Construction of houses

How to lay reinforced concrete slabs

A reliable and durable house is not only strong stable walls and a leak-proof roof, but also no less strong earthquake-resistant ceilings. For the arrangement of interfloor floors and between the basement and the first floor, solid and hollow-core reinforced concrete slabs are used. These products are made from hard or lightweight concrete and reinforced with special reinforcement. The floors are durable, fire-resistant, resistant to mechanical stress and extremely durable. In total, there are several types of reinforced concrete slabs, each of which is used in a particular situation. Therefore, in order not to be mistaken with the choice, it is necessary to pay attention to the marking and understand what is behind the designations in it. But an even more important and responsible task is the laying of reinforced concrete slabs, which is carried out with the help of a crane and a team of workers. How to lay reinforced concrete slabs on floors according to the TTK, we will tell in this article so that you can control the performance of the work.

What are reinforced concrete slabs

To an uninitiated person it may seem that the reinforced concrete floor slabs are all the same, it is enough just to call the factory and say the required amount. In fact, precast concrete factories produce slabs and blocks of various designs, purposes, and even from concretes of different brands. Therefore, first of all, pay attention to the marking of the plates..

Reinforced concrete slab marking

Dimensions of reinforced concrete slabs

For example, brand PK57-15-8T means:

PC – product name / type of plate. In this case, a floor slab with round voids.

57-15 – dimensions of reinforced concrete slabs indicated in dtsm. In this case, the plate is 5680 mm long and 1500 mm wide..

eight – permissible load on the slab. In this case, the design load is 800 kgf / m2.

T – concrete grade. In this case, heavy concrete is used..

Sometimes the marking indicates the thickness of the reinforced concrete slab. Then it looks like P-27-15-12-8T. This designates a solid reinforced concrete slab 2690 mm long, 1490 mm wide, 120 mm high, with a load of 800 kgf / m2 made of heavy concrete.

Types of reinforced concrete slabs

As we have already found out, the first letter values ​​in the marking indicate the type of plate. Let’s find out what they are and what is behind them..

Solid floor slabs

NS – reinforced concrete solid slabs, used for the installation of floors in residential and public buildings. They are produced in different sizes: length from 1790 mm to 6260 mm, width 1190 – 1490 mm, thickness 120 mm, 160 mm, 220 mm. The weight of a solid reinforced concrete slab depends on its dimensions and ranges from 0.625 t to 3.6 t. For example, a P-48-12-22-8AT5 slab weighs 2.65 t, and a P-30-15-16-8A3 slab weighs 1,775 tons. Such slabs are much heavier than hollow-core ones. Plates with a height of 160 and 220 mm provide sufficient soundproofing of the room due to their mass, but if you use slabs with a height of 120 mm, then you need to take additional measures for sound insulation, for example, make laminated floors.

Reinforced concrete slabs with round voids

PC – reinforced concrete floor slabs with round voids. They are also used for floors, but unlike solid slabs, they provide exceptional sound and thermal insulation of the room due to the air trapped in the voids. They are produced in the following sizes: slabs 100 mm wide have a length from 238 mm to 1198 mm; slabs 120 mm wide have a length of 168 – 898 mm; slabs with a width of 150 mm have a length of 238 – 898 mm. The height of slabs with round voids is the same – 220 mm. For information on how much a reinforced concrete slab weighs, it is advisable to immediately find out from the manufacturer on his website. For example, the most commonly used PK45-12-8 plate weighs 1.58 tons, the long PK72-15-8 plate weighs 3.33 tons, and the PK120-10-8 product with dimensions 1198x100x22 weighs all 5 tons.

Reinforced concrete slabs for special purposes

PS – reinforced concrete slabs for special purposes. This category includes slabs for balconies, loggias, bay windows and slabs for sanitary facilities. Their main difference from the rest of the plates is the method of support and the presence of additional holes for laying water and sewage pipes. The height of such slabs is 200 mm.

Reinforced concrete slabs ribbed

NS – ribbed reinforced concrete slabs. They are used for the installation of floors in brick residential and public buildings, as well as for arranging the load-bearing base of the roof. They are also sometimes called “tent”, as their size allows you to cover the entire room. The length of such slabs can reach 18 m, the width is 3 m, and the height is 300 – 600 mm..

RP – reinforced concrete spacers slabs. Installed between the columns of buildings. Can also be called spacer blocks. Usually their length does not exceed 1.5 m..

PT – heavy concrete slabs. Used for ceilings between columns in public buildings on the ground floor.

In addition to the above, there are also slabs made of lightweight concrete, as well as lightweight slabs of PNO, which can withstand the same load as from heavy concrete, although they have less weight and thickness..

For reinforced concrete slabs, the price depends entirely on their size and type. For example, a PK55-12-8 stove costs 150 USD. each, the most expensive slabs of large sizes PK76-15-8 – cost $ 500. a piece.

The device of a reinforced concrete slab for the foundation

Monolithic foundation slab

All of the above types of plates are manufactured at the factory and purchased ready-made. But there is one more category – reinforced concrete foundation slabs. Such slabs are made directly at the construction site..

At the place where it is planned to arrange a monolithic slab foundation, excavation is carried out, the base is tamped, crushed stone and sand is backfilled, and even more thorough tamping is carried out. Then the formwork is formed from metal panels with supports.

Next, the reinforcement cage is tied or welded, which is lowered into the formwork. For reinforcement, a rod of 8 – 12 mm in diameter is used. Then everything is poured with concrete. After solidification, a monolithic foundation slab is obtained – solid, without gaps, with exact dimensions and the required thickness. Typically, such a foundation is required for moving soils..

Reinforced concrete slab technology

The most popular slabs in private housing construction are hollow-core reinforced concrete slabs with round voids. They can be ordered at the manufacturing plant, from where the car with the goods will arrive at the appointed time. But what to do next? How should these slabs be stored so that they do not crack? And then, when the installation of the plates begins directly: how to cut off the excess? How to cut a hatch hole into the attic? There may be many similar questions, so let’s dwell in more detail on the technology of working with a reinforced concrete plate..

How to store reinforced concrete slabs

Storage of concrete slabs

Despite the strength of reinforced concrete slabs, the possibility of cracks appearing on them is not excluded. There are only two reasons – improper transportation and improper storage. Considering how much a reinforced concrete slab costs, each of them must be handled with care.

Storage of reinforced concrete slabs:

  • Only in horizontal position.
  • High enough so that the slabs do not touch the ground.
  • It is necessary to put a solid, reliable base under the slabs that can withstand a lot of weight, while it should not get wet and rot. Otherwise, moisture can get into the stove, it will get wet, and cracks will appear..
  • The height of the base should be such that, even if it subsides, the slabs do not touch the ground. If the bottom plate comes into contact with damp ground, cracks may appear not only on it, but also on the above.
  • Wooden slats 40-50 mm thick are placed between the slabs in one pile. They should be located strictly one above the other and at a distance of 20 – 40 cm from the edge.
  • The maximum number of boards in one stack, provided a sufficiently strong base, should be 8 – 10 pieces..
  • Do not store them vertically, leaning against the wall..

These tips will help keep slabs from cracking..

How to shorten a hollow reinforced concrete slab

Among all the typical products that a plant can produce, you can always find slabs of the right size. But there are situations when, for various reasons, the slab must be shortened either in length or in width. This will require a grinder, crowbar and a cam hammer..

Cutting the slab across / across the width:

Cutting the slab across / across the width

  • We lay the slab horizontally on the lining.
  • We draw a marking line on the surface of the slab, along which we will cut.
  • The lining must be strictly under this line..
  • Using a grinder with a disc on concrete, we cut the slab along the line, cutting the upper part of the slab.
  • With a hammer-cam, tap the slab in place of the voids along its entire width. Usually 3 – 5 blows are enough to cut the slab in the place of the voids.
  • To cut the ribs, we hit them with the same fist, only not from above, but from the side.
  • A piece of slab that is half-destroyed will sag under its own weight, so that scrap can be easily inserted between the parts. With the help of a crowbar, we break through the bottom wall at the thinnest point of the round hole of the plate.
  • There should be reinforcement below, we clean it from the remnants of concrete and cut it with a grinder.

The edge of the slab will not be as flat as that of the factory product, so it must be buried at a sufficient distance on the support wall.

Slab cutting lengthwise / lengthwise:

Cutting reinforced concrete slabs along

  • We also lay the plate on supports in a horizontal position, draw a cutting line.
  • With a grinder we make an incision along the line.
  • Then tap with a hammer along the entire line. It will be easy to destroy the top wall of the slab, since the notch will follow the line of the hollow hole.
  • We destroy the bottom wall in the same way.
  • If there are reinforcing bars with a diameter of 3 – 8 mm, we cut them with a grinder.

Important! Please note that the reinforcement in the reinforced concrete slab can be stressed, so it cannot be cut to the very end. Otherwise, the fittings can pinch the grinder disc. The rod is not cut completely, and the remaining piece is beaten off with a hammer or crowbar.

How to put reinforced concrete slabs if they are not enough across the width of the room

What to do if the total width of all slabs is not enough to cover the entire room. There remains, for example, 500 mm, which can be cut off from the new board, or you can try to seal it in another way..

Method 1. Leave gaps on the sides:

The gap between the floor slab with the wall

  • We divide the total gap into two parts, 250 mm each. The first floor slab is laid at a distance of 250 mm from the edge of the wall..
  • All other plates are laid end-to-end, without gaps.
  • There should also be a gap of 250 mm between the last slab and the wall..
  • We take a cinder block with a length of at least 500 mm, lay it with the butt side to the slab on a cement mortar.
  • We carry out masonry from a cinder block according to the sample, pushing it against the slab. On both sides of the room.

When the wall continues to be erected, its masonry will press the cinder block even more and fix it completely. For greater reliability when performing floor screed on the upper floor, you can use a reinforcing mesh from a rod with a diameter of 6 mm.

Method 2. Leaving gaps between the plates:

Filling voids between floor slabs

  • We distribute the total size of the gap between all the plates. For example, the width of the room is 7800 mm, the slab is 1200 mm wide. We make calculations: 7800/1200 = 6.5. We multiply the whole number of slabs by the width of each 6×1200 = 7200 mm, subtract 7800 – 7200 = 600 mm from the total width of the room. We have 6 whole slabs, so there will be 5 gaps between them, we divide 600/5 = 120 mm. In total, we should have five gaps of 120 mm.
  • We lay the first slab back to back against the wall.
  • The next one with an indent of 120 mm.
  • All the others are also indented 120 mm. The latter must adjoin the wall.
  • We tie the formwork under the gaps.
  • We insert a frame made of reinforcement inside and tie it to the slabs.
  • Fill with concrete.

All further work can be continued only after the concrete in the gaps between the slabs has gained maximum strength..

How to cut an attic hatch in a hollow reinforced concrete slab

When laying reinforced concrete slabs on an attic floor, there is almost always a need to cut out a hatch in the ceiling leading to the attic.

The main rule: the hatch is always cut at the junction of two slabs, and not in one slab.

The permissible dimensions of the hatch depend on the width of the reinforced concrete slab and its load. The wider the slab and the less loaded, the larger the hatch can be cut. The dimensions of the hatch are selected based on the size of the stairs: 600×1200 mm, 600×1300 mm, 700×1200 mm, 700×1300 mm and 700×1400 mm.

The large side of the hatch is placed along the slabs. For example, a 600×1200 mm hole is made like this: an incision is made at the junction of the slabs, then one slab is cut by 300 mm, the opposite one by 300 mm, and then a cut is made along 1200 mm.

How to lay reinforced concrete slabs

With the main questions about working with slabs sorted out, now the most important thing is the laying of floors. Despite the seeming simplicity of the work algorithm, there are still nuances that must be known and taken into account. Even before ordering the slabs from the factory, it is necessary to complete all the preparatory measures, since when the machine arrives with the slabs, everything should be ready for laying..

Preparatory work

Preparatory work before laying the floor

First task – ideal bearing surface. This means an ideal horizon without a monstrous height difference of 4 – 5 cm. This is unacceptable. We check the surface of the walls, if there are significant flaws, we level the plane with a concrete solution. Accordingly, you will have to wait until it gains maximum strength, and only then start laying..

Second task – bearing zone strength. If the house is made of stone materials – brick, concrete, blocks, then no additional action is required.

Important! If the walls are made of aerated concrete blocks or foam blocks, then before laying reinforced concrete floor slabs, it is necessary to fill in the armopoyas. Formwork is carried out along the entire perimeter of the building, a reinforcing cage from a rod of 8 – 12 mm is inserted inside. Then everything is poured with concrete. Further work is possible only after the concrete has set..

The third task – installation of mounting towers. They are needed in order to take on the weight of the plate, if for some reason it slides off the bearing surface. The tower is used only during the installation process, then it is removed.

Laying reinforced concrete slabs with a crane

When all the preparatory work is completed, everything that needs to dry and gain strength has dried and gained strength, you can order plates. To unload and lay them, you will need a crane, depending on the size and weight of the reinforced concrete slab, it can have a lifting capacity of 3 to 7 tons.

Plates can be laid directly from the machine without unloading. To do this, the foreman at the construction site must have project documentation for the house, which indicates the layout of the plates..

Laying reinforced concrete slabs – scheme

Layout of reinforced concrete slabs

Stages of work:

Smearing the base supporting the floor slab with mortar

  • First you need to prepare the bearing surface. At a depth of 150 mm, concrete mortar is applied in a layer of 2 – 3 cm. It is necessary to cover the entire surface on which the slabs will now be laid. If the method is supported on two sides, then only from opposite walls. If the method is supported on three sides, then it is necessary to apply the solution to three walls. You can lay the slab on top when the solution gains 50% of its strength.
  • During this time, the crane operator can hook and lift one of the plates..
  • A signal is given to the crane operator, you can lower the plate to the prepared place. The person goes to a safe distance. Holding the slab with hooks, unfold it to extinguish the swing.

Laying the cover plates - feeding the slab with a crane

  • When the stove is already very close, two people – one on one wall, the other on the opposite, carefully guide the stove to the right place. The slab should rest on the walls by at least 120 mm, preferably 150 mm. The slab will squeeze out the excess mortar and take a convenient place, evenly distributing the load on the base.
  • After the slab is fully aligned, which can be done with a crowbar, the slings are removed from the mounting lugs. The leveling of the slab can only be done along the laying area, in no case across, otherwise the walls may collapse. A signal is given to the crane operator to pick up the slings.

Leveling floor slabs

  • Then the procedure is repeated for all other plates. In this case, it is necessary to align the plates along the lower edge, which will be the ceiling in the room. To do this, the slabs are laid with the wider side down, and the cone-shaped notch up.

Important! In some sources, you can find a recommendation, in addition to the mortar, to put reinforcement under the slabs in the support area. This is due to the fact that it is more convenient to move and level it this way than without anything. In fact, reinforcement cannot be placed, it is prohibited by the TTK. Firstly, the load will be unevenly distributed, and secondly, the plate will easily slide over the reinforcement, so it can move out of place.

If a non-standard option for supporting the plate is provided, then there are special steel elements for this. But it is better not to perform such work without a specialist..

Tying the slabs together – anchoring

Anchoring floor slabs

The so-called anchoring can be carried out in various ways – by tying the plates together with reinforcement or by arranging an annular anchor in which the plates will be clamped from all sides.

Rods with a diameter of 12 mm are welded to special fasteners on a reinforced concrete slab, connecting the slabs to each other. Different manufacturers provide for the arrangement of such elements in different ways. It is considered the most optimal when these rods are located diagonally to the slab, i.e. connect points not at the same level, but with an offset.

The slabs are anchored not only to each other, but also to the wall. For this, reinforcement must be embedded in it in advance..

The ring anchor is somewhat reminiscent of an armored belt. Around the entire perimeter of the slabs, formwork with a width of 10 – 15 cm is made, a frame is inserted into it, in the corners of which the reinforcement is bent. Then concrete is poured into the formwork. The resulting construction is very durable..

Sealing joints between reinforced concrete slabs

Sealing joints between floor slabs

The joints between floor slabs, they are also called rusty, are filled with fine-grained concrete of the M150 brand. If the gaps are large, then a board / formwork is installed under them. All work on the embedding of rusts begins only after all the slabs are connected to each other. The plate will be able to withstand the full load the very next day. Naturally, if the gaps between the plates are not too large.

Sealing voids at the ends in slabs

Sealing voids at the ends of floor slabs

The voids at the ends of the slabs must be filled with something at least 20 – 30 cm deep. This is necessary so that the slabs do not freeze and do not let the cold pass from the street. Mineral wool can be pushed into the voids, you can fill them with concrete mortar, plug them with ready-made concrete plugs, or fill them with rubble bricks and seal them up with mortar.

It is necessary to close up voids in floor slabs not only from those sides that rest on the outer walls, but also from those that are inside the house and rest on internal partitions.

All slab laying work takes several hours, from 2 to 4 hours. Since the payment of the crane is hourly, it can be released immediately after laying the slabs on the floor. And anchoring, filling of rusty and voids in the ends can be done independently, without haste and without looking back at the time..