What is Fiber Reinforced Concrete
The Concrete which includes fibrous substance to increase structural strength and cohesion, it is called as a Fiber Reinforced Concrete. Fiber Reinforced Concrete has a small distinct of Fibers, which are homogeneously dispersed and oriented haphazardly.
Before Moving Forward let us understand what is Fiber in Construction
What is Fiber?
- Fiber is small reinforcing material shape circular or flat the Fiber is described by a parameter called aspect ratio (AR)
- Fiber concrete is enhanced toughness and durability of residential concrete such as elevation design, patios, they can help, this product which is made of synthetic Fiber is uniformly distributed and provide secondary reinforcement for improving the durability of concrete.
- For the industrial project, Fiber is used to improve the durability of concrete. Made from synthetic materials, these Fibers are long and thick in size and may be used as a replacement for bar and fabric reinforcement
- The aspect ratio (AR) of the Fiber is the ratio of its length to its diameter.
- Typical expect ratio ranges from 30 To 150
History of Fibers
The use of Fibers in construction goes back at least 3500 years. Horsehair was used in mortar and the straw is used as reinforcing Sun-baked bricks in Mesopotamia. In 19th-century asbestos, Fiber was used in concrete. After that, the use of Steel glass and synthetic Fibers started.
Recently high-performance FRC and ultra-high performance FRC are introduced. Researches to improve the qualities of Fiber-reinforced concrete continuous event today.
Where we use Fiber?
- RCC and PCC i.e, column, flooring and wall plastering lintel, beam.
- Rising design and bold size of plasterwork
- Foundation, tanks, manhole cover, and tiles
- Roads and pavements
- Hollow blocks and precast
Top Reasons to use Fiber in Concrete
● Fiber increase the structural integrity
● Fiber can provide high tensile strength to plain concrete
● Greater reduction in permeability of concrete
● More resistance to impact load
● Fiber can reduce the number of Rebars, without loss of strength.
● Greater abrasion and shatter resistance
● Elimination of cracks by bridging action of Fibers.
● Increase toughness and durability
● Decrease cracking
● Improve freeze-Thaw resistance
● Reduce the effect of shrinkage
How to use Fiber in Concrete
- Concrete: Use 12mm fiber 900 grams/cubic meters.
- Plaster: Use 6mm Fiber 125 gram/ bag of cement of 50 kilograms, in 1:4 cement and sand ratio
- The dosage rate can be charge as per requirement.
Different Types of Fiber
There are many different types of Fiber used in Concrete, but not all of them are effectively or economically used.
Each Different type of Fiber has its own characteristic and limitation.
1. Steel Fiber
- The basic function of steel fiber is to control cracking
- Steel Fiber, polypropylene, nylons, asbestos, coir, glass, and carbon Steel Fiber are
- Round Fiber, hooked Fiber
- Aspect Ratio 20 to 100
- A Diameter of Steel Fiber is about 0.25 to 0.75 mm
- It has a High structural strength
- It Reforms flexural, impact and fatigue strength of concrete
- Polypropylene and nylon increase the impact strength
- Low models of elasticity higher elongation do not contribute to flexural strength
- Use in precast and structural applications, Highway and airport pavements, refractory and canal lining, industrial flooring, bridge decks, etc.
- Applied in overlays of roads, airfield pavements, and bridge decks.
- Tensile strength: 560 to 980 N/mm^2
- High flexural strength than Portland cement paste
- For unimportant Fiber concrete organic Fiber like coir, jute, cane splits, are used.
2. Glass Fiber
The limitation of glass fiber occurs as it becomes damaged. This is why the damage is done. Because we are mixing aggregate and cement and glass fiber, it gets damaged due to the up reason and impact forces of the aggregate. Therefore, we have to add it in a much more controlled condition.
- Elevated tensile strength 1020 to 4080 N/mm^2
- Generally, Fibers of length 10 mm to 50 mm are used.
- Increase flexural strength ductility and resistance to thermal shock
- Used in building renovation works, ducts, and roofs, sewer lining, bridge, and tunnel lining panels, acrostic barriers, and screens, etc.
3. Synthetic fiber
Synthetic Fibers are man-made Fibers from petrochemical and textile industries and these are derived from polymer-based materials i.e. nylon, polyethylene. These fibers also add in the same way
- High chemical resistance
- Low modulus of elasticity
- Cheap, abundantly available
- Application in cladding panels and shotcrete
4. Carbon Fiber
Carbon Fiber is also known as a Graphite Fiber, carbon fiber is a polymer and it is a very strong material and its also a very lightweight. It is a very five times stronger than steel and twice as stiff.
Tensile Strength of Carbon Fiber is about 2110 to 2185 Nmm2 . Carbon Fiber used in Structure like Cladding, Panels, which shell has a promising future.
Properties of Concrete will Enhance by Fiber
Following are the properties of concrete will enhance by fiber
- Flexural strength
- Impact resistance
- Crack resistance
Why Fiber used in Concrete
- The main role of Fibers is to bridge the cracks that develop in concrete and increase the ductility of concrete elements.
- There is considerable improvement in the post cracking behavior of concrete containing Fibers due to both plastic shrinkage and drying shrinkage.
- They also reduce the permeability of concrete and thus reduce the bleeding of water.
- Imparts more resistant to impact load
- It increases the durability of the concrete
Normal Concrete is made up of Coarse aggregate, fine aggregate, Cement (OPC — Ordinary Portland Cement), and Water.
Though, it is becoming common to use minerals and chemicals to obtain desired strength in fresh and hardened concrete.
- Cement + Water = Cement Paste
- Cement Paste + Sand = Cement Mortar
- Cement Mortar + CA = Concrete (Where, CA is Course aggregate)
Using Fiber as a Concrete Reinforcement
- Fiber + Concrete = Although, Crack exist effect of the size of crack may become small = Reducing the spacing of Fiber = Increases addition of fibers ( Fiber Content )
Reinforced of Concrete by discreet short Fibers
- Voids and microcrack serve as crack imitators
- Fiber presents prevent track elongation and increase of crack width
- Increase in strength by Fiber spacing Theory
Using Short fiber in Concrete
- Fiber length at least 1.5 times the G>max considering the ease of Fiber dispersing
- While a Fiber length of 30mm or more is generally recommended.
- Fibers of about 60 mm with a high reinforcing effect are used for slabs.
Flexural Strength of Concrete
- Design of some concrete structure is ‘governed’ by flexural strength
- Determine the flexural strength of concrete by the third point loading and the center point loading of prismatic concrete specimens.
What is Fiber Reinforcement Concrete?
- A composite material consists of mixture cement mortar or concrete and discontinuous, discrete, uniformly dispersed suitable fibers they increase its structural integrity is known as Fiber reinforcement concrete (FRC)
- Plain concrete has low strength, of tensile only 1/10 of its compressive strength.
- Poor tensile strength is due to presence of micro cracks and their propagation
- Concrete undergoes significant volumetric changes cause internal stresses within the concrete matrix due to which microbe cracks get developed in the concrete.
- The presence of such microcracks at the motor aggregate interface is responsible for the tensile failure of concrete. These microcracks propagate and open up resulting in inelastic deformation of the concrete
- The closely spaced and dispersed Fiber are added to the concrete it obstructs the propagation of cracks the concrete with dispersed Fiber is known as Fiber reinforcement concrete
- Fibers include Steel Fibers, glass Fibers, synthetic Fibers and natural Fibers – each of which land varying properties to the concrete.
- Mass of Fibers added to a concrete mix is articulated as a percentage of the total mass of the composite (concrete & Fibers), typically ranges from 0.1 to 3
- THE uses of Fibers in the concrete controls the crack due to plastic shrinkage
- These types of concrete reduce the permeability of concrete and also reduce the bleeding of water
The uses of Fiber in the concrete does not increase the flexural strength of concrete. Even so, some of the Fibers even reduce the strength of concrete
Advantages of Fiber Reinforced Concrete
- Resistance to crack propagation
- Resistance to thermal and moisture stress
- Increase ductility
- Decrease permeability
- Decrease mix water bleed rate
- Greater resistance to crack formation. This increases durability.
- Ductility impact and Abrasion resistance
- Improves toughness of concrete
- flexural strength is improved up to 30% by decreasing the propagation of cracks
- Less prone to corrosion
- Increase moment capacity and Torsional strength
- An alternative way to reinforce concrete
- Increase fire resistance
- Less labor-intensive then placing Rebar
- Can be made into thin sheets and irregular shapes
- Fiber increases the shear capacity of reinforced concrete beams up to 100%
- FRC pavements offer good resistance
- FRC slabs offer high strength while compared with conventional concrete slab
All this enhancement depends on the type of fiber used and the concentration in the mix Design.
Disadvantages of Fiber Reinforced Concrete
- Very Low tensile power, one by the tenth of its compressive potency.
- Require mixing, casting and curing, strength is affected
- Cost of forms and artisanry is relatively high
- Lower compressive strength than Steel
- Cracks can develop due to shrinkage and live loads.
- Greater reduction of workability
- The high cost of the material.
- Require a more precise configuration than plain concrete.
- Quantity of Fibers increase, the workability is a decrease
- Its proper techniques and proportion do not use the Fibers may also cause a finishing problem, with the Fiber coming out of the concrete.
Application of Fiber Reinforced Concrete
- Pre-cast application
- Impact resisting structures
- Highway and airfield payments
- Dams and hydraulic structures
- Manholes, roof tiles, panels
- Structural application
- Slope stabilization
- Thin shell, sheets, walls, pipes
- Fiber shotcrete etc…
Factors affecting properties of Fiber Reinforced Concrete
- FRC is a mixture of Fibers in cement matrix orderly manner or randomly distributed
- Its properties mainly depend upon the efficient transfer of stresses between the Matrix and the Fibers.
- Volume of Fiber
- The aspect ratio of Fiber (I/D)
- Fiber matrix stiffness
- Size of coarse aggregate
- Mixing and compaction
Aspect Ratio of Fiber (I/D)
Increase in the aspect ratio of Fibers up to 75 there is increase in toughness and strength Beyond this limit it may cause the decrease in toughness and strength
|Type of Concrete||ASPECT RATIO OF FIBER||RELATIVE STRENGTH||RELATIVE TOUGHNESS|
Transfer of Stress
- Type of Fiber
- Geometry of Fiber
- Fiber content
- Orientation and distribution of Fibers
- Size and shape of aggregates
- Mixing and compaction technique of concrete
- Efficient stress Transfer: E of matrix < E of Fiber
- the interfacial bond between the Fiber and mix also plays an important role in stress transfer.
- Improvement in bond: larger area of contact improving the frictional properties and degree of gripping, treating the Steel Fiber with sodium hydroxide or acetone.
Structure Behavior of Fiber Reinforced Concrete
- Delay and control in tensile cracking
- By distribution of Fibers, composite shows ductile behavior.
- Shading of tensile load
- Until the matrix cracks:- (Fiber and matrix)
- Once matrix cracks — (Fiber)
- Absorption of energy by Fibers
- 20% increase of compressive strength
- Higher toughness — prevents failure in case of EQ and Blast type loads
Test Results of Fiber Reinforced concrete
- Modulus of elasticity increased slightly with an increase in Fiber content one percent increase in Fiber content results 3% modulus of elasticity
- Toughness is increased about 10 to 40 times that of PCC
- Flexural strength increase by 2.5 times using 4% of Fiber
- 90% increase in fatigue strength
- Impact strength is 5 to 10 times increase depending on the volume of Fiber
- The workability of FRC is low, but the durability of a structure is very high
- The bridging action of Fibers keeps the Bond strength between Fiber and concrete, so, the compound will stiffer
- we can use FRC to reduce the depth of beam without loss of its Bearing capacity
- FRC has high capacity of taking shear stress, bending moment, tensile stress than conventional concrete.
- In some cases, we can replace Steel bars with steel Fibers.