10 Things to Consider When Buying astm a615 rebar

In the world of construction and engineering, choosing the right reinforcement bar can be the difference between a project that stands the test of time and one that falls short. Among the most debated choices are ASTM A706 and ASTM A615, two standards that, while appearing similar, serve distinct purposes in structural applications.

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What sets these standards apart? Is it their mechanical properties, their chemical composition, or perhaps their weldability? This article delves into a detailed comparison, unraveling the complexities of tensile strength, yield strength, and elongation, while also exploring the chemical nuances and welding requirements that define these reinforcements. So, which standard should you choose for your next project, and why does it matter? Dive in to discover the nuances that could influence your decision.

Introduction to ASTM A706 and ASTM A615

Overview of ASTM A706 and ASTM A615

ASTM A706 and ASTM A615 are two key standards for reinforcing steel bars (rebar) used in concrete construction. These standards specify the mechanical properties, chemical composition, and other requirements to ensure the rebar performs effectively in various construction applications.

ASTM A706

ASTM A706 specifies low-alloy steel deformed and plain bars for concrete reinforcement, known for its weldability and ductility. It is particularly suitable for applications where these characteristics are essential. ASTM A706 rebar meets stringent requirements for mechanical properties and chemical composition, ensuring reliable performance in demanding construction environments.

Key features of ASTM A706 include:

• Grades: Available in Grade 60 and Grade 80.
• Yield Strength: 60 ksi for Grade 60 and 80 ksi for Grade 80.
• Tensile Strength: Minimum tensile strength of 80 ksi for Grade 60 and 100 ksi for Grade 80.
• Chemical Composition: Controlled elements like carbon, manganese, phosphorus, sulfur, and silicon to improve weldability.

ASTM A615

ASTM A615 is a specification for deformed and plain carbon-steel bars for concrete reinforcement. This standard is widely used in the construction industry due to its availability and cost-effectiveness. Unlike ASTM A706, ASTM A615 does not prioritize weldability, making it less suitable for applications where welding is a key requirement.

Key features of ASTM A615 include:

• Grades: Available in four grades – Grade 40, Grade 60, Grade 75, and Grade 80.
• Yield Strength: Ranges from 40 ksi to 80 ksi, depending on the grade.
• Tensile Strength: Varies by grade, with tensile strengths from 60 ksi for Grade 40 to 105 ksi for Grade 80.
• Chemical Composition: Less restrictive compared to ASTM A706, which can affect weldability.

Comparison and Applications

The main differences between ASTM A706 and ASTM A615 are in their mechanical properties, chemical composition, and suitability for welding. ASTM A706 is designed with enhanced weldability and ductility, making it ideal for seismic and other critical applications where these properties are necessary. In contrast, ASTM A615 is commonly used in general concrete reinforcement where welding is not a primary concern.

Understanding these distinctions is crucial for selecting the appropriate rebar for specific construction needs, ensuring safety, and meeting performance requirements.

Mechanical Properties Comparison

Yield Strength

Yield strength is a critical property for reinforcing steel bars, indicating the stress at which a material begins to deform plastically. To enhance clarity, the yield strength ranges for both ASTM A706 and ASTM A615 grades are summarized in the table below:

Tensile Strength

Tensile strength refers to the maximum stress that a material can withstand while being stretched or pulled before breaking. This property is crucial in practical applications, such as ensuring the structural integrity of buildings and bridges under heavy loads.

ASTM A706

• Grade 60: Minimum tensile strength of 80 ksi.
• Grade 80: Minimum tensile strength of 100 ksi.

ASTM A615

• Grade 40: Minimum tensile strength of 60 ksi.
• Grade 60: Minimum tensile strength of 90 ksi.
• Grade 75: Minimum tensile strength of 100 ksi.
• Grade 80: Minimum tensile strength of 105 ksi.

Elongation

Elongation measures the ductility of the rebar, indicating how much it can stretch before breaking. This property is essential for assessing the rebar’s ability to undergo significant deformation before failure. The elongation requirements are listed below:

ASTM A706

• Bars #3 through #6:
• Grade 60: 14% in 8 inches.
• Grade 80: 12% in 8 inches.
• Larger bar sizes: 10% to 14%.

ASTM A615

• Bars #3 through #6:
• Grade 60: 9% in 8 inches.
• Grade 75: 7% in 8 inches.
• Grade 80: 7% in 8 inches.
• Other bar sizes: 7% to 12%.

Fatigue Behavior

Fatigue behavior is an important consideration for rebar, especially in applications subject to cyclic loading. Low-cycle fatigue refers to the repeated application of high stress or strain, leading to material failure after a relatively low number of cycles.

ASTM A706

Research indicates that ASTM A706 Grade 80 specimens tend to have higher mean values for energy dissipated per cycle compared to ASTM A615 Grade 80 specimens. This suggests better performance under low-cycle fatigue conditions.

ASTM A615

ASTM A615 rebar’s fatigue life is influenced by factors such as lateral support spacing, reinforcing bar diameter, and maximum tensile strain. Despite having a broad range of mechanical properties, its performance under cyclic loading conditions may not match that of ASTM A706 rebar.

Chemical Composition and Carbon Equivalent

Chemical Requirements

The chemical composition of reinforcing steel bars significantly influences their properties and suitability for specific applications, particularly in terms of weldability and ductility.

ASTM A615 Chemical Composition

The ASTM A615 specification applies to deformed and plain carbon-steel bars used in concrete reinforcement. This standard does not impose stringent limits on the chemical composition, which means there is no maximum limit on carbon content.

Consequently, the focus is more on achieving cost-effectiveness and availability rather than enhancing weldability. The lack of controlled chemical requirements can result in variability in weldability and performance, particularly in applications where welding is necessary.

ASTM A706 Chemical Composition

ASTM A706 covers low-alloy steel deformed and plain bars, with a focus on enhanced weldability through strict chemical composition limits. Key elements are controlled as follows: carbon is limited to a maximum of 0.30%, manganese up to 1.50%, phosphorus up to 0.035%, sulfur up to 0.045%, and silicon up to 0.50%. These controlled parameters help maintain consistent weldability and mechanical properties, making ASTM A706 preferable in applications requiring reliable welding and ductility.

Carbon Equivalent

The carbon equivalent (C.E.) is a crucial factor in assessing the weldability of steel, providing an indication of how the steel will react during welding processes.

ASTM A615 Carbon Equivalent

To find the carbon equivalent (C.E.) for ASTM A615, you use the chemical analysis of the material. The formula used to calculate the C.E. is:

C.E.=%C+%Mn6+%Cu40+%Ni20+%Cr10−%Mo50−%V10

Due to the absence of a defined upper limit on carbon content, the C.E. values can vary widely, which affects weldability. When welding ASTM A615 rebar, it is essential to evaluate the C.E. to determine if preheating or specific welding procedures are needed to ensure quality welds.

ASTM A706 Carbon Equivalent

With a controlled C.E. of up to 0.55%, ASTM A706 rebar is easier to weld, often requiring minimal or no preheating. This controlled C.E., along with strict chemical composition limits, ensures that ASTM A706 rebar can be welded with fewer precautions, making it ideal for projects where welding is crucial.

Weldability and Welding Requirements

Welding Processes

When selecting the right welding processes for ASTM A706 and ASTM A615 reinforcing steel bars, it’s essential to consider each standard’s unique requirements and characteristics.

Shielded Metal Arc Welding (SMAW)

Shielded Metal Arc Welding (SMAW), also known as stick welding, is widely used for welding reinforcing steel bars. It is suitable for both ASTM A706 and ASTM A615, but special attention must be given to the weldability of ASTM A615 due to its variable chemical composition.

• ASTM A706: SMAW is highly compatible with ASTM A706 rebar due to its controlled chemical composition and lower carbon equivalent (C.E.). This results in fewer welding defects and a more straightforward welding process.
• ASTM A615: When welding ASTM A615 rebar, SMAW can be used; however, preheating and careful control of interpass temperatures are necessary to prevent cracking due to its higher and less predictable carbon content.

Gas Metal Arc Welding (GMAW)

Gas Metal Arc Welding (GMAW), commonly known as MIG welding, is another process suitable for welding reinforcing bars. GMAW provides cleaner welds and faster speeds.

• ASTM A706: The controlled composition of ASTM A706 makes it well-suited for GMAW, allowing for efficient and high-quality welds with minimal preheating.
• ASTM A615: For ASTM A615, GMAW can be used, but additional precautions are necessary. Preheating and selecting appropriate filler metals are crucial to avoid welding defects.

Flux-Cored Arc Welding (FCAW)

Flux-Cored Arc Welding (FCAW) is similar to GMAW but uses a tubular wire filled with flux. This process is advantageous in outdoor environments or where shielding gas may be impractical.

• ASTM A706: FCAW is effective for ASTM A706, given its enhanced weldability and controlled chemical limits, resulting in consistent and reliable welds.
• ASTM A615: Using FCAW on ASTM A615 requires careful management of welding parameters, including preheat and interpass temperatures, to mitigate the risk of cracking.

Filler Metals

Selecting the correct filler metals is crucial for ensuring the integrity and strength of welded joints in reinforcing steel bars.

AWS D1.4/D1.4M Guidelines

The American Welding Society (AWS) D1.4/D1.4M standard provides comprehensive guidelines for welding reinforcing steel, including recommendations for filler metals.

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• ASTM A706: Recommended filler metals for ASTM A706 are those that match the alloying elements and carbon content of the base metal, ensuring compatible mechanical properties and weldability.
• ASTM A615: For ASTM A615, filler metals must be chosen carefully to accommodate the higher and more variable carbon content. The selected filler metals should provide adequate toughness and resilience to prevent weld failures.

Preheat and Interpass Temperatures

Proper management of preheat and interpass temperatures is critical to avoid weld cracking and ensure sound welds.

ASTM A706 Requirements

• #6 Bars and Smaller: No preheat required.
• #7 to #11 Bars: Moderate preheat of 50°F (10°C).
• #14 and Larger Bars: Higher preheat of 200°F (90°C) if the chemical composition is known.

ASTM A615 Requirements

• #6 Bars and Smaller: Higher preheat of 300°F (150°C) if the chemical composition is unknown.
• #7 Bars and Larger: Very high preheat of 500°F (260°C) due to the higher carbon content and lack of specific weldability provisions.

Welding Procedure Specifications (WPS)

A Welding Procedure Specification (WPS) outlines the necessary parameters and practices to ensure a quality weld.

ASTM A706 WPS

For ASTM A706, the WPS should follow AWS D1.4/D1.4M guidelines, taking advantage of the controlled chemical composition and lower C.E. to achieve consistent and high-quality welds.

ASTM A615 WPS

For ASTM A615, the WPS must account for the higher and variable carbon content, necessitating careful control of preheat, interpass temperatures, and filler metal selection to prevent weld failures.

Identification and Marking

Proper identification and marking of reinforcing steel bars ensure that the correct material is used in welding applications.

ASTM A706 Marking

Rebars that meet ASTM A706 standards are often marked with a ‘W’ in their deformations, signaling their weldability and compliance with strict requirements.

Applications and Standards

Concrete Reinforcement

General Construction and Seismic Applications

ASTM A615 rebar is commonly used in general construction because it is widely available and affordable. It is suitable for various concrete reinforcement applications, such as residential and commercial buildings, foundations, and pavements. When structures require high weldability and ductility, like bridges and seismic-resistant buildings, ASTM A706 rebar is ideal. Its enhanced properties make it suitable for critical components that need to withstand significant forces.

Building Structures

High-Rise Buildings

In high-rise buildings, the choice of rebar depends on specific structural needs. ASTM A706 is preferred for core walls, transfer beams, and coupling beams due to its superior weldability and ductility. On the other hand, ASTM A615 is used for general reinforcement in less critical areas where these properties are not as crucial.

Infrastructure Projects

For infrastructure projects, ASTM A706 is often chosen for its weldability and strength, making it suitable for bridge decks, piers, tunnels, and water treatment plants. In contrast, ASTM A615 can be used for less critical components that do not require these enhanced properties.

Standards and Codes

ASTM Standards

Both ASTM A615 and ASTM A706 rebars must meet specific ASTM standards. These standards ensure the rebars possess the required mechanical properties and chemical composition. ASTM A615 specifies requirements for carbon-steel bars, while ASTM A706 focuses on low-alloy steel bars with controlled tensile properties.

AWS Structural Welding Code

The American Welding Society (AWS) provides guidelines for welding reinforcing steel through the AWS D1.4 Structural Welding Code. This code covers welding procedures, filler metal specifications, and temperature guidelines, ensuring both ASTM A615 and ASTM A706 rebars are welded effectively.

Building Codes

Building codes, such as the International Building Code (IBC) and local regulations, reference ASTM standards and AWS codes to ensure the safety and integrity of concrete structures. Compliance with these codes is essential for the approval and successful completion of construction projects.

Case Studies and Practical Examples

Case Study: Oregon Department of Transportation

The Oregon Department of Transportation conducted an experimental program to evaluate the low-cycle fatigue behavior of ASTM A615 and ASTM A706 reinforcing bars under cyclic loading conditions. The study aimed to determine which type of rebar performed better under cyclic loading conditions, which are critical in seismic applications.

Experimental Setup

• Materials Tested: ASTM A615 Grade 60 and ASTM A706 Grade 60 and Grade 80 rebar.
• Loading Conditions: Cyclic loading to simulate seismic activity.
• Measurements: Energy dissipation per cycle, fatigue life, and onset of buckling.

Findings

• Energy Dissipation: ASTM A706 Grade 80 rebar showed higher mean values for energy dissipation per cycle compared to ASTM A615 Grade 80, indicating better performance during seismic events.
• Fatigue Life: Despite the higher energy dissipation, statistical analyses revealed no significant difference in overall fatigue life between ASTM A706 Grade 80 and ASTM A615 Grade 80 under most test conditions.
• Buckling: The spacing of lateral supports played a crucial role. Shorter lateral support spacing resulted in more inelastic cycles before buckling, while longer spacing led to earlier onset of buckling.

Practical Example: Seismic-Resistant Construction

In seismic-resistant construction, the choice of rebar is critical to ensure the structure can withstand significant stress and strain without failure. ASTM A706 is often selected for its superior weldability and ductility, making it ideal for seismic applications.

Application in High-Rise Buildings

• Core Walls and Transfer Beams: ASTM A706 rebar is used in the core walls and transfer beams of high-rise buildings to provide enhanced ductility and energy dissipation during seismic events.
• Coupling Beams: The weldability of ASTM A706 allows for reliable welding of coupling beams, ensuring structural integrity under cyclic loading.

Experimental Study by American Concrete Institute (ACI)

The American Concrete Institute conducted a study comparing the fatigue life of ASTM A706 Grade 60 and higher-strength reinforcing bars.

Study Parameters

• Grades Tested: ASTM A706 Grade 60 and higher-strength rebar.
• Focus: Impact of steel grade and bar properties on low-cycle fatigue performance.
• Manufacturing Processes: The study compared the impact of different manufacturing processes, such as microalloying and quenching-and-tempering, on the fatigue life of the rebar.

Results

• Fatigue Performance: The study highlighted that ASTM A706 Grade 60 bars exhibited favorable fatigue performance due to their controlled chemical composition and mechanical properties.
• Manufacturing Impact: Differences in manufacturing processes, such as microalloying versus quenching-and-tempering, significantly influenced the fatigue life of the rebar.

Real-World Application: Bridge Construction

In bridge construction, selecting the appropriate rebar is vital for ensuring long-term durability and safety. ASTM A706 is often preferred for critical components due to its weldability and controlled tensile properties.

Example Project: Bridge Deck Reinforcement

• Materials Used: ASTM A706 Grade 60 rebar for the bridge deck.
• Benefits: Enhanced weldability allowed for precise and reliable welding of rebar joints, ensuring the structural integrity of the bridge deck under heavy traffic loads and environmental conditions.

Outcome

• Durability: The use of ASTM A706 rebar in the bridge deck resulted in improved durability and reduced maintenance requirements, thanks to its superior mechanical properties and weldability.

Summary of Practical Insights

These case studies and practical examples illustrate the advantages of using ASTM A706 rebar in applications requiring enhanced weldability and ductility, making it suitable for critical construction projects, particularly in seismic zones and infrastructure applications. The controlled chemical composition and superior mechanical properties of ASTM A706 make it suitable for critical construction projects, particularly in seismic zones and infrastructure applications.

Frequently Asked Questions

Below are answers to some frequently asked questions:

What are the key differences between ASTM A706 and ASTM A615 rebar?

The key differences between ASTM A706 and ASTM A615 rebar lie in their chemical composition, mechanical properties, and weldability. ASTM A706 has controlled chemical limits with a maximum carbon content of 0.30% and a carbon equivalent not exceeding 0.55%, enhancing weldability. It is available in Grades 60 and 80, designed for specific tensile properties.

ASTM A615, available in Grades 40, 60, and 70, lacks an upper carbon limit, leading to variable weldability. ASTM A706 is suited for applications requiring reliable weldability, while ASTM A615 is versatile for general construction needs.

Which rebar standard is more welder-friendly and why?

ASTM A706 rebar is more welder-friendly than ASTM A615 due to its controlled carbon equivalent (C.E.) of no more than 0.55%, which enhances weldability by reducing the risk of weld cracking and hardening.

Additionally, ASTM A706 generally does not require preheat for commonly used bar sizes, simplifying the welding process. It also has specific tensile properties suitable for seismic applications and is compatible with 80 series filler metals, ensuring better weld quality. These characteristics make ASTM A706 ideal for applications where welding is a critical requirement.

What are the mechanical properties of ASTM A706 and ASTM A615 rebar?

ASTM A706 rebar, known for its weldability, offers higher yield and tensile strengths, with Grade 60 having a tensile strength of 80 ksi and yield strength between 60-78 ksi, and Grade 80 with 100 ksi tensile and 80-98 ksi yield strengths. It also provides better ductility.

ASTM A615 rebar, primarily used in general construction, has tensile strengths ranging from 70 to 90 ksi for Grade 60 and yield strengths typically between 40 to 60 ksi, with elongation around 12-14%. A706 is preferred for structures requiring high strength and ductility, particularly in seismic zones.

What are the chemical composition requirements for ASTM A706 and ASTM A615 rebar?

The chemical composition requirements for ASTM A706 rebar are more stringent compared to ASTM A615, with specific maximum limits for carbon (0.30%), manganese (1.50%), phosphorus (0.035%), sulfur (0.045%), and silicon (0.50%). ASTM A706 also mandates a carbon equivalent (CE) not exceeding 0.55% to ensure better weldability.

In contrast, ASTM A615 does not have strict limits on these elements or a controlled carbon equivalent, allowing for greater flexibility but less emphasis on weldability. These differences underscore ASTM A706’s focus on enhanced weldability and consistent mechanical properties, while ASTM A615 is used for general concrete reinforcement.

What welding processes and filler metals are recommended for ASTM A706 and ASTM A615 rebar?

When welding ASTM A706 and ASTM A615 rebar, Shielded Metal Arc Welding (SMAW), Gas Metal Arc Welding (GMAW), and Flux Cored Arc Welding (FCAW) are recommended. For ASTM A706 rebar, use 80 series filler metals due to its controlled chemical composition and lower carbon equivalent (CE).

For ASTM A615 rebar, use 70 series filler metals, considering its higher CE and the need for higher preheat and interpass temperatures to prevent cracking. Always ensure proper electrode storage and verify chemical composition, especially for ASTM A615, from certified mill test reports or independent analysis.

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Hi all,

Welding of reinforcing steel, including A615, has been done successfully for years. There are several other considerations that must be made but most significantly, the higher the CE, the higher the preheat needed before welding. Contractor's don't want to hear this either, but it is crucial to a successful weld in this kind of material. It is also an easy place to cheat, when no one is looking .

AWS D1.4 is an excellent document. It requires destructive tests to validate the welding procedure. It also sets preheat and filler metal requirements. Your contactors' methods will be safe if they follow the requirments of the Code. Unfortunately, I have found that there is a steep learning curve among reinforcing steel contractors. They haven't used this Code even though it has been around for years.

Require your contractors submit welding procedures, procedure qualification records noting the successful acceptance of the tests, and the qualifications of the welders. Regardless of the reinforcing steel used, if the welding procedure has been proven by test, I am inclined to accept the weld, unless D1.4 prohibits the welding of that type of steel. I am 85% sure, however, you will find your contractors procedures or personnel qualifications don't meet Code for the joint configuration you are trying to accomplish. D1.4 Code testing gets real expensive, real fast!

Rebar tests per D1.4 are required even when welding reinforcing steel to structural members!!!

D1.4 also establishes allowable joint designs and stresses. If you are designing reinforcing steel, you must have this welding standard. It costs less than $100 and will reduce your errors and liability. Don't just quote it in your specs, use it in your design.
Koz Hi all,

I just waded through the thread that CWIC referenced. Boy, that thread goes far afield. Here are my comments.

Hats off to dik for his code information. It is right on.

It doesn't take a "good" welder to weld reinforcing steel. A commonly certified welder will do. The techniques used are taught in the 1st year of a 2-yr welding program at any technical college or union trades program. It takes a conscientious welder to preheat the reinforcing steel in accordance with the tested welding procedure parameters.

It takes someone with welding technology or welding engineering skills to develop a good welding procedure. This step cannot be left to the common craftsman performing the work. These skills are not being taught in welding programs and are not being taught in civil engineering classes.

The stainless to carbon welds talked about in the thread are completely beyond the scope of AWS D1.4. While I am hearing about this connection more and more, it leaves D1.4 in the dust. AWS D1.6, Structural Stainless, appears to have provisions for this combination.

Previously, I said I would be inclined to accept "any" welding procedure that survived mechanical testing. In light of this thread, I have to retract that statement. Welding reinforcing steel to 300 series stainless with E308L is bad practice. I agree with the manufacturer that the qualifying group responsible for the welding procedure "lucked out". E308L will work for small sections if there is not much dilution from the reinforcing steel base metal. But it is not normally the "right" decision. I bite my tongue to say use the more common E309L. We need to know the joint configuration and the service conditions i.e. temperature and cycles before we can stand behind E309L. This rod is built for joining carbon to stainless base metals and will work in most cases. But it has it's limits. I would say make sure you stay within the electrode manufacturer's recommendations for filler metal and electrical parameters. Allow excursions only from top-notch welding technology/engineering groups and then make them prove it to you the hard way.

There was also some discussion regarding the quadruple certification of A36,A572 gr 50, A992 (wide flanges), and A709. It is all the same material. I have answered this question before. A careful read of the above specs shows that they all cross-qualify and there is no difference. A992 has a mechanical limit that the others don't have, so it may not qualify in some instances. And with the exception of some angles and round bar and heavy plate, you can't get A36 with 36 ksi yield any more. Check your certs. That is why we use low-hydrogen type electrodes on virtually all structural steel anymore. Again, we can't leave this decision up to the craftsman. It must come from welding engineering.

Fun!
Koz The original post by EIT2 inquired about the weldability of:
A 615, A 616 & A 617 vs. A 706 (known to be weldable).

All of the above materials (depending on the grade used) are weldable and are listed in Table 5.1 of the AWS D1.4-98. As I noted in another thread, these and any other materials welded in accordance with the D1.4 code require procedure qualification, there are no prequalified joints, welds or processes.

I have inspected countless rebar welds over the years, here in the US and in several other continents. I respectfully disagree with "A commonly certified welder will do." Commonly certified welders often repairs many of their own welds even though they have been certified/qualified to perform these welds for a number of years. Not all of these welders have gone through an apprenticeship program or any other formal training. Even the ones who have training (ironworkers, pilebutts, millwrights, etc.) often ignore what they know to be code and SOP throw most of that knowledge out the window in the name of production. All of the rebar welding performed at the now famous "Orange Crush" in CA was performed by trained, experienced, journeyman trademan. I guess they knew what they were doing - despite the taxpayers having to foot the bill to repair about 70% of these joints (replaced by mechanical couplers). I have only been on a few jobs (just a few) in the last 12 years where the welders did EXACTLY what they were required to do with rebar.



While the topic reinforcing steel to stainless steel is slightly off from EIT2's original post, naturally I have a few comments on this subject as well:
thread330-

If dissimilar metals are joined, overlapping codes occur or the weld does not fall within the scope of any code whatsoever, I often use the AWS B2.1 Specification for Welding Procedure and Performance Qualification. This spec. is widely accepted by the designers who send their "unusual projects" to my office. For most of my projects that involve "nonstandard" welding procedures, we typically perform full scale mock-up tests in addition to the procedural mechanical, nondestructive and metallurgical testing.