Fiber-Reinforced Concrete | Steel and Glass Fiber-Reinforced Concrete
What is Fiber-Reinforced Concrete
Fiber-reinforced concrete (FRC) is a type of concrete that contains fibrous material to improve structural stability. It is made up of short discrete fibers that are uniformly dispersed and orientated randomly.
Steel fibers, glass fibers, synthetic fibers, and natural fibers are all types of fibers that add different qualities to concrete.
Furthermore, the nature of fiber-reinforced concrete varies depending on the concrete, fiber materials, geometries, distribution, orientation, and densities used.
Steel and Glass Fiber-Reinforced Concrete
Steel and glass Fiber-reinforced concrete is a type of concrete that has been strengthened with fibers.
The use of fibers as reinforcement is not a new notion. Fibers have been utilized for reinforcement since antiquity. Horsehair was traditionally used in mortar and straw in mudbricks.
Asbestos fibers were employed in concrete in the early 1900s. The notion of composite materials emerged in the 1950s, and fiber-reinforced concrete was one of the areas of discussion.
Once the health dangers linked with asbestos were revealed, a substitute for the chemical in concrete and other building materials became necessary. Steel, glass (GFRC), and synthetic (such as polypropylene) fibers were employed in concrete by the 1960s. Today, research on novel fiber-reinforced concretes is ongoing.
Fibers are commonly utilized in concrete to prevent cracks caused by plastic shrinkage and drying shrinkage. They also limit the permeability of concrete, resulting in less water bleeding.
Some fibers have higher impact, abrasion, and shatter resistance in concrete. In some cases, larger steel or synthetic fibers can totally replace rebar or steel.
Fiber reinforced concrete has almost entirely replaced bar in the subterranean construction business, such as tunnel segments, where practically all tunnel linings are fiber reinforced rather than rebar. Some fibers, in fact, lower the compressive strength of concrete.
The volume fraction of fibers added to a concrete mix is stated as a percentage of the total volume of the composite (concrete and fibers) (Vf). Vf normally varies from 0.1 to 3%.
The aspect ratio (l/d) is obtained by dividing the length of the fiber (l) by its diameter (d) (d). For non-circular cross-section fibers, an equivalent diameter is used to calculate aspect ratio.
If the modulus of elasticity of the fiber is greater than that of the matrix (concrete or mortar binder), they aid to carry the load by enhancing the material’s tensile strength.
Increasing the aspect ratio of the fiber usually segments the matrix’s flexural strength and toughness. Longer length results in a better matrix inside the concrete, while smaller diameter enhances fiber count.
It is advisable to utilize fibers that are longer than the aggregate’s maximum size to guarantee that each fiber strand is effective. Normal concrete has 19 mm equivalent diameter aggregate, which accounts for 35-45 percent of the total weight of the concrete; fibers longer than 20mm are more effective.
Fibers that are too long and are not appropriately treated at the time of processing, on the other hand, tend to “ball” in the mix and cause workability issues.
Fibers are added to concrete to increase its long-term durability. Glass and polyester degrade in alkaline concrete, as do other additives and surface treatments.
The High Speed 1 tunnel linings used concrete containing 1 kg/m3 or more polypropylene fibers with diameters of 18 and 32 m, providing the benefits listed below.
Adding fine diameter polypropylene fibers not only reinforces the tunnel lining, but also avoids “spalling” and lining damage in the event of a fire caused by an accident.
What are the Advantages of Fiber-Reinforced Concrete?
The following are some of the benefits of fiber-reinforced concrete:
1) When compared to non-reinforced concrete, fiber-reinforced concrete has higher tensile strength.
2) It improves the durability of the concrete.
3) It inhibits crack propagation while increasing impact strength.
4) Concrete with fiber reinforcement is more resistant to freezing and thawing.
5) Fiber reinforcement of concrete improves fatigue strength.
What are the Disadvantages of Fiber-Reinforced Concrete?
The following are some of the drawbacks of fiber-reinforced concrete:
1) The fibers may be exposed if it rains.
2) If the orientation of the fibers in the concrete is not uniform, it might result in poor quality concrete.
3) Reinforced concrete is around 10% to 15% more expensive than non-reinforced concrete.
Types of Fiber-Reinforced Concrete
There are several types of fibers used in reinforced concrete. Descriptions of the most common types follow.
1. Glass Fibers Reinforced Concrete
Glass fibers are light and strong, and can be produced as single strands up to three millimetres in diameter. Glass Fiber has good tensile strength, and good resistance to crushing.
Glass fibers can be woven or coiled into solid rods, but the same advantages also apply to carbon nanotubes.
Benefits of Glass Fiber Reinforced Concrete (GFRC)
This type of concrete has many potential benefits, including:
1) Good tensile strength and good resistance to crushing.
2) It is resistant to chemical attack.
3) It has excellent jointing behavior, and it has good resistance to cracking.
4) It has good thermal and sound insulation qualities.
5) It is very tough and fire resistant.
6) It is less elastic compared to Portland cement, so it can be used in many different forms of concrete.
7) Ultra-high performance (UHP) GRP – This is discussed below in more detail under the main heading “High-Performance Concrete”.
8) It is waterproof.
9) It is resistant to damage from salt water and marine organisms.
10) It is resistant to attack by chemicals that can cause corrosion.
2. Steel Fiber Reinforced Concrete
Steel fibers (steel wool) consist of rolled-up steel sheet. They are useful for reinforcing concrete in the form of continuous mats or by using a woven mesh in a coating that is applied to the surface of the concrete.
Steel fiber or macro synthetic fibers can completely replace typical steel reinforcing bar (“rebar”) in reinforced concrete under certain conditions.
This is most commonly used in industrial flooring, but it can also be seen in various other precasting applications.
Typically, these are backed up by laboratory testing to ensure that the performance standards are met. Care should be taken to ensure that local design code requirements, which may mandate minimum amounts of steel reinforcement within the concrete, are also met.
A growing number of tunneling projects are utilizing precast liner segments reinforced solely with steel fibers.
Benefits of Steel Fiber Reinforced Concrete
1) Improve structural strength
2) Reduce steel reinforcement requirements
3) Reduce crack widths and control the crack widths tightly, thus improving durability
4) Improve impact– and abrasion–resistance
5) Improve freeze-thaw resistance
3. Polypropylene Fibers Reinforced Concrete
Polypropylene fiber is a high-performance composite which has mechanical strength, impact resistance, and elasticity similar to that of steel. It is used in the production of reinforced gypsum and concrete.
4. Kevlar Fibers Reinforced Concrete
Kevlar fibers are a man-made fiber that look like a white cotton thread. It is very strong and is often used as ropes or cords for parachute suspension lines, fishing lines, and sailboat rigging.
5. Carbon Fibers Reinforced Concrete
Carbon fiber is strong and light, making it ideal for reinforcing concrete. It can also be used in the form of continuous mats or as a woven mesh in a coating applied to the surface of concrete.
6. Plastic Fibers Reinforced Concrete
Plastic fibers are made from polyethylene (PE), polypropylene, or other materials that are compatible with these two types of materials. These fibers resist rot and fungi growth, have good tensile strength, and low permeability.
7. Modified-Porous Concrete (MPC)
MPC is developed by adding a high-density glass fiber reinforcement to the concrete. This reinforced concrete can be used for many applications, such as: reinforced walls in footings, foundations and columns; pilings and piling caps; slabs, beams and roofing systems; wet areas such as pools, walkways and dams.
8. Cellulose Fibers Reinforced Concrete
Cellulose fibers are found in natural or synthetic forms. They can be woven into mats or sheets, coiled onto rope, fiber-reinforced composites and fabricated in plates and profiles. This type of fiber can be used in the production of reinforced concrete, gypsum plaster and as plaster coatings on a wide range of substrates.
9. Glassy Carbon Fiber Reinforced Concrete
This fiber-reinforced concrete is composed of a high-performance glass fiber reinforcement in a combination of cement paste and fibers. The glass fibers are used as both matrix and reinforcement material.
10. Plastic Fibers/Glass fibers Reinforced Concrete
Glass-reinforced plastic (GRP) has improved durability benefits over traditional reinforced concrete, due to the use of glass fiber reinforcements, which impart strength to the product, resulting in improved durability and stability for many applications.
11. Boron Fiber Reinforced Concrete
Boron fibers are approximately 1/3 the diameter of glass fibers. They have a higher strength rating than glass fibers because of their higher density relative to glass. Boron is also a more flexible fiber than glass.
12. Titanium Dioxide Fibers Reinforced Concrete
Titanium dioxide fibers are approximately 1/10 the diameter of glass fibers, making them very thin and flexible. Their flexibility is due to their asymmetric structure, which includes a hollow channel inside the fiber.
The hollow channel allows the titanium dioxide to bend by collapse of this hollow space. The benefit to using titanium dioxide as reinforcement in concrete is that it provides good tensile strength, while maintaining flexibility.
13. Polymeric Fibers Reinforced Concrete
Polymeric Fibers are woven polypropylene fibers that are commonly used as fiberglass reinforcement for concrete. These fibers are hollow tubes, and in some applications, the ends of them were left open after weaving.
This “open-end” type of reinforcement is useful in prestressed concrete where the placement of a tie (rebar) at every meter or so would be difficult.
Steel-polymeric fiber blends are frequently used in building projects to combine the benefits of both products: structural enhancements supplied by steel fibers and resistance to explosive spalling and plastic shrinkage supplied by polymeric fibers.
14. Polyvinyl Chloride (PVC) Fibers Reinforced Concrete
Used in fiber-reinforced polymer concrete. These fibers are woven into polyvinyl chloride (PVC) that has been formed into a solid block, known as a “caul”.
15. Expanded Polystyrene Fibers Reinforced Concrete
Expanded polystyrene fibers are used to reinforce unbound mixes for poured and sprayed concrete. The mixture of the plastic and concrete usually has about 0.35% of the reinforcement.
Fiber Reinforced Concrete Vs Rebar
What is best concrete reinforcement rebar or fiber mesh?
Both are made of steel. Both are used to reinforce concrete, and both can be found in floor slabs. … To put it simply, steel fibers prevent cracks, while rebar limits the width of cracks. The fiber mesh strengthens the concrete and the steel rebar reinforces the extra load areas.
Do you need rebar with fiber reinforced concrete?
Fiber concrete still needs reinforcements with rebar. The fiber mesh strengthens the concrete and the steel rebar reinforces the extra load areas. Steel fibers and rebar work differently and accomplish different goals. Sometimes you need steel fibers, and sometimes you need rebar, and only in a few limited situations can one effectively replace the other.
To put it simply, steel fibers prevent cracks, while rebar limits the width of cracks. Let’s consider two examples: a wide-slab floor and a continuously-reinforced concrete highway.