Steel is the most common reinforcing material used in concrete construction, providing essential tensile strength and ductility to concrete structures. One key advantage of steel is its similar thermal expansion properties to concrete, allowing both materials to expand and contract at nearly the same rates under temperature changes. This compatibility helps steel and concrete work together effectively as a single structural unit.
However, one major challenge with steel reinforcement is corrosion. When steel rusts, the volume of rust can be up to five times greater than the original steel, which causes cracking and deterioration of the concrete around it. To address this problem, several alternative types of reinforcement have been developed, including stainless steel reinforcement, fiber-reinforced polymer (FRP) reinforcement, and epoxy-coated carbon steel. This article explains these reinforcing materials to help you choose the best option for your construction needs.
Steel Reinforcement Bars
Steel reinforcement bars, or rebars, are specified by their diameter and grade according to ASTM standards, particularly ASTM A615/A615M-20. For example, a Grade 40 steel bar has a minimum yield strength of 40,000 psi. Bar sizes are available in both inch-pound and metric units.
Steel rebars are the conventional choice for reinforcement and are readily available worldwide. They perform well in environments where corrosion is not a significant concern. For projects requiring higher tensile strength, higher-grade steel rebars can be selected. However, in corrosive environments, standard steel reinforcement may not be the best option without additional protection.
Fiber Reinforced Polymer (FRP) Reinforcement
Fiber-reinforced polymer (FRP) rebars consist of fibers embedded in a resin matrix, combined with fillers and additives. This composition makes FRP reinforcement highly resistant to corrosion, lightweight, and tough compared to traditional steel bars.
FRP reinforcement improves concrete stiffness and tensile strength, making it an effective alternative in environments where corrosion risk is high. The resin used in FRP has high compressive strength, which helps bind the concrete mass firmly.
Common types of fibers used in FRP rebars include aramid, carbon, and fiberglass. Fiberglass is the most economical, while carbon fiber is more costly but offers superior performance.
Stainless Steel Reinforcement Bars
Stainless steel reinforcement is made from low-carbon steel alloyed with at least 10.5% chromium, which forms a passive oxide layer on the surface. This layer makes stainless steel highly resistant to corrosion.
Though stainless steel rebars are more expensive than standard steel bars, they provide excellent strength and durability, especially in harsh environments such as marine structures, roadways exposed to salts, parking garages, piers, and retaining walls.
ASTM A955/A955M defines the standard specifications for stainless steel reinforcing bars, ensuring quality and performance.
Epoxy-Coated Reinforcement
Epoxy-coated rebars, often called green bars, are conventional steel bars coated with an epoxy layer to protect against corrosion. The coating is applied before transportation to the construction site.
Epoxy-coated reinforcement is commonly used in pavements, bridges, parking structures, and marine environments exposed to deicing salts. A well-manufactured and carefully handled epoxy coating can significantly delay the onset of corrosion.
However, the durability of epoxy-coated bars depends on the quality and integrity of the coating. Damage during handling or installation can reduce corrosion resistance, making stainless steel a better choice in some applications despite the higher cost. On the cost scale, epoxy-coated rebars are approximately eight times less expensive than stainless steel bars.
Frequently Asked Questions (FAQs)
What are the different types of reinforcement bars based on material?
- Standard steel reinforcement
- Stainless steel reinforcement
- Epoxy-coated steel reinforcement
- Fiber-reinforced polymer (FRP) reinforcement
How to choose between epoxy-coated and stainless steel reinforcement bars?
Epoxy-coated bars can effectively delay corrosion if their coating remains intact, but stainless steel offers superior corrosion resistance and durability. The choice depends on the project’s budget and the required longevity of the structure. Stainless steel is significantly more expensive but guarantees better durability.
What are the types of fibers used as concrete reinforcement?
The main fibers used in FRP reinforcement are aramid, carbon, and fiberglass. Fiberglass is the least expensive, whereas carbon fiber is more costly but offers enhanced strength and performance.