Fiber reinforced concrete: All you need to know

Introduction

Fiber-reinforced concrete (FRC) contains fibrous material to strengthen its structural integrity. It has uniformly distributed, randomly orientated short discrete fibers. Steel, glass, synthetic, and natural fibers are some of the threads that can be used to give concrete different qualities. With various concretes, fiber materials, geometries, distribution, orientation, and densities, fiber-reinforced concrete also takes on other characteristics.

Historical Perspective

It is not a novel idea to use fibers as reinforcement. Since the beginning of time, fibers have been employed for support. In the past, mudbricks and mortar were made of straw and horsehair. Concrete in the 1900s included asbestos fibers. The idea of composite materials emerged in the 1950s, and fiber-reinforced concrete was a hotly debated subject. After the health hazards of asbestos were identified, a substitute for the material was required for concrete and other building materials. By the 1960s, concrete was made with steel, glass (GFRC), and synthetic fibers like polypropylene. There is still research being done on novel fiber-reinforced concretes.

Fibers are typically used to prevent concrete cracking by drying and plastic shrinkage. They also lessen the permeability of concrete, lessening water bleeding. The certain thread gives concrete a higher impact, abrasion, and shatter resistance. Rebar or steel can occasionally be replaced by larger steel or synthetic fibers. In the underground construction sector, where tunnel segments are concerned, fiber-reinforced concrete has all but replaced rebar in the tunnel linings. Some fibers weaken concrete’s ability to resist compression.

The phrase “volume fraction” refers to the proportion of the composite material’s (concrete and fibers) total volume that is made up of fiber additions (Vf). Vf normally falls between 0.1 and 3%. Calculating the aspect ratio (l/d) requires dividing the fiber’s length (l) by its diameter (d). An equivalent diameter calculates the aspect ratio in fibers with non-circular cross-sections. The fibers assist in carrying the load by boosting the material’s tensile strength if its elastic modulus is higher than that of the matrix (concrete or mortar binder). The flexural strength and toughness of the matrix are typically divided as the aspect ratio of the fiber is increased.

“Volume fraction” refers to the proportion of the composite’s (concrete and fibers) total volume that is made up of fiber additions to concrete mixtures (Vf). Typically, Vf lies between 0.1 to 3%. By subtracting the fiber’s diameter from its length, one can determine the aspect ratio (l/d) (d). An equivalent diameter calculates the aspect ratio for fibers with non-circular cross-sections. The fibers increase the material’s tensile strength if their elastic modulus is higher than that of the matrix (concrete or mortar binder), which aids in carrying the load. The matrix’s flexural strength and toughness are frequently divided as the fiber aspect ratio increases.

For concrete to be durable over time, fibers are added. Polyester and glass degrade in an alkaline environment with various additives and surface treatments.

Concrete with at least 1 kg/m3 of polypropylene fibers, measuring 18 and 32 mm in diameter, was used to line the High Speed 1 tunnel, providing the advantages listed below. Fine-diameter polypropylene fibers are added to the tunnel lining to offer strength and prevent “spalling” and lining damage in an accident-related fire.

Types

Concrete fibers come in a variety of sizes and forms. The proportion of fibers, their fraction, diameter, and length are the main variables influencing the characteristics of fiber-reinforced concrete. The various kinds of fiber-reinforced concrete used in buildings are listed below.

Concrete with steel fiber reinforcement –  A type of metal reinforcement is steel fiber. Concrete’s physical characteristics can vary qualitatively when steel fiber is present in concrete at a given quantity. It can improve tenacity, durability, and other qualities like resistance to cracking, impact, fatigue, and bending. SFRC is utilized in buildings, including flooring, housing, precast, bridges, tunneling, heavy-duty pavement, and mining, for improving long-term behavior and enhancing strength, toughness, and stress resistance. Type I: cold-drawn wire, Type II: cut sheet, Type III: melt-extracted, Type IV: mill cut, and Type V: modified cold-drawn wire are the types of steel fibers specified by ASTM A820.

Concrete with polypropylene fiber reinforcement (PFR) –  Concrete reinforced with polypropylene fibers is also referred to as polypropene or PP. It is a synthetic fiber from propylene employed in several different applications. Typically, these fibers are added to concrete to prevent cracking brought on by drying shrinkage and plastic shrinkage. Additionally, they lessen the permeability of concrete, reducing water bleeding. Polypropylene fiber is non-polar, partly crystalline, and a member of the polyolefin family. Although it is stronger and more heat resistant than polyethylene, it shares many of the same qualities. It is made of a tough, white substance that is chemical resistant. Propylene gas is used to make polypropylene when a catalyst, such as titanium chloride, is present. In addition to having excellent heat-insulating qualities, polypropylene fiber is also very resistant to acids, alkalis, and organic solvents.

Concrete reinforced with glass fiber – These incredibly fine fibers are used to strengthen concrete in large quantities. Glass fiber is comparable to other fibers like polymers and carbon fiber in terms of its mechanical qualities is glass fiber. Even though it is not as rigid as carbon fiber, it is substantially less brittle and much cheaper when used in composites. Therefore, glass fibers are employed as a reinforcing agent in many polymer goods to create glass-reinforced plastic (GRP), also known as “fiberglass,” which is a very strong and comparatively lightweight fiber-reinforced polymer (FRP) composite material. This substance is substantially denser than glass wool, contains little air or gas, and performs far worse as a thermal insulator.

Polyester fibers – Polyester fibers are used in fiber-reinforced concrete for precast products, pavement, overlays, and industrial and warehouse flooring. When appropriately built, polyester micro- and macro-fibers improve toughness and the ability to deliver structural capacity in concrete, respectively, and offer greater resistance to forming plastic shrinkage cracks than welded wire fabric. When appropriately built, polyester micro- and macro-fibers improve toughness and the ability to deliver structural capacity in concrete, respectively, and offer greater resistance to forming plastic shrinkage cracks than welded wire fabric.

Carbon fibers – Carbon fibers have a diameter of 5 to 10 micrometers and are primarily made of carbon atoms. High stiffness, good tensile strength, low weight, high chemical resistance, high-temperature tolerance, and minimal thermal expansion are only a few benefits of carbon fibers. To create a composite, carbon fibers are typically mixed with other materials. The carbon-fiber-reinforced polymer, also known as carbon fiber, is formed when carbon fiber is impregnated with plastic resin and baked. It has a very high strength-to-weight ratio and is exceedingly rigid but is also slightly fragile. Carbon fibers are also composited with other materials, such as graphite, to create reinforced carbon composites with very high heat tolerance.

Large-scale synthetic fibers –  Initially created as a substitute for steel fibers in some applications, macro synthetic fibers are composed of various polymers. They were first noted as a potential substitute for steel fibers in sprayed concrete, but further investigation and development revealed that they also had a place in the planning and construction of ground-supported slabs and a host of other uses. They are especially well-suited for minimal reinforcement in hostile settings, such as maritime and coastal constructions, as they are not subject to the staining and spalling issues that can occur when steel corrodes. 

The cellulose fibers – Ethers or esters of cellulose, found in the bark, wood, or leaves of plants or other plant-based materials, are used to create cellulose fibers. In addition to cellulose, the threads may also contain hemicellulose and lignin; the proportions of these substances in the fibers affect their mechanical characteristics. Due to their similar characteristics to designed fibers, cellulose fibers are mostly used in the textile sector as chemical filters and fiber-reinforcement composites, providing another choice for biocomposites and polymer composites.

Benefits

Fiber Glasses can:

• At little expense, increase the strength of concrete.
• Unlike rebar, it adds support for tensile forces in all directions.
• They may be seen in the final concrete surface and add a decorative appearance.

Nylon and polypropylene fibers can:

• Boost mix cohesiveness to make the mixture easier to pump over long distances
• Improved resistance to freeze-thaw
• Enhance explosive spalling resistance in the event of a major fire
• Boost resistance to impact and abrasion
• Increasing structural strength and decreasing the need for steel reinforcement while improving flexibility and reducing resistance to plastic shrinkage during curing
• Improve durability by narrowing crack widths and precisely controlling the crack widths.

Metallic fibers can:

• Boost structural toughness
• Lessen the need for steel reinforcement
• Improve durability by narrowing crack widths and precisely controlling the crack widths.
• Boost resistance to impact and abrasion
• Improved resistance to freeze-thaw

For structural enhancements supplied by steel fibers and increases in resistance to explosive spalling and plastic shrinkage provided by polymeric fibers, blends of steel and polymeric fibers are frequently employed in construction projects.

In some rare situations, macro synthetic fibers or steel fiber can completely replace traditional steel reinforcement bars (also known as “rebar”) in reinforced concrete. However, there are several other precasting uses where it is less typical, such as industrial flooring. These are typically validated through laboratory testing to verify that performance standards are met. It is important to make sure that local design code standards are satisfied, as they can require a minimum amount of steel reinforcement in the concrete.

Precast lining segments are solely strengthened with steel fibers in many tunneling projects.

Additionally, the micro-rebar has just undergone testing and received approval to replace conventional reinforcement in vertical walls created by ACI 318 Chapter 14.

Developments

In a typical building component, the steel reinforcement is shielded from corrosion by at least half of the concrete. Saving concrete and the associated greenhouse effect is possible when only fiber is used as reinforcement in concrete.  Designers and engineers have more versatility with FRC because it can be molded into various shapes.

According to High-Performance FRC (HPFRC), compared to regular concrete or ordinary fiber-reinforced concrete, it can withstand strain-hardening up to several percent strain with material flexibility of at least two orders of magnitude higher. HPFRC also asserts a distinctive cracking style. Even when distorted to several percent tensile strains when loaded beyond the elastic limit, HPFRC retains crack width to below 100m.

Early-age cracking was seen in field tests with HPFRC and the Michigan Department of Transportation.

Recent research on a bridge deck made of high-performance fiber-reinforced concrete showed that adding fibers increased residual strength and reduced cracking. Even though the FRC shrank more than the control, there were fewer and smaller cracks. The amount of fiber present directly relates to residual strength.

Waste carpet fibers have been used in concrete in several experiments as an environmentally friendly way to use leftover carpets. The two layers of a carpet’s backing, commonly made of polypropylene tape yarn, are linked by CaCO3-filled styrene-butadiene latex rubber (SBR) and face fibers (the majority being nylon six and nylon 66 textured yarns).

These nylon and polypropylene fibers can be utilized as reinforcement in concrete. Recycled polyethylene terephthalate (PET) fiber is one new idea for using recycled materials as fibers.

Advantages

• Fibers Where high tensile strength and reduced cracking are desired or conventional reinforcement cannot be installed; reinforced concrete may be advantageous.

• It increases the strain capacity of the composite material, reduces fracture formation, and strengthens the concrete’s impact resistance.

• Macro-synthetic fibers are utilized to increase the durability of concrete for industrial projects. These long, thick synthetic fibers can be used in place of bars or fabric reinforcement because they are made of synthetic materials.

• Adding fibers to the concrete will increase its resistance to freeze-thaw and keep it firm and appealing for longer periods.

• Boost mix cohesiveness to make the mixture easier to pump over long distances

bolster the plastic’s resistance to shrinkage during curing reduces the need for steel reinforcement

• Firmly limits the crack lengths, increasing durability and decreasing bleed-water and segregation.

• The hardness of FRC is approximately 10–40 times that of regular concrete.

• The inclusion of fibers increases fatigue strength.

• Fibers increase the shear strength of reinforced concrete beams.

Applications

Using fiber-reinforced concrete depends on how well the builder and applicator take advantage of the material’s static and dynamic properties. Some of its applications include:

• Pavements for Runway Aircraft Parking

• Stabilize the slope of the tunnel lining

• Pipes with thin shell walls

• Manholes \Dams

• Hydraulic Building

• Raised decks

• Roads

• Bridges

• Storeroom floors

Conclusion

From durability to appearance, Concrete with fiber reinforcement can assist your project. Since builders and homeowners began to realize its many advantages, fiber-reinforced concrete has expanded quickly throughout the construction sector. Due to its faster construction and lower labor expenses, fiber-reinforced concrete is gaining popularity among concrete professionals. In addition to cost considerations, fiber-reinforced concrete also satisfies the requirements for quality in construction.