How to Identify Reinforcing Bars?

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Reinforcement bar or reinforcement steel, widely known as rebar, is a steel bar that is used in masonry and concrete structures to reinforce and strengthen the concrete in tension. Generally, all types of rebars have more or less the same appearance making it difficult to differentiate between them. This could result in unnecessary confusion, probable increase in material costs, and delay in completing activities.

Different markings are made on rebar that help identify the reinforcement bar precisely. One of the most followed marking systems providing information regarding the composition and manufacturing of the rebar is discussed in this article.

ASTM reinforcement bar (rebar) markings

ASTM International, previously known as the American Society for Testing and Materials, is an organization that develops technical standards for a broad range of materials, systems, products, and services and publishes the same. It has also published specifications for reinforcing bars that have been widely accepted across the various parts of the globe.

Each rebar is manufactured with a series of markings embossed on it. These individual markings reveal the true identity of the bar. There are four major marking symbols.

1. Code for manufacturer

The first mark identifies the producing mill and/or the manufacturer of the reinforcement bar. It is either an alphabet or a symbol that has been predesignated to the manufacturer.

2. Number code for the size of the bar

The number code indicating the size of the bar is expressed in the standard bar designation number. The standard bar designation number indicates the number of eighths of an inch of the nominal diameter of the bar up to size 8. For example, a bar with designation number 4 has the same mass per foot as the plain bar 4/8 inch (0.500 inches) in diameter.

The bar with designation number 9 has the same weight per foot as a 1-inch square bar. Sizes 10, 11, 14, have the same weight per foot as a 1-inch square bar, whereas size 18 has the same weight per foot as a 2-inch square. The table below provides a clear interpretation of the same.

Designation number of bar (Bar size)	Metric designation number	Nominal diameter in inches (excluding deformations)	Nominal Mass (kg/m)	Nominal Diameter (mm)
3	10	0.375	0.560	9.5
4	13	0.500	0.994	12.7
5	16	0.625	1.552	15.9
6	19	0.750	2.235	19.1
7	22	0.875	3.042	22.2
8	25	1.00	3.973	25.4
9	29	1.128	5.059	28.7
10	32	1.270	6.404	32.3
11	36	1.410	7.907	35.8
14	43	1.693	11.380	43.0
18	57	2.257	20.240	57.3

3. Letter code for the type of steel

The third character i.e. an alphabet refers to the type of steel. Five alphabets depict five different types of steel and have an ASTM specification each. It is as follows:

3.1. S

S stands for billet steel and has an ASTM specification edition named A615-81 “Standard Specifications for Deformed and Plain Billet- Steel Bars for Concrete Reinforcement.”

 3.2. I

I stands for rail steel and has an ASTM specification edition named A616-79 “Standard Specification for Rail-Steel Deformed and Plain Bars for Concrete Reinforcement.”

 3.3. A

A stands for axial steel and has an ASTM specification edition named A617-79 “Standard Specification for Axle-Steel Deformed and Plain Bars for Concrete Reinforcement.”

 3.4. W

W stands for low alloy steel and has an ASTM specification edition named A706-80 “Standard Specification for Low-Alloy Steel Deformed Bars for Concrete Reinforcement.”

4. Grade of steel

The fourth marking (or no marking) depicts the steel grade of the bar. The grade highlights the tensile strength of the bar in pounds per square inch. The marking represents the grade mentioned below:

1. 40 or no marking      : Grade 40

2. 60 or 4                         : Grade 60 (Metric Grade 420)

3. 70 or 5                          : Grade 75 (Metric Grade 520)

4. 80                                  : Grade 80

5. 100                                : Grade 100

6. 120                               : Grade 120

The grade can also be identified by the number of lines running for at least five spaces. It is smaller in size than the two main ribs and is located between them. One line represents grade 60, two lines represent grade 70, and no lines depict grade 40.

The only possible variation in the system is that the orientation of bar identification marks might be changed by 90 degrees to read horizontally.

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READ MORE: What is Rebar? Types and Grades of Steel Reinforcement