Construction of monolithic walls. Technology, its advantages and disadvantages

• 1 Benefits
• 2 Disadvantages
• 3 How thick should the wall be?
• 4 Construction of monolithic walls
• 5 Formwork
• 6 Reinforcement
• 7 Fill
• 8 Where are they used?
• 9 Conclusion

Monolithic reinforced concrete is a popular building material that is used in the construction of expensive projects. It has found its application in the construction of shopping centers, buildings with a large number of floors and for the construction of designer 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, durability of buildings and the ability to withstand heavy loads. The construction of monolithic reinforced concrete structures can be carried out at any time of the year, which significantly reduces the time for the construction of buildings and structures.

Advantages

Monolithic reinforced concrete has the following advantages:

• resistance to fire;
• possibility of manual installation;
• minimal physical costs during the construction of a reinforced concrete monolithic structure;
• there is no need for additional equipment and lifting mechanisms;
• resistant to corrosion;
• not susceptible to oxidation;
• the same technological process for all cycles;
• installation speed;
• ability to withstand heavy loads;
• relatively low cost for monolithic housing construction;
• seismic resistance 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 amount of machinery and equipment;
• light weight of the element, the construction of which does not require the construction of a heavy foundation;
• the ability to use any house layout;
• reducing costs for finishing work due to the smooth surface of the material;
• reliability and strength.

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Requirements according to GOSTs and SNiPs

Concreting of monolithic wall structures is strictly regulated by state urban planning standards. The basic one is SNiP 3.03.01-87.

The requirements for monolithic structures are detailed in each building construction project, on the basis of which a project for the production of monolithic works is developed.

It provides:

1. stages of work preparation;
2. installation of formwork;
3. filling;
4. control and care until the solution hardens and compliance with safety regulations at each production stage.

The standard establishes the following violations that should not be present on the surfaces of a monolithic structure:

• Areas with uncompacted concrete are prohibited;
• structures with exposed reinforcement are prohibited, except for its technological outlets;
• on concrete of classes: A/B/C there should be no oil stains or rusty stains;
• On the walls, only shrinkage cracks of no more than 0.1 mm for grades A, and 0.2 mm for grades B/V/G are allowed.

Flaws

The following disadvantages are identified:

• the need to use soundproofing material;
• there are difficulties in disassembling;
• the likelihood of cracks, detachments and other similar deformations;
• complexity of formwork installation;
• the need to hire skilled workers;
• the need to warm up the concrete when constructing a structure in the cold season;
• the need for laying heat-insulating material;
• providing additional care during the hardening period of the solution.

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Concreting stages

The concreting process itself includes the following steps:

• Waterproofing
• Surface reinforcement
• Setting up landmarks
• Preparation of concrete solution
• Pouring concrete
• Finishing operations
• Expansion joints (technological gaps)

Waterproofing.

Waterproofing is necessary in order to protect the concrete from water that comes from the top layer of soil, as well as to prevent the solution from leaking into the ground after pouring. In addition, waterproofing will protect the concrete from weeds growing through it.

Surface reinforcement.

It is a mandatory step in pouring concrete with your own hands. Thanks to the surface reinforcement, the concrete will become stronger and will not crack or crumble. It is better to take reinforced rods and drive them into the ground, but to such an extent that the upper part of the rod does not interfere with the subsequent pouring of concrete and does not stick out from it in the end. After the rods have been driven in, it is necessary to stretch an ordinary welded mesh over them. You can weld the mesh to the rods or tie it using knitting wire.

Setting guidelines.

Guidelines are needed in order to take into account the height of pouring the solution. They are made of wooden slats or metal profiles. It is desirable that the surface has a slight slope to drain water. Landmarks are set transversely to the site. Using a level, 2 main beacons are installed and then secured with sand-cement mortar. Now you need to wait for the solution to set and pull the cords between the landmarks. Other landmarks are established based on them.

Preparation of the solution.

Now the proven “old-fashioned” method of preparing the solution will be described. It is necessary to mix sand, crushed stone and cement according to the proportion: for 1 part of cement, take 3 parts of sand and 1 part of crushed stone.

Pouring concrete

Filling occurs in this way: the mixed solution is taken with shovels and placed between the previously established landmarks. This is done to cover the tops of the landmarks. If suddenly too much solution was added, it must be removed. This is usually done with a putty knife or other level tool so that the surface remains level after hardening and there are no pits or unwanted bumps. To remove excess parts of the mortar, you must first fix the strip perpendicular to the guidelines, and only after that can you use a spatula, thereby leveling the surface.

Finishing operations

These operations will strengthen the concrete; for this purpose, special impregnations are usually used, for example, a polymer-cement coating. You can buy such a solution at a hardware store. It is especially necessary where there are constant mechanical loads, sudden temperature changes and other destructive factors. It is recommended to saturate the corners and edges of the concrete with the solution so that they do not begin to collapse over time. It is necessary to treat the surface with a polymer cement coating immediately after pouring. This is done by simply pouring the product onto the required areas of the poured solution. You can also use impregnation after the concrete has hardened, but to do this you will need to remove several 1-centimeter strips from the surface and fill the mixture with diluted water. After the concrete has completely hardened, the surface must be treated.

Expansion joints (technological gaps)

Expansion joints are an important procedure that will prevent concrete from changing under climatic conditions. It is a known fact that at cold temperatures concrete can contract, and at warm temperatures, on the contrary, it can expand. Such changes can cause deep cracks in the concrete, especially at joints. To prevent this, thin slats are laid at the concrete laying stage, and after the solution has hardened, the slats are removed. Thus, gaps remain that will prevent the concrete from cracking at the joints. You can make gaps after the solution has hardened.

Construction of monolithic walls

Slab foundation and monolithic walls.
Installation of monolithic structures of various thicknesses is carried out directly on the construction site. First of all, formwork is installed that fits the size of the building. Next, install the reinforcing layer and begin concreting. The design of monoliths is similar to the construction of precast concrete, only in this case the elements are manufactured in a factory and delivered to the construction site, where they are assembled.

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

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Structural reinforcement

To increase the strength of a monolithic structure, a special concrete reinforcement system is used by installing structures made of metal or polymer rods for special purposes. Depending on the thickness of the wall, the reinforcing frame can be made in the form of a flat mesh or a spatial structure with reinforcing strings arranged in several rows.

The minimum permissible diameter of longitudinal steel reinforcing bars is 10 mm, transverse ligation is at least 8 mm. Polymer fiberglass reinforcement can be used one standard size smaller than metal. The pitch of the transverse inserts is no more than 250 mm. This will ensure normal fixation of the longitudinal rods and the stationary shape of the entire structure.

All reinforcing elements are connected to each other using knitting wire. The use of electric welding is allowed only in extreme cases, since with strong heating and subsequent cooling, the physical and mechanical properties of the reinforcing steel may deteriorate.

Formwork

When erecting structures, you will need to install durable formwork, which will serve as protection for the solution to flow out. Formwork comes in the following types:

• block, which is used for monolithic filling of objects without overlaps;
• collapsible, consisting of separate parts ensuring the rigidity of the building;
• sliding, which is used in the construction of multi-story buildings;
• pneumatic, has a breathable durable shell;
• non-removable, used as decoration;
• tunnel, necessary in buildings with ceilings.

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

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Scope of application

The first monolithic house structure was erected in 1908 by Thomas Edison, after which such houses began to be built everywhere.

Today, multi-storey residential and public buildings are constructed using permanent formwork, which subsequently acts as a protective layer. Monolithic structures are suitable for all types of basement construction.

When and where is it prohibited to build concrete walls?

Monolithic construction has virtually no restrictions; the method is applicable to both high-rise buildings and small individual buildings. The only prohibition exists for the design of frameless monolithic buildings over 25 floors on normal soils, in non-seismic areas, from climatic zones 2 to 4.

A cold climate can be an obstacle to monolithic construction, since when the temperature reaches 5 C, the concrete solution needs to be heated or frost-resistant components must be included in it, which significantly increases the cost of construction and does not guarantee the high-quality formation of a monolithic structure.

In addition, concrete must be poured continuously and evenly throughout the entire formwork area to minimize the number of seams and obtain excellent structural strength characteristics. Concrete compaction must be done efficiently, which can only be achieved using special equipment.

Fill

After installing the reinforcing layer, they begin pouring concrete mortar, which is laid with a layer thickness of no more than fifty centimeters. The mixture is poured only after the previous layers have dried. During the concreting process, the solution is compacted with a vibrator, which will remove air bubbles. After pouring, the concrete mixture is left to dry until its maximum strength characteristics are achieved, this will take a month. After 30 days, insulation and finishing work begins.

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Brand and material characteristics

Brands of concrete differ in the content of components, their varieties and proportions. to the solution , which can improve many technical parameters of the design:

1. frost resistance (F);
2. moisture resistance (W);
3. plasticity (P) .

The required class of building concrete by grade and its distinctive characteristics are established taking into account the standards, requirements of SNIP, technical conditions and the project for the building under construction with the required parameters of monolithic structures.

An essential characteristic of concrete is its maximum weight of one cubic meter of solution; standards require that this figure not exceed 1500 kg/m3.

Today on the Russian construction markets there is material with various characteristics of grades from M100 to M500 . The numbers that are indicated in the marking of the solution, for example, M100, show the average indicator of ultimate compressive strength, calculated in kgf/cm2.

It determines the resistance of monolithic products to all kinds of mechanical overloads, humidity and temperature, and also affects the final cost of the object.

How to make the right choice?

When purchasing a specific brand of concrete solution, they are guided by the project for building a house. If there is no project for a simple object, then the choice is entrusted to experienced builders, based on practice.

Application of concrete mix grades:

1. 
   M100/B7.5 is not used in complex, critical work; it is usually used as an unloaded layer, which is a preparatory layer for monolithic load-bearing structures to ensure their strength characteristics.

2. M150/B12.5 acts as a preparatory layer for pouring reinforced concrete slabs.
3. M200/B15 is the most frequently purchased modification; it has a wide range of use from foundations to flights of stairs, but can only be used on objects located on stable soils with a deep groundwater level.
4. M250/B20 - production of monolithic foundations.
5. M300/B22 is a universal material, since it works equally well for monolithic and strip foundations, and has an optimal cost-quality ratio.
6. M350/B25 - the main purpose is pouring foundations and reinforced concrete monolithic wall structures.
7. M400/B30 - the main purpose is transverse beams, plinths, retaining walls, monolithic objects.
8. M450/B35 is used for bridge construction and subway construction.

Where are they used?

Monolithic reinforced concrete is used in the construction of residential buildings with load-bearing walls, public and industrial buildings, in buildings with two floors, as well as in the construction of frames with lightweight wall fences, partitions made of high quality materials, which help reduce the total weight of the building. During the construction of industrial structures, namely in the construction of stadiums, large workshops, exhibition halls. Monolithic reinforced concrete is often used when it is necessary to strengthen the foundation, floors, walls and columns.

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Varieties of monolith

If initially monolithic houses were only made of reinforced concrete, today there are variations on the theme - instead of DSP they use wood concrete or sawdust concrete, and instead of a reinforcement frame they use wooden racks.

But the essence remains the same - enclosing structures are not assembled or laid out from individual elements, but rather are poured. As a result, monolithic, seamless walls of almost any geometric shape are formed, which frees up the hands of architects. That is, if the abundance of bay windows and arches during construction from block/brick/wood significantly complicates the process, then no special effort will be required when pouring.

Since ordinary reinforced concrete turns out to be too cold, due to its high thermal conductivity and thin walls, foam concrete, polystyrene concrete or expanded clay concrete are used to do without additional insulation. In the first case, the thermal conductivity of the wall is reduced due to the formation of a large number of air pores in the concrete due to foam, in the second - due to the addition of polystyrene or expanded clay granules. But according to its varieties, the monolith is divided not by the type of concrete poured, but by the type of formwork - it can be removable or permanent.

Removable formwork

In the private sector, it is usually made of moisture-resistant or laminated plywood; boards, metal or plastic are less commonly used. The sheets are used whole or cut into pieces, depending on the scale of the fill. The elements are fastened together and, as they are poured, moved to a new location, since only specialized companies can afford to assemble the formwork for the entire house at once. And self-builders fill houses in stages, mainly horizontally. Plywood is deservedly popular, as it holds its shape well and allows you to get a smooth wall surface, and if it is also laminated, then the set can be enough for more than one construction site. As for fasteners, everything is individual.

Plywood 12 mm thick, increased moisture resistance, 2500 × 1200 mm, cut in half along the length (600 mm), four ties per sheet (sheets were drilled through, folded together, 100 mm from the bottom), the top was tied together with bars. Ties with two jammed nuts at one end, 250 mm long, 8 mm in diameter, were lowered into the spindle. Drive-in nuts are driven into the formwork from the outside; you only need to turn it (with a screwdriver) from inside the walls.

Rearranging removable formwork as it is poured is considered one of the most labor-intensive and time-consuming processes, and the fewer operations required, the better.