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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:
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.
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 ReinforcementSteel 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.
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 ReinforcementThe 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.
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 BarsCompared 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.
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 ReinforcementThey 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.
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
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.
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.
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What is Rebar? Types and Grades of 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.
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 like BA-CTR Flush Universal Access Door with Hidden Flange 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:
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.
For more information, please visit Stainless Steel Fiber For Refractory.