concreting tunnels and rectangular collectors consists of sections 3.2 m long.

The internal formwork section consists of four U-shaped steel frames sheathed with planed boards, plywood or sheet steel. Each frame consists of two side posts and two: semi-crossbars connected to each other by three hinges. The outer frames of the formwork section have in the middle one sliding rack made of pipes, pulled together by screw jacks. The frames are supported by means of middle racks and retractable horizontal beams on a trolley moving along a rail track.

c. Vaults of tunnel structures

The outer formwork section consists of five frames with braces and detachable crossbars. Racks of frames from the inside are sheathed with boards. The outer formwork is fastened with inner bolts passed through removable girders. The formwork allows concreting tunnels with a width of 2100-2800 mm and a height of 1800-2200 mm: The mass of one formwork section reaches 3 tons.

The outer formwork is usually moved by crane. When stripping the formwork, the tie bolts are removed, the joints of the crossbars are disconnected: the frames of the outer formwork, after which the formwork is removed. To remove the inner formwork with the help of jacking devices available in the extreme racks, half-bars with ceiling shields are lowered.

Concreting of tunnels is carried out, as a rule, in two stages: first the bottom, and then the walls and ceilings (vault) of the tunnel.

The vaults of tunnel structures are concreted simultaneously on both sides from the heels to the castle with radial layers. The castle is concreted in inclined layers along the vault, while the formwork is laid as the concrete is poured in short sections - from circle to circle.

In powerful vaults of tunnel structures, arranged working seams should be radial. The desired direction of the surfaces of the seams is ensured by the installation of formwork: shields. Before concreting the castle, the cement film from the surface: the concrete must be removed.

d. Tunnel finishes

Tunnel finishes are advisable to be concreted in parallel with the tunneling, since in this case the total time for constructing the tunnel is reduced. However, with small cross-sectional dimensions of the tunnel, due to cramped conditions, the finish is erected at the end of the tunneling of the entire tunnel or individual sections between intermediate faces.

Tunnel lining is concreted either continuously over the entire cross section of the working, or in parts in the following sequence: tunnel tray, vault and walls, or vice versa.

For the formwork, the concrete mixture is fed from the end or through hatches in the formwork using concrete pumps or pneumatic blowers. In the side walls and the tunnel tray, the concrete mixture can also be fed by tipping trolleys using distribution chutes.

The concrete mixture is compacted layer by layer with deep vibrators through the windows in the formwork or with external vibrators attached to the formwork.

If the walls of the tunnel finish are concreted after the vault (the “supported vault” method), then before concreting, the formwork from the lower surface of the vault feet is removed and the surface is thoroughly cleaned. The walls are concreted in horizontal layers with the simultaneous build-up of the formwork to a mark less than the mark of the bottom of the heel of the vault by up to 400 mm. The space between the fifth arch and the adjoining wall is filled with a rigid concrete mixture and carefully compacted. Previously, pipes are laid at the junction for the subsequent injection of cement mortar.