Nowadays, a variety of building materials are used, both known from ancient times, and recently appeared. Hollow walls made of reinforced concrete began to be erected in the twentieth century. At first concrete appeared, but in Russia and England at the same time it was invented by two people who did not even know each other. This happened at the beginning of the 19th century.

Reinforced concrete was not created at all by a builder, engineer, constructor or architect. A simple French gardener in 1867 made concrete instead of wooden flower tubs by placing wire in concrete.

Wall reinforcement technology

Steel wire or rods that are placed in concrete to increase its bending and tensile strength are called reinforcement. The word in Latin means "weapons."

Armed and steel-reinforced concrete (more precisely, reinforced concrete) is a completely new material in which the components have high adhesion strength. Properly executed technology for reinforcing walls will make them strong for many years. For example: a steel rod with a diameter of 1.2 cm, immersed in concrete 30 cm, can be pulled out of concrete, with a force of about 400 kg. This adherence is not affected by temperature changes (both in steel and concrete, the thermal expansion coefficients are almost the same).

In reinforced concrete, each component does its job: the tensile load is steel, and the concrete is compressive. And if steel equips concrete, then concrete protects steel from corrosion and strong heating, which allows reinforced concrete to withstand strong fires. Therefore, wall reinforcement in construction is used very often. Appearing hair cracks are inevitable at ultimate loads, but these cracks are not critical either from the point of view of material strength, or from the point of view of steel resistance to corrosion.

In construction practice, such reinforced concrete products: concrete beams   over door and window openings, floor slabs, panels made of reinforced concrete, beam beams, crossbars of shop buildings in industrial buildings, monolithic walls, etc.

For better adhesion, steel reinforcement has a relief surface, various notches are applied to it.Reinforcement of monolithic walls will be much better and stronger when connecting the reinforcing cage into one welded structure.

Not always the materials from which these or other structures are erected, endure the maximum loads. Therefore, wall reinforcement can be made with fiberglass mesh. Covered with a layer of plaster, it also participates in the thermal insulation of the structure. Thus, reinforcing monolithic walls is one of the important steps in the construction of houses.

Cast-in-place retaining walls

Monolithic reinforced concrete is a very successful and economical material for creating the following structures:

• sexes;
• overlappings;
• stairs
• roofing;
• walls, including retaining ones.

The retaining wall is being erected on those slopes where staircases and platforms are designed, since its direct purpose is to strengthen inclined sections of the landscape and to connect various sections with a contrasting relief. They keep the soil from slipping. Such hollow walls should not only be solid engineering structures, but also fit into the landscape, not disfiguring it, but emphasizing the originality and participating in the formation of the overall landscape composition.

Retaining walls are made of various materials, but reinforced concrete is one of the most successful solutions, since when using it there is no need to make a very deep trench under the foundation. For a retaining wall made of reinforced concrete, a depth of 15-20 cm is sufficient. Also, due to the high strength of reinforced concrete, the retaining structure fully performs its function at a thickness of 10 cm. At the same time, the cost of the structure is also reduced due to the cheapening of the foundation. When installing monolithic reinforced concrete retaining walls, the result is a seamless design that not only looks good from an aesthetic point of view, but also is more durable and durable.

Retaining walls from monolithic reinforced concrete   casting method in the formwork, which is assembled, depending on the configuration, from boards or finished panels with a curved or broken configuration.

The first formwork walls are installed on the lower terrace: the finished panels are mounted to the wall of the dug trench, are interconnected, and outside they are equipped with supports, the purpose of which is to help the panels stand directly under the weight of the concrete mass.

In order for the retaining wall to be even, the inside of the formwork is sheathed with the appropriate material, roofing material or plywood.

When the first row of shields is already installed, you can put the second. When it is ready, it is strengthened with props, like the first, and at the top both rows are connected by bars.

Since we are talking about reinforced concrete, 2 rows of steel reinforcement in the form of a grid are placed between the shields inside the formwork, but it is allowed to use metal rods and even scraps of water pipes connected by wire.

When installing a monolithic beam, one must not forget about drainage. To drain ground water due to a monolithic wall of reinforced concrete, in the lowest part, 5 cm above the surface level, drainage pipes of plastic of the desired diameter are laid, the distance between them should be 1 m.

Wall formwork

Formwork is something without which the formation of monolithic structures, both concrete and reinforced concrete, is impossible. These structures, depending on the folding, are divided into 2 types:

• removable wall formwork;
• fixed formwork.

The most common formwork is removable, in a variety of variations. The name "removable" implies that the panels or boards of which the formwork of the walls is made are removed after the concrete has completely dried or its initial setting. Removable formwork is used not only to form the foundation - it is a full-fledged participant in the construction of monolithic walls and frames high-rise buildings, with its help spans of stairs and decor elements are made.

What is used for the manufacture of removable formwork:

• wood (boards, boards, etc.);
• plywood;
• steel sheet;
• aluminum (both sheet and form);
• polyvinyl chloride;
• various combinations of the above materials.

Regardless of the formwork material, there are a number of requirements that are the same for everyone:

1. The frame must have sufficient rigidity and be fixed in place.
2. The gaps between the structural elements should be minimal, for which you need to carefully adjust them. Cement milk may leak through the gaps, which will affect the quality of the finished concrete product.

Fixed wall formwork is a structure that, after pouring concrete and solidifying it, remains in the concrete mass as part of the overall structure. The materials used for its manufacture should be:

• heat insulating;
• strong (when pouring concrete, significant pressure forms on the formwork design);
• with low thermal conductivity (a monolithic concrete structure has high thermal conductivity, so concrete and formwork must form a single heat-insulating pair).

When using non-removable formwork, concrete is more reliable than in a removable structure, it is protected from various adverse external factors, primarily from moisture and extreme temperatures. This is a kind of multi-layered sandwich of formwork and concrete, where concrete provides strength and formwork - thermal insulation. In this case, a design scheme should be made indicating the proportions of the mixture.

Fixed wall formwork can also be constructed from cladding panels, which is very beneficial to achieve an aesthetic result. In private housebuilding, heat-insulating materials such as polystyrene foam and arbolite (material from a mixture of wood industry waste with cement mortar with the subsequent formation of hollow blocks) are very interesting for use as formwork.

The construction of hollow walls made of reinforced concrete

Due to the specificity of the design, hollow walls need to be made thicker than monolithic. To erect a low-rise building, you need to take hollow reinforced concrete walls with a thickness of 20 cm or more. A cavity, also called an air pocket, is located in the middle of the wall, occupying from 3 to 6 cm. This cavity is not left empty: the pocket is filled with foam or mineral wool.

The use of foam suggests the absence of additional waterproofing. This material is simply placed in the formwork with the already installed fittings and poured concrete mortar. When concrete hardens, the wall is obtained with great strength and retains heat well. Of the minuses, it can be noted that such a phenomenon as a cold bridge is inevitable in this design, but the plus is that when warming you can do with less.

When to mold hollow reinforced concrete walls   they use mineral wool as a heater, first they make formwork with a cavity in the middle, fittings are set in the formwork, then concrete is poured. After a day, the formwork is removed, and the structure rests for several days. Before filling the air pocket with mineral wool, the insulation is placed in moisture-resistant briquettes and already in this "sheathed" form it is mounted in the structure. The peculiarity of these hollow walls is that they need to be further strengthened with special columns.

Monolithic reinforced concrete is a popular building material that is used in the construction of expensive facilities. Found its application in the construction of shopping centers, buildings with a large number of floors and for the construction of copyright houses. Reinforced concrete structures are called monolithic if they are poured directly at the construction site. The popularity of monolithic housing construction is due to the low price, the strength of buildings and the ability to withstand heavy loads. Erection of monolithic reinforced concrete structures   can be carried out at any time of the year, which significantly reduces the time for construction of buildings and structures.

Monolithic reinforced concrete has the following advantages:

• resistance to fire;
• possibility of hand-made installation;
• minimal physical costs during the construction of reinforced concrete monolithic structures;
• there is no need for additional equipment and lifting mechanisms;
• resistant to corrosion;
• not amenable to oxidation;
• same technological process   for all cycles;
• installation speed;
• ability to withstand heavy loads;
• relatively low cost for monolithic housing construction;
• seismic stability of structures;
• after many years of operation, reinforced concrete material is able to increase its strength properties;
• durability;
• there is no need for a large number of machinery and equipment;
• light weight of the element, the construction of which does not require the construction of a heavy foundation;
• the possibility of applying any layout of the house;
• reduction of costs for finishing work due to the smooth surface of the material;
• reliability and durability.

disadvantages

The following disadvantages are distinguished:

• the need for the use of soundproofing material;
• there are difficulties in disassembling;
• the likelihood of cracking, peeling, and other similar deformations;
• the complexity of mounting the formwork;
• the need to hire skilled workers;
• the need for concrete heating during construction in the cold season;
• the need for laying insulating material;
• providing additional care during the period of solidification of the solution.

How thick should the wall be?

The thickness of the walls depends on the type of building. For buildings with one floor, a wall with a thickness of not more than twenty centimeters is chosen, for structures with a large number of floors, walls with a thickness of at least 55 centimeters will be required. Thus, we can conclude that the thickness of reinforced concrete walls for different buildings ranges from twenty to 55 centimeters.

The device of monolithic walls

  Tiled foundation and monolithic walls.

Installation of monolithic structures of various thicknesses is carried out directly at the construction site. First of all, formwork is installed, which is suitable for the size of the building.   Next, mount the reinforcing layer and begin concreting. The design of monoliths resembles construction, only in this case the elements are manufactured at the factory and delivered to the construction site, where they are assembled.

For the assembly of a prefabricated structure, the use of special equipment and lifting mechanisms will be required, which means additional financial costs and the need for an increased workforce. However, during the construction of the monolith, transportation of structural elements and the use of special equipment are not required, which significantly reduces construction costs.

Formwork

When erecting structures, installation of a solid formwork will be required, which will serve as protection for the outflow of the solution. Formwork is of the following types:

• block, which is used when casting objects without overlapping;
• collapsible, consisting of separate parts providing rigidity of the building;
• sliding, which is used in the construction of multi-storey buildings;
• pneumatic, has a breathable durable shell;
• fixed, used as a decor;
• tunnel, necessary in buildings with overlap.

The installation process of the formwork is simple and consists of digging a pit and installing shields. When installing the formwork, it is important to monitor the evenness of the structure and avoid deformations under the influence of large masses of concrete.

For reinforcement, a two-layer frame is inserted, which will prevent the deflection of the walls as a result of the load. When laying longitudinal reinforcement, a step of twenty centimeters is observed, with horizontal reinforcement - thirty-five centimeters. Reinforcing mesh is laid around the entire perimeter of the formwork.

Pouring

After installing the reinforcing layer, they begin to fill with concrete mortar, which is laid with a layer thickness of not more than fifty centimeters. The mixture is poured only after the previous layers have dried. During concreting, the solution is compacted with a vibrator, which will remove air bubbles. After pouring, the concrete mixture is left to dry until it reaches its maximum strength characteristics, it will take a month. After 30 days, they start insulating and finishing work.

Where are they used?

Monolithic reinforced concrete is used in the construction of residential buildings with bearing walls, public and industrial facilities, in buildings with two floors, as well as in the construction of frames with lightweight wall fencing, partitions made of high quality materials, which contribute to reducing the total mass of the building. In the construction of industrial structures, namely in the construction of stadiums, large workshops, exhibition halls. Monolithic reinforced concrete is often used, if necessary, to strengthen the foundation, floors, walls and columns.

Conclusion

The use of monolithic reinforced concrete structures have advantageous aspects with respect to other building materials. Its wide scope makes reinforced concrete monolith a popular element of buildings and structures.

However, when choosing a material, it is important to build on not only its positive qualities, but also pay attention to the shortcomings, which can play a large role in the construction of monolithic structures.

The process of erecting foundations and walls from reinforced concrete includes breaking down the axes of foundations, formwork, assembling and installing reinforcement, and concreting the foundation.

The choice of technology for the construction of foundations from monolithic reinforced concrete depends on the structural solutions of foundations and buildings, as well as on the available technological equipment and mechanisms.

The breakdown of the axes of foundations from monolithic reinforced concrete is carried out in the same way as in the construction of prefabricated foundations.

The complexity and cost of the device monolithic foundations performed in the formwork, largely depend on the surface module of the base M. With the increase in surface modulus increases the complexity of all processes, especially formwork.

The choice of formwork type depends on the type of concrete structures and their repeatability and is based on feasibility studies for possible options. The determining indicators are the cost of materials and labor, as well as the cost of one turn of formwork.

The study of the consumption of materials, the complexity of T0 and the cost of various types of formwork depending on the turnover of n0 clearly shows the effectiveness of combined inventory and metal formwork with a large turnover.

Inventory formwork is wooden, metal and combined. The use of inventory formwork allows to reduce labor costs for formwork by 1.5-2 times and reduce the consumption of materials.

Formwork can be made of separate panels, enlarged spatial blocks, panels and reinforcement blocks.

The formwork from individual panels is used with a complex geometric shape of the foundation and with a small repeatability of the types of foundations. Collapsible paneling wooden formwork can be made of small and large panels

The formwork of small panels on stitched slats is used when arranging small and medium-sized tape and columnar foundations.

The formwork panels are fixed to the ribs with nails and bolts or strips and pins. For the perceived lateral pressure of the concrete mixture, the shields are fixed with wire twists or bolts. On the formwork assembled in the block, the middle of the box is marked, on top of which the rails are nailed crosswise, so that the edges of the rails are located along the axes. The assembled unit is served by a crane to the installation site and the rails are combined with the tensioned axles. After alignment, the formwork is fixed, and the slats are removed.

With the device formwork of high stepped foundations, the installation of overlying formwork blocks is carried out similarly.

The formwork of small panels is set manually by individual panels. Its turnover is not more than 5-7 times.

At large sizes   of foundations and walls, collapsible shield panel wooden formwork is assembled from large panels at the site of the foundation. The formwork is fastened with struts, contractions and bolt ties.

The panels of the combined formwork UKO-67 of the design TsNIIOMTP consist of a steel frame welded from corners and a deck of boards. Shields are fastened with quick-release couplings. When designing panels for combined formwork, a module of 600 mm was adopted.

Inventory combined formwork of the UKO-67 series is used when concreting small and medium foundations. The formwork kit includes: main panels of eight sizes, corner panels of two sizes, contractions of four sizes, as well as mounting corners, supporting trusses, inventory for assembling panels. The turnover is 100 times.

In the construction of monolithic foundations, formwork of the USO-67, "Monolith-72" series and other types are also used.

With a large repeatability of foundations of small volume and simple shape, inventory metal block forms are used, which are installed in place by a crane.

Block forms are made one-piece, the formwork of which is carried out entirely at an early age of the design (up to 24 hours), and split, dismantled by the elements.

The Uralalyuminstroy trust used concrete foundations for concreting the foundations, which were assembled from spatial blocks or large panels. The FM-2 formwork had four ledges, each of which was assembled from four panels, the stiffening ribs of which were made of angular steel with a section of 50X X50X6, and the deck was made of sheet steel with a thickness of 8 mm. In the shelves of the corners, holes were drilled for attaching the shields to each other. The spatial block was assembled in the workshop and transported to the installation site in finished form. After concreting, the block is not dismantled, but assembled, it is lifted by a crane, having previously torn it off from concrete with the help of four jacks installed in the lower corners of the block.

The design of the formwork FM-12 is designed for foundations of high height. It consists of two ledges and a pillar box with ledges for rand beams. The lower two ledges are made similar to the formwork FM-2. The upper box consists of four shields, which are bolted together. Formwork at the facility is collected using a crane. The large height of the column and the presence of two protrusions do not allow to remove the formwork without disassembling it, so it is disassembled into separate panels.

During the construction of one of the shops of the metallurgical plant during the construction of stand-alone foundations, formwork was used, assembled from 2-3 spatial blocks. Such formwork having a total height of up to 2.5 m was removed from the foundation in assembled form. Formwork 3-5 m high was removed in parts. First, the fasteners between the lower and upper blocks were removed. Full disassembly    the upper block was not done. Before lifting it with a crane bolted connections between the shields forming the block, weakened. The lower block was removed entirely without disassembly.

Formwork blocks were made of steel panels, which were fastened with bolts. The stiffeners of the shields were made of angular steel, the cross section of which was selected depending on the load. To increase the rigidity of the panels, stiffeners made of strip steel are welded from the outside to the sheet.

Transforming block forms are also used, which change their size and shape by expanding the form, followed by fixing the elements with special devices.

In the practice of construction, in some cases, fixed formwork made of flat and spatial reinforced concrete elements finds application. Such formwork can be used in the construction of columnar foundations, when, according to the production conditions, it is difficult to dismantle the formwork or it is necessary to quickly backfill the pits. The stepped part of the foundations can be performed in conventional or fixed formwork.

When erecting columnar foundations up to 5 m high, flat slabs 60-90 mm thick are used. The formwork of the lower part of the stepped foundation is assembled from flat plates, which are installed on concrete preparation   by welding embedded parts in the corners. Then the reinforcing mesh is laid and the armature frame of the column is mounted, after which the plates of the next steps and the column are mounted.

When arranging the formwork, it is necessary to ensure its stability and immutability of the geometric shape in the process of concreting the foundation. For this, racks and others

the supporting elements of the formwork are installed on a reliable foundation, and the racks are also fixed with horizontal and diagonal stitches. The correctness of the formwork device must be checked before the installation of the reinforcement.

Reducing the complexity of formwork can be achieved by unifying and reducing the number of standard sizes of foundations; due to the use of multi-turnable formwork, thanks to the widespread use of mechanized installation of formwork from reinforced elements. With great repeatability of the same type of foundations, the formwork is assembled once and after concreting one foundation is transferred to the next. When using block forms, the level of mechanization of formwork is 90-95%.

Separate foundations are reinforced with reinforcement of classes A-I, A-II, A-III, B-I diameter   8-22 mm.

Installation of fittings is performed by enlarged elements in the form of grids and spatial frames, which are fed to the installation site by self-propelled cranes using special traverses. Self-balancing slings are used for the installation of foundation frames and large-pillar columns with a height of more than 2 m.

The bottom reinforcing mesh of the foundation is installed before the formwork is installed. The reinforcing frame of the column head can be mounted both before and after the formwork installation.

Separate rods of nets and frames at the place of their installation should be joined by electroslag or bath welding.

Labor costs for the construction of 1 m3 of foundations from monolithic reinforced concrete is 3-5 people- hours. The most time-consuming are formwork and reinforcement work. Reducing the complexity of the construction of foundations can be achieved through the use of reinforcing-formwork blocks with embedded parts welded to them.

In the construction of strip foundations, various schemes of complex mechanization are used.

Reinforcement begins with laying reinforcing mesh at the bottom of the foundation. To create a protective layer of concrete, fixators are installed in a checkerboard pattern with a step of 1 m. Then reinforcing frames are installed and fixed using clamps. Temporary fastenings from the frames are removed after welding to the mesh of the sole of the foundation. Then make the installation of formwork.

The formwork of strip foundations of constant cross-section is collected depending on the height of the foundation. At a height of 2-2.5 m, the shields are installed sequentially vertically, connecting them together on locks, and temporarily unfastened with inventory struts. The contractions are attached to them, and then the formwork planes are connected with screeds. Shields of the second tier are fixed on the lower formwork after straightening and placed horizontally.

With a foundation height of more than 2.5 m, the assembly of the formwork begins with the installation of the frame from the contractions. The mounting stability of vertically placed contractions is ensured at the beginning of the assembly using struts from telescopic racks, and then due to horizontal ties made from the same contractions. The struts are installed after 3-4 m. Above the level of the concrete foundation, the contractions are connected with screeds and secured with spacers, which ensures the spatial stability of the whole frame. Shields are attached to contractions and placed horizontally. They can be installed on the entire height of the foundation on both sides or on one side to part of the height, facilitating the production of reinforcing and concrete work.

Small-panel or large-panel formwork of strip foundations of variable cross-section is also installed according to two schemes. With small sizes of foundations, the formwork of the lower part of the foundation is first assembled. The upper part of the formwork can be installed after concreting the lower part of the foundation.

The second scheme provides for the suspension of the upper part of the formwork for contractions to the portals. Reinforcing mesh stack before installing screeds that connect the formwork plane.

Before laying the concrete mix, carefully prepare the soil base. Loose, organic and silty soils should be removed. Enumeration of the soil should be filled with compacted sand or gravel. Weathering products of rocky bases are also subject to removal.

For the construction of foundations, heavy concrete of classes B15-VZO is used. The mobility of the concrete mixture should correspond to the cone draft for unreinforced and low-reinforced foundations of 10-30 mm, when moving by conveyor belts, not higher than 60 mm, when transporting concrete pumps 50-80 mm.

The largest grain size of coarse aggregate in concrete mix should not exceed 1/3 of the smallest size of the structure, and in reinforced structures, 3/4 of the smallest distance in the light between the reinforcement bars.

To achieve solidity reinforced concrete foundations    concreting must be carried out continuously, avoiding the formation of seams.

The concrete mixture is laid in horizontal layers with a thickness of 20-50 cm, and the layer thickness should not exceed 1.25 of the length of the working part of the vibrator. Each subsequent layer of concrete mix is \u200b\u200blaid after compaction of the previous one and, as a rule, before it begins to set. To obtain a uniform degree of compaction, it is necessary to observe the distances between each setting of the vibrator, which should not exceed 1.5 of the radius of the vibrator. When compacting the layer, the depth vibrator must penetrate 10-15 cm into the previously laid layer, as a result of which a more reliable coupling of the concrete layers is achieved.

The concrete mix in low-reinforced foundations is compacted with depth vibrators S-825 and S-826, as well as vibration packages. With dense reinforcement, vibrators S-727, S-800 or others with a flexible shaft are used.

When concreting columnar foundations from the side of the cross-section of the column of 0.4-0.8 m and in the absence of intersecting collars, the height of free fall of the concrete mixture is allowed up to 5 m, with side sizes of 0.8-3 m. With a larger height of the foundation, trunks are used.

Foundations with pillars reinforced with intersecting collars are continuously concreted with sections 1.5–2 m high with mixture feeding through windows arranged in the side walls of the formwork.

Concreting of columnar foundations for columns is carried out in two or three stages.

In two stages, small (10-15 m3) foundations are concreted. Initially, the step formwork is filled. Compact the concrete mixture with a vibrator. Then, the concrete mix is \u200b\u200bcontinued to be placed in the window-sill up to the bottom of the glass under the column or the bottom of the anchor bolts, and in the second stage, the top of the column is concreted after installing the glass-forming element of the glass or anchor bolts. With three-stage concreting of large foundations, the concrete mixture is laid separately in the lower steps and the armrest.

When concreting the foundation immediately to the entire height in the transition zone of the stepped part into the column, the formation of shrinkage cracks is possible, which can reduce the bearing capacity of the foundation. To prevent the formation of shrinkage cracks at the end of the concreting steps take a technological break to gain strength and concrete shrinkage. Then the column is concreted.

The glass of foundations is concreted below the design level, so that later, when installing the column, it is possible to make a gravy under the design mark of the column.

Anchor bolts are installed before concreting using conductors fixed to the formwork or frame remaining in the concrete mass. The conductor design should exclude the possibility of deviation of the bolts from the design position during concreting.

When arranging foundations, the method of formworkless concreting is also used, which consists in the fact that in building conditions reinforcing and formwork blocks with fixed formwork are manufactured. The finished block is installed by crane in the design position and then filled with concrete mixture. This method can be used for the installation of columns and walls. underground facilities. The reinforcing block with embedded parts and latches of the protective layer fixed to it is delivered to a special stand located at the installation site. The stand is a platform lined with reinforced concrete slabs, on which a metal bath is installed with a height and dimensions in plan, slightly larger than the side face of the block. The reinforcing unit is installed with a tap in the bathtub and with the help of vibrators is embedded into concrete until the latches of the protective layer touch the surface of the stand. After the concrete has gained the necessary strength, the block is removed from the bath and immersed in the concrete layer with the following face. The finished block is installed in the design position, backfill and concreted.

Strip foundations are concreted, depending on the design features, in one, two and three stages.

One-stage layer-by-layer concreting is used when arranging strip foundations of rectangular cross-section at random or variable cross-section with a cross-sectional area of \u200b\u200bless than 3 m2. Strip foundations with steps with a cross-sectional area of \u200b\u200bmore than 3 m2 are concreted in two stages, first the steps, and then the wall. In three stages, the strip foundations are concreted with the kneecaps used in frame buildings.

The features of concreting the walls of the underground part of the building depend on the thickness and height of the walls, as well as the type of formwork.

When concreting walls, the following types of formwork are used: a unified panel board folding collapsible, lifting and collapsible and other types of formwork.

Collapsible panel formwork is installed in two stages: first, on one side, to the entire height of the wall, and after installing the reinforcement, on the other. At high heights and wall thicknesses, the formwork of the second side is set in layers in the process of concreting. If the formwork is installed to the entire height of the wall, then a hole for supplying the concrete mixture is provided in the formwork. Wall formwork with a thickness of more than 0.5 m can be erected to the entire height of the wall with the mixture being fed from above using trunks.

To ensure stability, the wall formwork is fastened with struts or braces, coupling bolts and wire ties. Spacers installed inside the formwork are removed during the concreting of the walls. When tier concreting the walls, the panels of the second and third tiers can rely on lower ones or on supports after dismantling the panels of the first tier. Supports for panels of the second and third tiers are assembled from telescopic or trellised racks.

The technology of concreting walls depends on the design of the formwork. A tiered laying of concrete mix to a height of 400-600 mm may be provided. The concreting cycle works are performed in the following order: first, scaffolding is installed, then the concreting working seam is processed, reinforcement is installed, and then the formwork is moved from the lower tier to the upper one. The cycle is completed by laying and compacting the concrete mixture and keeping the concrete in the formwork.

When concreting walls in collapsible formwork, the height of sections performed without interruption should not exceed 3 m. With a greater height of wall sections concreted without working joints, it is necessary to establish breaks of at least 40 minutes, but not more than 2 hours, to precipitate the concrete mixture and preventing the formation of sedimentary cracks. With a wall length of more than 20 m, it is divided into sections of 7-10 m and a wooden distribution partition is installed at the border of the sections. The concrete mixture is fed into the formwork at several points along the length of the site. If an opening is provided in the wall, concreting should be interrupted at the level of the upper edge of the opening or a working seam should be made in this place. The resulting working seams must be carefully processed before concreting.

The supply of concrete mix is \u200b\u200bcarried out by tubs, vibratory gutters, concrete pumps. With a wall height of more than 3 m, trunks are used. The concrete mixture is laid continuously with a thickness of 0.3-0.5 m with compulsory compaction with vibrators. In the process of concreting, they monitor the position of the reinforcement and prevent its displacement from the design position. The next highest section is concreted after a concrete strength of at least 0.15 MPa. In thin and densely reinforced walls, more mobile concrete mixtures (6-10 cm) are laid.

Concrete mixture in the formwork of foundations can be supplied by cranes, pavers and concrete pumps. The most widespread was the laying of concrete in tubs using cranes.

Delivery of concrete mix to the place of laying is carried out by concrete trucks and concrete mixer trucks. To receive the concrete mixture, two wooden floors with a size of 2.4X3.3 m are laid in the crane's coverage area. Swivel buckets are mounted on the flooring one next to the other. For concreting detached foundations of small volume and walls, it is recommended to use tubs with a capacity of 0.5-1 m3. For foundations of medium volumes, it is recommended to use tubs with a capacity of 1-2 m3. The use of rotary bucket eliminates the need for the construction and dismantling of overpasses and improves the use of crane equipment. The capacity of the cranes for the supply of concrete mix in tubs is 25-100 m3 per shift.

It is advisable to use tower cranes when concreting foundations of significant volume and concreting rates of more than 50 m3 per shift. It is advisable to use self-propelled jib full-turn cranes for concreting freestanding foundations at concreting rates of 25-100 m3 per shift. The distance between the trenches and pits makes it possible to arrange temporary roads for the movement of self-propelled jib cranes.

An example of the construction of foundations for columns of an industrial building using a self-propelled jib crane. Work on the installation of foundations was organized as follows. Since the distance between the axes of the foundations was 6 m, then excavation   performed in the form of a common trench. After the crushed stone preparation was arranged with a K-161 crane, reinforcing nets were laid, and then shuttering block forms of one or more blocks. Inventory bridges and platforms were installed along the perimeter of the top of the foundations. One end of the bridge rested on the edge of the pit, and the other on the upper block of the formwork. Brackets were attached to the upper part of the formwork, on which flooring boards were laid, forming scaffolds.

The platform and the bridge were fenced. After the installation of the sites, reinforcing frames of the columns were installed.

Concreting was carried out using a K-161 crane. The concrete mix was discharged from dump trucks into three vibratory tubs with a capacity of 0.8 m3. Compaction of the concrete mixture was performed by deep vibrators.

Anchor bolts were installed in the upper part of the sub-column for fastening steel columns using inventory conductors.

The inventory conductor was welded from pipes with a diameter of 60 mm and had movable clamps for securing the bolts and extendable racks connected to the formwork block. Anchor bolts were mounted on movable clamps using nuts. In the horizontal plane, the bolts were verified with movable clamps, and in the vertical, with the help of sliding racks, along which the conductor was lowered or raised.

The formwork was dismantled 4-5 hours after the concreting of the foundation. This was achieved by using hard concrete mixtures (cone sediment 2-4 cm). When dismantling the shuttering block forms were previously torn off with jacks.

Concreting of foundations was carried out in two shifts, a link of four people worked in each shift: a crane operator, two installers-concrete workers of the 3-4th category and a slinger.

Concrete installers in the first shift prepared the base for the installation of formwork, dismantled it from the concrete foundation and mounted the formwork. Slinger hooked parts, cleaned and lubricated molds, and also participated in the assembly of formwork and preparation of the base. The second link, having the same composition of workers, laid the concrete mix in the second shift. Slinger accepted concrete mixture and hooked tubs with the mixture. Two concrete installers laid and compacted the concrete mixture using vibrators. They installed anchor bolts.

With the full organization of the construction of foundations, the production per concrete worker for laying concrete mixture amounted to 5-7 m3 / shift.

At higher rates of concreting (50-150 m3 per shift), it is advisable to use pavers and vibrotransport equipment

Self-propelled paver is a conveyor belt mounted on a tractor or excavator and moving on top of the pit. To receive the concrete mix, the paver is equipped with a receiving vibratory hopper, which delivers the concrete mixture to the conveyor belt through the metering shutter. When concreting foundations and walls located below the surface of the earth, vibratory gutters can be used to transport the concrete mixture. In addition to vibratory chutes, a vibratory hopper, intermediate funnels, supports and pendants for vibratory chutes are used.

When using a concrete pump truck, the concrete mix from the concrete mixer is fed through the discharge funnel to the concrete hopper of the concrete pump, from which it goes to the place of laying along the concrete pipeline of the boom. The end link of the concrete pipeline is equipped with a flexible sleeve that provides the supply of concrete mix to each foundation. The transportation of concrete mix through pipelines should be continuous so that it does not set and thicken.

The main advantages of conveying concrete mixture through pipes because of their flexibility and maneuverability are high productivity and the ability to supply mixture over long distances (up to 400 m).

Concrete work should be organized so that the largest amount of work can be performed from one parking lot, using the main concrete pipeline without disassembling it. The concrete pipeline must be mounted in such a way as to ensure the supply of concrete mix from the most distant foundations with a constant approach to the foundations located near the concrete pump installation. When the concrete mixture is fed to a high height, the concrete pump is connected to the main concrete pipeline.

Large-panel formwork of foundations and walls is removed by cranes using lever devices. Formwork turnover depends on the quality of the formwork. If the block formwork is made inseparable for concreting small foundations (4-6 m3) in volume, then it is dismantled after concrete reaches a strength of 1 -1.5 MPa.

At the end of concreting of foundations and walls, executive surveys are performed at the intersection points of the axes and after 5-10 m in the intervals between the axes. Marks and actual deviations of the axes of the foundations and walls from the design position in the plan are applied to the executive circuit.

When installing foundations in the winter, the following methods of curing concrete can be used: the thermos method, the thermos method using concrete hardening accelerators, the use of anti-frost additives, preliminary electric heating, electric heating, the use of heating formwork and other methods.

The thermos method is to use the heat released during the hydration of cement grains, as well as the heat introduced into the concrete at the time of its preparation (heating water and aggregates).

In order to accelerate the hardening of concrete, hardening additives are introduced into its composition: sodium sulfate, calcium chloride, calcium nitrate.

Steam heating is carried out using steam shirts, capillary formwork, steam baths or pipes.

Pre-heating the concrete mixture is its additional heating to the maximum possible temperature before laying into the formwork. The use of preliminary electric heating allows to increase the cooling period of the concrete structure, and therefore, to provide higher strength of concrete at the time of its freezing compared to the method of thermos.

The essence of electrode heating is that an alternating electric current passing between the electrodes through a concrete mixture having electrical resistance generates heat, which heats the concrete during the period of gaining strength.

Infrared heating is based on the use of thermal energy of infrared radiation, which is fed onto exposed or formwork surfaces of foundations or walls.

The construction of monolithic foundations and walls should be carried out in a complex mechanized way, in which all labor processes are performed using specially selected sets of machines. At the same time, continuity of production and the required rate of work should be ensured.

When laying the foundations, three streams can be distinguished: reinforcement, formwork installation and concreting.

The leading process in the construction of foundations is concreting, so the number of workers in each stream is determined by the leading stream so that work in all flows goes in the same rhythm.

To organize in-line work, foundations and walls are divided into grips, which can be span, part of the span or foundations along one axis. Each link, having completed work on one gripper, moves to another, and the link of the next stream takes its place.

The process of concreting foundations includes the processes of transportation, supply, reception, distribution and compaction of concrete. A set of concreting machines is selected based on the required type of concrete laying, taking into account the delivery conditions of the concrete mixture and the design features of the foundations and walls of the underground part of the building.

In accordance with the productivity of the lead stream, sets of machines for private flows are selected for the installation of formwork, reinforcement, and the preparation of concrete mix.

It is advisable to select a system of machines so that with the help of a host machine, such as a crane, perform the largest number of operations in the host and in private flows. When calculating the flow, the timing of the dismantling of foundations should be taken into account, since they determine the total duration of work and the required number of sets of formwork. To reduce the time of formwork, methods of accelerated hardening of concrete are used, for example, preliminary electric heating of concrete mix, the introduction of additives, thermoactive formwork, etc.

In technological standards, PPR for the construction of monolithic foundations gives the development of formwork inventory boards, the installation location of connecting locks and fasteners, as well as additional elements. Schedules of the movement of formwork sets as concrete is concreted and concrete is held in the foundations are given. The diagrams indicate the installation locations of lifting mechanisms, pavers, concrete pumps, material storage, traffic patterns of mechanisms and vehicles delivering concrete mix.

To determine the need for material and technical resources, you can use the data given in table. 6.1, which provides several types of leading machines and concreting options.

Traditional constructions of foundations from monolithic reinforced concrete have increased material consumption, as they are massive. The strength properties of reinforced concrete are not fully used, which is one of the main disadvantages. Reducing the volume of foundations can be achieved by the device in the body of the foundation of voids, as well as the use of thin-walled structures. IN monolithic foundations   for columns, the concrete savings during the formation of voids increase with increasing depth of the foundation: at a depth of 1.5-2 m, 3-7% of concrete is saved; with a depth of 2-4 m - 5-15% and with a depth of more than 4 m - 20% or more.

Analysis of design solutions for the foundations of industrial buildings shows a significant number of sizes for each object. Sometimes for each size there are 3-5 foundations. The variety of types of foundations makes it difficult to typify the technology of their construction and does not contribute to increasing labor productivity.

Foreword

Simplified technology for the construction of monolithic walls is as follows: in a special form formwork, which has the contours of the future structure, install iron reinforcement and pour concrete mixture. When it freezes, the formwork elements are disassembled and transferred to the next level (floor).

Necessary tools and materials

FittingsConcrete mixerBulgarianBucketWaterNailsNail clipperPlaned boardExpanded clayShovelMaster OKSandRuberoidRouletteScrewsSquareExtensionLevelCement

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Contents

A monolithic house is the strongest building that can withstand even small fluctuations in the soil. A couple of decades ago, it was decided to apply the technology of monolithic walls only for serious industrial facilities and multi-storey residential buildings. But now more and more often the construction of monolithic walls is practiced in private suburban construction.

Simplified technology for the construction of monolithic walls is as follows: in a special form formwork, which has the contours of the future structure, install iron reinforcement and pour concrete mixture. When it freezes, the formwork elements are disassembled and transferred to the next level (floor). Brick can also play the role of formwork, this allows you to get a wall whose surface does not need further decoration or cladding. In addition, when installing monolithic walls, the formwork can be combined: for the outer surface of the wall, brick, and inside-removable, from metal or wooden panels. True, this somewhat reduces the bearing capacity of the wall, but for the construction of one-, two- or even three-story country houses this is the best option.

The walls of low-rise residential buildings do not experience heavy load. Therefore, light concrete is usually used as a concrete mixture using the technology of building monolithic walls. Such mixtures are made of filler: slag, expanded clay, polystyrene foam, brick fight, sawdust and straw using cement, and sometimes even lime, clay and gypsum as a binder. But usually they are used as additives, which reduces cement consumption and makes the mixture more plastic and convenient for masonry. Thanks to the fillers, lightweight concrete is much better in its heat-shielding qualities than a solid brick, and at a cost much cheaper than it. Walls made of lightweight concrete are relatively durable, but have a not very presentable appearance and need good moisture protection (that is, they require further).

Wall thickness of a monolithic house and formwork

The wall thickness of a monolithic house largely depends on the calculated outdoor temperature. For a wall with a thickness of 250 mm, it is -20 ° C, 350 mm -30 ° C and 450 mm -40 ° C.

For convenience, when performing work, the formwork elements are made 40-60 cm high. These can be chipboard sheets, metal and wooden panels. If necessary, inside the shields are covered with a synthetic film or glassine. In the process, the boards are pressed against the racks installed on both sides of the wall being erected to its entire height. The distance between adjacent racks should not exceed 1.5 m. Each pair of racks located one against the other is pulled together by wire strands, and temporary struts are installed inside the formwork.

Today, in suburban housing construction technology for the construction of monolithic concrete walls provides for the use of fixed formwork. The construction of a monolithic wall is actually a combination of monolithic housing construction and masonry from hollow blocks. In this case, the blocks perform the function of formwork, however, unlike a collapsible design, they are not dismantled when the concrete mixture reaches the required strength, but become part of the wall. As a result, this technology can significantly accelerate the pace of wall construction, without compromising on their quality. Moreover, the blocks playing the role of formwork can be made of heat-insulating material, for example polystyrene foam (polystyrene), which allows simultaneously with the construction of the wall to solve the problem of its insulation.

Typically, blocks for fixed formwork are two plates interconnected by special ties. The main element of the block system is a basic wall module of several sizes.

In addition, the system usually includes corner blocks, end caps, as well as additional elements, such as a block with a protrusion for masonry, conical block, etc.

The construction of monolithic walls of the house

The construction of monolithic walls of the house begins with the installation of corner blocks, a cord is stretched between them, along which the blocks of the row are laid out. At the same time, they are not fastened together with a solution (as is usually done when laying walls from traditional concrete blocks or bricks) - they are kept from displacement by grooves and ridges on the end planes.

As reinforcing elements, vertical and horizontal bars of reinforcement with a diameter of 8-10 mm are used. Then they put the second row of blocks, putting them on the vertical reinforcement protruding from the bottom row, and again lay the longitudinal reinforcement and connect it to the vertical rods with a thin wire. Ligation is done by shifting the upper row by half the block. After 3-4 rows are collected, the inner space of the blocks is filled with one of the above-described mixture of light concrete, which after solidification forms a monolithic wall. According to experts, walls using this method can be built extremely quickly and this does not require high qualifications.

Skeletons with walls of cast concrete   and reinforced concrete

Currently, it is becoming more widespread. monolithic technology   construction of buildings. The structural material in this case is reinforced concrete based on heavy concrete. A mandatory element of such a constructive solution is the formwork - the form-structure that forms the surface of the skeleton of the building. In construction practice, mainly two types of formwork are used - movable and sliding. Repositionable formwork can be used both in the form of separate panels, and in the form of volumetric elements. For low-rise construction, it is advisable to use formwork in the form of separate panels, and of small size. Sliding formwork is used for the construction of vertical elements of buildings with a height of usually tens of meters and is inappropriate for use in the construction of low-rise buildings. There is another type of formwork - pneumatic (inflatable), which is used only for thin-walled curved structures (arches and domes), the use of which in low-rise construction is very limited. At the same time, the main criterion for using this or that type of formwork will be its turnover, so the main formwork during the construction of the skeletons of low-rise buildings will, of course, be the small-panel formwork, which allows the most mobile to obtain a variety of structural forms.

When erecting the skeletons of low-rise buildings, the use of lightweight concrete based on expanded clay, perlite, agloporite and other porous aggregates is more appropriate in the form of small blocks, rather than in the form of a solid monolithic building element, which is confirmed by practice.

Monolithic technology assumes that with its help only the supporting part of the skeleton is erected, which then needs to be supplemented with layers of insulation and decoration.

For the erection of walls of various types of low-rise residential buildings - individual houses, cottages, villas, villas, etc., similar to them, the most appropriate is the use of light, manually assembled, removable shield formwork or small-sized fixed formwork.

Formwork of the first type includes panel formwork of modules based on durable waterproof five-layer plywood 21 mm thick, reinforced on both sides with a special cladding (laminate) and enclosed in metal frames from steel profiles based on galvanized or alloy steel. The frame of the panels can be made of aluminum profiles or using wooden panels.

Proven in practice, the maximum size of such a shield module is 2 640 x 750 mm with a mass of 61 kg, i.e. It can be mounted by two workers. Such shields are interconnected either using a bolt clamp, or special brackets. Such formwork allows it to be used for concreting both walls and columns, foundations and ceilings. The turnover of these shields is up to 300-400 times. Options for using such a formwork are shown in Fig. IV.25.

Reinforcement of the reinforced concrete part of the structures of low-rise buildings is most often undertaken for structural reasons. At the same time, the calculated reinforcement of the lintels and vertical faces of all openings, as well as the angles and intersections of walls and, of course, ceilings, is mandatory. Reinforcement is recommended to be made by welded frames and nets.

The minimum thickness of a monolithic reinforced concrete layer in the construction of low-rise buildings is 120 mm for walls and 150-160 mm for floors (from reinforcement conditions).

Concreting should be carried out only by moving plastic concrete mixtures manufactured centrally, which more reliably ensures their quality. The concrete grade used must not be lower than M300 (class B 25), based on the conditions that monolithic structures should be dismantled when concrete reaches a strength of about 10 MPa (100 kg / cm2). For M300 concrete, this strength occurs approximately three days after its laying under standard hardening conditions (temperature 15-18 ° C and humidity over 80%).

Using the so-called fixed formwork avoids waiting for the start time of formwork.

Fixed formwork is the second type of formwork in which the formwork remains in the concrete structure. This method is preferable when the repeated use of inventory formwork is excluded or when it is necessary to reduce the time of construction of the building.

Several variants of this type of formwork are known, in which slabs made of fiberboard, arbolite, DSP (cement-bonded particle boards) or other materials in which cement is an integral part, or bulk formwork elements based on various types of cement concrete - heavy concrete, fine-grained concrete are known , expanded clay concrete, etc.

Some types of fixed formwork, which are advisable to use in low-rise construction, are presented in Fig. IV.26.

When using plates or thick sheets of the listed materials, it must be borne in mind that they perform not only the role of forming elements, but also the role of a heat-insulating casing. Therefore, in the outer walls, the outer side of the formwork will always be thicker than the inner one due to thicker sheets (plates), and in cases necessary for thermotechnical reasons even with the use of foam plates (PSB-S).

Valves in such systems are installed in the same way as described above.

When using hollow volumetric concrete elements as permanent formwork, the voids contained in them should be used to create an additional heat-insulating layer or to place vertical reinforcement, if it is necessary for design or structural reasons. It is possible to fix an additional heat-insulating layer from the outside with the help of targeted anchors.

There is also a system of non-removable formwork based on polystyrene foam hollow elements, in which the supporting functions are performed by concreted middle parts of such elements, which are installed apart. In these systems, three types of elements are used: wall, lintel and special, necessary to ensure the support of the floor. This type of formwork is shown in Fig. IV.27.

It should be noted that the polystyrene sheath of such a formwork requires protection both from the external and internal sides in the form of plaster or cladding.

Due to the monolithic connection of all elements, the supporting frame of the building is characterized by a high degree of rigidity and stability. Foundations under monolithic houses   more often design tape from butobeton or from short bored piles with a monolithic grillage, the technology of which also includes elements cast concrete. For winter work, prefabricated foundation options are usually used. The basement of lightweight concrete walls is easier to carry out in the form of an additional coating of an atmosphere-resistant mortar or cladding with frost-resistant plates. The remaining surface of the external walls is protected by weather-resistant plaster with the addition of dyes or tiled with decorative tiles.

Local building materials for the walls of low-rise residential buildings are various soil masses based on clay or lime-cement bonding. Such material does not have high strength and is usually used for the construction of walls of one-story houses. Soil and mud walls have a relatively high thermal conductivity, so they are used for construction in southern climatic zones.

To reduce thermal conductivity and increase the strength of mud walls, a section of plant dry fibers is added to the clay mass. Such material is called adobe. Monolithic walls   from adobe, with proper use, serve for at least 25 years. The manufacture of adobe does not require the use of cement and lime, and the walls of adobe provide a favorable microclimate of the premises. For the design of residential buildings from adobe, it is necessary to know the basic structural requirements for walls of this material. The cornice part of the adobe walls should have a roof overhang of at least 45 cm, while admission of adobe outside the wall plane is not allowed, i.e. eaves overhang can be made only by removing the eaves boards of the roof (filly). The supporting part of the roof is designed only according to an undisturbed scheme, i.e. it is recommended to use a roof with hanging rafters. The use of a roof with lay-on rafters is possible provided that the wall beam (Mauerlat) is attached to the wooden joists, for example, with steel brackets (Fig. IV.28 b, 14).

In this case, the roof should have a slope that coincides with the direction of the floor beams. Mauerlat is made in the form of a flat wooden beam recessed into the wall material in the center of its cross section to evenly distribute the load from the roof. For the same purpose, floor beams rest on the wall in its center; a flat wooden beam is placed under their supporting part. In this case, the Mauerlat can be supported on the ends of the floor beams. Lintels above the openings are made of boards or wooden bars with crossbars. Between the jumper and the box of the opening leave a free gap, providing for the possibility of subsidence of the wall up to 10% of the height of the opening. The gap is filled with tarred tow. Spans of openings make no more than 2 m, and the width of the piers in the corners is at least 1.5 m. Unloading boards are installed at the bottom of the window openings, to which the windowsill and drain boards are attached. Unloading boards and Mauerlat are installed continuously around the entire perimeter of the walls, rigidly linking them in the corners. The base is made of weatherproof stone or other similar materials. The surface of the adobe wall is carefully protected from moisture.