The use of scientific and technological innovations is especially noticeable in construction - in different areas of the planet there are structures that would have been unthinkable some time ago.
New materials, new machines and tools make it possible to build faster, higher and more reliably. But there are elements in the construction technology that do not lose their relevance for a very long time. Such is the reinforced concrete slab - the principle was invented a century and a half ago, but the most futuristic projects cannot do without it.
1867 Patent
Many people know the story of the French gardener Joseph Monnier, who reinforced a thin-walled concrete barrel he made with a frame of metal rods and covered it with a layer of cement mortar. The resulting monolithic product had properties unattainable for other materials. Monier patented in different countries methods for the production of various structures from reinforced concrete, including a reinforced concrete slab for walls and partitions.
Professional builders have made their own amendments to the invention of the inventor: he placed the reinforcement accuratelyin the middle of the concrete layer, and the calculations showed that the location of the reinforcing cage should be chosen based on the specific situation, taking into account the loads acting on this structural unit. So, it is more logical to reinforce horizontal reinforced concrete slabs by placing the rods closer to the bottom plane of the slab, where the greatest tensile forces are.
Improving technology
Today, reinforced concrete is given the properties necessary for the most exclusive situations. Strength elements - reinforcing cages - can be spatial and flat; prestressed (string, beam) reinforced concrete with improved structural qualities has appeared. Various additives in concrete slow down or accelerate setting and gaining strength. Reinforced concrete is widely used in the construction of both unique, single objects, and massive, economical buildings.
Manufacturability, strength, durability, moisture-, bio- and fire resistance, efficiency - these advantages will determine the use of reinforced concrete in the future. Monolithic reinforced concrete slabs or made for prefabricated housing construction will be in demand for a very long time, because, among other things, consisting of natural components, these structures are environmentally friendly and easily recyclable and reusable.
Types of reinforced concrete slabs
According to the place of application, foundation, road and floor slabs are distinguished. Such a product can be manufactured in the factory, then delivered to the construction site and mounted. Most often, a reinforced concrete slab, like other prefabricated productshousing construction, is fixed by welding by means of embedded metal parts.
The slab can be made locally. A monolithic slab, both for the foundation and for the installation of intermediate floors and roof coverings, is especially often used in objects of non-standard architecture or where it is difficult to use cranes necessary for the installation of precast concrete products. The market offers a sufficient number of devices (including formwork) that make this process affordable for self-construction.
Floating foundation
This construction of the base under the building is not the cheapest option, but often the most logical. A monolithic reinforced concrete slab, repeating in terms of the outline of all the outer walls of the first floor, is often called a floating foundation. This means that the load from individual parts of the building is transferred to the ground base evenly, the slab works as a single element, it is not subject to deformation due to heaving soil, large freezing depths or high groundwater. Of course, this is all valid for a foundation slab made with proper quality.
An important and rather costly stage in the construction of such a foundation from all points of view is the preparation of a sandy base, on which the slab will be cast. It is necessary to do some earthwork, fill and compact the sand - by spilling water or tamping.
Installation of the foundation slab
The bottom layer is usually rollgeotextile, which prevents the solution from seeping into the ground. Then concrete leveling preparation for waterproofing is done. After this layer has hardened, roll waterproofing is rolled out with overlap and gluing.
Reinforcement is a device of two interconnected mesh layers. The reinforcing bars of the lower layer are installed in special clamps so that it is deepened into the concrete layer. It is convenient to carry out concreting directly from the automixer along the tray, concrete pump, etc. After the prescribed period of curing, the reinforced concrete foundation slab is ready for the construction of the house.
Monolithic floor slab
In low-rise construction, such a floor slab, cast in the formwork in place, is used very often. There are specific prerequisites for this. In addition to the positive qualities common to reinforced concrete - strength, fire resistance, uniform distribution of perceived loads - there are specific advantages when choosing this technology. The main ones are the absence of the need for heavy construction equipment and the possibility of arranging a floor of any shape in plan.
It is better to entrust the calculation of the required thickness of the slab and the scheme of its reinforcement to specialists. Otherwise, you need to know the following. The slab is made no thinner than 150 mm, while the thickness of the floor slab is determined based on the length of the opening to be covered, in the ratio range of 1:30 - 1:35. When reinforcing, remember to reinforce the edge of the slab with U-shaped and L-shaped brackets.
Featurestechnology
There are many options for reusable formwork for monolithic slabs on the market. But buying it for an amateur builder is too expensive. Although there are opportunities to rent such professional equipment, this would be the best option - a guarantee of the speed and quality of the flooring device. In any case, it is much more convenient to use telescopic stands as a support than boards or bars, because it is very important to set the formwork along the level.
Concreting must be carried out in one step, with compaction and vibration of the mixture. For the first three days, the concrete should be dampened by spraying to avoid cracking from uneven drying.
Precast concrete
The construction of buildings from reinforced concrete products made on special factory lines is considered the most suitable for mass multi-storey housing construction. But even for small-sized cottages, prefabricated floor slabs are quite a suitable option. Reinforced concrete prefabricated slabs are a cheaper option for flooring, they can be mounted in any weather, and the installation speed is much higher.
The use of prefabricated floors is difficult due to the heavy weight that reinforced concrete slabs have. Their dimensions are standard - this should be taken into account at the design stage. Another problem is the need to use a crane even for a small floor area.
Types of prefabricated floor slabs
Solid, full-bodied slabs are used for special structures and assemblies: inas additional elements or for arranging channels for laying communications. They are distinguished by high strength and high weight.
Slabs with round or arcuate longitudinal voids are lighter and have better sound and heat insulating characteristics. Reinforced concrete multi-hollow slabs are the most used type of products for prefabricated floors. They are used for buildings with a power reinforced concrete frame, panel housing construction, brick walls, etc. Voids can be used for laying cables for various purposes - electrical, low-current.
The third type is ribbed or tented, more often used in industrial construction to cover large spans. The thickness of the floor slab, excluding power ribs, is 140-160 mm.
For the production of floor slabs, prestressed reinforcement is used, which makes their strength indicators similar to those of monolithic reinforced concrete floors.
Standard board sizes
The use of prefabricated hollow flooring should be considered at the design stage of the future house. The standard dimensions of the slabs can be a determining factor in the development of the layout of the future home. A floor that requires slabs of non-standard shapes or sizes can be too costly.
Therefore, the design should provide for the use of standard formats: the thickness of the slab is 220 mm, the width is 1, 1, 2 and 1.5 m, and the length is from 2.4 to 9 m, a multiple of 100 mm.
Methods for the production of floor slabs
In the production of hollow core slabstwo main methods are used. One is more traditional, using reusable formwork molds to produce slabs of a fixed, standardized size. After installing the reinforcement and elements that form voids, the mold is filled with concrete mix and heated in order to accelerate the process of concrete hardening and gaining strength. Reinforced concrete slabs obtained in this way, GOST 9561-91 prescribes to be marked with the letters PK.
In another - more progressive - the slab is stretched on stands, on a heated track in the form of a continuous tape 100-200 m long using a special molding machine. Prestressed reinforcement has the form of stretched steel ropes of the required section. When the mixture reaches a certain degree of strength, the tape is cut with a diamond tool into sections of the desired length and even at the required angle. Reinforced concrete slabs are obtained, the price of which is 20% lower than that of products of the usual - cassette - production method. Such plates are marked with PB symbols.
Designations for hollow core slabs have several alphanumeric character groups. They mean the type, length and width in decimeters, design load (in kPa), type and class of reinforcement. Example: PK 63-12-8-ATV - slab with round voids 63 dm long, 12 dm wide, allowable load - 800 kg per m2, ATB - type of prestressed reinforcement.
Installation of prefabricated slabs
The quality of a prefabricated floor made of hollow-core slabs directly depends on the correct preparation for installation, on careful andaccurate execution of the slab installation process while constantly monitoring the process with a measuring tool.
It is possible to ensure the reliability of the structure only if the assembly of supporting the slab on the walls or columns is correctly performed. The optimal depth of such support is selected based on the design of the wall, the material from which the supporting structures are made. For example, 70 mm of slab support is enough for metal beams, 75 mm for reinforced concrete crossbars, 90 mm for a brick wall.
For walls where elements with low bearing capacity are used as a material - lightweight concrete blocks, gas silicate or polymer concrete panels, most often professionals recommend creating reinforcement in the form of reinforced concrete armored belts on top, on which the floor slabs will rest.
The professionalism of builders is clearly expressed during the installation of prefabricated floors. If the floor slabs are fastened by welding embedded parts to each other using not unitary parts, but random waste of reinforcement, you should be wary, the risk of destruction of the entire building structure is too high.
Road plates
A product called a plate is a parallelepiped with overall dimensions in which the thickness is much less than the length or width. This fully applies to road slabs. They are used for pavement of roads or airfield runways. Such a coating can be permanent or temporary, i.e. these slabs can be used several times, and this is one of the advantages of the technology. Calculationreinforced concrete slab is carried out based on the area of application, the planned load on the coating and the service life.
When laying road slabs, it is very important to perform the necessary preparation of the base with high quality - usually these are layers of crushed stone and gravel, as well as a sand cushion of the desired thickness and density.
Distinguish between road and airfield slabs, for permanent and temporary coverage. They differ in the thickness of the product and the type of reinforcement used in its manufacture. All these data are reflected in the marking applied to the plates.
Example: 1P30.18-30AV - reinforced concrete slabs, dimensions - 3000x1750 mm, for permanent coating (2P - for temporary), designed for a car weighing 30 tons, class AB reinforcing steel was used.
The right choice
A well-designed design stage will help you choose the right option for the design of the foundation, walls, ceilings or pavement of roads and runways. Modern precast concrete plants offer a wide range of prefabricated parts for the most specific needs of the building process.
It is quite possible to buy reinforced concrete slabs, the price of which will be quite reasonable, and the quality will meet the norms and standards.
