Reinforcing steel bars are used to help concrete withstand tension forces. Concrete is sufficiently strong to compression forces by nature, but tension forces can crack it.
Deformed rebars on reinforcing steel have been a standard requirement since 1968, but plain rebars are also used in situations where the reinforcing steel is expected to slide. This is typically the case when they're installed in highway pavement and segmental bridges.
The deformed pattern on a rebar helps the concrete adhere to the reinforcing steel surface. The pattern on a deformed bar isn't specified, but the spacing and the height of the "bumps" are regulated.
Rebar: Reinforcing Steel Bar Specifications
Reinforcing bars are hot-rolled using different steel materials. Most rebars are rolled from new steel billets, but others are rolled from steel debris or railroad rails. Rebars are required to contain some sort of identification that can be used to identify the mill that produced the reinforcing steel bar.
The American Society for Testing and Materials (ASTM) has created a standard identification ruling that all rebars must comply with:
- The number must identify the bar size.
- The type of steel symbol must be noted. For example, "N" means the bar was rolled from a new billet, "W" stands for weldable steel, and "A" designates rolled axle steel.
- The rebar grade identification must be cited: This is either 60 or 75, or metric 420 or 520. The grade indicates the rebar yield strength.
- A symbol identifying the manufacturer that rolled the bar must be included: This is usually a single letter or a plain symbol.
Lower-strength reinforcing steel bars have only three marks that identify the mill that produced the bar, the rebar size, and the type of steel used. High-strength reinforcing steel uses a continuous line system to show steel grade. If the rebar contains two lines, it indicates that the rebar was rolled into the 75,000-psi bars. When a single line is present, it represents a 60,000-psi bar.
Types of Rebar
- Carbon Steel Rebars: This is the most common type of rebar and is sometimes referred to as a "black bar." It's extremely versatile but it corrodes more easily than other types, making it inappropriate in areas that are subject to high humidity or in structures that are frequently exposed to water. Many consider carbon steel rebars to be the best option in all other types of construction, however.
- Welded Wire Fabric: Welded wire fabric (WWF) is made from a series of steel wires arranged at right angles and electrically welded at all steel wire crossings. It can be used in slab-on-ground slabs where the ground has been well compacted. A heavier fabrication of welded wire fabric can be used in walls and structural floor slabs. This is commonly used in road pavement, box culverts, drainage structures, and in small concrete canals.
- Sheet-Metal Reinforcing Bars: Sheet-metal reinforcement is commonly used in floor slabs, stairs, and roof construction. Sheet-metal reinforcing is composed of annealed sheet steel pieces bent into corrugations of about one-sixteenth of an inch deep with holes punched at regular spacing.
- Epoxy-Coated Rebars: Epoxy-coated rebars are expensive and used in areas that will be in contact with salt water or where a corrosion problem is imminent. The only problem is that the coating can be very delicate, so bars should be ordered from a reputable supplier.
- European Rebars: These rebars are typically made of manganese so they tend to bend more easily. They're not suitable for use in areas that are prone to extreme weather conditions or geological effects, such as earthquakes, hurricanes, or tornadoes. They can be cost-effective, however.
- Stainless Steel Rebars: Stainless steel can be used as an alternative reinforcing steel bar with carbon steel reinforcement. Using stainless steel reinforcing bars will not create galvanic corrosion, and it can be a cost-effective solution in areas subject to corrosion problems or where repair is difficult and expensive. These rebars will cost at least eight times more than epoxy-coated rebars, however.
- Galvanized Rebars: Galvanized rebars are 40 times more resistant to corrosion than carbon steer rebars, making them ideal for structures that will be heavily exposed to wet and humid conditions. They're pricey, however.
- Expanded Metal or Wire Mesh Rebars: Expanded metal or wire mesh reinforcement is another good product for concrete. Expanded metal is made by shearing a sheet of steel into parallel lines that are then expanded to form a diamond shape or a square shape between each cut. Expanded metal is commonly used as reinforcement in areas where a considerable thickness of plaster is required, or to reinforce light concrete construction. Wire mesh reinforcement can be used on sidewalks, small concrete pads, or walkable surfaces that don't receive high live or load charges.
- Glass-Fiber-Reinforced-Polymer (GFRP) Rebars: Similar to carbon fiber, GFRP rebars will not corrode — ever, under any conditions. You'll pay dearly for that, however. These rebars can run 10 times the cost of epoxy-coated rebars.
Rebar Prices and Cost
The cost of rebar can be estimated on a per-foot basis or per ton. The cost of steel can vary from month to month and even from day to day, so if you find a good price, be sure to lock it in ahead of time.