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Rebar is a long bar made of steel and come in various sizes. Rebar production can be both plain and ribbed, with construction rebars generally being ribbed. The reason for ribbing is to prevent the rebar from moving within the concrete during sudden pressures caused by floods, earthquakes, or other such events.

Rebars are produced using the hot rolling process, with steel ingots or scrap iron sometimes used as raw materials. Different companies produce rebars in various sizes, and each may adhere to specific standards during production. This variation can lead to differences in the quality of rebars among different brands, which should be taken into consideration.

Rebars are manufactured in two types: plain and ribbed, and they are classified according to the following table:

Type of RebarCharacteristic Sign of RebarRebar Code
Plainس 240A1 S240
Spiral Treadsآج 340A2 S340
آج 350A2 S350
Twill Treadsآج 400A3 S400
آج 420A3 S420
Compound Treadsآج 500A4 S500
آج 520A4 S520
Plain Rebar

Plain rebar, also known as A1 and code S240, is a type of rebar that has a smooth and polished appearance. In other words, plain rebars do not have any treads on their outer surface. They are used to increase the tensile strength of concrete but are limited in their use in construction.

Plain rebars are produced and available in different diameters ranging from 6 to 200 mm, and they come in lengths of 6 or 12 meters, each offering its own performance characteristics. It’s important to note that simple rebars have lower tensile strength compared to other types of rebars, classifying them as soft steels.

These rebars find applications in various industrial cases, including the production of industrial and automotive parts, agricultural tools, hinges, iron fittings, hot forging, trans bars, bolts, and nuts. They are also preferred for forging and welding due to their ease of cutting and bending compared to other rebar types. As mentioned, simple rebars are mostly used in the industry, but they also serve the construction industry for making bolts and work rabbits.

Ribbed Rebar

Ribbed rebars have cuts on their outer surface, known as ribs. One of the most significant differences between plain and ribbed rebar, which holds paramount importance in building construction, is their adhesion strength to concrete. The treads on ribbed rebars allow concrete to adhere more effectively to the rebar, making it challenging to pull the rebar out of the concrete. The primary purpose of these rebars is to enhance the strength and resistance of concrete. Ribbed rebars are produced in two types: bars and coils, with sizes ranging from 5.5 to 40 mm.

Ribbed rebars are identified as A2, A3, and A4 (while the name A1 is used for plain rebar). The difference among these rebars lies in their tread patterns: A2 rebar (code S340 and S350) has spiral treads, A3 rebar (code S400 and S420) has twill treads, and A4 rebar (code S500 and S520) has compound treads.

The use of ribbed rebars is common in construction, and they find various applications in this field, including:

  1. Concreting the walls
  2. Increasing the strength of concrete
  3. Strengthening the foundation
  4. Enhancing shear force
  5. Concreting the floor of the structure
Physical Characteristics

The ability of an object to return to its original shape (elastic property) after loading and unloading is called the elastic modulus. This characteristic is considered one of the most important mechanical properties of rebars. The modulus of elasticity of concrete typically ranges between 14 and 41 pascal, which makes concrete a brittle material prone to cracking.

To enhance the elastic performance of concrete, steel bars are used. The modulus of elasticity of steel bars is approximately 200 GPa, though this value may vary for different diameters and dimensions of rebars. If the modulus of elasticity is less than 200 MPa, it is necessary to increase the number of rebars used to improve the elasticity of the structure and reduce the possibility of cracking. The modulus of elasticity for the steel used in rebars can be determined from the stress-strain curve of their material. The table below displays the types of rebar based on ductility.

Classification Based on DuctilityCharacteristic Sign of RebarFeature
Soft Steelس 240The yield point is obvious in the stress-strain curve.
Semi-Hard Steelآج 340The yield range in the stress-strain curve is very small.
آج 350
آج 400
آج 420
Hard Steelآج 500The yield point in the stress-strain curve is not known.
آج 520

“Elongation” refers to the ability of a material to change its longitudinal shape under axial (tensile) loads. When additional loads are applied to the structure, the rebars significantly change their shape, and in this way, they control the expansion of cracks in the concrete. The increase in the length of the rebar is measured by applying a tensile force to it, a test known as the tensile test. This feature has a direct relationship with the tensile strength of the rebar.

Steel retains its elastic property until it reaches its yield strength. As a result, if the load is below the yield point, the reinforced concrete structure returns to its original shape after loading. The yield strength of steel bars typically falls between 275 and 690 MPa, and this resistance is independent of the diameter of the rebar.

By using a suitable arrangement and combination of rebars, the required resistance can be achieved without changing the area (number) of rebars. This characteristic increases the flexibility of using rebars in different concrete structures to attain similar properties. According to Iranian standard 3132, elongation, tensile strength, and minimum yield strength for plain and ribbed rebars should conform to the table below:

Type of RebarCharacteristic Sign of RebarElongation A5Elongation A10Tensile Strength (MPa)Yield (MPa) (Min)Yield (MPa) (Max)
Plainس 2402518360240
Spiral Treadsآج 3401815500340
آج 35017500350455
Twill Treadsآج 4001612600400
آج 42016600420545
Compound Treadsآج 50010865500
آج 52013690520675
Chemical Characteristics

Rebars can exhibit different chemical compositions depending on their intended applications. The chemical composition varies slightly between the molten state during casting and the final product. The table below presents the maximum amounts of elements allowed in the chemical composition of the molten metal for casting simple and ribbed rebars, presented in mass percentages and in accordance with Iran’s 3132 standards.

Type of RebarCharacteristic Sign of RebarSilicon CarbideManganesePhosphorusSulfurNitrogenMaximum Carbon Equivalent
Plainس 2400.220.550.750.050
Spiral Treadsآج 3400.320.601.300.0450.50
آج 3500.270.601.600.0400.0120.51
Twill Treadsآج 4000.370.601.600.045
آج 4200.300.551.500.0400.0120.56
Compound Treadsآج 5000.400.601.800.045
آج 5200.320.551.800.0400.0120.61

Asan Form Kimia Company is a prominent and well-known supplier of various types of plain and ribbed rebars in different shapes and sizes in Iran.