Reinforced Concrete: What is it? Structures, Advantages and Disadvantages
You have certainly been in a building erected by means of reinforced concrete. Used in the most different properties, the material option is very resistant. It can support a structure only with the help of a few pilasters, and it has enormous durability.
The product’s advantages, however, go well beyond. As well as its history, still dated to the Roman Empire. Are you curious to know about reinforced concrete? Follow this text! In it, we will clarify from its origin to the points of attention to its use. Check out!
Reinforced concrete: history
The first record of the use of what would become reinforced concrete is quite old. It is dated to 211 AD, during the reigns of the Roman emperors Seventh Severus and Caracalla. An ambitious work, the construction formed an area with swimming pools in water of different temperatures (hot, warm and cold), exfoliations, massages and baths for health. More than that: the place even housed gyms for sports, making it a kind of SPA.
To guarantee the enormous strength of the construction – which even allows you to see part of the ruins today in Rome – the combination of mortar and metal bars was used.
Then, I will be able to notice the use of a similar technique in the Church of Santa Genoveva, in Paris. The place is today called Panthéon de Paris and was built between 1764 and 1790, by the architect Jean-Baptiste Rondelet. Since the purpose of the construction was to maintain the lightness of the Gothic and the purity of Greek architecture, it was necessary to keep a few columns on the facade. Thus, the solution for transferring construction loads was to use reinforced concrete.
In this case, holes were made in the structure, in which the bars should be fitted. Afterwards, these holes were covered with lime paste, guaranteeing their best solidity. Folded bars were also used, absorbing the shear stresses of the structure.
Between 1824 and 1850, entrepreneurs had different experiences and obtained the recipe for concrete. At the same time, Frenchman Joseph Louis Lambot decided to build a boat with reinforced cement. Excited about his discovery, as the boat floated with great performance, he decided to put his work on display.
Exhibition, enhancement and patents
In a gallery, however, the product did not attract as much attention. But it piqued the interest of Joseph Monier, a farmer who planted orange trees. With his production in greenhouses, the worker had problems with the wooden and ceramic boxes in which the plants were accommodated. After all, they ended up breaking or rotting in a few months.
Then the idea came up: why not use reinforced concrete innovation to build the boxes? Monier carried out the experiment successfully. Then, he realized the incredible application of the material to other projects and changed the branch. From agriculture, he went to Civil Construction! So much so that, in 1875, he was responsible for the construction of a 16.5-meter bridge with reinforced concrete.
The new business paid off, and the former farmer patented the invention. For this reason, it is considered today the inventor of reinforced concrete. Then, the German engineer Gustav Adolph Wayss obtained the patents for the product. As it was still new, however, the construction process created uncertainties. Therefore, the German needed to invest in a series of tests, which ´proved the resistance of the structuring.
In the tests, it was proved, for example, that the iron armor has an enormous capacity to absorb traction. Concrete, on the other hand, can withstand compressions very well. Together, the materials create a very resistant and durable structure.
In Brazil, the first structure built in reinforced concrete dates from 1908. In Rio de Janeiro, the work gave rise to a 9.0 meter span bridge, designed by engineer François Hennebique.
Reinforced concrete what is it?
Reinforced concrete is material, as mentioned so far, formed by mortar and metal bars. Together, the products create a stronger structure than ordinary concrete.
There are two types of reinforced concrete available on the market: ordinary and prestressed.
In the first, the metal bars do not undergo pre-elongation. In the second case, yes, which gives the structure even greater strength.
The pre-elongation of the metal bars is an industrial process. In it, one end of the steel is fitted into the prestressing track. The other is fitted with a hydraulic cylinder, which applies a tensile tension to the metal. Then, the steel is placed in the formwork, involving the bars already positioned.
As a result, a reinforced concrete slab is obtained. Taken to work, it can be positioned more simply.
With this process, the concrete acquires enormous resistance. This is because the steel, when it stops being stretched, applies the propensity force to the part. Therefore, when the tension of a building is exerted on the structure, it will already be prepared to support it. A feature that, in fact, allows to increase the spacing between free spans of the work.
Of the advantages of the option, it is also interesting to highlight its accuracy. At the plant, it is easier to maintain the correct measurements for each manufacturing material. This is thanks to the use of production-specific scales, meters and concrete mixers.
Reinforced concrete: characteristics
The durability of the reinforced concrete structure is one of its main characteristics. Its use eliminates the need for a very large number of beams or columns. After all, the structure can support the space of large spans alone.
This does not mean, however, that beams and columns are not required. In fact, there are essentials to keep the building upright! Their number, however, maybe less. All dimensions are calculated based on specific standards of the Brazilian Association of Technical Standards (ABNT).
Dimension calculations must be present in the building design. Only a specialist in the field should produce them, so that errors do not damage the structure. The dimensions define both the steel gauge, beams, slabs, blocks and everything necessary for the work.
In addition, the reinforced iron structure can take any shape. This is because it is possible to bend it according to the needs of the work. The metal also receives protection against corrosion, so that the structure remains intact for years.
Reinforced Concrete Composition
Reinforced concrete is formed, first, by steel bars. The pieces are produced by the steel industry, through the metallic alloy between iron and carbon. United, the products create a material of intense resistance and hardness, perfect for the most varied areas of Civil Construction.
Concrete is produced by mixing cement, sand, boulders, crushed stones and water. In this composition, additives are also added, such as accelerators, dyes, fibers, silica fume, rice husk ash and others.
Reinforced concrete applications
The use of reinforced concrete occurs in the most varied structures of Civil Construction. It is possible to use it, for example, in sanitation works, dams, hydroelectric plants, viaducts, bridges and buildings. The important thing in these applications is to define the use of ordinary or prestressed concrete. Therefore, it is essential to have the help of a specialist in the field. With the correct calculations and a well-planned structure, the most suitable type of material can meet the needs.
Different, ordinary and prestressed reinforced concrete are indicated for different works as well. The common type of product is widely used for buildings, residential, eating or residential. The prestressed, in turn, is suggested for buildings that need large spans between pillars. As well as bridges and large shopping malls.
The common type of reinforced concrete is mounted on the construction site. In this case, the iron structure is assembled, and shortly thereafter I receive a concrete layer.
Reinforced concrete is indicated for wide spaces because it allows greater spacing between the beams and columns of the environment. For a shopping mall, for example, the option makes the space more spacious for installing as many stores as possible. As well as a hospital, which gains space to structure more rooms and spaces for the care of patients.
Reinforced concrete Advantages
There are many advantages to using reinforced concrete. There is, for example, its economic characteristic. This is because the raw materials of the product are cheap. The cost of maintaining concrete is also very low.
There is also a certain speed of construction with this type of structure. If used concrete coming directly from the industry. However, if the structure is assembled at the construction site, the time is longer. After all, it is necessary to wait for a large amount of concrete used to dry.
Another benefit of reinforced concrete is its ease of handling. For the process, only basic tools are needed. Labor does not need to be specialized either.
At the same time, the pieces have various resistances. Physics, to support structures; to water, since the material is impermeable; fire, reducing the risk of fire; the influences of time; shocks and vibrations.
Two rules regulate the use of this type of texture in Brazil. The first is the technical standard ABNT NBR 6118 – Design of concrete structures – Procedure. It lists the rules for designs with the material, including how dimension calculations should be done.
ABNT NBR 14931 – Execution of concrete structures, on the other hand, defines the rules for the execution of the work. Following the rules will guarantee the durability of the building, as well as its safety.
When choosing the type of material that will structure the property, it is essential to be careful and help from a specialist in the field of Civil Construction. More than that: it is interesting to know some caveats about the material so that there are only benefits in your choice.
The observation must start with the high weight of structures built in reinforced concrete. This weight requires the help of cranes and many workers to lift the structure built at the factory.
At the same time, it is difficult to renovate or demolish a reinforced concrete structure. After all, the iron bars do not sag or are easily cut. Thus, it is essential to design the property as correctly as possible. That is, without the need for modifications to the structure soon after. If that happens, the second work becomes laborious and expensive.
Despite being widely used, reinforced concrete cannot deliver good insulation. Neither thermal nor acoustic. Mainly because it is common for the slabs to have less thickness than the common. Therefore, it is necessary that the building gains a second layer of coverage, with specific materials for this insulation. Foams suitable for this installation, for example, usually handle the task.
Care with the execution and conservation of the projects
Cracking, that is, small breaks in the concrete, are inevitable. If it does not, the steel mesh inside the structure cannot adjust. Therefore, it will not be able to withstand the stresses for which it was designed, improving the strength and quality of the building’s structure.
It is essential, in any case, to keep this crack within control. Its reasonable limits are indicated in the technical standards ABNT NBR 6118 – Design of concrete structures – Procedure and ABNT NBR 14931 – Execution of concrete structures. If these limits are exceeded, it is important to request the evaluation of an engineer. Only the specialist can indicate the existence of risk or not to the structure.
With excessive cracking, for example, acceleration of the oxidation of reinforcement can occur. The oxidation process is normal and will happen over time in the steel mesh of reinforced concrete. This process, however, must take place in hundreds of years. Not soon after construction.
Corrosion of steel occurs due to the action of carbon dioxide in the materials. The substance is present in the atmosphere, released by all living beings – including humans. CO2 triggers the process known as carbonation, and the chlorides then reach the armature. The result is a rusty material with little resistance.
Impaired, steel can also cause stains on the walls and, in extreme cases, part of the building may fall. To avoid accelerating the problem, it is recommended to avoid the contact of reinforced concrete directly with rainwater. Therefore, the indication of the use of tiles and coverage on this material. Equally important to design an efficient drainage system for construction.