12-03-2011, 12:56 PM
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HISTORICAL DEVELOPMENT
The concept of using fibres as reinforcement is not new. Fibres have been used as reinforcement since ancient times. Historically, horsehair was used in mortar and straw in mud bricks
In the early 1900s, asbestos fibres were used in concrete, and in the 1950s the concept of composite materials came into being and fibre reinforced concrete was one of the topics of interest.
There was a need to find a replacement for the asbestos used in concrete and other building materials once the health risks associated with the substance were discovered.
By the 1960s, steel, glass (GFRC), and synthetic fibres such as polypropylene fibres were used in concrete, and research into new fibre reinforced concretes continues today.
THE MAIN PROPERTIES INFLUENCING TOUGHNESS AND MAXIMUM LOADING OF FIBRE REINFORCED CONCRETE
Type of fibers used
Volume percent of fiber(vf =o.1 to 3%)
Aspect ratio (the length of a fiber divided by its diameter)
Orientation of the fibers in the matrix
Shape, dimension and length of fiber is important. A thin and short fiber, for example short hair-shaped glass fiber, will only be effective the first hours after pouring the concrete (reduces cracking while the concrete is stiffening) but will not increase the concrete tensile strength.
A normal size fibre (1 mm diameter, 45 mm length—steel or "plastic") will increase the concrete tensile strength.
MATERIALS USED IN FIBRE REINFORCED CONCRETE
Polypropylene
Glass fibres
Steel fibres
POLYPROPYLENE FIBRE REINFORCED CONCRETE
Polypropylene fibres can:
Improve mix cohesion
Improve freeze-thaw resistance
Improve resistance to explosive spalling in case of a severe fire
Improve impact resistance
Increase resistance to plastic shrinkage during curing
FREEZE -THAW
SPALLING OF CONCRETE
POLYPROPYLENE FIBRES
Polypropylene Fiber Reinforced Precast Concrete Blocks for Roads and Pavements
TEMPORARY WALL MADE BY PFRC
GLASS FIBER REINFORCED CONCRETE
Glass fiber reinforced concrete is most popular fiber that is being successfully used since the last 25 years for concrete reinforcement, in addition to steel.
Glass Fiber Reinforced Concrete is similar to concrete in its characteristics, but it is 80% lighter.
Although GRC has a similar density to concrete the products made from it are many times lighter due to the thin 10-15mm skin thickness used.
A cladding panel manufactured from 100mm thick precast concrete would weigh 240kgs per m2 compared to a similar GRC panel of 40-50kgs/m2.
GFRC is finished in a wide selection of colors and textures, eliminating finishing costs and reducing the maintenance cost since there is no need for painting.
GFRC is easily molded into desired shapes with clean lines and sharp details.
CLADDING PANNEL
FUNCTIONS OF GFRC
Impervious to chloride ion and chemical attack
Tensile strengths greater than steel
Modulus approaching that of steel and three times that of GFRP Rebar
1/5th the weight of steel reinforcing
Surface treatment to enhance bond to portland cement
GLASS FIBRE REINFORCED POLYMER
LOCATING PRESTRESSED GFRC
STRUCTURES MADE BY GFRC
STEEL FIBER REINFORCED CONCRETE
STEEL FIBER REINFORCED CONCRETE (SFRC)
Steel fiber reinforced concrete is a composite material that can be sprayed. It consists of hydraulic cements with steel fibers that are dispersed randomly.
The steel fibers reinforce concrete by withstanding tensile cracking.
The flexural strength of fiber reinforced concrete is greater than the un-reinforced concrete.
Reinforcement of concrete by steel fibers is isotropic in nature that improves the resistance to fracture, disintegration.
Steel fiber reinforced concrete is able to withstand light and heavy loads.
STEEL FIBRES
PROPERTIES OF STEEL FIBRE
Length:6-60mm
Diameter:0.2-1.0mm
Appearance: Clear and Bright
Tensile Strength:800-2500mpa
Steel fibres can:
Improve structural strength
Reduce steel reinforcement requirements
Improve ductility
Reduce crack widths
Improve impact & abrasion resistance
Improve freeze-thaw resistance
HALF JOINT STRUCTURE MADE BY SFRC
Engineered Cementitious Composite (ECC)
A fiber reinforced concrete has been developed recently that is called Engineered Cementitious Composite (ECC).
It is claimed that this concrete is 40 % lighter than normal concrete, resistance to cracking exceeds 500 times, and strain hardening exceeds several percent strain.
Thus, the ductility is significantly greater than normal concrete. It is also known as bendable concrete since it can easily be molded and shaped.
It can self repair minor cracks by the reaction with carbon dioxide and rainwater making the concrete stronger.
The Mitaka Dam near Hiroshima was repaired using ECC in 2003.
The surface of the then 60-year old dam was severely damaged, showing evidence of cracks, spalling, and some water leakage.
A 20 mm-thick layer of ECC was applied by spraying over the 600 m2 surface.
ECC was intended to minimize this danger, after one year only microcracks of tolerable width were observed.
ADVANTAGES AND DISADVANTAGES OF FIBER REINFORCED CONCRETE
Concrete is quite brittle; it has very good compressive strength but comparatively little tensile strength, which makes it likely to crack under many conditions. Cracking leads to further damage. Fiber reinforced concrete is less likely to crack than standard concrete.
Concrete reinforced with fibers while still increasing the tensile strength many times than ordinary concrete.
Fiber reinforced concrete has started to find its place in many areas of civil infrastructure applications where the need for repairing, increased durability arises.
Also FRCs are used in civil structures where corrosion can be avoided at the maximum. Fiber reinforced concrete is better suited to minimize cavitation /erosion damage in structures such as sluice-ways, navigational locks and bridge piers where high velocity flows are encountered.
HISTORICAL DEVELOPMENT
The concept of using fibres as reinforcement is not new. Fibres have been used as reinforcement since ancient times. Historically, horsehair was used in mortar and straw in mud bricks
In the early 1900s, asbestos fibres were used in concrete, and in the 1950s the concept of composite materials came into being and fibre reinforced concrete was one of the topics of interest.
There was a need to find a replacement for the asbestos used in concrete and other building materials once the health risks associated with the substance were discovered.
By the 1960s, steel, glass (GFRC), and synthetic fibres such as polypropylene fibres were used in concrete, and research into new fibre reinforced concretes continues today.
THE MAIN PROPERTIES INFLUENCING TOUGHNESS AND MAXIMUM LOADING OF FIBRE REINFORCED CONCRETE
Type of fibers used
Volume percent of fiber(vf =o.1 to 3%)
Aspect ratio (the length of a fiber divided by its diameter)
Orientation of the fibers in the matrix
Shape, dimension and length of fiber is important. A thin and short fiber, for example short hair-shaped glass fiber, will only be effective the first hours after pouring the concrete (reduces cracking while the concrete is stiffening) but will not increase the concrete tensile strength.
A normal size fibre (1 mm diameter, 45 mm length—steel or "plastic") will increase the concrete tensile strength.
MATERIALS USED IN FIBRE REINFORCED CONCRETE
Polypropylene
Glass fibres
Steel fibres
POLYPROPYLENE FIBRE REINFORCED CONCRETE
Polypropylene fibres can:
Improve mix cohesion
Improve freeze-thaw resistance
Improve resistance to explosive spalling in case of a severe fire
Improve impact resistance
Increase resistance to plastic shrinkage during curing
FREEZE -THAW
SPALLING OF CONCRETE
POLYPROPYLENE FIBRES
Polypropylene Fiber Reinforced Precast Concrete Blocks for Roads and Pavements
TEMPORARY WALL MADE BY PFRC
GLASS FIBER REINFORCED CONCRETE
Glass fiber reinforced concrete is most popular fiber that is being successfully used since the last 25 years for concrete reinforcement, in addition to steel.
Glass Fiber Reinforced Concrete is similar to concrete in its characteristics, but it is 80% lighter.
Although GRC has a similar density to concrete the products made from it are many times lighter due to the thin 10-15mm skin thickness used.
A cladding panel manufactured from 100mm thick precast concrete would weigh 240kgs per m2 compared to a similar GRC panel of 40-50kgs/m2.
GFRC is finished in a wide selection of colors and textures, eliminating finishing costs and reducing the maintenance cost since there is no need for painting.
GFRC is easily molded into desired shapes with clean lines and sharp details.
CLADDING PANNEL
FUNCTIONS OF GFRC
Impervious to chloride ion and chemical attack
Tensile strengths greater than steel
Modulus approaching that of steel and three times that of GFRP Rebar
1/5th the weight of steel reinforcing
Surface treatment to enhance bond to portland cement
GLASS FIBRE REINFORCED POLYMER
LOCATING PRESTRESSED GFRC
STRUCTURES MADE BY GFRC
STEEL FIBER REINFORCED CONCRETE
STEEL FIBER REINFORCED CONCRETE (SFRC)
Steel fiber reinforced concrete is a composite material that can be sprayed. It consists of hydraulic cements with steel fibers that are dispersed randomly.
The steel fibers reinforce concrete by withstanding tensile cracking.
The flexural strength of fiber reinforced concrete is greater than the un-reinforced concrete.
Reinforcement of concrete by steel fibers is isotropic in nature that improves the resistance to fracture, disintegration.
Steel fiber reinforced concrete is able to withstand light and heavy loads.
STEEL FIBRES
PROPERTIES OF STEEL FIBRE
Length:6-60mm
Diameter:0.2-1.0mm
Appearance: Clear and Bright
Tensile Strength:800-2500mpa
Steel fibres can:
Improve structural strength
Reduce steel reinforcement requirements
Improve ductility
Reduce crack widths
Improve impact & abrasion resistance
Improve freeze-thaw resistance
HALF JOINT STRUCTURE MADE BY SFRC
Engineered Cementitious Composite (ECC)
A fiber reinforced concrete has been developed recently that is called Engineered Cementitious Composite (ECC).
It is claimed that this concrete is 40 % lighter than normal concrete, resistance to cracking exceeds 500 times, and strain hardening exceeds several percent strain.
Thus, the ductility is significantly greater than normal concrete. It is also known as bendable concrete since it can easily be molded and shaped.
It can self repair minor cracks by the reaction with carbon dioxide and rainwater making the concrete stronger.
The Mitaka Dam near Hiroshima was repaired using ECC in 2003.
The surface of the then 60-year old dam was severely damaged, showing evidence of cracks, spalling, and some water leakage.
A 20 mm-thick layer of ECC was applied by spraying over the 600 m2 surface.
ECC was intended to minimize this danger, after one year only microcracks of tolerable width were observed.
ADVANTAGES AND DISADVANTAGES OF FIBER REINFORCED CONCRETE
Concrete is quite brittle; it has very good compressive strength but comparatively little tensile strength, which makes it likely to crack under many conditions. Cracking leads to further damage. Fiber reinforced concrete is less likely to crack than standard concrete.
Concrete reinforced with fibers while still increasing the tensile strength many times than ordinary concrete.
Fiber reinforced concrete has started to find its place in many areas of civil infrastructure applications where the need for repairing, increased durability arises.
Also FRCs are used in civil structures where corrosion can be avoided at the maximum. Fiber reinforced concrete is better suited to minimize cavitation /erosion damage in structures such as sluice-ways, navigational locks and bridge piers where high velocity flows are encountered.
