A construction must be able to withstand the weather and the instability of the ground without deforming… or collapsing! The iron arms the concrete to make it dimensionally stable. Foundations, slabs, walls, each concrete element can thus be reinforced by inserting metal elements. What is the principle of rebar, what is it used for, how to use it, what is the reinforcement technique?
Concrete iron… what does it look like?
In bulk, here are the main characteristics of the rebar:
- The concrete iron is in steel, which is a mixture of iron and carbon (2% maximum). Why ? Steel and concrete are two materials that adhere easily to each other. Once the steel rod is embedded in the concrete, it is naturally wrapped in a film which protects it from any corrosion.
- The reinforcing steel comes in the form of a round, twisted or hollow stem. This is to give the concrete optimum adhesion. For the contact surface between the two materials to be maximized, the rebar is never smooth! It is hollowed out with indentations or forged in relief, the protruding elements being called locks or flares.
- Rebars are forged on Mount Destiny. In fact, it is not sure… On the other hand, they are forged in different diameters, corresponding to different construction needs. The most frequently used standard diameters are 6, 8, 10, 12, 14, 20, 25, 32 and 40 millimeters. Up to 50mm.
- The bars rebar are long straight rods. In different lengths (2, 12 or 18 meters), they are then cut, bent, welded or assembled to form the desired reinforcement. But there are also ready-to-use reinforcement elements: welded mesh, soles, chaining, posts, flat sheets, corner pieces, etc. Rebar is also available in reels to be unrolled, which simplifies the transport and use of large volumes.
- The reference of a rebar indicates its elasticity limit you know bearable limit, the latter being expressed in Mpa (1 Mpa = 1 Newton per mm2). The yield strength is indicated by the initials Fe-e (classic), Fe-te (drawn steel) or Fe-tle (very high elasticity).
Why is it essential in construction?
As you have understood, rebar is used to form reinforcement intended to reinforce concrete. Its performance comes from several qualities that have made it essential to all kinds of constructions, especially the most ambitious ones.
Reinforced concrete is super-resistant!
Without this metal skeleton, the concrete would lack strength and flexibility. Indeed, if the concrete has an excellent compressive strength, it shows a low tensile strength. Subject to a possibility of concrete failure, the construction would be too fragile. However, steel resists both traction and compression. A steel reinforcement therefore gives the concrete a resistance to any test.
The concrete iron adapts to the needs
The rebars are inserted into the concrete by a formwork. Depending on their shape, they are used for different purposes. For example, irons are used to reinforce concrete to carry a heavy load; trellises are preferred to prevent the appearance of cracks… A reinforced concrete continuous footing will perfectly support the load-bearing walls of a house built on potentially unstable ground. As long as the construction is small, does not undergo compression, has no mechanical function or does not cause structural problems with the appearance of cracks, ordinary concrete can be used. But most of the time, reinforced concrete is unavoidable. It is used for any construction subject to vertical and horizontal constraints (such as a simple house), and for what requires a high tensile strength: slabs, posts, beams, foundations, retaining walls, etc.
Reinforced concrete is creative
And we understand why. Thanks to the combination of iron and concrete, you can build buildings of all shapes! Reinforced concrete makes possible the construction of complicated vaults and volutes, large arcs and arches, arrows or suspended elements… In addition to the aesthetic aspect, all audacities being permitted by reinforced concrete , the reinforcements made it possible to develop the anti-seismic construction. By associating the walls, the foundations, in short all the elements, the reinforcement gives the building the flexibility necessary to withstand earthquakes without damage.
How to achieve a good reinforcement?
To properly reinforce construction concrete (foundations, footings, elevation), professionals take three elements into account: the size of the foundations, the concrete load to come and the nature of the ground. Unstable ground, heavy concrete load? A correspondingly larger iron diameter will be chosen for the reinforcement.
The reinforcement is done in four stages:
- Pour protect the frames, we avoid putting them in contact with the ground. They are placed on wooden wedges. The frame is firmly mounted. The mesh panels are joined using steel wires or iron wire. It must not let go during the pouring of the concrete.
- Vertical waiting structures are set up at the location future poles. Additional reinforcement is installed for the corners of the construction. The pipes must pass in the right places…
- It’s time to realize the formwork. Thick planks are installed and assembled around the element to be built. The concrete will be poured inside this receptacle. The boards are supported by iron bars, which will be removed after formwork.
- The concrete is then sunk in the formwork. Attention is paid to the thickness of the coating, which must be thick enough to ensure the quality of the concrete.
For successful formwork, the important thing is to use the appropriate reinforcements, to position them correctly in the formwork and not to miss the pouring of the concrete. You can make reinforced concrete yourself for a simple or small-sized construction. But for a more complex work or subject to heavy loads, the help of a professional is necessary.
A specialist operates according to European standards, Eurocodes, which regulate the design and calculation of buildings and civil engineering structures. He carries out a preliminary calculation of resistance and dimensioning, with the objectives of the resistance of the structure (in reinforced concrete), its durability, its serviceability and its bearing capacity in the event of fire. From this study, he determines the needs in terms of type of reinforcement (diameter, geometric characteristics, etc.), the particularities of the materials (iron and concrete) and proposes the most suitable reinforcement.
Concrete iron, where to buy it?
Reinforcing iron can be found, like all metals, in building supply stores. It is better to turn to specialists (you can find them on the Internet) to get you rebar of sufficiently good quality. Plan to have it delivered, because steel is heavy! Also get a concrete iron cutting bender (you can rent one).
To give you an idea of the price, know that the twisted rebar in HA steel (high resistance) is 3 euros per bar of six meters, in section 8 mm. Count double for a diameter of 10 mm. For 3 euros, you can also buy a ready-to-use welded mesh, 3 square meters in area, with a 7 mm section iron.
What about reinforced concrete? The structural fiber…
New concretes are designed with integrated metallic or macro-synthetic fibres, which play the same role as iron reinforcements. These concretes are in some cases good alternatives to reinforced concrete.