23-08-2012, 10:37 AM
Fibre Reinforced Concrete
Fibre Reinforced.doc (Size: 627 KB / Downloads: 90)
Definition:
Fibre reinforced concrete (FRC) is a concrete (unifotm paste of cement, aggregate & water)containing fibrous material which increases its structural integrity. It contains short discrete fibres that are uniformly distributed and randomly oriented.
Origin of FRC:
The concept of using fibers as reinforcement is not new. Fibers have been used as reinforcement since ancient times. Historically, horsehair was used in mortar and straw in mud bricks. In the early 1900s, asbestos fibers were used in concrete, and in the 1950s the concept of composite materials came into being and fiber-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 fibers such as polypropylene fibers were used in concrete, and research into new fiber-reinforced concretes continues today.
Why should we use fibres in concrete?
Some types of fibres produce greater impact, abrasion and shatter resistance in concrete. Generally fibres do not increase the flexural strength(?) of concrete, and so cannot replace moment resisting or structural steel reinforcement.
Fibres are usually used in concrete to control cracking due to both plastic shrinkage (volumetric contraction due to plastic strain) and drying shrinkage(development of tensile stress due to evaporation of capillary water due to hydration heat). They also reduce the permeability(pores interconnected) of concrete and thus reduce bleeding of water.
Different types of fibres:
Fibres include-
Natural fibres:
Fibers or fibre are a class of hair-like materials that are continuous filaments or are in discrete elongated pieces , similar to pieces of thread. They can be spun into filaments , thread, or rope. They can be used as a component of composite materials. They can also be matted into sheets to make products such as paper or felt . Fibers are of three types: natural fiber , cellulose fiber, and synthetic fiber. The earliest evidence for humans using fibers is the discovery of wool and dyed flax fibers found in a prehistoric cave in the Republic of Georgia that date back to 36,000 BP.
Steel fibres:
Fibres are made from prime quality hard-drawn steel wire to ensure high tensile strength and close tolerances. The wire is deformed with hooked ends and cut to lengths, for reinforcement of concrete, mortar and other composite materials. The performance of fibres depends on both the dosage (kg/m3) and the fibre parameters (tensile strengths, length, diameter and anchorage). A key factor for quality for quality fibre is the relationship between the length and the diameter of the fibres. the higher the l/d ratio, the better the performance.
Synthetic fibres:
Synthetic fibers are the result of extensive research by scientists to improve on naturally occurring animal and plant fibers. In general, synthetic fibers are created by forcing, usually through extrusion, fiber forming materials through holes (called spinnerets) into the air, forming a thread. Before synthetic fibers were developed, artificially manufactured fibers were made from cellulose, which comes from plants. These fibers are called cellulose fibers.
Synthetic Fibers are made from synthesized polymers or small molecules. The compounds that are used to make these fibers come from raw materials such as petroleum based chemicals or petrochemicals. These materials are polymerized into a long, linear chemical that bond two adjacent carbon atoms. Differing chemical compounds will be used to produce different types of fibers. Although there are several different synthetic fibers, they generally have the same common properties.
FRC From Design Point Of View:
Indeed, some fibres actually reduce the strength of concrete. The amount of fibres added to a concrete mix is expressed as a percentage of the total volume of the composite (concrete and fibres), termed volume fraction (Vf). Vf typically ranges from 0.1 to 3%. Aspect ratio (l/d) is calculated by dividing fibre length (l) by its diameter (d). Fibres with a non-circular cross section use an equivalent diameter for the calculation of aspect ratio. If the modulus of elasticity of the fibre is higher than the matrix (concrete or mortar binder ), they help to carry the load by increasing the tensile strength of the material. Increase in the aspect ratio of the fibre usually segments the flexural strength and toughness of the matrix.
Mechanical properties of high-strength steel fiber-reinforced concrete:
The marked brittleness with low tensile strength and strain capacities of high-strength concrete (HSC) can be overcome by the addition of steel fibers. This paper investigated the mechanical properties of high-strength steel fiber-reinforced concrete. The properties included compressive and splitting tensile strengths, modulus of rupture, and toughness index. The steel fibers were added at the volume fractions of 0.5%, 1.0%, 1.5%, and 2.0%. The compressive strength of the fiber-reinforced concrete reached a maximum at 1.5% volume fraction, being a 15.3% improvement over the HSC. The splitting tensile strength and modulus of rupture of the fiber-reinforced concrete improved with increasing the volume fraction, achieving 98.3% and 126.6% improvements, respectively, at 2.0% volume fraction. The toughness index of the fiber-reinforced concrete improved with increasing the fraction. The indices I5, I10, and I30 registered values of 6.5, 11.8, and 20.6, respectively , at 2.0% fraction. Strength models were established to predict the compressive and splitting tensile strengths and modulus of rupture of the fiber-reinforced concrete. The models give predictions matching the measurements.
Fibre Reinforced.doc (Size: 627 KB / Downloads: 90)
Definition:
Fibre reinforced concrete (FRC) is a concrete (unifotm paste of cement, aggregate & water)containing fibrous material which increases its structural integrity. It contains short discrete fibres that are uniformly distributed and randomly oriented.
Origin of FRC:
The concept of using fibers as reinforcement is not new. Fibers have been used as reinforcement since ancient times. Historically, horsehair was used in mortar and straw in mud bricks. In the early 1900s, asbestos fibers were used in concrete, and in the 1950s the concept of composite materials came into being and fiber-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 fibers such as polypropylene fibers were used in concrete, and research into new fiber-reinforced concretes continues today.
Why should we use fibres in concrete?
Some types of fibres produce greater impact, abrasion and shatter resistance in concrete. Generally fibres do not increase the flexural strength(?) of concrete, and so cannot replace moment resisting or structural steel reinforcement.
Fibres are usually used in concrete to control cracking due to both plastic shrinkage (volumetric contraction due to plastic strain) and drying shrinkage(development of tensile stress due to evaporation of capillary water due to hydration heat). They also reduce the permeability(pores interconnected) of concrete and thus reduce bleeding of water.
Different types of fibres:
Fibres include-
Natural fibres:
Fibers or fibre are a class of hair-like materials that are continuous filaments or are in discrete elongated pieces , similar to pieces of thread. They can be spun into filaments , thread, or rope. They can be used as a component of composite materials. They can also be matted into sheets to make products such as paper or felt . Fibers are of three types: natural fiber , cellulose fiber, and synthetic fiber. The earliest evidence for humans using fibers is the discovery of wool and dyed flax fibers found in a prehistoric cave in the Republic of Georgia that date back to 36,000 BP.
Steel fibres:
Fibres are made from prime quality hard-drawn steel wire to ensure high tensile strength and close tolerances. The wire is deformed with hooked ends and cut to lengths, for reinforcement of concrete, mortar and other composite materials. The performance of fibres depends on both the dosage (kg/m3) and the fibre parameters (tensile strengths, length, diameter and anchorage). A key factor for quality for quality fibre is the relationship between the length and the diameter of the fibres. the higher the l/d ratio, the better the performance.
Synthetic fibres:
Synthetic fibers are the result of extensive research by scientists to improve on naturally occurring animal and plant fibers. In general, synthetic fibers are created by forcing, usually through extrusion, fiber forming materials through holes (called spinnerets) into the air, forming a thread. Before synthetic fibers were developed, artificially manufactured fibers were made from cellulose, which comes from plants. These fibers are called cellulose fibers.
Synthetic Fibers are made from synthesized polymers or small molecules. The compounds that are used to make these fibers come from raw materials such as petroleum based chemicals or petrochemicals. These materials are polymerized into a long, linear chemical that bond two adjacent carbon atoms. Differing chemical compounds will be used to produce different types of fibers. Although there are several different synthetic fibers, they generally have the same common properties.
FRC From Design Point Of View:
Indeed, some fibres actually reduce the strength of concrete. The amount of fibres added to a concrete mix is expressed as a percentage of the total volume of the composite (concrete and fibres), termed volume fraction (Vf). Vf typically ranges from 0.1 to 3%. Aspect ratio (l/d) is calculated by dividing fibre length (l) by its diameter (d). Fibres with a non-circular cross section use an equivalent diameter for the calculation of aspect ratio. If the modulus of elasticity of the fibre is higher than the matrix (concrete or mortar binder ), they help to carry the load by increasing the tensile strength of the material. Increase in the aspect ratio of the fibre usually segments the flexural strength and toughness of the matrix.
Mechanical properties of high-strength steel fiber-reinforced concrete:
The marked brittleness with low tensile strength and strain capacities of high-strength concrete (HSC) can be overcome by the addition of steel fibers. This paper investigated the mechanical properties of high-strength steel fiber-reinforced concrete. The properties included compressive and splitting tensile strengths, modulus of rupture, and toughness index. The steel fibers were added at the volume fractions of 0.5%, 1.0%, 1.5%, and 2.0%. The compressive strength of the fiber-reinforced concrete reached a maximum at 1.5% volume fraction, being a 15.3% improvement over the HSC. The splitting tensile strength and modulus of rupture of the fiber-reinforced concrete improved with increasing the volume fraction, achieving 98.3% and 126.6% improvements, respectively, at 2.0% volume fraction. The toughness index of the fiber-reinforced concrete improved with increasing the fraction. The indices I5, I10, and I30 registered values of 6.5, 11.8, and 20.6, respectively , at 2.0% fraction. Strength models were established to predict the compressive and splitting tensile strengths and modulus of rupture of the fiber-reinforced concrete. The models give predictions matching the measurements.