Rebar is used to improve the tensile strength of concrete. In specific applications, welding rebar instead of using wire ties may be a requirement. But, can any type of rebar be welded? And if so, how do you choose the correct grade of rebar to weld?
Rebar made with low-alloy steel (A706) is weldable. Rebar with high carbon content (A615) is not weldable, as the steel is brittle and may fracture from the heat of welding. Rebar with a Grade 40 or 60 has a steel-to-carbon content that is ideal for welding.
This article will walk you through:
- how to identify the different rebar types
- the rebar grading system
- tips for welding rebar
Which Rebar Can Be Welded?
The Structural Welding Code AWS D1.4 states that low-alloy steel rebar can be welded. Rebar with low-alloy steel (A706) will have a steel-to-carbon ratio that will make it weld-able. The strength of the weld on this type of rebar will stay together under large loads when it is sealed in concrete.
Rebar with high carbon content (A615) cannot be welded, as the steel is brittle and less likely to weld. This high carbon steel is more likely to fracture under welding stress.
Types Of Rebar That Can Be Welded
There are many different types of rebar on the market, but only the following steel rebar is weld-able.
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Mild Steel Rebar
Mild steel rebar is round and has a smooth surface, and can be found in sizes from 6mm to 50mm. Mild steel rebar is only used in special projects that will require steel bars to slide into a metal sleeve and where an expansion joint is required. This rebar is easy to bend, cut, and weld very easily.
Deformed Steel Rebar
Deformed steel rebar has a higher tensile strength than mild steel rebar. The deformed rebar has a distorted surface with ribs and lugs on it. The deformed surface of this rebar aids in the strength of the concrete and steel bond, improving its tensile strength. Deformed steel rebar is suitable for welding.
Thermo-Mechanically Treated rebar is heat treated to provide excellent reinforced strength to concreate. TMT rebar is perfect for welding and bending.
High-Strength Deformed Rebar
High–strength, deformed rebar is cold treated and features twists, ribs, lugs, and other deformations on its surface. This is one of the most popular types of rebar on the market. It offers excellent strength and is very easy to weld due to the very low carbon content.
How To Identify Weldable Rebar?
Two identifying systems can be found on rebar. This is the “line “system and the “number” system. Both identity systems are similar to one another, so keep an eye out for both when checking rebar.
The Rebar Line Identification System
The identification marks will be stamped between the lines running across the diameter of the rebar. There will be three markings.
- The first mark will identify the manufacturer of the rebar.
- The second will be the size of the rebar
- The third will be the type of steel used.
There may be a “W” symbol included; this indicates that the rebar is weldable.
For example, if the following marking is present on the rebar, “M-4-S”, then this is how to interpret it:
- the “M” is the manufactures code
- the “4” is the size of the rebar
- the “S” is the steel used for the rebar.
If these are the only marks on the rebar, it is grade 40 rebar and weldable. Some manufacturers will mark weld-able rebar with “W.”
Look for an identifying line that runs down the length of the rebar, as this is also a grade mark. If the rebar has a line running down, it is grade 60 and weldable. The line is the only noticeable difference between grade 40 and grade 60 rebar.
The Number System
The number system will have the same markings as the line system but will have a “60” or a “6” with a “0” below it for grade 60 and a “40” for grade 40. Some manufacturers will mark weldable rebar with “W.”
What Are The Rebar Grades?
Rebar is graded to identify the amount of tensile strength it has in pounds per square inch. The lowest grade is Grade 33, and as the number increases, so does the tensile strength.
- Grade 40 has a minimum yield strength of 40,000psi and a minimum tensile strength of 60,000psi.
- Grade 60 has a minimum yield of 60,000psi and a minimum tensile strength of 90,000psi.
What Are The Welding Methods For Welding Rebar?
Three welding methods and weld types can be used when welding rebar. These are:
- SMAW – Shielded Metal Arc Welding
- GMAW – Gas Metal Ark Welding (MIG)
- FCAW – Flux Core Arc Welding
Before welding, the welder must ensure that the welded pieces are parallel and perpendicular to each other. There are only three types of welds that are permitted when welding rebar, these are:
- Lap Joints – Lap joints are similar to butt joints, but the ends of two pieces of rebar must be ‘overlapped’ instead of butted together.
- Butt Joints – The two pieces of rebar would be butted together end to end and then welded.
- Splices – Splices are similar to lap joints and one of the ideal ways to weld rebar together.
Before any welding takes place on the rebar, it is advised to ensure that the pieces of the rebar are locked into place. This is to prevent them from moving during the pre-heating or welding process.
The rebar should also be cleaned with a wire bristle brush to remove contaminants such as oil or rust. This will improve the quality of the weld and prevent sticking.
Low-alloy steel rebar can be welded. This will be A706 grade 40 and grade 60 steel rebar. Rebar with high carbon content, such as A615 steel is not weldable, as the rebar is brittle and will fracture under welding stress.
The different rebar grades can be identified using the line or number method. These methods are similar and will give the manufacturer’s details, rebar size, and material used. If the rebar has a “W” imprinted on it indicates that the rebar is weldable.