Most people are familiar with reinforcing steel, commonly called rebar. It is used in bridges, buildings, skyscrapers, homes, warehouses, and foundations to increase the strength of a concrete structure. Reinforcing steel is used in concrete to provide additional strength, as concrete is weak in tension, while steel is strong in both tension and compression.
Steel is the product of choice for reinforcing concrete due to a combination of unique factors:
- Elastic properties – The modulus of all steel reinforcement is 29,000,000 psi and this value may be used in design. This uniform modulus for all grades and bar sizes simplifies the design process. Materials with lower moduli may require additional bars to provide the same serviceability and structures designed with these materials may experience increased deflections and additional cracking. Steel has similar elastic properties under both tensile and compression loads.
- Elongation under load – Steel reinforcement has significant elongation under load providing for well-defined cracks in the structure during overload conditions. Such cracking provides suitable warning for occupants regarding the loading of a structure. Materials that do not exhibit non-elastic behavior under load may not provide sufficient ductility to warn of impending failure.
- Uniform properties in 3D – Steel reinforcement generally has uniform properties in all directions and the shear strength is similar to the longitudinal yield strength.
- Fatigue – The fatigue properties of steel reinforced concrete structures are well understood.
- Bond development – The development strength of reinforcing steel in both straight and bent conditions is well researched and understood.
- Yield – At loads less than yield, steel exhibits elastic properties that enable a structure to rebound upon reloading. Steel reinforcement is available with yield strengths from 40 to 100 ksi. The yield strength of steel is not dependent on the bar diameter and substitution of different combinations of bars with the same bar area may be readily provided. This provides flexibility in the methods of obtaining the same properties in a concrete structure.
- Thermal properties – The modulus of thermal expansion of steel reinforcement is very similar to that of concrete. Due to the similarity of concrete and steel thermal properties additional stresses or deflections are not introduced upon heating the concrete structure.
- Strength retention – Under heating from fire, steel is able to withstand high temperatures before strength and ductility properties change. Many concrete structures that have been subjected to fire can be rehabilitated using the existing reinforcing steel.
- Joining – Steel reinforcement can be joined using welding or couplers that have strengths similar to that of the reinforcing steel.
- Code Acceptance – Steel reinforcement is accepted by all concrete design codes worldwide.
- Recycled content – The recycled content of reinforcing steel is greater than 75 percent and in most circumstances greater than 95 percent.
- Ability to be recycled – Reinforcing steel is able to be readily recycled at the end of the structure design life.
- Ability to be bent – Reinforcing steel can be bent after being manufactured. This simplifies the construction and provides for rapid delivery of fabricated materials.
- Robustness – Reinforcing steel is robust and able to withstand rigors of construction.
- Compatibility with concrete – Reinforcing steel does not need to be tied directly to the formwork and does not float in concrete.
- Availability – Reinforcing steel is available in every region of the country. Due to the number and distribution of plants, LEED and other sustainability credits are available.
Steel reinforcing bars are produced from molten steel, by forming it into large rectangular billets and then running it through a series of dies, which shape the steel into reinforcing bars. During the forming process, deformations are formed in the surface of the bars that are used to help in transferring loads between the concrete and the reinforcing steel.
Reinforcing bar is generally produced to meet ASTM or AASHTO specifications:
- A615/A615M: Standard Specification for Deformed and Plain Carbon-Steel Bars for Concrete Reinforcement
- A706/A706M: Standard Specification for Deformed and Plain Low-Alloy Steel Bars for Concrete Reinforcement
- A955/A955M: Standard Specification for Deformed and Plain Stainless-Steel Bars for Concrete Reinforcement
- A996/A996M: Standard Specification for Rail-Steel and Axle-Steel Deformed Bars for Concrete Reinforcement
- A1035/A1035M: Standard Specification for Deformed and Plain, Low-Carbon, Chromium, Steel Bars for Concrete Reinforcement