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Two bundles of full-length rebar, which will be placed, bent, or cut as required by installation

Rebar (short for reinforcement bar or reinforcing bar), known when massed as reinforcing steel or steel reinforcement,[1] is a tension device added to concrete to form reinforced concrete and reinforced masonry structures to strengthen and aid the concrete under tension. Concrete is strong under compression, but has low tensile strength. Rebar usually consists of steel bars which significantly increase the tensile strength of the structure. Rebar surfaces feature a continuous series of 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 embossed into its surface. Steel and concrete have similar coefficients of thermal expansion,[2] so a concrete structural member reinforced with steel will experience minimal differential stress as the temperature changes.

Other readily available types of rebar are manufactured of stainless steel, and composite bars made of glass fiber, carbon fiber, or basalt fiber. The carbon steel reinforcing bars may also be coated in zinc or an epoxy resin designed to resist the effects of corrosion, especially when used in saltwater environments. Bamboo has been shown to be a viable alternative to reinforcing steel in concrete construction.[3][4] These alternative 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.

History

[edit]
Further information: Reinforced concrete § History
An early version of rebar inside the Leaning Tower of Nevyansk

Reinforcing bars in masonry construction have been used since antiquity, with Rome using iron or wooden rods in arch construction.[5] Iron tie rods and anchor plates were later employed across Medieval Europe, as a device to reinforce arches, vaults, and cupolas.[6][7] 2,500 meters of rebar was used in the 14th-century Château de Vincennes.[8]

During the 18th century, rebar was used to form the carcass of the Leaning Tower of Nevyansk in Russia, built on the orders of the industrialist Akinfiy Demidov. The wrought iron[citation needed] used for the rebar was of high quality, and there is no corrosion on the bars to this day. The carcass of the tower was connected to its cast iron tented roof, crowned with one of the first known lightning rods.[9]

However, not until the mid-19th century, with the embedding of steel bars into concrete (thus producing modern reinforced concrete), did rebar display its greatest strengths. Several people in Europe and North America developed reinforced concrete in the 1850s. These include Joseph-Louis Lambot of France, who built reinforced concrete boats in Paris (1854) and Thaddeus Hyatt of the United States, who produced and tested reinforced concrete beams. Joseph Monier of France is one of the most notable figures for the invention and popularization of reinforced concrete. As a French gardener, Monier patented reinforced concrete flowerpots in 1867, before proceeding to build reinforced concrete water tanks and bridges.[10]

The Alvord Lake Bridge in San Francisco's Golden Gate Park, the first reinforced concrete bridge built in the United States

Ernest L. Ransome, an English engineer and architect who worked in the United States, made a significant contribution to the development of reinforcing bars in concrete construction. He invented twisted iron rebar, which he initially thought of while designing self-supporting sidewalks for the Masonic Hall in Stockton, California. His twisted rebar was, however, not initially appreciated and even ridiculed at the Technical Society of California, where members stated that the twisting would weaken the iron.[11] In 1889, Ransome worked on the West Coast mainly designing bridges. One of these, the Alvord Lake Bridge in San Francisco's Golden Gate Park, was the first reinforced concrete bridge built in the United States. He used twisted rebar in this structure.[12]

At the same time Ransome was inventing twisted steel rebar, C.A.P. Turner was designing his "mushroom system" of reinforced concrete floor slabs with smooth round rods and Julius Kahn was experimenting with an innovative rolled diamond-shaped rebar with flat-plate flanges angled upwards at 45° (patented in 1902). Kahn predicted concrete beams with this reinforcing system would bend like a Warren truss, and also thought of this rebar as shear reinforcement. Kahn's reinforcing system was built in concrete beams, joists, and columns.

The system was both praised and criticized by Kahn's engineering contemporaries: Turner voiced strong objections to this system as it could cause catastrophic failure to concrete structures. He rejected the idea that Kahn's reinforcing system in concrete beams would act as a Warren truss and also noted that this system would not provide the adequate amount of shear stress reinforcement at the ends of the simply supported beams, the place where the shear stress is greatest. Furthermore, Turner warned that Kahn's system could result in a brittle failure as it did not have longitudinal reinforcement in the beams at the columns.

This type of failure manifested in the partial collapse of the Bixby Hotel in Long Beach, California and total collapse of the Eastman Kodak Building in Rochester, New York, both during construction in 1906. It was, however, concluded that both failures were the consequences of poor-quality labor. With the increase in demand of construction standardization, innovative reinforcing systems such as Kahn's were pushed to the side in favor of the concrete reinforcing systems seen today.[13]

Requirements for deformations on steel bar reinforcement were not standardized in US construction until about 1950. Modern requirements for deformations were established in "Tentative Specifications for the Deformations of Deformed Steel Bars for Concrete Reinforcement", ASTM A305-47T. Subsequently, changes were made that increased rib height and reduced rib spacing for certain bar sizes, and the qualification of “tentative” was removed when the updated standard ASTM A305-49 was issued in 1949. The requirements for deformations found in current specifications for steel bar reinforcing, such as ASTM A615 and ASTM A706, among others, are the same as those specified in ASTM A305-49.[14]

Use in concrete and masonry

[edit]
"Primary reinforcement" and "Secondary reinforcement" redirect here. For primary reinforcement and secondary reinforcement in psychology (operant conditioning), see Reinforcement § Primary reinforcers and Reinforcement § Secondary reinforcers.
Rebar has been placed atop a temporary wooden formwork deck prior to pouring concrete. The large horizontal rebar "cages" will be encased within a beam, while several thick vertical rebar stubs will stick out of the pour to form the base of a future column.

Concrete is a material that is very strong in compression, but relatively weak in tension. To compensate for this imbalance in concrete's behavior, rebar is cast into it to carry the tensile loads. Most steel reinforcement is divided into primary and secondary reinforcement:

  • Primary reinforcement refers to the steel which is employed to guarantee the resistance needed by the structure as a whole to support the design loads.
  • Secondary reinforcement, also known as distribution or thermal reinforcement, is employed for durability and aesthetic reasons, by providing enough localized resistance to limit cracking and resist stresses caused by effects such as temperature changes and shrinkage.

Secondary applications include rebar embedded in masonry walls, which includes both bars placed horizontally in a mortar joint (every fourth or fifth course of block) or vertically (in the horizontal voids of cement blocks and cored bricks, which is then fixed in place with grout. Masonry structures held together with grout have similar properties to concrete – high compressive resistance but a limited ability to carry tensile loads. When rebar is added they are known as "reinforced masonry".

A similar approach (of embedding rebar vertically in designed voids in engineered blocks) is also used in dry-laid landscape walls, at least pinning the lowest course in place into the earth, also employed securing the lowest course and/or deadmen in walls made of engineered concrete or wooden landscape ties.

In unusual cases, steel reinforcement may be embedded and partially exposed, as in the steel tie bars that constrain and reinforce the masonry of Nevyansk Tower or ancient structures in Rome and the Vatican.

Physical characteristics

[edit]

Steel has a thermal expansion coefficient nearly equal to that of modern concrete. If this were not so, it would cause problems through additional longitudinal and perpendicular stresses at temperatures different from the temperature of the setting.[15] Although rebar has ribs that bind it mechanically to the concrete, it can still be pulled out of the concrete under high stresses, an occurrence that often accompanies a larger-scale collapse of the structure. To prevent such a failure, rebar is either deeply embedded into adjacent structural members (40–60 times the diameter), or bent and hooked at the ends to lock it around the concrete and other rebar. This first approach increases the friction locking the bar into place, while the second makes use of the high compressive strength of concrete.

Common rebar is made of unfinished tempered steel, making it susceptible to rusting. Normally the concrete cover is able to provide a pH value higher than 12 avoiding the corrosion reaction. Too little concrete cover can compromise this guard through carbonation from the surface, and salt penetration. Too much concrete cover can cause bigger crack widths which also compromises the local guard. As rust takes up greater volume than the steel from which it was formed, it causes severe internal pressure on the surrounding concrete, leading to cracking, spalling, and, ultimately, structural failure. This phenomenon is known as oxide jacking.

This is a particular problem where the concrete is exposed to salt water, as in bridges where salt is applied to roadways in winter, or in marine applications. Uncoated, corrosion-resistant low-carbon/chromium (microcomposite), silicon bronze, epoxy-coated, galvanized, or stainless steel rebars may be employed in these situations at greater initial expense, but significantly lower expense over the service life of the project.[16][17]

Extra care is taken during the transport, fabrication, handling, installation, and concrete placement process when working with epoxy-coated rebar, because damage will reduce the long-term corrosion resistance of these bars.[18] Even damaged epoxy-coated bars have shown better performance than uncoated reinforcing bars, though issues from debonding of the epoxy coating from the bars and corrosion under the epoxy film have been reported.[19] These epoxy-coated bars are used in over 70,000 bridge decks in the US, but this technology was slowly being phased out in favor of stainless steel rebar as of 2005 because of its poor performance.[20][21]

Requirements for deformations are found in US-standard product specifications for steel bar reinforcing, such as ASTM A615 and ASTM A706, and dictate lug spacing and height.

Fibre-reinforced plastic rebar is also used in high-corrosion environments. It is available in many forms, such as spirals for reinforcing columns, common rods, and meshes. Most commercially available rebar is made from unidirectional fibers set in a thermoset polymer resin and is often referred to as FRP.

Some special construction such as research and manufacturing facilities with very sensitive electronics may require the use of reinforcement that is non-conductive to electricity, and medical imaging equipment rooms may require non-magnetic properties to avoid interference. FRP rebar, notably glass fibre types have low electrical conductivity and are non-magnetic which is commonly used for such needs. Stainless steel rebar with low magnetic permeability is available and is sometimes used to avoid magnetic interference issues.

Reinforcing steel can also be displaced by impacts such as earthquakes, resulting in structural failure. The prime example of this is the collapse of the Cypress Street Viaduct in Oakland, California as a result of the 1989 Loma Prieta earthquake, causing 42 fatalities. The shaking of the earthquake caused rebars to burst from the concrete and buckle. Updated building designs, including more circumferential rebar, can address this type of failure.

Sizes and grades

[edit]

US sizes

[edit]

US/Imperial bar sizes give the diameter in units of 1⁄8 inch (3.2 mm) for bar sizes #2 through #8, so that #8 = 8⁄8 inch = 1-inch (25 mm) diameter.

There are no fractional bar sizes in this system. The "#" symbol indicates the number sign, and thus "#6" is read as "number six". The use of the "#" sign is customary for US sizes, but "No." is sometimes used instead. Within the trades rebar is known by a shorthand utilizing the bar diameter as descriptor, such as "four-bar" for bar that is four-eighths (or one-half) of an inch.

The cross-sectional area of a bar, as given by πr², works out to (bar size/9.027)², which is approximated as (bar size/9)² square inches. For example, the area of #8 bar is (8/9)² = 0.79 square inches.

Bar sizes larger than #8 follow the 1⁄8-inch rule imperfectly and skip sizes #12–13, and #15–17 due to historical convention. In early concrete construction bars of one inch and larger were only available in square sections, and when large format deformed round bars became available around 1957,[22] the industry manufactured them to provide the cross-sectional area equivalent of standard square bar sizes that were formerly used. The diameter of the equivalent large format round shape is rounded to the nearest 1⁄8 inch to provide the bar size. For example, #9 bar has a cross section of 1.00 square inch (6.5 cm2), and therefore a diameter of 1.128 inches (28.7 mm). #10, #11, #14, and #18 sizes correspond to 11⁄8 inch, 11⁄4, 11⁄2, and 2-inch square bars, respectively.[23]

Sizes smaller than #3 are no longer recognized as standard sizes. These are most commonly manufactured as plain round undeformed rod steel but can be made with deformations. Sizes smaller than #3 are typically referred to as "wire" products and not "bar" and specified by either their nominal diameter or wire gage number. #2 bars are often informally called "pencil rod" as they are about the same size as a pencil.

When US/Imperial sized rebar are used in projects with metric units, the equivalent metric size is typically specified as the nominal diameter rounded to the nearest millimeter. These are not considered standard metric sizes, and thus is often referred to as a soft conversion or the "soft metric" size. The US/Imperial bar size system recognizes the use of true metric bar sizes (No. 10, 12, 16, 20, 25, 28, 32, 36, 40, 50 and 60 specifically) which indicates the nominal bar diameter in millimeters, as an "alternate size" specification. Substituting a true metric size for a US/Imperial size is called a hard conversion, and sometimes results in the use of a physically different sized bar.

Steel reinforcement bars with color codes indicating the grade
US rebar size chart
Imperial

bar size

Metric bar

size (soft)

Linear Mass Density Nominal diameter Nominal area
lb⁄ft kg⁄m (in) (mm) (in2) (mm2)
#2[a] No.6 0.167 0.249 0.250 = 2⁄8 = 1⁄4 6.35 0.05 32
#3 No.10 0.376 0.560 0.375 = 3⁄8 9.53 0.11 71
#4 No.13 0.668 0.994 0.500 = 4⁄8 = 1⁄2 12.7 0.20 129
#5 No.16 1.043 1.552 0.625 = 5⁄8 15.9 0.31 200
#6 No.19 1.502 2.235 0.750 = 6⁄8 = 3⁄4 19.1 0.44 284
#7 No.22 2.044 3.042 0.875 = 7⁄8 22.2 0.60 387
#8 No.25 2.670 3.973 1.000 = 8⁄8 25.4 0.79 510
#9 No.29 3.400 5.060 1.128 ≈ 9⁄8 28.7 1.00 645
#10 No.32 4.303 6.404 1.270 ≈ 10⁄8 32.3 1.27 819
#11 No.36 5.313 7.907 1.410 ≈ 11⁄8 35.8 1.56 1,006
#14 No.43 7.650 11.384 1.693 ≈ 14⁄8 43.0 2.25 1,452
#18 No.57 13.60 20.239 2.257 ≈ 18⁄8 57.3 4.00 2,581
  1. ^ Historic size designation that is no longer in common use.[citation needed]

Canadian sizes

[edit]
Concrete betraying corroded rebar within it at the Queen Elizabeth Way bridge over the Welland River in Niagara Falls, Ontario, Canada

Metric bar designations represent the nominal bar diameter in millimeters, rounded to the nearest 5 mm.

Metric

bar size

Linear Mass Density

(kg/m)

Nominal diameter

(mm)

Cross-sectional

Area (mm2)

10M 0.785 11.3 100
15M 1.570 16.0 200
20M 2.355 19.5 300
25M 3.925 25.2 500
30M 5.495 29.9 700
35M 7.850 35.7 1000
45M 11.775 43.7 1500
55M 19.625 56.4 2500

European sizes

[edit]

Metric bar designations represent the nominal bar diameter in millimetres. Preferred bar sizes in Europe are specified to comply with Table 6 of the standard EN 10080,[24] although various national standards still remain in force (e.g. BS 4449 in the United Kingdom). In Switzerland some sizes are different from European standard.

Steel reinforcement in storage
Metric

bar size

Linear mass

density (kg/m)

Nominal

diameter (mm)

Cross-sectional

area (mm2)

6,0 0.222 6 28.3
8,0 0.395 8 50.3
10,0 0.617 10 78.5
12,0 0.888 12 113
14,0 1.21 14 154
16,0 1.58 16 201
20,0 2.47 20 314
25,0 3.85 25 491
28,0 4.83 28 616
32,0 6.31 32 804
40,0 9.86 40 1257
50,0 15.4 50 1963

Australian sizes

[edit]

Reinforcement for use in concrete construction is subject to the requirements of Australian Standards AS3600 (Concrete Structures) and AS/NZS4671 (Steel Reinforcing for Concrete). There are other standards that apply to testing, welding and galvanizing.

The designation of reinforcement is defined in AS/NZS4671 using the following formats:

Reinforcement steel bar Grade 500 Class N
Nominal Diameter (mm) Cross-sectional area (mm sq) Mass per metre length, kg/m
12 113 0.888
16 201 1.58
20 314 2.47
24 452 3.55
28 616 4.83
32 804 6.31
36 1020 7.99

Shape/ Section

D- deformed ribbed bar, R- round / plain bar, I- deformed indented bar

Ductility Class

L- low ductility, N- normal ductility, E- seismic (Earthquake) ductility

Standard grades (MPa)

250N, 300E, 500L, 500N, 500E

Examples:
D500N12 is deformed bar, 500 MPa strength, normal ductility and 12 mm nominal diameter – also known as "N12"

Bars are typically abbreviated to simply 'N' (hot-rolled deformed bar), 'R' (hot-rolled round bar), 'RW' (cold-drawn ribbed wire) or 'W' (cold-drawn round wire), as the yield strength and ductility class can be implied from the shape. For example, all commercially available wire has a yield strength of 500 MPa and low ductility, while round bars are 250 MPa and normal ductility.

New Zealand

[edit]

Reinforcement for use in concrete construction is subject to the requirements of AS/NZS4671 (Steel Reinforcing for Concrete). There are other standards that apply to testing, welding and galvanizing.

'Reinforcement steel bar Grade 300 & 500 Class E

Nominal Diameter (mm) Cross-sectional area (mm sq) Mass per metre length, kg/m
6 28.3 0.222
10 78.5 0.617
12 113 0.888
16 201 1.58
20 314 2.47
25 491 3.85
32 804 6.31
40 1260 9.86

India

[edit]

Rebars are available in the following grades as per IS:1786-2008 FE 415/FE 415D/FE 415S/FE 500/FE 500D/FE 500S/FE 550, FE550D, FE 600. Rebars are quenched with water at a high level pressure so that the outer surface is hardened while the inner core remains soft. Rebars are ribbed so that the concrete can have a better grip. Coastal regions use galvanized rebars to prolong their life. BIS rebar sizes are 10, 12, 16, 20, 25, 28, 32, 36, 40 and 50 millimeters.

Jumbo and threaded bar sizes

[edit]

Very large format rebar sizes are widely available and produced by specialty manufacturers. The tower and sign industries commonly use "jumbo" bars as anchor rods for large structures which are fabricated from slightly oversized blanks such that threads can be cut at the ends to accept standard anchor nuts.[25][26] Fully threaded rebar is also produced with very coarse threads which satisfy rebar deformation standards and allow for custom nuts and couplers to be used.[27] These customary sizes, while in common use, do not have consensus standards associated with them, and properties may vary by manufacturer.

Jumbo rebar size chart
Imperial

bar size

Metric bar

size (soft)

Linear Mass Density Nominal diameter

(outside of threaded zone)

Nominal area

(outside of threaded zone)

lb⁄ft (kg/m) (in) (mm) (in2) (mm2)
#14J - 9.48 14.14 1.88 47.8 2.78 1794
#18J - 14.60 21.78 2.34 59.4 4.29 2768
Threaded rebar size chart
Imperial

bar size

Metric bar

size (soft)

Linear Mass Density Maximum diameter Nominal area
lb⁄ft (kg/m) (in) (mm) (in2) (mm2)
(#18 and smaller are the same as US/Imperial sizes)
#20 No.63 16.70 24.85 2.72 69 4.91 3168
#24 No.75 24.09 35.85 3.18 81 7.06 4555
#28 No.90 32.79 48.80 3.68 94 9.62 6207
1" No.26 3.01 4.48 1.25 32 0.85 548
1 1⁄4" No.32 4.39 6.53 1.45 37 1.25 806
1 3⁄8" No.36 5.56 8.27 1.63 41 1.58 1019
1 3⁄4" No.46 9.23 13.73 2.01 51 2.58 1665
2 1⁄2" No.65 18.20 27.08 2.80 71 5.16 3329
3" No.75 24.09 35.85 3.15 80 6.85 4419

Grades

[edit]

Rebar is available in grades and specifications that vary in yield strength, ultimate tensile strength, chemical composition, and percentage of elongation.

The use of a grade by itself only indicates the minimum permissible yield strength, and it must be used in the context of a material specification in order to fully describe product requirements for rebar. Material specifications set the requirements for grades as well as additional properties such as, chemical composition, minimum elongation, physical tolerances, etc. Fabricated rebar must exceed the grade's minimum yield strength and any other material specification requirements when inspected and tested.

In US use, the grade designation is equal to the minimum yield strength of the bar in ksi (1000 psi); for example, grade 60 rebar has a minimum yield strength of 60 ksi. Rebar is most commonly manufactured in grades 40, 60, and 75 with higher strength readily available in grades 80, 100, 120 and 150. Grade 60 (420 MPa) is the most widely used rebar grade in modern US construction. Historic grades include 30, 33, 35, 36, 50 and 55, which are not in common use today.

Some grades are only manufactured for specific bar sizes; for example, under ASTM A615, Grade 40 (280 MPa) is only furnished for US bar sizes #3 through #6 (soft metric No.10 through 19). Sometimes limitations on available material grades for specific bar sizes is related to the manufacturing process used, as well as the availability of controlled quality raw materials used.

Some material specifications cover multiple grades, and in such cases it is necessary to indicate both the material specification and grade. Rebar grades are customarily noted on engineering documents, even when there are no other grade options within the material specification, in order to eliminate confusion and avoid potential quality issues such as might occur if a material substitution is made. "Gr." is the common engineering abbreviation for "grade", with variations on letter capitalization and the use of a period.[28]

In certain cases, such as earthquake engineering and blast-resistant design where post-yield behavior is expected, it is important to be able to predict and control properties such as the maximum yield strength and minimum ratio of tensile strength to yield strength. ASTM A706 Gr. 60 is an example of a controlled property range material specification which has a minimum yield strength of 60 ksi (420 MPa), maximum yield strength of 78 ksi (540 MPa), minimum tensile strength of 80 ksi (550 MPa) and not less than 1.25 times the actual yield strength, and minimum elongation requirements that vary by bar size.

In countries that use the metric system, the grade designation is typically the yield strength in megapascals (MPa), for example grade 400 (similar to US grade 60; however, metric grade 420 is actually the exact substitution for the US grade).

Common US specifications, published by ACI and ASTM, are:

  • American Concrete Institute: "ACI 318-14 Building Code Requirements for Structural Concrete and Commentary", ISBN 978-0-87031-930-3 (2014)
  • ASTM A82: Specification for Plain Steel Wire for Concrete Reinforcement
  • ASTM A184/A184M: Specification for Fabricated Deformed Steel Bar Mats for Concrete Reinforcement
  • ASTM A185: Specification for Welded Plain Steel Wire Fabric for Concrete Reinforcement
  • ASTM A496: Specification for Deformed Steel Wire for Concrete Reinforcement
  • ASTM A497: Specification for Welded Deformed Steel Wire Fabric for Concrete Reinforcement
  • ASTM A615/A615M: Deformed and plain carbon-steel bars for concrete reinforcement
  • ASTM A616/A616M: Specification for Rail-Steel Deformed and Plain Bars for Concrete Reinforcement
  • ASTM A617/A617M: Specification for Axle-Steel Deformed and Plain Bars for Concrete Reinforcement
  • ASTM A706/A706M: Low-alloy steel deformed and plain bars for concrete reinforcement
  • ASTM A722/A722M: Standard Specification for High-Strength Steel Bars for Prestressed Concrete
  • ASTM A767/A767M: Specification for Zinc-Coated (Galvanized) Steel Bars for Concrete Reinforcement
  • ASTM A775/A775M: Specification for Epoxy-Coated Reinforcing Steel Bars
  • ASTM A934/A934M: Specification for Epoxy-Coated Prefabricated Steel Reinforcing Bars
  • ASTM A955: Deformed and plain stainless-steel bars for concrete reinforcement (Supplementary Requirement S1 is used when specifying magnetic permeability testing)
  • ASTM A996: Rail-steel and axle-steel deformed bars for concrete reinforcement
  • ASTM A1035: Standard Specification for Deformed and Plain, Low-carbon, Chromium, Steel Bars for Concrete Reinforcement

ASTM marking designations are:

Historically in Europe, rebar is composed of mild steel material with a yield strength of approximately 250 MPa (36 ksi). Modern rebar is composed of high-yield steel, with a yield strength more typically 500 MPa (72.5 ksi). Rebar can be supplied with various grades of ductility. The more ductile steel is capable of absorbing considerably more energy when deformed – a behavior that resists earthquake forces and is used in design. These high-yield-strength ductile steels are usually produced using the TEMPCORE process,[29] a method of thermomechanical processing. The manufacture of reinforcing steel by re-rolling finished products (e.g. sheets or rails) is not allowed.[30] In contrast to structural steel, rebar steel grades are not harmonized yet across Europe, each country having their own national standards. However, some standardization of specification and testing methods exist under EN 10080 and EN ISO 15630:

  • BS EN 10080: Steel for the reinforcement of concrete. Weldable reinforcing steel. General. (2005)
  • BS 4449: Steel for the reinforcement of concrete. Weldable reinforcing steel. Bar, coil and decoiled product. Specification. (2005/2009)
  • BS 4482: Steel wire for the reinforcement of concrete products. Specification (2005)
  • BS 4483: Steel fabric for the reinforcement of concrete. Specification (2005)
  • BS 6744: Stainless steel bars for the reinforcement of and use in concrete. Requirements and test methods. (2001/2009)
  • DIN 488-1: Reinforcing steels - Part 1: Grades, properties, marking (2009)
  • DIN 488-2: Reinforcing steels - Part 2: Reinforcing steel bars (2009)
  • DIN 488-3: Reinforcing steels - Part 3: Reinforcing steel in coils, steel wire (2009)
  • DIN 488-4: Reinforcing steels - Part 4: Welded fabric (2009)
  • DIN 488-5: Reinforcing steels - Part 5: Lattice girders (2009)
  • DIN 488-6: Reinforcing steel - Part 6: Assessment of conformity (2010)
  • BS EN ISO 15630-1: Steel for the reinforcement and prestressing of concrete. Test methods. Reinforcing bars, wire rod and wire. (2010)
  • BS EN ISO 15630-2: Steel for the reinforcement and prestressing of concrete. Test methods. Welded fabric. (2010)

Placing rebar

[edit]
Rebar bender
Steel wire used to secure rebar before it is set in concrete. A centimeter rule is provided for reference.

Rebar cages are fabricated either on or off the project site commonly with the help of hydraulic benders and shears. However, for small or custom work a tool known as a Hickey, or hand rebar bender, is sufficient. The rebars are placed by steel fixers ("rodbusters" or concrete reinforcing iron workers), with bar supports and concrete or plastic rebar spacers separating the rebar from the concrete formwork to establish concrete cover and ensure that proper embedment is achieved. The rebars in the cages are connected by spot welding, tying steel wire, sometimes using an electric rebar tier, or with mechanical connections. For tying epoxy-coated or galvanized rebars, epoxy-coated or galvanized wire is normally used, respectively.

Stirrups

[edit]
Stirrup sample

Stirrups form the outer part of a rebar cage. The function of stirrups (often referred to as 'reinforcing steel links' and 'shear links') is threefold: to give the main reinforcement bars structure, to maintain a correct level of concrete cover, and to maintain an equal transferance of force throughout the supporting elements.[31] Stirrups are usually rectangular in beams, and circular in piers and are placed at regular intervals along a column or beam as defined by civil or structural engineers in construction drawings.

Welding

[edit]

The American Welding Society (AWS) D 1.4 sets out the practices for welding rebar in the US. Without special consideration the only rebar that is ready to weld is W grade (Low-alloy — A706). Rebar that is not produced to the ASTM A706 specification is generally not suitable for welding without calculating the "carbon-equivalent". Material with a carbon-equivalent of less than 0.55 can be welded.

ASTM A 616 & ASTM A 617 (now replaced by the combined standard A996) reinforcing bars are re-rolled rail steel and re-rolled rail axle steel with uncontrolled chemistry, phosphorus and carbon content. These materials are not common.

Rebar cages are normally tied together with wire, although spot welding of cages has been the norm in Europe for many years, and is becoming more common in the United States. High strength steels for prestressed concrete cannot be welded.[citation needed]

Reinforcement placement in rolls

[edit]

Roll reinforcement system is a remarkably fast and cost-efficient method for placing a large quantity of reinforcement over a short period of time.[32] Roll reinforcement is usually prepared off-site and easily unrolled on site. Roll reinforcement placement has been applied successfully in slabs (decks, foundations), wind energy mast foundations, walls, ramps, etc.

Mechanical connections

[edit]

Also known as "mechanical couplers" or "mechanical splices", mechanical connections are used to connect reinforcing bars together. Mechanical couplers are an effective means to reduce rebar congestion in highly reinforced areas for cast-in-place concrete construction. These couplers are also used in precast concrete construction at the joints between members.

The structural performance criteria for mechanical connections varies between countries, codes, and industries. As a minimum requirement, codes typically specify that the rebar to splice connection meets or exceeds 125% of the specified yield strength of the rebar. More stringent criteria also requires the development of the specified ultimate strength of the rebar. As an example, ACI 318 specifies either Type 1 (125% Fy) or Type 2 (125% Fy and 100% Fu) performance criteria.[33]

For concrete structures designed with ductility in mind, it is recommended that the mechanical connections are also capable of failing in a ductile manner, typically known in the reinforcing steel industry as achieving "bar-break". As an example, Caltrans specifies a required mode of failure (i.e., "necking of the bar").[34]

Safety

[edit]
Rebars with temporary plastic safety caps installed

To prevent injury, the protruding ends of steel rebar are often bent over or covered with special steel-reinforced plastic caps.[35]

Designations

[edit]

Reinforcement is usually tabulated in a "reinforcement schedule" on construction drawings. This eliminates ambiguity in the notations used around the world. The following list provides examples of the notations used in the architectural, engineering, and construction industry.

New Zealand
Designation Explanation
HD-16-300, T&B, EW High strength (500 MPa) 16 mm diameter rebars spaced at 300 mm centers (center-to-center distance) on both the top and bottom face and in each way as well (i.e., longitudinal and transverse).
3-D12 Three mild strength (300 MPa) 12 mm diameter rebars
R8 Stirrups @ 225 MAX D grade (300 MPa) smooth bar stirrups, spaced at 225 mm centres. By default in New Zealand practice all stirrups are normally interpreted as being full, closed, loops. This is a detailing requirement for concrete ductility in seismic zones; If a single strand of stirrup with a hook at each end was required, this would typically be both specified and illustrated.
United States
Designation Explanation
#4 @ 12 OC, T&B, EW Number 4 rebars spaced 12 inches on center (center-to-center distance) on both the top and bottom faces and in each way as well, i.e. longitudinal and transverse.
(3) #4 Three number 4 rebars (usually used when the rebar perpendicular to the detail)
#3 ties @ 9 OC, (2) per set Number 3 rebars used as stirrups, spaced at 9 inches on center. Each set consists of two ties, which is usually illustrated.
#7 @ 12" EW, EF Number 7 rebar spaced 12 inches apart, placed in each direction (each way) and on each face.

Reuse and recycling

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Rebar is frequently recycled, and rebar is often made entirely from recycled steel.[36] Nucor, the largest steel producer in the United States, claims its steel bar products are made from 97% recycled steel.[37]

Workers extracting rebar from demolition rubble in China

References

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Rebar

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from Grokipedia
Rebar, short for reinforcing bar, is a rod or typically used in to enhance the material's tensile strength, compensating for concrete's inherent weakness in tension while leveraging its . These bars are usually deformed with ridges, lugs, or indentations along their surface to improve bonding with the surrounding , preventing slippage and ensuring structural integrity in applications such as , bridges, highways, and dams. By distributing tensile loads and resisting cracking or failure under stress, rebar enables the creation of durable structures capable of withstanding environmental forces like earthquakes, wind, and . The concept of reinforcing concrete with steel emerged in the early 19th century, with French engineer Joseph Monier credited for patenting reinforced concrete in 1867 using iron rods embedded in concrete for garden tubs and pipes, though earlier experimental uses date back to the 1820s in Europe. By the late 1800s, twisted steel bars were introduced to improve adhesion, and the first formal specifications for reinforcing bars were issued in 1910, marking the standardization of rebar in modern construction. This evolution transformed concrete from a brittle material into a versatile building component, revolutionizing infrastructure development worldwide throughout the 20th century. Rebar is produced in various types to suit different environmental and structural demands, with being the most common due to its cost-effectiveness and high yield strength, often graded at 40, 60, or 80 (kips per ) to indicate minimum yield stress. Other variants include epoxy-coated rebar for resistance in chloride-exposed areas like bridges; galvanized rebar with a coating for moderate protection against rust; and rebar for highly corrosive environments such as marine structures, offering superior longevity but at higher cost. Additional forms encompass welded wire fabric for slab reinforcement and glass-fiber-reinforced polymer (GFRP) rebar as a non-metallic alternative that avoids in sensitive applications. Sizes range from #3 (3/8 inch diameter) to #18 (2-1/4 inches), with lengths typically 20 or 60 feet, selected based on load requirements and design codes. Rebar must conform to established standards for quality and performance, primarily governed by the American Society for Testing and Materials (ASTM). The key specification, ASTM A615/A615M, covers deformed and plain carbon-steel bars for , detailing (e.g., maximum 0.06% and ), mechanical properties like elongation, and dimensional tolerances to ensure reliability. For weldable low-alloy steel, ASTM A706 applies, while ASTM A955 addresses bars, and ASTM A767 specifies coating requirements for galvanized rebar. These standards, enforced through testing for tensile strength, bendability, and corrosion resistance, underpin rebar's role in safe, long-lasting construction projects globally.

Overview and Applications

Definition and Purpose

Rebar, short for reinforcing bar, is a or of wires used as a tension device in and structures to strengthen and support the under tensile loads. Concrete possesses high but is inherently weak in tension, making it prone to cracking and when subjected to pulling forces; rebar addresses this limitation by providing the necessary tensile , thereby enhancing the overall structural integrity and preventing brittle fractures. The bond between rebar and surrounding is primarily mechanical, achieved through surface deformations such as or lugs that interlock with the matrix, ensuring effective load transfer and composite action. First introduced in the mid-19th century, rebar revolutionized by enabling the design of durable, load-bearing elements like beams and columns. As of 2025, global rebar production exceeds 368 million tons annually, underscoring its indispensable role in modern infrastructure.

Primary Uses in Construction

Rebar is integral to , where it is embedded within elements to enhance structural integrity across a wide range of applications. Primary uses include foundations, beams, columns, slabs, and walls, where rebar provides to counteract 's inherent weakness under tension. In larger projects, such as bridges, , and highways, rebar reinforces decks, girders, abutments, and pavement slabs to withstand heavy loads, environmental stresses, and dynamic forces. Additionally, in , rebar is incorporated into or walls, either vertically in cores or horizontally in bed joints, to improve load-bearing capacity and stability. In these structures, rebar serves critical roles beyond basic tensile support, including providing shear resistance through configurations like stirrups in beams and ties in columns, which prevent diagonal cracking under load. It also controls cracking induced by shrinkage and temperature changes, particularly in slabs and pavements, by distributing stresses and limiting crack widths. In seismic zones, rebar configurations such as hoops and spirals enhance and energy dissipation in columns and walls, enabling structures to better absorb forces. Representative examples illustrate rebar's practical integration: in high-rise buildings, rebar forms dense cages around columns to confine and support vertical loads over multiple stories. For highways and roads, longitudinal and transverse rebar in slabs resists bending moments from traffic and , as seen in continuously reinforced pavements that minimize joint-related failures. Rebar's usage is essential in modern and is mandated by building codes such as ACI 318 , which specifies requirements for its placement and performance in structural elements.

Historical Development

Early Invention and Adoption

The concept of reinforcing with iron emerged in the mid-19th century in , with early experiments focusing on combining the of with the tensile strength of metal. Experimental uses of date back to the 1820s in , though practical applications began later. In 1848, French inventor and farmer Joseph-Louis Lambot developed , a thin-layer using fine iron wire mesh embedded in a , which he applied to construct a small tested on local ponds. Lambot patented this "ferciment" system in 1855 and exhibited the at the Universal Exposition that year, marking one of the first practical demonstrations of metal-reinforced composites. Building on such innovations, François Coignet advanced the application to structural building in 1853 by constructing the world's first iron-reinforced concrete house, a four-story structure at 72 Rue Charles Michels in ' suburbs, using prefabricated panels with embedded iron rods to enhance load-bearing capacity. Coignet further promoted the technique through a 1861 publication detailing its uses in construction, emphasizing its potential for fire-resistant and durable buildings. The material gained broader visibility in 1867 when gardener Joseph Monier patented a system of iron mesh-reinforced concrete for horticultural troughs and exhibited it at the Paris Universal Exposition, where it attracted attention for applications beyond gardening, such as pipes and bridges. Early spread internationally by the 1890s, with adoption in the driven by François Hennebique's 1892 patent for a systematic framing method using rods, which enabled widespread commercial use in and bridges. In the United States, engineer Ernest L. Ransome introduced improvements to address bonding issues, patenting twisted square bars in 1884 to create mechanical interlock and reduce slippage between plain round bars and —a common early problem that limited structural reliability. Ransome's system was notably applied in the 1903 in , , the first skyscraper, demonstrating the material's viability for high-rise construction. Initial reinforcements often consisted of plain round or square mild bars, which relied primarily on and but frequently suffered from bond failure under load, prompting the shift to deformed profiles for enhanced performance.

Modern Innovations and Standards Evolution

The post-World War II era marked a significant expansion in the use of , driven by reconstruction efforts and rapid , which spurred innovations in rebar to meet growing demands for durable infrastructure. This boom facilitated advancements such as the standardization of deformed bars, which featured surface deformations to enhance bonding with and prevent slippage, building on earlier lugged bar designs from the 1910s-1930s. The first formal specification for these deformations appeared in ASTM A305 in , improving structural integrity in large-scale projects. In the 1970s, epoxy-coated rebar emerged as a key innovation for corrosion resistance, particularly in environments exposed to chlorides like deicing salts, with the first U.S. bridge application in 1973 providing a protective barrier that extended service life. Standards for rebar evolved concurrently, with ASTM A15 establishing the first U.S. specification for billet-steel bars in 1911, later superseded by ASTM A615 in 1968, which defined grades for deformed bars emphasizing tensile strength. In Europe, Eurocode 2 (EN 1992-1-1) was published in 2004, providing unified rules for concrete structures including rebar ductility classes to ensure safety and serviceability across member states. Key events like the 1989 Loma Prieta earthquake highlighted vulnerabilities in non-ductile reinforced concrete, prompting updates to standards such as the promotion of ASTM A706 for weldable, low-alloy bars with enhanced ductility in seismic zones. In the 2020s, revisions have incorporated sustainability considerations, with rebar typically containing recycled content exceeding 75%. By 2025, standards increasingly emphasize low-carbon steel rebar under regulations like the U.S. Inflation Reduction Act's Buy Clean provisions, setting global warming potential thresholds to reduce embodied emissions in construction materials.

Materials and Manufacturing

Steel Composition and Types

Rebar is primarily composed of , an of iron and carbon with controlled levels of other elements to achieve desired mechanical properties. The carbon content typically ranges from 0.15% to 0.30% by weight, which provides a balance between strength and without making the steel overly brittle. is added at levels of 0.30% to 1.50% to improve , tensile strength, and resistance to wear, while , present at 0.10% to 0.50%, acts as a deoxidizer during and enhances elasticity. Phosphorus content is limited to a maximum of 0.06%, and is typically limited to 0.05-0.06%, to prevent and ensure . For higher-strength grades, microalloying elements such as (typically 0.01% to 0.15%) or (0.005% to 0.05%) are incorporated to refine grain structure and promote , allowing yield strengths up to 100 ksi without sacrificing . These elements enable the production of advanced rebar suitable for seismic applications by increasing and resistance. The overall composition is governed by standards like ASTM A615 for billet-steel bars and ASTM A706 for low-alloy weldable bars, ensuring consistency across production. Common types of rebar include mild , which features low content (under 0.25%) for superior weldability and formability in general . Deformed bars, made from similar compositions, are designed for enhanced bonding through their material properties. Specialty types address corrosive environments: rebar, alloyed with (at least 10.5%) and for inherent resistance, is used in marine or chemical-exposed structures. Galvanized rebar applies a coating to for sacrificial protection against , while epoxy-coated variants fuse a layer to the surface, extending in chloride-rich settings like bridges. The compositional elements directly influence key performance metrics, such as yield strength, which spans from 40 in basic grades to 100 in high-strength variants, enabling lighter designs. , critical for earthquake-prone areas, is quantified by elongation at , with standards requiring at least 7% to 12% for grades to ensure deformability under load. As of 2025, approximately 71% of rebar production incorporates recycled scrap, reflecting industry sustainability efforts aligned with USGS estimates for recycling rates.

Production Processes

The production of rebar primarily involves two main steelmaking routes: the (EAF) process, which melts scrap steel using electric arcs generated by graphite electrodes, and the basic oxygen furnace (BOF) process, which refines molten from in a by blowing oxygen to reduce carbon content. In both methods, the molten steel is refined for composition, cast into billets or blooms via , and then reheated for further processing. The billets are heated to approximately 1100–1200°C in a reheating furnace before entering the hot rolling mill, where they are progressively deformed through a series of grooved rolls to form elongated bars of the desired diameter. This hot rolling process reduces the cross-section while elongating the material, typically achieving final bar sizes ranging from 6 mm to 50 mm in diameter. Following rolling, the bars are cooled on a controlled cooling bed to stabilize the microstructure, then sheared or sawn to standard lengths of 6 to 60 feet, depending on regional specifications and end-use requirements. During the final stages of hot rolling, deformations such as transverse ribs, lugs, or indentations are impressed onto the bar surface using specially designed roll grooves, enhancing bond strength with ; alternatively, some rebars undergo cold twisting post-rolling for similar deformation effects. Quality control is integral throughout production, with employed to detect internal defects like cracks, inclusions, or voids in the bars by sending high-frequency sound waves through the material and analyzing echoes for anomalies. Recent advancements in rebar manufacturing include the implementation of automated production lines featuring robotic systems and AI-driven monitoring to improve precision and reduce labor, as seen in unmanned rebar processing facilities. Additionally, energy-efficient processes, such as increased use of hydrogen injection in EAFs and optimized scrap recycling, have contributed to ongoing decarbonization efforts. In 2025, global rebar production reached approximately 369 million tons, with China accounting for about 50% of output.

Physical and Mechanical Properties

Surface Features and Deformations

Rebar surfaces are typically equipped with deformations, including , lugs, or indentations spaced uniformly along the bar, to facilitate superior to surrounding . These features consist of transverse protrusions that inhibit longitudinal slippage and may include longitudinal for additional grip. Plain bars, lacking such deformations and featuring smooth surfaces, are reserved for specialized uses like spiral ties or stirrups where mechanical is not required. The primary purpose of these deformations is to enhance mechanical interlock and frictional resistance between the steel rebar and , thereby improving overall structural integrity by distributing tensile forces more effectively. Standards such as ASTM A615/A615M outline precise deformation patterns, mandating similar shapes and sizes on opposite sides of the bar, with transverse deformations forming angles of at least 45 degrees and gaps between them limited to no more than 25% of the bar's nominal perimeter. Spacing between deformations must average no more than 0.7 times the nominal bar diameter, while minimum heights vary by bar size, ranging from 0.38 mm for smaller diameters to 2.59 mm for larger ones, ensuring consistent performance across applications. Deformations significantly boost bond strength, with studies showing deformed bars achieving 2-3 times the bond capacity of plain bars in pullout tests conducted per ASTM protocols. Common types of deformed rebar include cold-twisted deformed (CTD) bars, manufactured by twisting mild rods at ambient temperature to induce surface irregularities that heighten both tensile yield and bonding efficacy, as specified in standards like IS 1786. Thermo-mechanically treated (TMT) bars, widely adopted in , incorporate ribbed deformations through a controlled heating, , and tempering process, yielding enhanced and resistance compared to CTD variants while maintaining robust surface grip.

Strength and Durability Characteristics

Rebar exhibits key mechanical properties that ensure its effectiveness in reinforcing concrete structures. The modulus of elasticity for rebar steel is typically 200 GPa (29,000 ksi), providing the stiffness necessary for load-sharing with concrete. For common Grade 60 rebar under ASTM A615, the minimum yield strength is 60 ksi (420 MPa), allowing it to withstand significant tensile stresses before permanent deformation occurs. The minimum ultimate tensile strength for these bars is typically 90 ksi (620 MPa) for sizes #3 through #18, representing approximately 1.5 times the yield strength, though recent revisions in ASTM A615-20 have adjusted the minimum to 80 ksi (550 MPa) for enhanced manufacturability while maintaining structural integrity. Ductility is quantified by elongation, with minimum values ranging from 9% to 12% depending on bar size, enabling the rebar to deform without brittle failure under load. Durability aspects of rebar focus on long-term performance in harsh environments. Corrosion resistance is enhanced through protective measures such as coatings, which form a barrier against and chlorides in , and hot-dip galvanizing, which provides sacrificial . alloys offer inherent resistance to pitting, , and , particularly in aggressive marine or de-icing salt exposures. Under cyclic loading, rebar demonstrates resistance with stress ranges of 150 to 280 MPa sustainable for up to 1 million cycles, though can reduce this limit significantly in aggressive environments. Creep behavior of rebar in is minimal at ambient temperatures, as steel's creep strain is negligible compared to concrete's; however, the presence of redistributes long-term stresses, reducing effective creep in the composite with ratios up to 3% under sustained loads. These properties are verified through standardized testing protocols. Tensile tests, conducted per ASTM A370, measure yield and ultimate strengths by applying uniaxial load until , ensuring compliance with grade specifications. Bend tests assess by deforming a bar sample around a without cracking, confirming the material's ability to accommodate construction bends and seismic deformations. High-strength rebar, such as Grades 80 and above, has gained adoption in bridge applications during the for its potential to reduce weight and material volume by up to 4% compared to Grade 60, as supported by updates in AASHTO LRFD Bridge Design and ACI reports.

Standards, Sizes, and Grades

Regional Size Specifications

Rebar size specifications vary by region, reflecting differences in national standards, measurement systems, and practices. These variations primarily concern nominal , which determine the bar's cross-sectional area and load-bearing capacity, as well as standard lengths for straight bars or coils. While global efforts have promoted metric units, regional preferences persist, influencing procurement and design compatibility. , rebar sizes are designated using the imperial "# number" system under ASTM A615, where the number represents the diameter in eighths of an inch (e.g., #3 = 3/8 inch or 9.5 mm, up to #18 = 18/8 inches or 57.3 mm). These imperial sizes range from #3 (0.375 inches ) to #18 (2.25 inches ), with "soft metric" equivalents provided for international projects (e.g., #3 ≈ 10 mm, #18 ≈ 57 mm) to approximate metric dimensions without altering production. This system ensures compatibility with legacy and . European standards, governed by BS EN 10080, specify rebar diameters in metric units from 6 mm to 50 mm, with preferred sizes including 8 mm, 10 mm, 12 mm, 16 mm, 20 mm, 25 mm, 32 mm, and 40 mm to optimize material use and structural efficiency. Although imperial sizes occasionally appear in legacy applications, particularly in the United Kingdom, metric has been the dominant system since the adoption of harmonized European norms in the late 20th century. Other regions employ fully metric designations tailored to local standards. In Canada, sizes follow CSA G30.18 with "M" suffixes indicating approximate cross-sectional area in mm² (e.g., 10M has a nominal diameter of 11.3 mm and 100 mm² area), ranging from 10M to 55M (55.9 mm diameter). Australia and New Zealand use "N" prefixes under AS/NZS 4671, with diameters from N6 (6 mm) to N40 (40 mm), such as N12 at exactly 12 mm. In India, IS 1786 specifies diameters from 8 mm to 50 mm in increments like 8 mm, 10 mm, 12 mm, 16 mm, 20 mm, 25 mm, 28 mm, and 32 mm, with larger sizes up to 50 mm for heavy-duty applications. Jumbo bars, exceeding standard ranges, reach up to 64 mm in diameter for specialized uses like bridge piers or industrial foundations, often produced to custom specifications beyond routine ASTM or EN limits. Standard lengths for straight rebar are typically 12 meters globally, though variations exist: 6 meters or 9 meters in and for transport efficiency, and 20 feet (6.1 m), 40 feet (12.2 m), or 60 feet (18.3 m) in the . Coiled rebar, used for smaller diameters (up to 20 mm), is supplied in lengths up to 60 feet (18.3 m) or more in spools weighing 2,000–5,000 pounds to facilitate on-site fabrication. Since the 1980s, a global shift toward metric standards has occurred, driven by international trade and ISO harmonization, but the US retains imperial designations for rebar to maintain compatibility with existing designs and machinery, using soft conversions where needed.
Region/StandardNominal Diameter RangeExample SizesNotes
US (ASTM A615)9.5–57.3 mm (#3–#18)#3 (9.5 mm), #8 (25.4 mm), #18 (57.3 mm)Imperial "#n" (n/8 inch); soft metric equivalents used internationally.
Europe (BS EN 10080)6–50 mm6 mm, 12 mm, 25 mm, 40 mmFully metric; legacy imperial rare.
Canada (CSA G30.18)11.3–55.9 mm (10M–55M)10M (11.3 mm), 20M (19.5 mm)"M" denotes mm² area; fully metric.
Australia/NZ (AS/NZS 4671)6–40 mm (N6–N40)N12 (12 mm), N20 (20 mm)"N" prefix; stock lengths 6–12 m.
India (IS 1786)8–50 mm8 mm, 16 mm, 32 mm, 50 mmIncrements of 4–8 mm; up to 50 mm standard.

Grade Designations and Requirements

Rebar grades are classified primarily based on minimum yield strength, with designations varying by regional standards to ensure compatibility with structural demands. In the United States, the ASTM A615 specification for deformed and plain carbon-steel bars defines common grades such as 40, 60, 75, 80, and 100, where the numerical value represents the minimum yield strength in thousands of pounds per square inch (ksi); for instance, Grade 60 requires a minimum yield of 60 ksi (approximately 414 MPa). Similarly, ASTM A706 for low-alloy steel bars, suitable for welding, includes Grades 60, 80, and 100 with the same yield strength criteria but enhanced ductility provisions. In Europe, under BS EN 10080 and BS 4449, reinforcing steel is categorized by yield classes like B500A, B500B, and B500C, all with a characteristic yield strength of 500 MPa, differentiated by ductility levels—B500A for general use in mesh, B500B for bars requiring moderate ductility, and B500C for high-ductility applications. In India, IS 1786 specifies grades such as Fe415, Fe500, and Fe550, where "Fe" denotes iron and the number indicates the minimum yield strength in megapascals (MPa), with variants like Fe500D offering improved ductility for seismic zones. Grade requirements encompass chemical composition limits to control brittleness and enhance performance, alongside mechanical tests for deformation resistance. For ASTM A615, the only chemical requirement is a maximum phosphorus content of 0.060%. There are no specified limits for carbon or sulfur, as this specification is not intended for weldable applications. European BS 4449 imposes stricter controls, such as carbon equivalent (CEV) not exceeding 0.52% for weldable grades, with maximum carbon at 0.22% and phosphorus plus sulfur combined at 0.055%. Indian IS 1786 similarly limits carbon to 0.30%, phosphorus to 0.050%, and sulfur to 0.055%, emphasizing low-carbon equivalents below 0.42% for grades intended for welding. Mechanical requirements include bend and rebend tests: under ASTM A615, bars undergo a 180-degree bend around a mandrel of specified diameter without cracking, followed by a rebend to assess ductility; BS 4449 requires a 90-degree bend and rebend after aging to at least 60 degrees for B500B; IS 1786 mandates similar bend tests at 180 degrees and rebends to 135 degrees for Fe500, ensuring resistance to cracking under field conditions. Weldability is a critical requirement for higher grades, governed by low carbon equivalents to prevent brittle welds; for example, ASTM A706 limits CEV to 0.75% or less, while BS 4449 and IS 1786 use comparable formulas incorporating carbon, , , and other elements. Rebar markings, rolled into the bar surface, indicate grade, manufacturer, and deformation for and compliance verification. In the , ASTM standards require symbols like "S" for A615 Grade 60 or "W" for A706, alongside mill identifiers and size numbers spaced along the bar. European bars under BS 4449 feature a multi-rib deformation marked with the grade (e.g., "500B"), , and mill number in a sequential format. Indian IS 1786-compliant bars include the grade (e.g., "Fe500"), BIS certification mark, and manufacturer details, often with color coding for grades in supply chains. As of 2025, seismic grades like ASTM A706 in the mandate higher through stricter strain limits and deformation controls, essential for earthquake-prone areas to absorb energy without failure.

Installation and Placement

Reinforcement Layout Techniques

Reinforcement layout techniques in construction involve strategic positioning and spacing of rebar to ensure structural integrity, load distribution, and protection against environmental factors. These methods are governed by standards such as those from the (ACI), which emphasize precise placement to achieve uniform concrete bonding and prevent failures like cracking or . For slabs, grid layouts are commonly used, where rebar is arranged in orthogonal grids of in both directions to resist flexural and shear forces. In beams and columns, assemblies form three-dimensional frameworks, enclosing the core to provide confinement and tensile strength. Shear reinforcement is achieved through stirrups or ties, which are closed loops of smaller-diameter bars wrapped around longitudinal rebar at regular intervals to counteract diagonal tension. A critical aspect of layout is maintaining minimum concrete cover over the rebar, typically ranging from 1 to 3 inches depending on exposure conditions, to shield the steel from corrosion by isolating it from moisture, air, and soil. This cover is essential for durability, with thinner covers (around 0.75 to 1.5 inches) used in interior slabs and thicker ones (up to 3 inches) for elements in contact with ground or weather. Spacing rules dictate the distance between bars, determined by bar diameter, applied loads, and structural element type to facilitate concrete flow and ensure adequate bond. Per ACI guidelines, maximum spacing is limited to 18 inches for flexural reinforcement in slabs (the lesser of 3 times slab thickness or 18 inches) and similarly constrained for beams and columns to control cracking and distribute stresses effectively, while development length—the embedded distance required for full stress transfer via bond—must be sufficient to anchor bars without slippage. In columns, tie spacing is similarly constrained to maintain cage stability. Tools such as rebar chairs and spacers are employed to support and position the during placement, ensuring the specified cover and alignment are maintained before pouring. These devices, often made of , metal, or , prevent sagging or displacement under the weight of wet . For complex geometries, pre-assembly of rebar cages occurs in fabrication shops, allowing precise tying and bending prior to on-site installation, which enhances accuracy and efficiency. Since the 2010s, software like has been widely adopted for of rebar layouts, enabling optimization through , clash detection, and automated detailing to reduce errors and material waste in construction projects.

Joining Methods and Connections

In construction, rebar segments are connected using several established methods to ensure structural continuity and load transfer. splicing is the most traditional and widely used technique, where the ends of two bars are overlapped and embedded in the to develop full tensile strength through bond. The overlap length typically ranges from 40 to 60 times the diameter of the smaller bar, depending on factors such as strength, bar grade, and confinement provided by transverse . This method relies on the concrete's capacity and is economical for straight bars but requires sufficient development length to avoid slippage under load. Mechanical couplers provide an alternative to splicing, particularly in congested areas or where bar alignment is challenging, by directly joining bar ends without depending on bond. Common types include threaded couplers, which use upset or taper-threaded bar ends secured with internal threads and , and grouted couplers, where a high-strength fills a to interlock the bar deformations. These connections achieve full-strength development, often exceeding 125% of the bar's yield strength, and are classified under standards like ACI 318-25 as Class L (low , tension only), Class G (general, tension and compression), or Class S (seismic, for cyclic loading). represents another option for high-strength bars, employing with covered electrodes per AWS D1.4/D1.4M to fuse bar ends, or flash welding, a resistance-based process that heats and upsets the bars for a forge-like suitable for straight alignment. Stirrups and ties serve as transverse to connect and confine longitudinal bars, forming closed loops that enhance shear resistance in beams and columns. Stirrups, typically U- or closed-shaped bars with 135-degree hooks, are placed vertically at regular intervals in shear-critical zones to resist diagonal tension cracks and prevent of main bars under compression. Ties, used similarly in columns, provide lateral support and confinement to the core , improving and spalling resistance; both are tied to longitudinal bars using wire for stability during placement. For projects requiring long continuous runs, coiled rebar—commonly available in diameters up to 16 mm—is unrolled on-site to minimize joints, with segments cut to length and secured using wire ties at intersections to maintain positioning before concreting. This approach reduces handling and splicing needs, promoting efficient placement in slabs or walls. In seismic-prone regions, mechanical connections are preferred over in current building codes, such as ACI 318-25, due to their superior and energy dissipation under cyclic loading, which better accommodates earthquake-induced deformations without brittle failure.

Safety and Regulations

Handling and Installation Safety

Handling and installing on sites involves several inherent hazards that can lead to serious injuries if not properly managed. Workers face risks of cuts and lacerations from the sharp, jagged ends of rebar bars, which can easily pierce during manual handling or tying. Falls from heights during placement pose dangers, where unprotected protruding rebar can penetrate a worker's body if they fall onto it, contributing significantly to construction fatalities and injuries. Entanglement is another concern, particularly with coiled rebar, where loose ends or loops can snag clothing or limbs, pulling workers off balance or into machinery. Additionally, heavy lifting of rebar bars, which typically weigh between 2 and 10 pounds per linear foot depending on size (e.g., #7 bars at approximately 2 pounds per foot and #14 at 7.65 pounds per foot), can cause musculoskeletal strains, back injuries, or crush injuries if bars are dropped. To mitigate these hazards, employers must implement robust safety practices, starting with the provision of appropriate (PPE). Sturdy protect against sharp edges, hard hats and high-visibility vests reduce head and visibility-related risks during overhead work, and steel-toe boots safeguard feet from falling objects or punctures. Proper stacking and storage are essential to prevent collapses; rebar should be bundled securely, stacked on stable bases, and arranged to avoid tipping or rolling, ensuring overall stability per OSHA guidelines. Comprehensive aligned with OSHA's 29 CFR standards is required, covering recognition, safe lifting techniques (such as team lifts for heavy bars), and emergency procedures to ensure workers can identify and respond to rebar-specific dangers. During installation, additional risks arise that demand vigilant oversight. Overloading temporary supports or formwork with excessive rebar weight can cause shifts or collapses, destabilizing the structure and endangering workers beneath or nearby; loads must only be applied if certified safe by a qualified . To prevent , OSHA requires that all protruding reinforcing steel onto which workers could fall be guarded with rebar caps, wooden boxes, or other protective devices (29 CFR 1926.701(b)(2)). Exposure to weather elements before concrete pouring can lead to surface on rebar; light surface rust is generally acceptable and may even enhance the bond between and , but heavy rust, loose rust, or must be removed to ensure adequate , as per ACI 318 Section 26.6.1.2. Rebar-related accidents, including those from handling and , underscore the need for these protocols.

Compliance with Building Codes

In the United States, the American Concrete Institute's ACI 318 serves as the primary standard for the design and construction of structural , including detailed provisions for rebar placement, development lengths, and specifications to ensure structural integrity. The International Building Code (IBC) integrates ACI 318 by referencing its requirements for structures, mandating compliance in Chapter 19 to align with national building safety standards. In the , Eurocode 2 (EN 1992-1-1) governs the detailing of , specifying rules for anchorage, laps, and spacing to prevent bond failure and enhance in elements. Seismic provisions for rebar, such as minimum confinement in special moment frames, are outlined in ASCE 7, which complements ACI 318 by defining load combinations and detailing for earthquake-resistant design in high-seismic zones. Key requirements under these codes include minimum ratios to control cracking from and shrinkage; for instance, ACI 318 mandates a ratio of 0.0018 for Grade 60 deformed bars in slabs, calculated as the area of divided by the gross area. mandates are enforced through IBC Chapter 17, requiring special inspections for rebar size, placement, splicing, and to verify conformance before and during pouring, often conducted by certified inspectors to mitigate errors. For imported rebar, certification under ASTM A615 or A706 is required in the , with mill test reports and compliance documentation submitted to ensure material quality meets domestic standards, as stipulated in federal procurement rules like the American Iron and Steel (AIS) requirements. For customs classification of imports, concrete reinforcing bars fall under US HTS code 7214.20.0000, while rods in coils are classified under 7213.10.0000. Recent updates to ACI 318-25, effective in 2025, introduce a new Appendix N on and resilience, emphasizing rebar selection for against climate-induced and extreme events, while revising post-installed rebar provisions to enhance performance-based design. These changes build on Eurocode 2 amendments that promote low-carbon materials in reinforcement detailing to reduce environmental impact. Non-compliance with rebar continuity and cover requirements contributed to the 2021 , where corrosion of inadequately protected reinforcement led to progressive failure of the pool deck, as detailed in the NIST investigation report. This incident prompted stricter rules in Florida's building codes, including enhanced rebar inspection frequencies and mandatory continuity splicing in high-risk areas, influencing national updates to prioritize -resistant detailing.

Recycling and Sustainability

Reuse and Recycling Practices

Rebar recovery begins during the phase of projects, where sorting techniques are employed to separate reinforcing bars from and other debris. Workers manually or mechanically identify and extract rebar, often using tools like hydraulic shears for initial cutting to manageable lengths that facilitate and further . This on-site sorting minimizes and preserves the material's integrity for potential in non-critical structural elements, such as temporary supports or secondary reinforcements in low-load applications. Once extracted, rebar undergoes processing to prepare it for . is a primary method, utilizing powerful electromagnets to pull rebar from mixed rubble, achieving high recovery rates in crushing facilities. Following separation, the rebar is sheared into shorter segments using industrial or alligator shears to remove bends and standardize sizes, then baled into compact bundles for efficient shipping to mills. Quality checks, including visual inspections and chemical analysis, ensure minimal contamination from non-metallic residues or alloys, maintaining suitability for remelting. At steel mills, recovered rebar scrap is melted in furnaces (EAFs), where it serves as the primary feedstock—often comprising over 90% of the charge—to produce new rebar with properties equivalent to virgin steel. This closed-loop process avoids the need for extensive alloying adjustments, as rebar's composition remains stable post-. The Steel Recycling Institute, established by the North American steel industry, promotes these practices through education and infrastructure development, having facilitated the recycling of billions of tons of steel since 1988. Recycled steel production via EAF remains more cost-effective than primary routes due to lower energy use, though exact premiums vary with market conditions; as of mid-2025, global rebar prices averaged around $800-900 per metric ton. The global recycling rate for rebar reached approximately 71% in recent years, up from lower figures in the early 2010s, driven by circular economy policies that incentivize scrap utilization and waste reduction in construction; however, global recycled steel usage declined 6.9% year-on-year in the first half of 2025 amid reduced mill output.

Environmental Considerations

The production of steel rebar contributes significantly to global , with an average of approximately 1.85 tonnes of CO₂ emitted per tonne of produced through traditional blast furnace-basic oxygen furnace routes. This process also leads to substantial , primarily through the extraction of and coking , which are finite non-renewable materials essential for . Additionally, of rebar in structures can cause premature deterioration, necessitating early replacements and thereby amplifying the environmental footprint via increased material production and . To mitigate these impacts, the industry is advancing low-carbon production technologies, such as hydrogen-based direct reduction of , with ongoing pilot and demonstration projects including Sweden's HYBRIT initiative (scaling to industrial in 2025) and POSCO's HyREX technology (in advanced R&D as of late 2025). reinforced (GFRP) rebar serves as a non-corroding alternative in certain applications, reducing long-term replacement needs. certifications, such as , award credits for incorporating products with high recycled content, encouraging sustainable sourcing in projects. Policy measures are further driving reductions in rebar's . The European Union's Carbon Border Adjustment Mechanism, fully effective by 2026 and aligned with 2030 climate targets, imposes tariffs on high-carbon imports to prevent and promote cleaner global supply chains. , the world's largest producer, has issued plans for 2025 production cuts exceeding 25 million metric tons to address overcapacity and support decarbonization targets. The rebar sector, as part of the broader steel industry, is committed to achieving net-zero emissions by 2050 through strategies like enhanced and . In , average recycled content in rebar production reached about 44% in recent assessments, supporting goals while lowering virgin resource use.

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