Fibre Reinforcement Concrete
This is a composite material consisting of cement paste, mortar or concrete with fibers of asbestos, glass, plastic, carbon or steel. Such fibers reinforced concrete may be useful where high tensile strength and reduced cracking are desirable or when conventional reinforcement cannot be placed because of the shape of the number. Fibers improve the impact strength of concrete, limit the crack growth and lead to a greater strain capacity of the composite material.
The type of fiber and its volume fraction has a marked effect on the properties of fiber reinforced concrete. it is convenient to classify the fiber properties of fiber reinforced concrete. It is convenient to classify the fiber reinforced composites as a function of their fiber volume fraction -
Low Volume Fraction (<1%) -
The fibers are used to reduce shrinkage cracking. These fibers are used in slabs and pavements that have a large exposed surface leading to high shrinkage cracking. Disperse fibers offer various advantage or steel bars and wire mesh to reduce shrinkage cracks -
- The fibers are uniformly distributed in three-dimensions making an efficient load distribution.
- The fibers are less sensitive to corrosion than the reinforcing steel bars.
- The fibers can reduce the labor cost of placing the bars and wire mesh.
Moderate Volume Fraction (between 1 and 2 %) -
The presence of fibers at this volume fraction increases the modulus of rupture, fracture toughness, and impact resistance, These composites are used in construction methods such as shotcrete and in a structure that require energy absorption capability, improved capacity against delamination, spalling, and fatigue.High Volume Fraction (> 2%) -
The fibers used at this level lead to strain-hardening of the composites, Because of this improved behavior, these composites are often referred to as high-performance fiber-reinforced composites.
Properties of fiber reinforcement Concrete
Fiber reinforcement concrete is the composite material containing fibers in the cement matrix in an ordinary manner or randomly distributed manner. Its properties would obviously depend upon the efficient transfer of stress between cement matrix and the fiber, which is largely dependent on the type of fiber, fiber geometry, fiber content orientation and distribution of the fibers mixing and compaction techniques of concrete and size and shape of the aggregate. Important factors which affect the properties of FRC are given below -The volume of Fibres -
Increase in the volume of fibers increases approximately linearly with tensile strength and toughness of the composite.
The orientation of Fibres
The fibers aligned parallel to the applied load offered more tensile strength and toughness than randomly distributed or perpendicular fibers.
Workability and Compaction of Concrete - Poor workability if fibers are nonuniform distributed.
Size of Coarse Aggregate - Should not be greater than 10 mm to avoid an appreciable reduction in strength of the composite.
Mixing
It is important that the fibers should be dispersed uniformly throughout the mix.
Discrete Fiber Reinforced Concrete
The fibers can be imagined as an aggregate with an extreme deviation in shape from the rounded smooth aggregate. The fibers interlock and entangle around aggregate particles and considered reducing the workability, while the mix becomes more cohesive and less prone to segregation. The fibers suitable for reinforcing the concrete have been producing from steel, glass, and organic polymers, naturally occurring asbestos fibers and vegetable fibers, such as jute, are also used for reinforcement. Fibers are available in different size and shape. They can be classified into two basic categories, namely, those having a higher elastic modulus than concrete matrix called hard intrusion and those with lower elastic modulus called soft intrusion.The major factors affecting the characteristic of fiber-reinforced concrete are a water-cement ratio, percentage of fibers, diameter and length of fibers. The location and extent of creating under load will depend upon the orientation and number of fibers in the cross-section. The fibers restrain the shrinkage and creep movements of the unreinforced matrix. However, fibers have been found to be more effective in controlling compressive creep than tensile creep of the unreinforced matrix.
Uses of Fibre reinforcement Concrete
- It is applied on overlays of the airfield, road explosive resistant structures, refractory lining, etc.
- It is used for fabrication of precast products like pipes, boats, beams, stair cased step, wall panels, roof panels, manhole cover, etc.
- Using Glass fiber, it is used for doors and door frames, permanent and temporary formwork, pressure pipes, bus shelters, and park benches.