Introduction
Reinforcement bars, commonly known as rebars , play a critical role in modern construction. While concrete is strong in compression, it lacks tensile strength and can crack under stress. To overcome this limitation, steel rebars are embedded within the concrete to provide the necessary tensile support. This combination of concrete and steel results in Reinforced Cement Concrete (RCC) — a material that is both strong and durable.
Properties of Rebar
The use of steel as rebar is primarily due to its compatibility with concrete. Steel has a thermal expansion coefficient similar to that of concrete, which prevents internal stresses caused by temperature changes. Additionally, steel offers high tensile strength and bonds well with concrete, making it an ideal reinforcing material.
Grades of Rebar Across Different Standards
Different countries follow their own standards for classifying rebar grades based on yield strength and other mechanical properties:
| 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 | Fe – 415, Fe – 500, Fe – 500D |
| Grade 80 (550) | BST 500 M | GR 460 B | Fe – 550 |
These classifications help ensure consistency in design and construction across international projects.
Types of Steel Reinforcement Bars
1. Mild Steel Bars
Mild steel bars have a plain, round surface and are available in sizes ranging from 6 mm to 50 mm . They are often used in specialized applications such as dowels at expansion joints, contraction joints in roads, and column spirals.
Uses and Limitations
- Easy to cut and bend
- Low bonding strength with concrete
- Not recommended for major structures like bridges due to slippage and limited strength
Grades of Mild Steel Bars
- Grade I (Fe 410-S or Grade 60)
- Grade II (Fe 410-O or Grade 40)
- Medium Tensile Steel Bar (Grade 75)
Physical Requirements Table
| Nominal Size | Ultimate Tensile Stress (N/mm²) | Yield Stress (N/mm²) | Elongation % (min) |
|---|---|---|---|
| Up to 20 mm | 410 | 250 | 23 |
| 20–50 mm | 410 | 240 | 23 |
| Up to 16 mm | 540 | 350 | 20 |
| 16–32 mm | 540 | 340 | 20 |
| 32–50 mm | 510 | 330 | 20 |
2. Deformed Steel Bars
Deformed steel bars feature ribs, lugs, or indentations on their surface, which significantly improve the bond between the bar and the concrete. These bars offer superior tensile strength compared to mild steel bars.
i. Thermo Mechanically Treated (TMT) Bars
TMT bars are among the most advanced types of reinforcement steel. They are heat-treated during manufacturing to enhance their physical properties.
Characteristics:
- High yield strength and toughness
- Excellent ductility and malleability
- Earthquake and corrosion resistance
- No loss of strength at welded joints
- Economical and safe for structural use
ii. High Strength Deformed (HSD) Bars
HSD bars are cold-twisted steel bars with surface deformations that increase bonding with concrete.
Characteristics:
- Low carbon content ensures good weldability and ductility
- Superior bonding strength
- High tensile strength suitable for bending and rebending
- Ideal for residential, commercial, industrial buildings, and bridges
3. Other Types of Rebars Based on Material
a. European Rebar
Made from manganese , these rebars are easy to bend but not suitable for extreme weather or seismic zones. They are economical but less durable in harsh conditions.
b. Carbon Steel Rebar (Black Bar)
This type of rebar is made of carbon steel and gets its name from its dark color. It offers high tensile strength but is prone to corrosion , which can damage the surrounding concrete over time.
c. Epoxy-Coated Rebar
A black steel bar coated with epoxy resin , offering 70 to 1,700 times more corrosion resistance than uncoated bars. However, the coating is fragile and can be damaged during installation.
d. Galvanized Rebar
Galvanized rebar is coated with zinc , providing about 40 times more corrosion resistance than black rebar. The coating is more durable than epoxy, though it comes at a higher cost.
e. Glass-Fiber-Reinforced-Polymer (GFRP) Rebar
Made from fiber-reinforced polymer , GFRP rebar is highly corrosion-resistant and lightweight. However, it cannot be bent after production and is costly compared to traditional steel rebars.
f. Stainless Steel Rebar
Stainless steel rebar is the most expensive option, costing up to 8 times more than epoxy-coated rebar. It provides exceptional corrosion resistance (up to 1,500 times more than black bar) and can be bent on-site. It’s best suited for specialized or marine environments .
Conclusion
Rebar is an essential component of reinforced concrete structures, enhancing their strength and durability. From traditional mild steel bars to advanced options like TMT, HSD, GFRP, and stainless steel , each type of rebar serves a specific purpose depending on the structural requirements and environmental conditions.