What is Rebar?
Rebars, also known as steel reinforcement bars, serve the purpose of enhancing the tensile strength of concrete. While concrete is sturdy in compression, it is weak in tension. Therefore, steel is utilized exclusively as rebar since its elongation under high temperatures, also known as thermal expansion coefficient, is almost equivalent to that of concrete.
Fig 1: Reinforcement Steel Bar
Grades of Rebar in Different Codes
Table 1: Grades of Rebar in Different Codes
| American Standard (ASTM A 615) | Euro Standard(DIN 488) | British Standard BS4449: 1997 | Indian Standard (IS: 1786) |
| Grade 75 (520) | BST 500 S | GR 460 A | Grade Fe – 415, Fe – 500, Fe – 500D |
| Grade 80 (550) | BST 500 M | GR 460 B | Grade Fe – 550 |
Types of Steel Reinforcement Bars
Steel bars are a commonly used building material in construction. They are utilized in various applications, such as in the reinforcement of concrete structures, as well as in the fabrication of steel frames and supports.
There are several major types of steel bars that are used in construction. One such type is the mild steel bar, which is a carbon steel bar that is easy to weld and work with. Mild steel bars are commonly used for the reinforcement of concrete structures.
Another type of steel bar used in construction is the deformed steel bar, also known as a reinforcement steel bar or rebar. These bars are used to provide strength and support to concrete structures, and are often twisted or bent to increase their surface area and improve their grip on the concrete.
Stainless steel bars are another commonly used type of steel bar in construction. They are highly resistant to corrosion and staining, making them ideal for use in applications where exposure to moisture or other corrosive elements is a concern. Stainless steel bars are often used in the fabrication of architectural features, such as handrails and balustrades.
Finally, high tensile steel bars are a type of steel bar that is used in applications where high strength is required. These bars are commonly used in the construction of bridges, as well as in the fabrication of heavy machinery and equipment.
Overall, steel bars are a versatile and durable building material that are used in a wide range of construction applications. The different types of steel bars available allow builders and engineers to select the most appropriate material for their specific needs, ensuring that structures are strong, safe, and long-lasting.
1. Mild Steel Bar
Mild steel bars are commonly used in construction, and their surfaces are smooth and rounded in shape. These bars come in various sizes, ranging from 6 mm to 50 mm. They are specifically used for special purposes, such as dowels in expansion joints where they need to slide in metal or paper sleeves, contraction joints in roads and runways, and as column spirals. One of their advantages is that they are easy to cut and bend without sustaining damage.
Fig 2 : Mild Steel Bar
Mild steel bars are not recommended for use in structural buildings such as bridges and other heavy structures due to several reasons. Firstly, mild steel bars do not exhibit strong bonding characteristics with concrete, which can lead to issues with structural integrity. This lack of bonding can result in reduced load-bearing capacity and increased risk of failure under heavy loads or stress.
Secondly, mild steel bars are prone to slippage when embedded in concrete. This means that they may not provide sufficient anchorage or grip within the concrete, which can result in structural instability. This is especially critical in heavy structures where slippage can lead to reduced structural performance and compromise the safety of the building.
Lastly, mild steel bars may not possess the required strength properties needed for heavy structures. The low strength of mild steel bars may not be suitable for withstanding the high loads and stresses that heavy structures, such as bridges, are subjected to. This can result in premature failure or reduced structural performance, posing significant risks to the safety and durability of the structure.
In conclusion, mild steel bars are not recommended for use in structural buildings like bridges and other heavy structures due to their poor bonding characteristics with concrete, propensity for slippage, and inadequate strength properties. It is essential to use appropriate steel reinforcement materials that offer strong bonding, reliable anchorage, and sufficient strength to ensure the safety and durability of heavy structures.
Grades in mild steel bars
Mild steel bars come in two grades. The first grade is designated as Fe 410-S or Grade 60, while the second grade is designated as Fe-410-o or Grade 40. Meanwhile, there are also Medium Tensile Steel Bars, which are designated as Fe-540-w-ht or Grade 75.
Physical Requirement of Mild Steel Bars
Table 2:Physical Requirement of Mild Steel Bars
| Types of Nominal size of bar | Ultimate Tensile Stress in N/mm2 | Yield Stress N/mm2 | Elongation Percentage min |
| Mild Steel Grade I or Grade 60 | |||
| For Bars upto 20mm | 410 | 250 | 23 |
| For Bars above 20mm upto 50mm | 410 | 240 | 23 |
| Mild Steel Grade II or Grade 40 | |||
| For Bars upto 20mm | 370 | 225 | 23 |
| For Bars above 20mm upto 50mm | 370 | 215 | 23 |
| Medium Tensile Steel Grade -75 | |||
| For Bars upto 16mm | 540 | 350 | 20 |
| For Bars above 16mm upto 32mm | 540 | 340 | 20 |
| For Bars above 32mm upto 50mm | 510 | 330 | 20 |
2. Deformed Steel Bar
Steel bars used in construction are often designed with features such as ribs, lugs, and indentations on their surfaces. These features serve to address one of the major issues faced by mild steel bars, which is slippage. By providing better bonding between the concrete and rebar, deformed steel bars are able to reduce the risk of slippage and improve overall performance.
Compared to other types of rebars, deformed steel bars also boast higher tensile properties. They are available in a range of sizes, from 6 mm to 50 mm in diameter, and are typically produced in sections. Overall, the use of deformed steel bars in construction can help improve the strength and durability of structures.
Types of Deformed Steel Bars
1. TMT Bars (Thermo Mechanically Treated Bars)
Thermo Mechanically Treated Bars, commonly known as TMT bars, are a type of steel bars used in reinforced cement concrete (RCC) work. These bars are subjected to hot treatment, which gives them high strength and makes them a superior option compared to traditional MS steel bars. TMT bars are designed with superior properties such as strength, ductility, welding ability, bending ability, and the highest quality standards that meet international levels. These features make TMT bars a reliable and efficient choice for construction purposes.
Fig 3: Deformed TMT Steel Bar
Characteristics of TMT Rebars
To create materials that possess better ductility and malleability, high yield strength and toughness, more bonding strength, earthquake resistance, corrosion resistance, and high thermal resistance, there is a need for a careful selection of raw materials and manufacturing processes.
In addition to this, it is crucial to ensure that the materials used are economical and safe in use. One way to achieve this is by ensuring that there is no loss in strength at welded joints. To achieve this, it is necessary to use ordinary electrodes for welding the joints.
Using such electrodes ensures that the material maintains its strength and does not weaken during the welding process. This is important as it can help to prevent the material from becoming brittle or developing cracks, which can ultimately compromise its overall strength and durability.
Overall, creating materials with these properties requires a balance of various factors, including raw material selection, manufacturing processes, and welding techniques. By carefully considering each of these factors, it is possible to create materials that are both strong and durable, as well as safe and economical in use.
2. High Strength Deformed Bars
Deformed bars are a type of steel bars that are widely used for reinforcement in construction. These bars are known for their high strength and durability. They are cold twisted, which means that they undergo a process of deformation where lugs, ribs, projections or other deformations are created on the surface of the bars.
Deformed bars come in a range of sizes or sections, with diameters ranging from 4 mm to 50 mm. This makes them suitable for a variety of construction applications, from small-scale projects to large infrastructure developments. The deformations on the surface of the bars provide better grip or bonding with concrete, making them more effective at reinforcing concrete structures. Overall, deformed bars are an important component in modern construction and play a vital role in ensuring the safety and stability of buildings and other structures.
Fig 4: Deformed HSD Steel Bar
Characteristics of HSD Rebar
HSD bars are a type of reinforcement bar used in construction. One of the key features of these bars is their low carbon value. This lower carbon level results in good ductility, strength, and welding ability. This makes them an excellent choice for construction projects where welding is required.
Another advantage of HSD bars is their superior bonding strength. When used with concrete, these bars are known to provide excellent bonding strength. This ensures that the concrete structure is strong and stable.
In addition, HSD bars have a high tensile strength. This is an important asset in the construction process, where a lot of bending and re-bending is required. The bars can withstand the stress and strain of the bending process without breaking or losing their strength.
HSD bars are also versatile in their application range. They can be used in a variety of structures, including residential, commercial, and industrial buildings, as well as bridges. This wide range of applications makes HSD bars a popular choice among builders and architects.
Finally, HSD bars are satisfactorily malleable. They have a minimum weight and maximum strength, making them suitable for both compression and tension reinforcement. This makes them an ideal choice for construction projects that require both types of reinforcement. Overall, HSD bars are a reliable and effective choice for reinforcing concrete structures.
3. Other Types of Rebars
Rebars are an essential component in the construction industry, used to reinforce concrete structures and provide additional strength and durability. The type of material used in the production of rebar plays a crucial role in determining the strength and longevity of the reinforced concrete structure.
There are different types of rebars available, depending on the type of material used in their production. For instance, steel rebars are commonly used in construction projects due to their high strength and durability. Steel rebars are made from carbon steel, which is an alloy of iron and carbon. These rebars can be further classified into different types based on their carbon content, such as mild steel and high-strength steel.
Another type of rebar is the fiberglass rebar, which is made from fiberglass reinforced polymer. This type of rebar is ideal for applications where resistance to corrosion is necessary, such as in coastal areas or where the structure will be exposed to harsh chemicals.
Finally, there are also stainless steel rebars, which are made from an alloy of steel and chromium. These rebars are particularly resistant to corrosion and are ideal for use in structures that will be exposed to harsh environmental conditions, such as in bridges or buildings located in areas with high levels of pollution.
In summary, the type of material used in the production of rebar is a critical factor in determining the strength and durability of reinforced concrete structures. Depending on the specific requirements of the construction project, different types of rebars may be used, such as steel rebars, fiberglass rebars, or stainless steel rebars.
1. European Rebar
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Rebar used in Europe is composed of manganese, a material that gives it a flexible nature. However, this flexibility makes it unsuitable for construction in areas that are prone to severe weather conditions or geological effects such as earthquakes, hurricanes, or tornadoes. Despite this drawback, European rebar is relatively inexpensive.
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2. Carbon Steel Rebar
Black Bar is a type of rebar that is composed of carbon steel and is named so due to its dark color. The high tensile strength ratio, coupled with its cost-effectiveness, make it a popular choice among builders and construction professionals.
However, one significant disadvantage of Black Bar is its tendency to corrode over time, which can have a detrimental impact on both the concrete and overall structure. This corrosion can weaken the rebar and lead to structural failure, posing a significant safety risk.
Despite its vulnerability to corrosion, Black Bar remains a popular choice for construction projects, thanks to its high tensile strength and affordability. It is essential, however, to take proper precautions and measures to mitigate the risk of corrosion to ensure the longevity and safety of any structure built with Black Bar.
Fig 5: Carbon Steel Rebar
3. Epoxy-Coated Rebar
Epoxy-coated rebar is a type of reinforcing steel that has been given an additional layer of protection through the application of an epoxy coating. This coating gives the rebar a black color and provides it with a significant increase in resistance to corrosion, making it a popular choice for construction projects that require durability and longevity.
Despite its advantages, the epoxy coating on rebar is very delicate. Any damage to the coating, no matter how small, can significantly reduce its resistance to corrosion. This means that careful handling and installation of epoxy-coated rebar is essential to ensure its effectiveness in protecting against rust and other forms of deterioration.
Although the epoxy coating on rebar is fragile, its benefits in terms of corrosion resistance are significant. In fact, it can be between 70 to 1,700 times more resistant to corrosion than uncoated rebar with the same tensile strength. This makes it an attractive option for use in harsh environments where traditional steel reinforcements may not be able to withstand the conditions. Overall, the use of epoxy-coated rebar can help extend the lifespan of a structure and reduce maintenance costs over time.
Fig 6: Epoxy-Coated Rebar
4. Galvanized Rebar
Galvanized rebar and black rebar differ in their level of corrosion resistance, with galvanized rebar being forty times more resistant. Additionally, the coating on galvanized rebar is more durable and difficult to damage than that of epoxy-coated rebar. While epoxy-coated rebar may be less expensive, galvanized rebar’s increased durability and corrosion resistance make it a more valuable option in certain applications. It’s important to weigh the cost and benefits of each type of rebar before making a decision.
Fig 7: Galvanized Rebar
5. Glass-Fiber-Reinforced-Polymer (GFRP)
GFRP, or Glass Fiber Reinforced Polymer, is a material composed of carbon fiber. Unlike other types of materials, it does not allow for bending due to its fibrous nature. Despite being relatively expensive compared to other types of reinforcement bars, GFRP is highly resistant to corrosion.
Fig 8: Glass-Fiber-Reinforced-Polymer Rebar
6. Stainless Steel Rebar
Stainless steel rebar is known for its exceptional properties, making it one of the best reinforcing bars available in the market. Despite being the most expensive type of rebar, costing approximately eight times more than epoxy-coated rebar, its superiority makes it a popular choice for most projects. However, using stainless steel rebar for all projects is often unnecessary, except for unique circumstances where its benefits outweigh its cost.
Stainless steel rebar boasts of outstanding resistance to corrosion, surpassing black bar rebar by a whopping 1,500 times. It also outperforms all other types of corrosive-resistant or corrosive-proof reinforcing bars in terms of damage resistance. In addition, it can be bent in the field, making it flexible and versatile for various applications.
In summary, while stainless steel rebar may be the most expensive type of rebar, its exceptional properties make it the best choice for most projects. Its superior corrosion and damage resistance, coupled with its ability to be bent in the field, make it a versatile and reliable reinforcing bar for various construction applications.