How to Choose the Right Reinforcement Material?

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Steel is a conventional reinforcing material used in construction for imparting tensile strength and ductility to concrete structures. Steel and concrete possess similar thermal characteristics that make them to expand and contract at similar rates. Both of them, hence, work together as a single unit in concrete structures.

One of the biggest problems with steel reinforcement is corrosion, where the rust has a volume five times greater than the amount of the original steel. This results in the damage of concrete structures. To overcome this issue, few reinforcement types have been developed, namely:

1. Stainless steel reinforcement 
2. Fiber-reinforced polymer steel
3. Epoxy-coated carbon steel

This article explains the essential features of different reinforcing steel available in the construction market. This material guide can help in choosing the best reinforcing material as per the requirement.

1. Steel Reinforcement Bars

The selection of steel reinforcement bars is a simple process. The steel is specified in terms of its diameter and grade. The standard steel specifications are provided in ASTM A615/A615M-20 "Standard Specification for Deformed and Plain Carbon-Steel Bars for Concrete Reinforcement".

A Grade 40 steel means a steel bar of minimum yield strength of 40,000 psi as per ASTM standards and specifications. The bar sizes are designated in inch-pound bar sizes or metric bar sizes. 

Figure-1: Steel Reinforcement

Steel reinforcement bars are a good option when corrosion is not a concern for the structure. Being the conventional reinforcing option, it is readily available. For concrete structures that require higher tensile strength, a higher grade reinforcing steel can be employed.

2. Fiber Reinforced Polymer Reinforcement

The fiber reinforcement polymers (FRP) are made of fiber reinforcement, fillers, additives, and resin. Compared to steel reinforcement, FRP reinforcement is highly corrosion-resistant. It is also light in weight and tougher.

The use of fiber reinforcement in concrete structures increase the stiffness and tensile strength.

Figure-2: Fiber Reinforcement

The resin employed in FRP reinforcement possesses high compressive strength that can bind the whole concrete mix into a more firm mass.

The commonly used FRP reinforcement fibers are aramid, carbon, and fibers. The fiberglass is less expensive, while carbon fiber is one of the costliest fibers.

3. Stainless Steel Reinforcement Bars

The stainless steel forms a low-carbon steel, with a total carbon content of less than 1%. It contains a minimum of 10.5% chromium, which creates a layer on its surface to make it corrosion-resistant. This makes the steel stainless.

Figure-3: Stainless Steel Reinforcement Bars

Compared to standard steel bars, stainless steel bars are expensive. But they provide high strength and resistance to corrosion attacks, especially in harsh marine environments, attacks from road salts, etc.

Based on this property, stainless steel is best used for columns, piers, parking garages, retaining walls, jetties, and moorings.

The ASTM A955/A955M "Standard Specification for Deformed and Plain Stainless Steel Bars for Concrete Reinforcement" provides the standard recommendations for stainless steel reinforcement.

4. Epoxy-Coated Reinforcement

Epoxy-coated rebars or green bars replace conventional steel reinforcement to increase concrete strength and corrosion resistance. The steel reinforcement bars are coated with epoxy before their transportation to the construction site. The ASTM A775 specifies the specifications and recommendations for epoxy-coated reinforcement bars.

Figure-4: Epoxy-Coated Reinforcement
Image Courtesy: Harris Supply Solutions

They are used to construct pavements, bridges, parking structures, and structures exposed to marine water and deicing salts.

A properly manufactured and handled epoxy-coated rebar can play a significant role in delaying the corrosion of reinforcement. One challenge faced by epoxy-coated rebar is the quality of the coating. The more delicate the coating, the lesser is the corrosion resistance. This is one reason where stainless steel scores more over epoxy-coated rebar. In terms of cost, epoxy-coated rebars are eight times less costly than stainless steel. 

FAQs

What are the different types of reinforcement bars based on material?

The main types of reinforcement used in construction are:
1. Standard steel reinforcement
2. Stainless steel reinforcement
3. Epoxy-coated steel reinforcement
4. Fiber-reinforcement

How to choose between epoxy-coated and stainless steel reinforcement bars?

Good quality manufactured epoxy-coated steel reinforcement bars have a significant role in delaying the rate of corrosion. The more delicate the coating, the lesser is the corrosion resistance. This is one reason where stainless steel scores more over epoxy coated rebar.
Stainless steel provides excellent corrosion resistance and guaranteed durability, unlike epoxy-coated rebars. But stainless steel is eight times more expensive than epoxy-coated bars.
So, a choice is made depending on the durability required and the budget of the project.

What are the types of fibers used as concrete reinforcement?

The commonly used FRP reinforcement fibers are aramid, carbon, and fibers. Among the three, fiberglass is less expensive, while carbon fiber is one of the costliest fibers.

Read More

Corrosion of Steel Reinforcement in Concrete- Causes, and Protection

5 Tips to Improve Construction Quality

What is Rebar? Types and Grades of Steel Reinforcement

Stainless steel rebar types and properties

 

The building sector is increasingly using stainless steel materials. In any case, why not? Stainless steel is the most economical and highly corrosion-resistant steel reinforcing solution in most services. When structural steel reinforcement is used to build a structure, there is a significantly lower need for maintenance over the project&#;s lifespan. Because of this, even though stainless steel rebars initially seem pricey, they are far more economical in the long run.

However, what are stainless steel rebars, and how they can be useful? Rebars made of stainless steel have a low carbon steel content. Steel is more tenacious and corrosion-resistant because it contains 8 to 12% nickel and at least 12% chromium.

 

Stainless Steel Rebars Types

 

Martensitic Stainless Steel

Ironic Stainless Steel

Austenitic stainless steel

Stainless Steel that is Duplex Austenitic

All stainless steels&#;Austenitic and Duplex&#;make reinforcement bars. Select a highly durable form of steel product.

 

 Rebar made of austenitic stainless steel

 

Around 7% of austenitic steel is composed of nickel. Due to its outstanding malleability and weldability, as well as its high corrosion resistance, the alloy has these qualities. It also contains a considerable amount of chromium and 2% to 3% molybdenum. This increases its ability to resist corrosion in challenging environments, particularly when exposed to chlorides. The nitrogen concentration offers superior yield and tensile qualities. Austenitic steel is frequently used as reinforcing bars in industrial pipelines and construction projects because of its great flexibility, diamagnetic character, and wide temperature range. Depending on the number of materials it contains, it is classified differently.

 

Rebar made of Duplex Stainless Steel or Austenitic-Ferritic Stainless Steel

 

The subsea oil industry extensively uses duplex stainless steels, a superb combination of ferritic and austenitic steels stronger than both types. This is because of its exceptional resistance to corrosion, which enables it to withstand highly corrosive saline for extended periods. Rebar is the main product that this metal is used for. The combination of austenitic and ferritic stainless steel has provided a distinctive strength and durability for use in structure boards, obstruction, concrete structures, grounding processes and dovetail joints, chemical manufacturing facilities, coastline piers and wharves, structure railings, sidewalks, bridge pilings. Duplex stainless steel is less expensive because it contains less nickel than austenitic steel.

 

 Stainless Steel Rebars: Characteristics

 

To assess how they stack up against other rebars, stainless steel reinforcement bars have been put to various tests. Due to various alloys that distinguish them from other weak and ineffective rebar options, they have risen to the top of the rankings.

 

The steel of Excessive Hardness

 

The chromium content of stainless steel is 10% higher than that of several other alloying elements. Chromium is the major element that increases the material&#;s tensile strength and hardness. Additionally present is nickel, which offers comparable advantages while preserving ductility and hardness. In terms of strength, duplex steel bars surpass austenitic steel bars.

 

Resistance to Corrosion

 

Due to the high chromium content of stainless steel rebars, corrosion is prevented with an oxide coating. Because of this characteristic, it can withstand the harmful effects of chloride, which is present in concrete, ocean water, and even road salt. Austenitic stainless steel offers the best corrosion resistance since it includes at least 16% chromium.

 

Ductility

 

Rebar made of stainless steel is more ductile because of the nickel content. Due to their high ductility and corrosion resistance, these shielding materials are perfect for use in industries such as railroads, freezing operations, and earthquake-prone areas.

 

Magnetic Reaction

 

Due to the high nickel concentration in stainless steel, the magnetic response of the bars is minimal. Normal carbon steel cannot be utilized in various applications due to its high magnetic permeability. Stainless steel armor comes to the rescue!

 

Resistance to fire

 

Stainless reinforcement bars perform better at higher temperatures than regular carbon steel bars. They are more fire resistant due to their high potency retention factor at higher temperatures (over 500°C).

 

Resistance to Cryogenics

 

A wider temperature range may be tolerated by stainless steel reinforcement bars. Austenitic steel can be employed in several applications since it maintains its strength and elastic modulus even at temperatures below zero.

 

 

A Guide for Choosing the Right Rebar for Steel Reinforcement

There are many factors to consider before the actual construction commences during the planning stages of any building project. One of those considerations is the rebar that you are going to use. Rebar is short for steel reinforcement bars. Rebar performs well when subjected to tension. It is also an excellent material to reinforce concrete, which performs well under compression.

If you want to learn more, please visit our website stainless steel reinforcing fibers.

The quality of rebar chosen will determine your project's strength and durability; it will also ensure that the structure is safe for use and will last a long time even if subjected to the elements. Think of it as the skeleton in the human body but for buildings. It holds the concrete, so even if there is an earthquake, the building will still stand.

Installing an Access Panel will also improve your structure's safety, as discussed in the article "Enhancing Your Safety Through Access Panels," which covers this topic more in-depth.

What You Should Look for in Rebar

Quality is #1. You must first assess if the steel's quality fits your project. It's essential to familiarize yourself with the standards for rebar in North America. The main standards outline the requirements for chemistry, corrosion resistance, magnetic permeability, surface finish, and mandatory corrosion tests. These standards will assist you in choosing the right product and help to ensure that the rebar passes the test for the following categories:

Fatigue

Compression

Tensile strength

Bending

Selecting the Right Size and Weight: Choosing the correct rebar size and weight is critical to safe building practices. As we've already discussed, concrete is weak against compression and will bend or fracture if not reinforced. This weakness is the reason you have to consider the correct size for your rebar.

The usual rebar diameter size used for bearing minimal loads is 6mm, 8mm, and 10mm. For columns and walls, the recommended size is 8mm or greater. Foundations and building footings commonly require a 10mm diameter rebar or greater. The bigger the structure, the thicker the rebar. 204-334-

Yield Strength: Tensile or yield strength is the measurement that indicates the overall strength of the steel. High yield steel is best used for heavy-duty rebar and has a grade of 500 Mpa (or N/mm2).

*Note that increasing the rebar's diameter size does not make it twice as strong. The grade of your steel determines the strength.

Kinds of Rebar

We omitted Epoxy-Coated Rebar because it is under a ban in Quebec, Canada, and some parts of the United States. Reevaluations and further studies regarding the material are in progress.

Some of the common types of rebar you might consider are:

Thermo Mechanically Treated Bars (TMT Rebar): Hot treated bars high in strength primarily used in reinforced cement concrete (RCC) work.

High Strength Deformed Bars (HSD Rebar): This steel bar has deformation or projection on the surface. It is a cold twisted bar primarily used for reinforcement purposes in construction.

Carbon Steel Rebar: It is known as 'black bar' due to its carbon color. It has an excellent tensile strength ratio at an affordable price. The drawback is that it may rust over time.

Galvanized Rebar: It is forty times more resistant to corrosion than black rebar but is also more expensive.

Glass-Fiber-Reinforced-Polymer (GFRP): This rebar mustn't bend because it is carbon fiber, making it costly. The upside is it's highly resistant to corrosion.

Stainless Steel Rebar: This is the best rebar, but it is also the most expensive. It is 1,500 times more resistant to corrosion compared to a black bar. You will need hydraulic rebar cutting tool to cut through this.

Taking your time to carefully plan your project and becoming familiar with safety and quality standards is well worth your while. It will ensure that your building is strong, durable, and withstands the test of time and exposure to the elements.

Stainless Steel Rebar for Concrete Reinforcement

Stainless Steel Rebar for Concrete Reinforcement: An Update and Selection Guide

 

Use of high strength, corrosion resistant stainless steel rebar for concrete reinforcement in bridges, highways, buildings and other construction projects has been on the rise recently - especially when the life cycle costs of this material upgrade are appropriately weighed against the initially lower costs and perceived savings of carbon steel. The trend to stainless has been particularly evident in coastal areas of the United States, and in Canada and Europe.

Increasingly, the higher up-front costs of solid, spiral ribbed stainless steel rebar can be justified when compared with the initial costs, lifetime maintenance costs, replacement costs and operating costs incurred when using carbon steel rebar, with and without cladding or coating.

 

In practice, stainless steel rebar has been used in many concrete structures to provide high strength and long term resistance to the corrosive attack of chlorides from road salt and harsh marine environments, as well as chlorides formed by concrete in which the rebar is buried.

Possible applications for corrosion resistant stainless rebar could include a host of marine structures such as bridge decks, sidewalks, ramps, parapets, pilings, barriers, retaining walls, anchoring systems, parking garages, sea walls, columns, piers, jetties and moorings. Stainless rebar might be considered also for the infrastructure of chemical and other process plants where corrosion resistance may be important.

Stainless steel rebar, offering a good combination of high strength, toughness, ductility and fatigue resistance, along with corrosion resistance, has been used for construction of bridges and other structures in areas of high seismicity. Of paramount concern here is the need for high strength to preserve the structural integrity of any bridge subject to a seismic disturbance, and the safety of motorists using it.

The seismic retrofit of bridges, it should be noted, is one of six major categories earmarked for funding by the Federal Highway Administration (FHWA). Other FHWA infrastructure projects include innovative bridge research and construction, value pricing projects, and ferry boats and terminals. Any or all three of these projects may require a re-evaluation of rebar materials.

There are also an increasing number of rebar applications, requiring controlled magnetic permeability, where carbon steel cannot be considered an option. Non-magnetic stainless steel rebar has been used successfully in electric motor foundations, and in the construction of buildings housing MRI and similar equipment.

In addition, the same non-magnetic stainless alloys have been used in constructing "deperming" piers, where the proper function of instrumentation is restored in docked ships before they return to sea. Designers or materials specifiers who want a stainless steel with low permeability should specify that the material be checked in accordance with ASTM test method A 342. 

Cladding and Coating 

In an effort to improve corrosion resistance at less initial cost than stainless steel, some construction projects over the years have tried cladding with stainless Type 316 or epoxy coating carbon steel rebar, with mixed to poor results long term.

Cladding rebar is a relatively new process yet to be proven for long term use. Without an adherent and uniform clad thickness, the rebar will be susceptible to corrosive attack. Furthermore, cladding of carbon rebar is generally done on relatively short lengths. Thus, a large number of bars have to be individually capped and sealed at both ends. This operation is performed either by the bar fabricator or at the construction site, where work is labor intensive. After adding the hazards of transportation, the loading and unloading of stock, and fabrication of the rebar grid, the prospects of having unblemished clad bar have greatly diminished. Without a perfect cladding, carbon steel will be exposed.

Liquefied epoxy coatings, applied to carbon steel rebar by dipping or spraying, have lasted up to 20 years in mild corrosive environments. However, the coating must adhere perfectly to the bar surface and remain free of scratches or damage after application. Similar to cladding, the smallest spot that does not adhere or that suffers surface damage will expose the base metal to corrosion attack.

Since the defect usually cannot be seen or found in the concrete, the bar can seriously deteriorate, shortening the life of the structure in which it is used. Even without a surface flaw, coatings have been known to deteriorate prematurely due to variations in coverage and film thickness.

The problems associated with cladding and coating have caused many materials specifiers to re-think the merits and cost efficiency of stainless steel rebar, particularly for use in severe corrosive environments.

Stainless Properties 

Although ASTM designation A 276 lists a good number of stainless alloys that are suitable for use in concrete reinforcement, any one of four major stainless steels can be considered for most applications. These are  stainless (S), stainless Type 316LN (S), 18Cr-3Ni-12Mn stainless (S) and stainless Type 304LN (S). See Fig. 1 for their nominal chemical compositions.

For rebar applications, the alloy selection process should start with an evaluation of each alloy&#;s mechanical properties. ASTM specification A955 covering deformed and plain stainless steel bars for concrete reinforcement lists the standard property requirements. This standard allows stainless steel rebar to be produced at three strength levels.

However, Carpenter can achieve a yield strength of 75 ksi (518 MPa) or higher for all four alloys to be considered, and a tensile strength of 100 ksi minimum (690 MPa). These values represent the highest of the three strength levels listed by ASTM A955. The highest strength level can be reached in all standard bar diameters from No. 3 to No. 11 &#; or 0.375" dia. (10 mm) to 1.375" (35 mm). Strength levels, in fact, can be tailored to bar size by modifying hot rolling parameters.

All four stainless steels offer exceptional ductility, which allows the rebar to be easily formed and fabricated. Their elongation properties are in the range of 20 to 30 percent, which is two or even three times the 7 to 12 percent minimum elongation established by ASTM specification A955 for the same alloys at the 75 ksi yield strength level. Elongation is a key property of fabricators who perform numerous bending operations. (Photo 1) In addition, all four alloys have good toughness and fatigue resistance.

This unique combination of mechanical properties makes all four stainless steels candidates for construction projects in areas of active seismicity. Their high strength levels allow designers to use less material and conserve weight. Their good ductility permits structures to flex, without breaking, during any seismic disturbance.

The stainless is a duplex stainless steel with a microstructure consisting of austenite and ferrite phases. This duplex structure, along with the chemical composition, give the alloy an excellent combination of strength and corrosion resistance. In the annealed and hot rolled condition, stainless is ferromagnetic.

Stainless Type 316LN is a nitrogen-strengthened version of stainless Type 316L. It has a significantly higher yield and tensile strength than stainless Type 316L, without significantly affecting ductility, corrosion resistance or non-magnetic properties.

18Cr-3Ni-12Mn stainless is a high-manganese, nitrogen-strengthened austenitic stainless steel that provides substantially higher yield and tensile strengths than stainless Type 304. It can be considered for applications where the strength or magnetic permeability of stainless Type 304 is unsuitable.

Stainless Type 304LN is a nitrogen-strengthened version of stainless Type 304L available in the hot rolled condition. This grade has a much higher yield and tensile strength than Type 304L, without any loss in ductility, corrosion resistance or non-magnetic properties. 

Corrosion Resistance 

Selection of the best candidate stainless steel for a rebar application may depend on the amount of corrosion resistance required, particularly in view of the similarities in the alloys&#; key mechanical properties. Of the four rebar grades discussed, stainless offers the best overall corrosion resistance.

Compared with conventional stainless steels like Type 304 and Type 316, stainless has superior chloride pitting and crevice corrosion resistance due to higher chromium, molybdenum and nitrogen content. It also has superior resistance to chloride stress corrosion cracking because of its duplex microstructure. Under test conditions, its pitting resistance equivalent number was approximately 50 percent higher than that of the other three alloys.

In general, the corrosion resistance of stainless Type 316LN is similar to that of stainless Type 316L. The higher nitrogen content enhances its resistance to chloride pitting and crevice corrosion. Due to its low carbon content, stainless Type 316LN has good resistance to intergranular corrosion in the as-welded condition. It can be considered for use in severe coastal marine environments.

The 18Cr-3Ni-12Mn stainless provides general corrosion resistance between that of stainless Types 430 and 304. It can be considered for rebar applications where corrosion resistance approaching stainless Type 304 is adequate, but where the strength or magnetic permeability of stainless Type 304 is unsuitable. It also offers good resistance to atmospheric corrosion.

Stainless Type 304LN has corrosion resistance similar to that of the 18Cr-3Ni-12Mn alloy. It offers good resistance to atmospheric corrosion, and can be useful in other less severe environments. This grade also offers useful resistance to road salt environments and the chlorides in concrete. 

Magnetic Properties 

Three of the four alloys discussed may be considered for those rebar applications where controlled magnetic permeability is most important. Stainless Type 316LN offers low magnetic permeability, which is essential for rebar that could be used in structures close to sensitive electronic devices or magnetic resonance medical equipment.

Like the stainless Type 316LN alloy, the 18Cr-3Ni-12Mn stainless is also non-magnetic in the annealed and hot rolled conditions. It has been used successfully in a Norfolk, Va., "deperming" pier, and also may be considered for use near sensitive electronic devices and medical resonance imaging equipment.

Like the previous two alloys, stainless Type 304LN is also non-magnetic. It therefore may be a candidate for rebar applications close to sensitive electronic devices and MRI machines, so long as its mechanical properties and corrosion resistance are also suitable. 

Rebar Length 

Steel bars used to reinforce concrete must be connected to each other for maximum strength. They are joined usually by splicing them together with wire, or by means of mechanical couplers or connectors. A customary overlap of about 4 feet of bar at both ends, for splicing, reduces the effective bar length. The percentage of bar lost to overlap is smaller in a long bar than that lost in shorter bar lengths.

Sleeves also must be used to protect unions of dissimilar metals to prevent galvanic corrosion. In summary, the more splicing, connecting, overlapping and sleeving required in a reinforced structure, the more expensive it becomes.

This makes bar length important. Long stainless steel bars, currently made up to 40 feet in length, require less time and expense to join than a larger number of smaller bars. In addition to the time and labor savings, long bars with fewer connections also save weight and space without any loss of strength. 

Classic Example 

A coastal replacement bridge currently under construction at North Bend, Ore., graphically demonstrates the benefits of using stainless steel rebar instead of carbon steel rebar for critical structural elements in a harsh marine environment. Oregon Department of Transportation (ODOT), which has chosen to use duplex stainless from Carpenter Technology Corporation&#;s Talley Metals subsidiary in Hartsville, S.C., expects the new bridge to provide maintenance-free service for an amazing 120 years. That is 2.5 times the service life of the bridge it is replacing!

 

When finished by the end of , the bridge will cost approximately $12.5 million. The stainless rebar accounts for only 13 percent of the total bridge cost. For that small increase, ODOT will save the cost of normal bridge replacement in 50 years. That is an amount likely to be $25 million, or at least twice the cost of bridge construction today. In terms of life cycle costs, that is a real accomplishment.

The rebar had to have superior corrosion resistance to withstand the attack of salt-laden air and fog from the Pacific Ocean, and the chloride-containing moisture that used to initiate corrosion underneath the structures.

Extra high strength was required of the stainless rebar to facilitate design of the new bridge, and to deal with the potentially devastating seismic activity in this area. ODOT required a strength level of 75 ksi (520 MPa). This was a strength level new to bridge building, and substantially higher than that of the stainless rebar it used previously in the replacement of two other coastal bridges.

Along with such high strength, the rebar also had to provide good ductility (25 percent elongation) so it could be effectively fabricated. With a higher strength stainless alloy like stainless, ODOT is also enjoying an economic advantage of less stainless rebar weight than would have been required using an alloy of less strength.

 

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