Reinforced concrete is a type of structure that uses frames made with steel bars. These fittings are used due to the low tensile strength of the concrete, which has high compressive strength.
In an reinforced concrete structure , the use of steel in beams and columns becomes indispensable and the dimensioning needs to be well calculated following the current norms of the regulatory bodies.
Reinforced concrete is durable and economical solution
With easy access and use, material is widely used in different types of buildings
Although not the only option, reinforced concrete is the most widely used technique in the world for building structures. This solution arose from the need to merge the compressive strength and durability of the stone with the characteristics of the steel. The result is a material that has the advantages of being able to assume any form quickly and easily, besides providing the metal protection against corrosion.
“Despite the low complexity of execution, care is needed to ensure quality and safety,” says structural engineering specialist Narbal Marcellino, a professor at the Federal University of Santa Catarina (UFSC). “Good knowledge of material properties, design fundamentals, national and international standards and execution technology are indispensable for the construction of safe and durable concrete structures,” he says.
The union of the concrete with the steel reinforcement creates a component resistant to the tensions of compression and traction due to the characteristics of the two materials. However, for a good performance of the reinforced concrete, it is not enough to only combine them, it is necessary that there is adhesion among them, that is, the work of resisting the tensions has to be carried out jointly. “In addition to this collaboration, the association is possible because the coefficient of thermal expansion of both is approximately equal,” explains Marcellino.
Structural concrete reinforcement can behave in two distinct ways: pre-assembled or prestressed. “The so-called prestressed concrete is what gets a previous stretch of steel. In this case, the armature is active, that is, when the tensions begin it already has an answer and pre-compressed the concrete that is around it “, comments the professor.
In order to fabricate the prestretched prestressed parts, the armature is engaged at one end of the protrusion lane, at the other end a hydraulic cylinder draws the steel by applying a tensile stress within the elastic limit of the metal. Then the concrete is placed inside the mold and wraps around the armature. When the concrete acquires sufficient strength the steel is released, and as it tends to return to the initial shape, it will apply a force of protension in the piece, giving rise to the compressive stresses in the concrete.
Structural concrete can be supplied by plants or prepared on site. Compressive strength is the main factor that defines its quality. “To do this, we need a dosing of the concrete, or trace, that consists of establishing the amount of components that result in the resistance established by the project. The most common is to obtain the concrete made in plants, where there is a greater possibility of maintaining dosage control with the use of balances and concrete mixer trucks that provide the prepared material with the guaranteed concrete properties.
Reinforced concrete can be used as structural material in all construction, such as buildings, sanitation works, water treatment plants, sewage systems, dams, hydroelectric plants, buildings, bridges, viaducts, etc. The main question is to know when to use the preset or pre-drawn.
“It is only worth using pretension if the comparison between the two possibilities demonstrates the advantage. Today, to build a bridge of span greater than 20 meters, for example, neither is the common reinforced concrete. Already in a smaller dome, as of five meters, it may not be worth protecting, “says the professor. The main limitation of the prestender is its higher cost. The steel itself is more expensive than that used in ordinary reinforced concrete.
ADVANTAGES AND DISADVANTAGES
Among the main advantages of reinforced concrete is the fact that it is economical, since it has raw material with not very high cost, and the relative speed of construction. As it is a material that needs simple equipments for preparation, transport, densification and vibration, it does not require very specialized workmanship.
“It is a durable, impermeable structure if correctly dosed and resists fire, atmospheric influences, mechanical wear, shock and vibrations,” the professor said.
However, he points out that the solution also has some disadvantages, such as high weight and difficulty in carrying out reforms and demolitions, which become laborious and expensive. “Despite being widely used in roofs, reinforced concrete does not provide adequate insulation and thermal insulation, especially when installed in massive slabs with reduced thickness. Therefore, it will influence the comfort of the building “, he points out.
One of the characteristics of reinforced concrete is cracking, an unavoidable process. “If there is no cracking, there is no way for steel to help concrete resist tensions. It is necessary to live with this and what the technical norm preaches is to keep them under control and within reasonable limits, “he says.
He also advises the follow-up of the cracking as it can become harmful and cause damage as the acceleration in the oxidation of the armor. “Corrosion of steel is another action that cannot be avoided. When the piece is designed, it is already well known that after a certain time the CO2 in the atmosphere will trigger a carbonation process and, later on, the chlorides reach the armature. This action does not guarantee the beginning of the corrosion, although it usually occurs, as explained in the literature. It is a slow process, which can take hundreds of years, but there is a possibility. Thus, the standard defines the useful life of the structure and indicates the care to be taken, such as avoiding direct contact with rainwater and providing adequate drainage during the design phase, “he says.
Cement production is a process that consumes a high amount of energy. “The merit of current engineering is to be able to build with as little concrete as possible. The recommendation is to study the alternatives and whenever possible choose a more sustainable material. A good project of reinforced concrete can represent the smallest possible amount of raw material, “says the professional.
“Some buildings have stairs, cisterns and reservoirs all built in concrete. There is an exaggeration in this, because there are several possibilities, such as plastic boxes and metal or wooden stairs. But because designers and builders are already accustomed to concrete, they do not take into consideration other alternatives, “he adds.
In no particular order here is a list of some more advantages and Disadvantages of reinforce
Advantages of Reinforced Concrete
The concrete has a high compressive strength compared to other building materials.
Due to the frame, the reinforced concrete can also withstand a good amount of tensile stresses.
The cost of maintaining the reinforced concrete is very low.
A reinforced concrete structure can be shaped in a variety of ways and formats.
It requires less skilled labor for its execution, compared to metal structures, for example.
Good resistance to fire and weather.
A reinforced concrete structure is more durable than any other building system.
Good resistance to mechanical wear such as shocks and vibrations.
Disadvantages of Reinforced Concrete
The tensile strength of reinforced concrete is about one tenth of its compressive strength.
Because it is often produced in situ , the final strength of the concrete can be affected due to errors during the mixing and curing processes.
The reinforced concrete is used forms of wood or metal, increasing the project.
A reinforced concrete structure generates many construction waste and debris.
For a multi-story building, the section of pillars for a reinforced concrete structure is larger than the section of pillars in a metal structure.
Longer execution time than other building systems, due to curing time (can be reduced with use of additives).
The demolition of a reinforced concrete structure is difficult to execute and may not be feasible due to cost.