Overlapping Marko: design and installation features

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In individual construction, the choice of floors is not very rich. Marko slabs can be used as a modern alternative to concrete and frame structures. These are lightweight, technological and quick-to-assemble aerated concrete floors, which will be discussed in this review..

Overlapping Marko: design and installation features

Description of construction

From a technological point of view, Marko’s floors are a kind of “chimera”, being the result of combining the principles of monolithic and precast-monolithic construction in one structure. “Chimerism” means that concrete work is carried out not only to connect the units of the prefabricated structure, but also to form a solid monolithic surface. In turn, at the assembly stage, not ready-made concrete products are used, but metal structures and gas silicate blocks, due to which the volumetric weight and thermal conductivity are reduced.

In cross-section, the section of the floor resembles a prefabricated structure of hipped-roof blocks, however, the lower surface does not have protruding ribs, since the gaps between them are filled with gas silicate. Due to this, the thickness of the covering screed can be reduced to values ​​not exceeding the protective layer of the reinforcement. Even with a screed thickness of 40-50 mm, such an overlap will not have a trampoline, at the same time the mesh reinforcement provides a high operational load.

Construction of precast-monolithic floor slab MARKO

The main load-bearing element of Marko slabs are stiffening ribs, which are based on reinforcing beams. These include:

  • one thread of 8 mm working reinforcement of the upper belt;
  • two threads of 12 mm working reinforcement of the lower belt;
  • one strand of 24 mm of main reinforcement in the lower main zone of perception of loads;
  • two inclined belts of sinusoidal structural reinforcement.

Floor beam MARCO

The lines of structural reinforcement in section represent a triangle installed on a strip of profiled steel, at the tops of which there are threads of working reinforcement. Before embedment, the beams are self-supporting and can withstand the weight of the blocks without deflection, however, so that the structure does not bend under the mass of concrete mixture, support with scaffolds or jacks is required. After the concrete has hardened, the lower surface of the beams is used as a basis for attaching suspended ceiling structures.

Characteristics and features

Almost all Marko slabs are designed for an operating load of 400 kg / m2, despite the presence of several standard sizes. The difference between them lies in the cross-section, which allows spanning from 4.5 to 12 meters. An increase in the span is provided by increasing the floor section, but without increasing the thickness of the screed.

Prefabricated metal beams, which provide the main structural strength, deserve special attention. They are based on a profiled steel strip, which, due to stamping, acquires a sufficiently high rigidity. In addition, punching perforation is performed on the vertical parts of the beams, which also increases the resistance to deflection and increases the quality of adhesion to the concrete mixture..

Profiled floor beams MARCO

A natural question arises: will it be possible to recreate the technology with the help of handicraft elements in regions where the purchase of factory floors is impossible? On the one hand, if you carefully study the sample and take into account the structural features, you can replace the profiled tape with a welded one made of structural steel, and you can also make filling blocks yourself, for example, from expanded clay concrete, is also not a significant problem..

However, it should be remembered that Marko floors are designed taking into account the minimum material consumption and do not have any significant safety factor. While manufactured products successfully pass performance tests, the slightest mistake in handicraft production is almost guaranteed to result in a decrease in load-bearing capacity. This obliges to independently lay an additional safety margin, increasing the material consumption and the content of reinforcement in the stiffening ribs, which may make the reproduction of the technology not entirely expedient.

Reinforcement of floor slabs MARKO

If the goal of the handicraft production of Marko floors is set in principle, they should be made according to a project, in the development of which the following figures should be taken as a guide:

  • Operating load: 400 kg / m2 without deformation and not less than 1200 kg / m2 until reversible crack opening.
  • Fire resistance: the time of fire exposure until the limit states of the 1st group are reached – not less than 125 min at a load of 500 kg / m2.
  • Own weight – 200-350 kg / m2 with a floor thickness of 150–300 mm with a linear dependence of the parameters.
  • Basic sound absorption capacity – not less than 45 dB.

We also note that the thermal conductivity index for Marco floors is not regulated, since the structure is equipped with an impressive number of large thermal bridges – stiffening ribs, the total area of ​​which is about 20% of the floor area. This problem is partly solved in the energy-efficient slabs of Marco, during the development of which it was decided to abandon the monolithic connection of the screed and ribs. In such structures, the height of the filling blocks exceeds the stiffening ribs up to 150 mm, while gas silicate liners are located above the ribs, forming a single plane with the blocks, covered with a screed. In this version, the thermal conductivity of the floor can reach 0.95 W / K. It is also possible to improve the heat-saving properties by replacing concrete with lightweight or cellular concrete, for example, with expanded clay filler. However, such floor options are developed by the manufacturer according to an individual project..

Advantages and disadvantages of Marko floors

It remains to figure out where Marko floors can act as an effective technical solution and how they are superior to standard floors of various types.

Compared to Marco frame ceilings, they provide a higher degree of sound insulation between floors. To achieve comparable performance for the frame structure, it has to be partially filled with calcined sand and covered with a dry or semi-dry screed, which negatively affects its own weight and forces an increase in the cross-section of the bearing elements.

In comparison with precast-monolithic ceilings, the advantage of Marco is that they do not require special equipment for installation, and also differ in much lower weight. In addition, the purchase of floor slabs causes additional problems with their transportation and circulation of passport documentation..

In comparison with monolithic ceilings, the advantage when using Marco is also in reducing the weight of the ceiling, and in parallel – in reducing the cost of concrete and reinforcement in favor of cheaper gas silicate. In addition, the technology of installing Marko floors, although it is not simpler compared to monolithic work, is considered more advanced in terms of technical control over compliance with the installation rules.

Pouring precast-monolithic floors

The main disadvantage of Marco is not widespread in the regions, which imposes additional transport costs. True, unlike the elements of prefabricated and precast-monolithic floors, Marco’s parts are not large-sized and do not require special vehicles.

Another difficulty in using Marco slabs is the high degree of standardization. In practice, this is expressed in the need for design calculations of the enclosing structures both in terms of bearing capacity and in terms of geometric configuration. To do this, it is better to use the official installation manual and the album of technical solutions, where diagrams of the bearing capacity to span length are given for the main types of floors, the rules for assembly and embedding are indicated. To give you an approximate understanding of the main difficulties associated with the integration of Marko floors, below we give a short description of the installation process.

Installation procedure and features

Overlapping Marko does not require the construction of formwork, its role is played by profiled belts, filling blocks and wall flanges, a perimeter enclosing structure. The main area of ​​application is gas silicate buildings, in which the flanging along the supporting rim of the walls also performs the function of thermal protection of the end of the ceiling. They can also be used as a floor for lower floors, in such cases they are supported by a tape or grillage of a concrete foundation.

To strengthen the foundation on the main axes under the load-bearing walls, the beams must be supported by concrete or bored piles; the use of pile-screw supports is allowed only on artificially compacted soil. The sufficient width of the ledge to support the floor on the gas silicate wall is not less than the width of the stiffener in the lower part, on the concrete base – from 0.6 of this value. To maintain the floor slab for the period of concrete hardening, under the beams, every 1–1.5 m, it is necessary to install supports that can withstand the specific gravity of the concrete mixture without deformation with a 1.5-fold safety margin. It is also possible to use a fixing system with crossbars made of boards 50×150 mm and supports made of solid timber 100×100 mm When supporting the floor slab, non-removable supports in the form of a bar with thrust bearings should be used, the area of ​​which is calculated according to the supporting capacity of the soil, based on the requirement for its near-zero subsidence.

Formwork supports for precast-monolithic slabs

After the beams have been laid, the working reinforcement is tied using bent anchors with an overlap of at least 40-50 values ​​of its own diameter. What is important, at the junctions, the reinforcement of the lower belt is connected not with the nearest perpendicularly located thread, but with the far one. Annealed wire 0.8–1.2 mm thick is used for binding. The lower belts of the reinforcement must be installed on the spacer rings located every 1.2 meters..

Docking of floor beams MARCO

Along the contour of bearing on the walls, the main reinforcing belt of rectangular section is connected, connected from four threads, the diameter of which is equivalent to the lower main reinforcement of the beam, using U-shaped clamps of structural reinforcement, located with tails towards each other. The height of the reinforcing cage must be equal to the height of the triangular profile of the reinforcement of the beams.

Monolithic overlap belt

In the body of the floor, it is possible to lay engineering communications. As a rule, it is performed in a space free from reinforcement, that is, in grooves cut on the surface of the filling blocks. If the passage of communications through the reinforced sections is required, it is performed with a sleeve, while the distance from the body of the sleeve to the reinforcement should not be less than 3 diameters of the latter. Blocks are laid on the shelves of load-bearing beams and communications are installed together. If the screed and ribs have a monolithic design, the surface layer is reinforced with wire mesh VR-1 100x100x5 mm.

For concreting the floor, high-quality mixtures with a strength class of at least B20 are used. Casting is carried out evenly over all recesses, this is especially important for structures with significant rib heights. It is possible to use a deep vibrator, but it is not necessary: ​​for a high-quality shrinkage of the mixture, it is enough to first fill the ribs half the height, carefully tap the reinforcement with a hammer, then fill it slightly below the level of the upper line of the reinforcement, tap the frame again, and then pour the screed. The overlapping load can be perceived as early as 7-10 days after pouring, grinding can be done on 16-20 days, the operating load can be applied only after complete hydration of the cement for 4 weeks.

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