Types and properties of Fiber Reinforced ConcreteArticles > Types and properties of Fiber Reinforced Concrete
Concrete is widely used all over the world for many construction purposes. This concrete is undoubtedly the most reliable material used in the world of construction, but it lacks certain properties. It often undergoes cracking due to various reasons like insufficient curing, rapid gaining of strength, shrinking, bleeding and segregation and many more. Cracking is present in almost all types of concrete but the main difference between fibre reinforced concrete and ordinary concrete is the type of cracking. In ordinary concrete the cracking is sudden but this is not the case in fiber reinforced concrete. The cracking is not sudden as fiber reinforced concrete has a certain level of durability which gives sufficient time and indication that the structure is about to collapse. This level of flexibility is adopted in concrete by the use of fibres made of steel, glass, polypropylene, polyethylene, etc. Further, here the properties and types will be discussed in order to have a view about such concrete.
Properties of Fiber Reinforced Concrete
Researchers have been able to point out certain properties which make it more suitable for use. Some of them are-
RELATIVE FIBER MATRIX STIFFNESS : For sufficient transfer of stress, it is essential to have lower modulus of elasticity of matrix as compared to the fiber. Fibres like nylon and polypropylene have low modulus elasticity, so they don’t contribute much to strength, but they help in absorbing large amounts of energy and have greater resistance to impact, as well as having a greater degree of toughness. Whereas fibres that have a higher modulus of elasticity, like glass and carbon, promote strength and stiffness in the concrete.
VOLUME OF FIBRES : Volume of fibre should be sufficient to make the concrete strong and stiff. With increase in volume, the tensile strength as well as stiffness increases. But it should also be well remembered that higher percentage of fibre also causes segregation and harshness in concrete, hence the quantity should be optimal.
ASPECT RATIO OF THE FIBRE: It is found out that upto 75 the aspect ratio is directly proportional to the strength of concrete. However, beyond 75 the aspect ratio is inversely proportional to the strength and toughness.
ORIENTATION OF THE FIBER : Experiments were conducted to observe the effect of orientation of fibers on the strength and toughness of concrete. They found that fibres that were kept in parallel to the applied load offered more tensile strength and toughness compared to fibres that were oriented perpendicularly and randomly.
WORKABILITY AND COMPACTION : When fibers are included in the concrete mix then the workability is reduced to a great extent. This affects the compaction process as prolonged vibration doesn’t have much impact. Thus it mainly depends upon the length and diameter of fibre used. One of the reasons for low workability may include poor orientation of the fibers which doesn’t much facilitate easy mixing. The problem can only be solved by the use of water reducing admixtures.
Types of Fiber Reinforced Concrete
Some of the types of fiber reinforced concrete are -
STEEL FIBER REINFORCED CONCRETE: Steel fibres have a high modulus of elasticity. Implanting these fibers in concrete delivers changes in properties of concrete like resistance to fire, cracking, bending, segregation, bleeding, and many more. These types of fibres are widely used in bridges, tunneling, refractory linings, beams, columns, explosive resistance structures, boats, etc. The types of steel fibers stated by ASTM A820 are Type I: cold-drawn wire, Type II; cut sheet, Type III: melt-extracted, Type IV: mill cut and Type V: modified cold-drawn wire.
FIG 1: CONCRETE WITH STEEL FIBERS
GLASS FIBER REINFORCED CONCRETE : This type of concrete consists of 4 to 4.5 % of glass fibres. Such concrete imparts translucency and in some cases transparency. Such types of concrete can be used for decorative purposes and insulation purposes. These concrete can bear weight but not much heavy or dead load of the structures. Hence they cannot be used for load bearing purposes. These are significantly fragile in load bearing cases and are not recommended in columns and beams.
FIG 2 : CONCRETE WITH GLASS FIBERS
CARBON FIBERS : Carbon fibers have a high modulus of elasticity. Such fibers offer great advantages like high chemical resistance, tolerance towards high temperature, low thermal expansion and so on. When combined with plastic resin, it then forms a carbon-fiber-reinforced polymer. Such fibers have a very high strength to weight ratio and are very rigid.
FIG 3: STRUCTURE MADE FROM CARBON FIBERS CONCRETE
COURTESY: INNOVATIONS REPORT
NATURAL FIBRES: Natural fibers like cotton, wool, hair, straw, etc. can be incorporated in concrete. Earlier structures were made of natural fibres incorporated with other natural materials like eggs, rice, and more. Such natural materials impart greater strength than ordinary concrete. However, later on these natural materials got replaced by concrete as cost became the deciding factor in construction.
FIG 4: CONCRETE WITH NATURAL FIBERS
COURTESY: MATERIAL INTUITION.
POLYESTER FIBERS: Such fibers are mainly used for industrial purposes, warehouses, and in pre-stressed concrete products. This offers great resistance to cracking and shrinkage. Such fibers have two types - micro and macro polyester fibers. Polyester micro and macro fibers are used to provide enormous resistance to the formation of plastic shrinkage cracks and enhance toughness. They are capable of delivering structural capacity when structural elements made from these fibres are properly designed.
FIG 5: POLYSTER TO BE USED IN CONCRETE
Advancements are being made in these fields to produce more such long lasting fibres that can be incorporated in concrete to enhance properties of concrete. Researchers are continuously developing building codes for a better build in the construction. It is also to be noted that nowadays the construction industry is undergoing changes and these fiber reinforced concrete are way better than ordinary concrete. These fibres produce a good amount of resistance to any natural phenomena like earthquakes and winds. Thus, it can be said that durability with such concrete is possible now but cost has to be looked upon for making it economic to use.
Consofacilitator, “Fiber-reinforced concrete – Advantages, types and applications”- https://www.constrofacilitator.com/fiber-reinforced-concrete-advantages-types-and-applications/
Concrete Technology Theory and Practice, M.S. Shetty, S. Chand
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