Erection of walls on fixed formwork: technologies, communications, decoration

Recommendation points

• general description
• Technology value and technical challenges
• Block nomenclature
• Wall erection process
• Surface finishing and laying of communications

The technology of building walls, which will be discussed today, has been known for a long time, but undeservedly deprived of the attention of domestic specialists. At the same time, fixed formwork has a number of advantages and can pretend to be a technology that well combines heat-shielding and load-bearing functions..

general description

The first developments in the construction technology for permanent formwork in the form in which it is known now appeared in the Soviet state. Then it was a promising method for the rapid construction of housing infrastructure in regions that were actively assimilated in the needs of industry or fell victim to environmental disasters. Unfortunately, the weak development of the polymer materials industry did not allow the creation of a complete, integrated technology, and after all, the potential advantages would quite allow it to replace panel housing construction, which represents almost half of the communal housing stock in the CIS.

The essence of the technology is extremely simple: a shell of external walls made of light blocks is assembled on a concrete foundation. Their design ensures high-quality sealing of joints, while between the inner and outer walls of the shell, the space is not filled with anything except thin connecting bridges. As the shell is assembled, a reinforcing cage is knitted inside it, then the cavities are filled with concrete. As a result, a monolithic load-bearing core of the wall is formed, covered on both sides with a material with a low thermal conductivity..

Strictly speaking, insufficient production volumes of expanded polystyrene products were not the main obstacle to the widespread introduction of the technology, because the material of the permanent formwork can be both mineralized chips (Velox) and arbolite (Durisol). The main obstacle was the need for a complete technical re-equipment of construction sites and the training of a new generation of builders, which cannot be implemented in a short time. However, in private construction, fixed formwork has taken root very firmly..

Technology value and technical challenges

Strikingly, practically none of the apartment buildings built in the Soviet era meets the requirements of the modern standard SP 50.13330-2012, which sets the minimum value of heat transfer resistance for the walls of residential buildings, namely 2.1 m²* K / W. In the middle of the last century, the problems of energy saving were irrelevant, but now the construction technologies of those times have become irrelevant. Modern researchers are struggling with the task of creating a material that combines load-bearing and thermal insulation properties without compromise. But so far the most successful example of these developments remains autoclaved aerated concrete..

What can the fixed formwork offer in this regard? The total thickness of expanded polystyrene in most blocks is 120–130 mm, which corresponds to a heat transfer resistance of 3.25 m²* K / W. At the same time, from the outside, heat protection can be strengthened almost indefinitely: expanded polystyrene plates are firmly glued to the formwork without additional fixation.

Permanent formwork construction is characterized by a high speed of work. With the same external dimensions of the building, such walls allow you to gain about 5-7% of the useful internal area, and due to reliable thermal insulation, monolithic work can be carried out even in severe frost without using special concrete modifiers. All work is carried out without the use of heavy construction equipment, only scaffolding and mechanized concrete supply are required.

The technology also has a number of disadvantages, the most important of which is the inner wall covering with a layer of expanded polystyrene. Because of this, the thermal inertia of the premises is reduced to almost zero, for the preservation of which it is required to build internal partitions from solid bricks. Additional difficulties are caused by the laying of communications, in addition, the fire safety requirements oblige to use blocks only from PPS filled with carbon dioxide.

Block nomenclature

Structurally, the block of the fixed formwork consists of two PPS slabs connected by jumpers. The latter are of three types: full-bodied made of expanded polystyrene, spreader bars and plastic perforated partitions in the full height of the block. Blocks with lintels of the third type are most suitable for construction, they provide high-quality support for the reinforcement and prevent the walls from being squeezed out by the concrete mass.

According to their purpose, the blocks are divided into in-line, corner and closing end blocks. The width of the blocks can vary from 250 to 400 mm for the construction of buildings from 6 to 12 floors, that is, only blocks of the smallest standard size are used in IZHS. Row blocks are the main formwork element, their horizontal joints have a tongue-and-groove connection, vertical ones are on tongue-and-groove. The nomenclature of in-line blocks includes T-shaped and X-shaped products for the formation of abutments of load-bearing walls, and radial blocks with different curvature of rounding can also be made to order. Corner blocks are designed to close the formwork at corners and bends, there are two types of these elements at 90 ° and 45 °.

End blocks are designed to frame openings, they can also act as plugs for protruding wall elements. In some series of formwork, the final element is formed by inserting a polystyrene partition wall into a row block; this block can also be a separate item in the nomenclature. Particularly noteworthy are blocks with a rounded end, which are used in the decoration of the external parts of the supporting structure, for example, supporting walls, columns and buttresses..

Blocks of permanent formwork are purchased as a set, the set includes all the elements necessary for the construction of walls. At the same time, minor differences in the dimensions of the blocks should be taken into account in advance when constructing the base of the house, because during installation, the fixed formwork cannot undergo any mechanical processing, except for trimming the blocks protruding into the section of the opening.

Wall erection process

Before assembling the formwork along the perimeter of the walls, a horizontal waterproofing of 1-2 layers of glass insulation is glued to the foundation. After that, the first row is assembled according to the project plan: the main axes are coordinated, the diagonals and the outer dimensions of the box are checked. Before fixing the first row, holes are drilled in the foundation for vertical reinforcement to a depth of 6–8 cm. The rods are installed in two rows at each bridge of the block with an indent from the inner walls of 20 mm, the diameter of the reinforcement is determined according to the album of technical solutions.

To install the first row of formwork, a layer of cement mortar must be applied to the waterproofing, the thickness of which will allow leveling the curvature of the base. The blocks are installed on the mortar, aligned in a common horizontal plane along the level or mooring, then they are left until the mortar sets. After that, horizontal reinforcement is laid in the grooves of the jumpers, while the crosshairs are tied with wire. When tying the bottom row, a blind loop is put on a vertical rod 20-30 mm below the horizontal reinforcement, the ends of which are wrapped around the horizontal rods.

The blocks of the second and subsequent rows are put on the vertical reinforcement and connected to the lower ones, while the vertical joints must be displaced by at least a third of the block length. The groove-and-tenon joints must snap into place until the gap is completely eliminated. Before laying the horizontal reinforcement, it is necessary to tie the jumpers of the blocks to the previous row of reinforcement and tighten the wire with twisting to prevent the separation of the horizontal locks between the blocks. After the next row of blocks is assembled, the horizontal reinforcement is laid and ligated with the vertical.

Particular attention should be paid to the formation of the frame of the openings. The side faces are closed with plugs or end blocks, but at the same time the upper and lower faces do not have standard means of closing the formwork contour. In such cases, it is recommended to use PPS panels with a thickness of 25–30 mm, which are pressed against the formwork by a supporting structure assembled inside the opening. This construction is nothing more than a frame made of edged boards with transverse and diagonal internal struts..

When the formwork is assembled to the full height of the walls and verified by geodesy, the structure can be monolithic. Typically, concrete of class B15 or higher with aggregate size 10–25 is used. The mixture is fed from above, while feeding is carried out in layers, moving along the perimeter. Each successive portion is compacted with a pin and a submersible vibrator.

Surface finishing and laying of communications

Expanded polystyrene is extremely sensitive to atmospheric influences; in just a month of exposure to sunlight, surface adhesion is critically reduced. Because of this, exterior wall decoration should be carried out 1–2 days after pouring the concrete. As a rule, the technology of a wet facade is used, while the base reinforcing layer is either not applied at all, or has a purely nominal value. It is also often practiced to lining the house outside with facing bricks..

The situation is much more complicated with the systems of ventilated curtain facades. Although the concrete core provides high fastening strength, it is necessary to remove the PSA in the places where the consoles are installed, which inevitably leads to the formation of cold bridges. This disadvantage is partially compensated by the use of formwork blocks, the lintels of which protrude from the outside, forming small areas, to which the supporting base of the frame is attached.

Many copies have been broken in the debate over the best way of interior decoration. The contact of expanded polystyrene with room air is unacceptable, moreover, it is an extremely fire hazardous material, which requires absolute localizing ability and fire resistance from the finishing layer. The only way to lay electrical wiring in the BTS is inside steel pipes with welded or threaded connections, which is extremely costly. Plus, the inner wall covering with thermal insulation provokes strong temperature drops when changing heating modes, the building is simply devoid of inertia.

The first finishing method is gypsum or cement plaster with a layer of 30 mm or more, thrown over a galvanized mesh. This option is suitable only in cases where the internal partitions are lined with solid bricks. If a free layout is required with frame partitions, it is better to overlay the walls with half-brick masonry from the inside. Both finishing methods allow free laying of communications and at the same time guarantee fire safety and compliance with a comfortable thermal regime in any season.