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Fiber Reinforced Concrete(FRC)

Daniel M.

Fiber reinforced concrete is a composite material that is made of cement, mortar, or concrete mixed with appropriate fibers that are discrete, uniformly scattered, and discontinuous. Fiber reinforced concrete comes in a variety of forms and has several benefits.

Fiber is a tiny piece of reinforcing material that possesses specific qualities. They might be flat or spherical. The “aspect ratio” is a useful characteristic that is frequently used to define the fiber. The fiber’s length to diameter ratio is known as its aspect ratio. A normal aspect ratio falls between 30 and 150

Fiber reinforced concrete (FRC), also known as reinforced concrete containing fibrous material, provides a better level of structural stability than plain concrete. It has short discrete fibers that are evenly scattered and are randomly oriented. Fibers can be made of steel, glass, synthetic, or natural materials. The characteristics of fiber reinforced concrete vary within these varied fibers due to variable concretes, fiber materials, geometries, distribution, orientation, and densities.

Fiber reinforcement is most frequently used in shotcrete, however it can also be used in normal concrete. For a number of construction elements, such as beams, foundations, and pavements, fiber-reinforced normal concrete can be used, either alone or in conjunction with hand-tied rebars.

Compared to hand-tied rebar, concrete with fiber reinforcement—typically steel, glass, or “plastic” fibers—is less expensive while still significantly increasing tensile strength. A thin, short fiber, like a hair-like glass fiber, will only be helpful in the first few hours after concrete is poured (reducing cracking while the concrete is hardening), but it won’t increase the concrete’s tensile strength.

Components of Fiber Reinforced Concrete

The following are the primary components of fiber-reinforced concrete:

Cement

Hydraulic cement, which transforms into adhesive when it reacts with water, is the primary ingredient of fiber-reinforced concrete. In fiber-reinforced concrete, Portland cement is frequently utilized as the hydraulic cement.

Fibers

Depending on the type of fibrous material used, adding long fibers changes the qualities of freshly-poured concrete.

Aggregates

Concrete’s binding strength is provided by an aggregate, which also lowers the amount of cement needed. Sand, crushed stone, and gravel are a few examples of common aggregates.

Types of Fiber Reinforced Concrete

Concrete fibers are available in a range of shapes and sizes. The key factors affecting the properties of fiber-reinforced concrete are the amount of fibers, their percentage, diameter, and length. The following is a list of the various types of fiber-reinforced concrete used in construction.

Steel Fiber Reinforced Concrete (SFRC)

Steel fiber is a type of metal reinforcement. When steel fiber is added to concrete in a specific amount, the physical properties of the concrete might qualitatively change. Tenacity, durability, and other properties like resistance to fatigue, impact, and bending can all be considerably enhanced.

For better long-term strength, toughness, and stress resistance, SFRC is used in buildings including flooring, housing, precast, bridges, tunneling, heavy-duty pavement, and mining.

Polypropylene Fiber Reinforced (PFR) Concrete

Concrete reinforced with polypropylene fibers is also referred to as polypropene or PP. It is a synthetic fiber made from propylene that is employed in a number of different applications. Typically, these fibers are added to concrete to prevent cracking brought on by drying shrinkage and plastic shrinkage. Moreover, they lessen the permeability of concrete, which in turn lessens 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 very 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 also has a high acid, alkaline and organic solvent resistance.

Glass Fiber Reinforced Concrete (GFRC)

Large amounts of extremely thin glass fibers are utilized to reinforce concrete. Glass fiber has mechanical properties comparable to those of other fibers like polymers and carbon fiber. Despite the fact that it is not as hard as carbon fiber, It is considerably less brittle and far less expensive when used in composites. In order to generate glass-reinforced plastic (GRP), also known as “fiberglass,” a very strong and relatively lightweight fiber-reinforced polymer (FRP) composite material, glass fibers are used as a reinforcing agent in numerous polymer items.

Polyester Fiber Reinforced Concrete (PFRC)

Polyester fibers are utilized in fiber-reinforced concrete for precast products, pavement and 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 the formation of plastic shrinkage cracks compared to welded wire fabric.

Carbon Fiber Reinforced Concrete (CFRC)

Carbon atoms are the main component of carbon fibers, which are fibers with a diameter of 5 to 10 micrometers. Carbon fibers have many advantages, including high stiffness, high tensile strength, low weight, good chemical resistance, high temperature tolerance, and little thermal expansion. Carbon fibers are frequently combined with other materials to make composites. When carbon fiber is infused with plastic resin, baked, and dried, a carbon-fiber-reinforced polymer, also known as carbon fiber, is produced. It is incredibly stiff, has a very high strength to weight ratio, but is also somewhat fragile. Carbon fibers are also composited with other materials, such as graphite, to produce reinforced carbon composites, which have a very high heat tolerance.

Macro Synthetic Fiber Reinforced Concrete (MSFRC)

First created as a substitute for steel fibers in some applications, macro synthetic fibers are composed of a variety of 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 as well as a host of other uses. They are especially well-suited for serving as 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. Also, they have been utilized in tram and light railway advancements due to the fact that they are non-conducting.

Natural Fiber Reinforced Concrete (NFRC)

A natural fiber can be described as an accumulation of cells having a small diameter relative to their length. Natural fibers can be produced directly from an animal, vegetable, or mineral sources and can be spun into yarn to create woven cloth or nonwoven materials like felt or paper. Since many of these natural fibers are readily available locally and are abundant, it is advised to use them when producing concrete. These fibers, when added in measured quantities are shown to significantly improves the physical properties of plain concrete. The concept of adding such fibers to fragile materials to increase their strength and durability is not new; for instance, straw and horsehair are used to build bricks and plaster.

Importance of Fiber Reinforced Concrete

  • Fiber reinforced concrete can be helpful in situations where a high tensile strength and minimal cracking are desired or where conventional reinforcement cannot be installed.

  • Fibers increase the concrete’s impact resistance, slow the spread of cracks, and raise the composite material’s strain capacity.

  • Macro-synthetic fibers are utilized to increase the durability of concrete for industrial projects. These long, dense threads, which are made of synthetic materials, could take the role of fabric or bar reinforcement.

  • The addition of fibers to the concrete will increase its resistance to freeze-thaw and keep the concrete firm and appealing for longer periods of time.

  • Fibers increase mix cohesiveness, which enhances long-distance pumpability.

  • Fibers increase resistance to plastic shrinkage during curing.

  • They reduce the need for steel reinforcement.

  • Fibers firmly limits the crack widths, thereby increasing durability.

  • The presence of fibers boosts fatigue resistance.

  • The shear strength of reinforced concrete beams is increased by fibers.

Factors That Affect The Properties of Fiber Reinforced Concrete (FRC)

Fiber-reinforced concrete is a composite material made of fibers arranged either randomly or purposefully within the cement matrix. The effectiveness of the stress transmission between the matrix and the fibers will, of course, influence the material’s characteristics. Several factors that influence the properties of fiber-reinforced concrete are listed below:

Relative Fiber Matrix Stiffness

For effective stress transfer, the matrix’s elasticity modulus needs to be substantially lower than that of the fiber. As a result, low modulus fibers like nylon and polypropylene are unlikely to boost strength, but they do assist in absorbing significant amounts of energy and hence increase toughness and resistance. Steel, glass, and carbon fibers with high modulus give the composite its strength and rigidity. The efficacy of stress transfer from the matrix to the fiber is also determined by the interfacial connection between the matrix and the fiber.

Volume of Fibers

The amount of fiber utilized in the concrete mix has a significant impact on its strength. The tensile strength and toughness of the composite will improve as the fiber volume increases. However, concrete and mortar are prone to becoming segregated and harsh as a result of using too much fiber.

Aspect Ratio

The aspect ratio of the fiber is another crucial element that affects the composite’s characteristics and behavior. According to reports, increasing the aspect ratio will increase the strength and hardness of the concrete as long as the fibers' aspect ratio does not surpass 75.

Concrete Workability

The inclusion of fibers considerably reduces the workability of concrete. This situation has an adverse effect on the consolidation of freshly mixed concrete. As a result, the concrete mix is compacted with a great deal of effort. The mix's workability and compaction standard can be improved by adjusting the water/cement ratio or adding a water-reducing admixture.

Size of Coarse Aggregate

To prevent a noticeable decrease in the strength of the composite, the maximum size of the coarse aggregate should be limited to 10mm. In a way, fibers also function as an aggregate. While having a straightforward geometry, they have a complicated impact on the characteristics of freshly cast concrete. The orientation and distribution of the fibers, and subsequently the characteristics of the composite, are controlled by the inter-particle friction between the fibers and between the fibers and aggregates. The mix can be greatly enhanced by admixtures that lessen friction and enhance cohesion.

Mixing of Fiber Reinforced Concrete

Concrete with fiber reinforcement must be mixed under strict circumstances to prevent fiber balling, segregation, and generally problematic uniform mixing of the constituents. The challenges and tendency to ball up are made worse by an increase in the aspect ratio, volume percentage, and size and amount of coarse aggregate. It is challenging to blend materials with an aspect ratio of more than 100 and a steel fiber concentration of more than 2% by volume.

It is crucial that the fibers are evenly distributed throughout the mixture, which can be accomplished by adding the fibers before the water. Fiber distribution will be improved when introduced through a wire mesh basket when mixing in a laboratory mixer. Other workable techniques must be used for field use.

Applications of Fiber Reinforced Concrete

The use of 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:

  • Airport runways

  • Road pavements

  • Lining of tunnels

  • Slope stabilization

  • Thin Shell

  • Beams, slabs and columns

  • Pipes

  • Manholes

  • Dams

  • Retaining walls

  • Elevated decks

  • Bridges

  • Warehouse floors

  • Building walls

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