What is Steel Reinforcement? Types and Properties of Steel Rebars

What is Steel Reinforcement?

Steel reinforcement are steel bars that are provided in combination with plain cement concrete to make it reinforced concrete. Hence these structures form steel reinforced cement concrete structure (R.C.C). Steel reinforcement is commonly called as ‘rebars’.

Need for Steel Reinforcement

Plain concrete is weak in tension and strong in compression. Tensile property for concrete structures is obtained by incorporating steel reinforcement. The steel reinforcement is strong in both tension and compression. The tensile property provided by the steel reinforcement will prevent and minimize concrete cracks under tension loads.
The coefficient of thermal expansion of steel reinforcement and concrete are similar in that they undergo similar expansions during temperature changes. This property will ensure that the concrete is subjected to minimal stress during temperature variations.
The surface of the steel reinforcement bars is patterned to have a proper bond with the surrounding concrete material.
The two main factors that provide strength to the concrete structures are steel and concrete. The design engineer will combine both the elements and design the structural element such a way that the steel resists the induced tensile and shear force, while the concrete takes up the compressive forces.

Types of Steel Reinforcement

The steel reinforcement used in concrete construction is mainly of 4 types. They are:
  1. Hot Rolled Deformed Steel Bars
  2. Cold Worked Steel Bars
  3. Mild Steel Plain Bars
  4. Prestressing Steel Bars

1. Hot Rolled Deformed Bars

Hot rolled deformed bars are most commonly used steel reinforcement for R.C.C structures. As the name says, the hot rolling of the reinforcement is undergone leaving certain deformations on its surface in the form of ribs. These ribs help to form a bond with the concrete. The typical yield strength of hot-rolled deformed bars is 60000psi.
Hot Rolled Steel Bars
Fig.1: Hot Rolled Steel Bars; Image Courtesy-RIVA Stahl Gmbh

2. Cold Worked Steel Bars

A cold worked reinforcement bar is obtained by letting the hot rolled steel bars to undergo cold working. In the cold working process, the bars will undergo twisting and drawing. The process is performed at room temperature. The cold worked steel bars do not undergo a plastic yield thus have less ductility when compared with hot rolled bars.

3. Mild Steel Plain Bars

The mild steel plain reinforcement bars do not have ribs on their surface. They have a plain surface. These bars are used for small projects where the major concern is the economy. The tensile yield strength of these bars has a value of 40000psi.
Mild Steel Bars
Fig.2: Mild Steel Bars; Image Courtesy: Vision Alloys

4. Prestressing Steel Bars

The prestressing steel reinforcement are steel bars used in the form of strands or tendons. Multiple strands are employed in concrete in order to perform the prestressing action. The strands are made of multiple wires either 2 or 3 or 7 wire strands.
The wires used here are cold formed and have a high tensile strength ranging from 250000 – 270000 psi. This high strength helps to effectively prestress the concrete.

Advantages of Steel Reinforcement

Steel reinforcement is a reinforcing choice compared to other reinforcing materials due to its unique advantages. They are:
  1. Compatibility with Concrete: The fresh concrete is placed on the formwork mold already prepared with reinforcement. The steel reinforcement won’t float in concrete during the concrete placing procedure. Hence, steel reinforcement does not demand special tying up with formworks.
  2. Robustness of Steel Reinforcement: The steel bars are robust in nature that they have the ability to withstand the rigors, the wear and tear during the construction activities.
  3. Bent Property of Steel Reinforcement: The steel bars once manufactured to standard size, it can be bent to the required specifications. Hence fabricated steel bars are delivered easily at the site.
  4. Recycling Property: The steel reinforced left over after the service life of a structure is recycled again and used for new construction.
  5. Easily Available: Every region of a country will have a steel supplier or manufacturer. Hence steel reinforcement is easily available.

Disadvantages of Steel Reinforcement

The main disadvantages of steel reinforcement are mentioned below:
  1. Reactive Nature of Steel Reinforcement: In concrete structures where the cover is small and subjected to external moisture and salt action, the reinforcement undergoes reaction and starts to corrode. These can lessen the strength of concrete and finally to failure.
  2. Expensive: The cost of steel reinforcement in high. This will increase the cost of construction
  3. Melts at high temperature: At higher temperatures, the steel reinforcement may melt. This is the reason why the steel reinforcement are tied up and not welded.