Rebar (short for reinforcing bar), known when massed as reinforcing steel or reinforcement steel, is a steel bar or mesh of steel wires used as a tension device in reinforced concrete and reinforced masonry structures to strengthen and aid the concrete under tension. Concrete is strong under compression, but has weak tensile strength. Rebar significantly increases the tensile strength of the structure. Rebar's surface is often "deformed" with ribs, lugs or indentations to promote a better bond with the concrete and reduce the risk of slippage.
The most common type of rebar is carbon steel, typically consisting of hot-rolled round bars with deformation patterns. Other readily available types include stainless steel, and composite bars made of glass fiber, carbon fiber, or basalt fiber. The steel reinforcing bars may also be coated in an epoxy resin designed to resist the effects of corrosion mostly in saltwater environments, but also land based constructions. Bamboo has been shown to be a viable alternative to reinforcing steel in concrete construction. These alternate types tend to be more expensive or may have lesser mechanical properties and are thus more often used in specialty construction where their physical characteristics fulfill a specific performance requirement that carbon steel does not provide. Steel and concrete have similar coefficients of thermal expansion, so a concrete structural member reinforced with steel will experience minimal differential stress as the temperature changes.
ASTM A615 covers deformed and plain carbon steel bars for concrete reinforcement. This specification covers bars and coils in four grades, Grade 40, Grade 60, Grade 75, and Grade 80. The grade designates the yield strength of the material, i.e. Grade 60 has a 60ksi minimum yield.
ASTM A706 covers deformed and plain low alloy steel bars for concrete reinforcement with restrictive mechanical properties and chemical composition in order to enhance weldability. This specification covers bars and coils in two grades, Grade 60 and Grade 80. The grade designates the yield strength of the material, i.e. Grade 60 has a 60ksi minimum yield.
In addition to the above chemical requirements, A706 rebar must also have a carbon equivalent (CE) not exceeding 0.55%.
The way to calculate this is to plug the chemical composition figures for a given heat lot of steel into the following formula:
CE = %C + (%Mn / 6) + (%Cu / 40) + (%Ni / 20) + (%Cr / 10) – (%Mo / 50) – (%V / 10)
Rebar produced to this specification shall be marked with the letter “W” to indicate weldability.