The use of scientific and technological innovations is especially noticeable in construction - constructions appear in different areas of the planet whose construction would have been unthinkable some time ago.
New materials, new machines and tools allow you to build faster, higher, more reliable. But there are elements in building technology that do not lose relevance for a very long time. Such is a 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 Monier, who reinforced the 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 has patented in various countries methods of manufacturing various designs from reinforced concrete, including the offer of a reinforced concrete slab for walls and partitions.
Professional builders made amendments to the inventor's designs: he placed the reinforcement exactly in the middle of the concrete layer, and calculations showed that the location of the reinforcing cage should be selected 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, placing the rods closer to the lower plane of the slab, where the greatest tensile forces are.
Technology improvement
Today reinforced concrete is given the properties necessary for the most exclusive situations. Power elements - reinforcing cages - can be spatial and flat, pre-stressed (string, beam) reinforced concrete with improved structural qualities has appeared. Various concrete additives slow down or accelerate setting and gaining strength. Reinforced concrete is widely used in the construction of both unique, single objects and mass, economical buildings.
Manufacturability, strength, durability, moisture, bio and fire resistance, economy - these advantages will determine the use of reinforced concrete in the future. Monolithic reinforced concrete slabs or those 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 easy to recycle and reuse.
Types of reinforced concrete slabs
At 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 products of prefabricated housing construction, is fixed by welding by means of embedded metal parts.
The stove can be made locally. A monolithic slab, both foundation and for the installation of floor coverings 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. A sufficient number of devices (including formwork) are offered on the market that make this process available for independent construction.
Floating foundation
This construction of the base for the building is not the cheapest option, but often the most logical. A monolithic reinforced concrete slab, repeating in plan 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 soil base evenly, the slab works as a single element, it is not subject to deformation due to heaving soil, a large depth of freezing or a high location of groundwater. Of course, this is all true for a foundation slab made with proper quality.
An important and quite costly from all points of view stage of the construction of such a foundation is the preparation of a sand base, on which the slab will be cast. It is necessary to carry out a certain amount of earthwork, fill up and compact the sand - spilling it with water or tamping.
Foundation plate installation
The bottom layer is usually a rolled geotextile, which prevents the solution from seeping into the ground. Then a concrete leveling preparation for waterproofing is done. After the hardening of this layer, rolled waterproofing rolls with overlap and gluing.
Reinforcement is a device of two interconnected mesh layers. The reinforcement bars of the lower layer are installed in special clamps so that it is recessed into the concrete layer. Concreting is conveniently carried out directly from the mixer on the tray, concrete pump, etc. After the set period of the set of strength, the reinforced concrete slab foundation 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 lack of need for heavy construction equipment and the ability to arrange any type of ceiling in plan.
It is better to entrust the calculation of the required plate thickness and the scheme of its reinforcement to specialists. In other cases, you need to know the following. The slab is made no thinner than 150 mm, while the thickness of the slab is determined based on the length of the overlapping opening, in the range of ratios 1:30 - 1:35. When reinforcing, it is necessary to remember about strengthening the edge of the plate with U-shaped and L-shaped staples.
Technology features
There are many reusable formwork options for monolithic floors on the market. But buying it for an amateur builder is too expensive. Although there are opportunities to rent such professional equipment for rent, and this would be the best option - a guarantee of the speed and quality of the flooring device. In any case, using telescopic racks as a support is much more convenient than boards or bars, because it is very important to level the formwork.
Concreting must be carried out in one go, with compaction and vibration of the mixture. The first three days should be moistened with concrete by spraying to avoid cracks from uneven drying.
Precast Concrete
The construction of buildings from reinforced concrete products manufactured on special factory lines is considered the most suitable for mass multi-story housing construction. But for small-sized cottages, prefabricated floor slabs are quite a suitable option. Reinforced concrete prefabricated slabs are a cheaper option for overlapping, they can be mounted in any weather, and the installation speed is much higher.
The use of prefabricated ceilings is made difficult by the large 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 plates are used for special structures and assemblies: as additional elements or for arranging channels for laying communications. They are distinguished by high strength and high weight.
Plates having round or arch-shaped longitudinal voids are lighter and have better sound and heat insulating characteristics. Multi-hollow reinforced concrete slabs are the most used type of products for prefabricated floors. They are used for buildings with a power reinforced concrete frame, panel housing, brick walls, etc. Voids can be used for laying cables for various purposes - electrical, low-current.
The third type is ribbed or hipped, 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 plate sizes
The use of prefabricated hollow flooring should be provided even at the stage of designing the future home. The standard dimensions of the plates can be a determining factor in the development of the layout of the future home. Overlapping, which will require slabs of non-standard shapes or sizes, may be too costly.
Therefore, the design should provide for the use of standard formats: the thickness of the plate 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 manufacture of multi-hollow slabs, two main methods are used. One is more traditional, using reusable formwork forms for the manufacture of slabs of an unchanged, specified size standard. After installing the reinforcement and the elements forming the voids, the mold is filled with concrete mixture and warmed up in order to accelerate the process of concrete hardening and building strength. Reinforced concrete slabs obtained in this way are required by GOST 9561-91 to be marked with the letters PC.
With another - more progressive - the plate is stretched on the stands, on the heated track in the form of a continuous tape 100-200 m long using a special molding machine. Pre-stressed 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. It turns out reinforced concrete slabs, the price of which is 20% lower than that of conventional products - cassette - production method. Such plates are marked with PB symbols.
Designations of hollow core slabs have several alphanumeric groups of characters. They mean the type, length and width in decimeters, the design load (in kPa), the type and class of reinforcement. Example: PK 63-12-8- AtV - a plate with round voids 63 dm long, 12 dm wide, permissible load - 800 kg per m 2 , AtV - type of prestressed reinforcement.
Installation of prefabricated plates
The quality of prefabricated floors from hollow core slabs directly depends on the correct preparation for installation, on the thorough and accurate process of installing slabs with constant monitoring of the process using a measuring tool.
The reliability of the structure can be ensured only if the site of supporting the plate on the walls or columns is correctly executed. The optimal depth of such abutment is selected based on the wall structure, the material from which the supporting structures are made. For example, on metal beams, 70 mm of supporting the slab is enough, on reinforced concrete crossbars - 75 mm, on a wall of brick - 90 mm.
For walls where low-load-bearing elements such as light concrete blocks, gas silicate or polymer concrete panels are used, professionals most often recommend creating reinforcements in the form of reinforced concrete armored belts on top, on which floor slabs will rest.
The professionalism of builders is clearly expressed during the installation of prefabricated floors. If the fastening of floor slabs by welding embedded parts between themselves occurs using not unitary parts, but random reinforcement waste, you should beware, the risk of destruction of the entire building structure is too great.
Road plates
A product called a slab is a box 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 paving roads or aerodrome runways. Such a coating can be permanent or temporary, that is, these plates can be used several times, and this is one of the advantages of the technology. The calculation of the reinforced concrete slab is carried out based on the scope, the planned load on the coating and the period of operation.
When laying road slabs, it is very important to qualitatively perform the necessary foundation preparation - usually these are layers of crushed stone and gravel, as well as a sand cushion of the required thickness and density.
There are road and airfield plates 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 markings applied to the plates.
Example: 1P30.18-30AV - reinforced concrete slabs, dimensions - 3000x1750 mm, for permanent coating (2P - for temporary), designed for a vehicle weighing 30 tons, reinforcing steel of class AB is used.
Right choice
A well-designed design stage will help you choose the right option for the construction of the foundation, walls, ceilings or pavement of roads and runways. Modern factories of reinforced concrete products offer a wide selection of finished parts for the most specific tasks of the construction process.
To buy reinforced concrete slabs, the price of which will be quite reasonable, and the quality - to meet the norms and standards, the matter is quite real.