Reinforcing steel bars are used to help concrete withstand tension forces. Concrete by nature is sufficiently strong to compression forces, although tension forces can crack concrete. Deformed rebars on reinforcing steel was made a standard requirement since 1968, however, plain rebars are also used in situations where the reinforcing steel is expected to slide as usually installed in highway pavement and in segmental bridges. The deformed patter on a rebar will help the concrete to adhere to the reinforcing steel surface. The pattern on a deformed bar is not specified, however, the spacing, and the height of the ‘bumps’ is regulated.
Rebar: Reinforcing Steel Bar Specifications
Reinforcing bars are hot-rolled using different steel materials. Most rebars are rolled from new steel billets, while others are rolled from steel debris or railroad rails. Rebars are required to contain some sort of identification that could be used to identify the mill that produced the reinforcing steel bar.
The ASTM (American Society for Testing and Materials) has created a standard identification ruling that all rebars must comply with:
- The Number identifying the bar size.
- Type of steel symbol.for example, means the bar was rolled from a new billet, W for weldable steel (ASTM A-706), A for Axle (M 322 / ASTM 966) and so on.
- The rebar grade identification, either 60 or 75, or metric 420 or 520. This grade indicates the rebar yield strength.
- A symbol identifying the manufacturer that rolled the bar. It is usually a single letter or a plain symbol.
Lower strength reinforcing steel bars has 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, however, when a single line is present, it represents a 60,000 psi bar.
Rebar: Reinforcing Steel Bar Types
- Welded Wire Fabric
- Sheet-Metal Reinforcing Bars
- Stainless Steel Reinforcing Bars
- Expanded Metal and Wire Mesh Reinforcement
Welded wire fabric is made from a series of steel wires arranged at right angles and electrically welded at all steel wires crossings. Welded wire fabric, also known as WWF, 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 pavements, box culverts and drainage structures, and small concrete canals.
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 about 1/16 inch depth, with holes punched at regular spacing.
Stainless steel can be used as an alternative reinforcing steel bars with carbon steel reinforcement. Using stainless steel reinforcing bars will not create galvanic corrosion, and can be a cost-effective solution in areas subject to corrosion problems, or where repair is difficult and expensive.
Expanded metal or wire mesh reinforcement is also another good reinforcement product for concrete. Expanded metal is made by shearing a sheet of steel into parallel lines and the expanded to form a diamond shape or square shape between each cut. Expanded metal is commonly used as reinforcement in areas where great thickness of plaster is required, or to reinforced light concrete construction. Wire mesh reinforcement can be used on sidewalks, small concrete pads or walkable surfaces that do not receive high live nor load charges.