The use of concrete in the construction industry is widespread. In fact, concrete is the most commonly used material to lay the foundations of structures. No matter what the construction project involves, whether it is building walls, posts, or floor slabs, concrete is the primary construction material.
As common as the use of concrete is, it is highly prone to cracks and poses a risk of structures falling apart. Concrete is strong in compression but relatively weak in tension. This gives rise to the need to improve the tensile strength of concrete to make it a more reliable and durable material to be used in a construction project. This is achieved by creating reinforced concrete, which is done by incorporating rebar into concrete.
Continue reading this detailed blog post for answers to any question that you may have about welding rebar and reinforced concrete.
What Is Rebar?
Rebar is also known as reinforcement steel. Reinforcement steel bars are used to improve concrete in terms of tension and structural strength. Rebar compensates for the fact that concrete is weak in tension and makes it a strong and durable-enough material that can be used in the construction of massive structures. Reinforced concrete is able to carry greater tensile loads and withstand the usual stress that buildings are usually under. Steel is the only metal that is used in rebar, owing to the fact that its thermal expansion coefficient (elongation due to heat) is almost equal to that of concrete, which significantly reduces the chances of cracking.
How Does Rebar Add Strength to Concrete?
Of many questions related to rebar and concrete, the most common question is how rebar adds strength to concrete. Concrete is poured onto rebar frames, cages, or mats. As it is poured, the concrete hardens, and with that, the stone or gravel in concrete gets locked in place. This forms a strong, mechanical bond. The concrete that has been locked with rebar has greater tensile strength as compared to pure concrete. Concrete has great resistance to pressing forces, that is, compressive strength but poor resistance to stretching or bending forces (tensile strength), which is what rebar improves, making it suitable for any construction project.
Can Rebar Be Welded?
Rebar is available in different sizes and grades. While some grades of rebar can be welded, some cannot. To better understand which types of rebar can be welded and which cannot be welded, continue reading this blog post!
As per the Structural Welding Code AWS D1.4, a low-alloy steel rebar is weld-able. This grade of rebar has a steel-to-carbon ratio that makes it suitable to be welded. Not only is it suitable for welding, but the welds can stay together under significant load after it has been sealed in concrete. This is the only type of rebar that can be welded without taking any special considerations into account.
The chemical composition of steel determines whether it can be welded or not. If the steel has a high carbon content, it will be more brittle, and thus, less suitable to be welded. This type of steel is more likely to fracture when exposed to the stress of welding. Therefore, steel alloys that have a high level of strength are not suitable for welding.
Welding rebar will provide a rigid and strong structural connection that will not only ensure feasible transportation of rebar mats and cages but will also ensure that they deliver the strength to concrete structures that they are expected to. Welding rebar has been deemed difficult and even unacceptable by many, but in reality, it is one of the most practical ways of ensuring that rebar serves its purpose as closely as possible.
Welding rebar is acceptable and practical, provided that certain practices and standards are followed. These include:
- Selecting the correct type of rebar
- Determining if it is necessary to preheat it or not and performing it when needed
- Selection of the appropriate filler (welding wire or rod)
- Selection of a proper weld, preparation of metal, and the correct placement
Selecting the Correct Type of Rebar
The construction industry sees the use of numerous types of reinforced steel bars or rebar. They have been listed down below:
Mild Steel Bars
These bars have a plain surface and a round shape. These bars can be found in sizes ranging from 6mm to 50mm. Mild steel bars have their use in the reinforcement of concrete that is used for special projects only. For example, they’re used in situations where steel bars have to slide into a metal sleeve, in dowels at expansion joints, in runways and roads for contraction joints, and also for use in column spirals, etc. Mild steel bars are relatively easy to bend and cut without damage.
Deformed Steel Bars
As the name indicates, deformed steel bars sport a deformed surface due to lugs, ribs, or any other kind of deformation on their surfaces. These bars are easier to transport due to the minimal slippage they possess, and they increase the strength of the bond between steel and concrete. Their tensile strength is greater as compared to mild steel bars and also limits the cracks that more than often appear on reinforced concrete around mild steel bars.
Thermo-Mechanically Treated Bars (TMT Bars)
TMT bars are heat-treated bars. They provide excellent strength to reinforced concrete. This type of rebar is superior to other types of rebar in terms of ductility, strength, bending-ability, welding-ability, and quality.
High-Strength Deformed Bars
These cold-treated bars are twisted with ribs, lugs, projections, or deformations on their surface. It is the type of rebar that is most commonly used to reinforce concrete. It has great strength, ductility, and weld-ability, thanks to its low-carbon content. The welding capability of this rebar is an exceptional 100%, which is the reason for its widespread use in reinforcement concrete.
Other Kinds of Rebar
Other kinds of rebar include carbon steel rebar, European rebar, galvanized rebar, epoxy-coated rebar, stainless steel rebar, and glass-fiber-reinforced-polymer rebar. Each type has a different set of properties, with stainless steel rebar being the best in terms of quality and most expensive of all types.
The choice of the type of rebar that you’re going to use depends completely on the application you are reinforcing your concrete for.
The Need and Practice of Preheating
The need for preheating before rebar can be welded depends on its carbon equivalent and the size. It is necessary that you determine the carbon equivalent of the steel, which is the measure of its welding ability. Steels that have a high carbon equivalent are less weld-able, and thus, require more preheating and vice-versa.
To calculate the carbon equivalent of the steel, you need to have complete information on the steel’s chemical composition, which may or may not be provided in the mill certificate. It is always better to request this information to avoid bearing any un-needed preheating expenses.
Selecting the Correct Filler
The type of filler material that should be used to weld rebar depends on the type of welding method that is being employed. Three types of welding can be used for welding rebar, which are: SMAW- Shielded Metal Arc Welding (stick/ arc welding), GMAW- gas metal arc welding (MIG), and FCAW- Flux Core Arc Welding.
For example, if you’re using rebar of A615 grade 60, you could either use SMAW or GMAW methods. If SMAW welding is being used, the correct filler will be electrodes of E9016-X, E9018-X, E9015-X, or E9018M. However, for the GMAW method, the correct filler will be an electrode of ER90C-XXX or ER90S-XXX.
The choice of filler varies with the type of rebar and the method of welding used.
Selection of Proper Weld, Preparation of Metal, and the Correct Placement
Not all types of welds can be used for rebar welding. There are certain allowable welds. The types of joint welds that can be done on rebar are lap joints, butt joints, and splices. According to the Structural Welding Code (AWS D1.4), there is no provision pertaining to steel bars that are perpendicular to each other. The only thing that the welder must ensure is that all steel bars are ‘substantially parallel and perpendicular to one another’ (Ref: ASTM A184/A184M- Standard Specification for Welded Deformed Steel Bar Mats for Concrete Reinforcement).
Is it okay to weld rebar?
It is okay to weld rebar only if it has been graded as Grade-W. Rebar that can be welded is always labeled with a W. In case the rebar lacks this label, it is not suitable for welding.
What happens if you weld the wrong rebar in concrete?
If you weld the wrong grade of rebar (high-strength, non-Grade-W rebar), the concrete will have poor tensile strength, and it will crack under stress and load. As such, the durability and reliability of the structure made from reinforced concrete having non-grade-W rebar will be compromised.
Can A615 rebar be welded?
A615 rebar is a high-strength steel alloy which is not suitable for welding. A615 rebar is susceptible to cracking. In case there is a need to weld A615 rebar, it is necessary to preheat it adequately.
What grade of rebar is weld-able?
Low-alloy rebar, such as A706 rebar, is weld-able.
Can you weld rebar in concrete?
Yes, rebar can be welded in concrete to form reinforced concrete. However, not all grades of rebar can be welded in steel. Only low-alloy, grade-W rebar is weld-able.