Abstract

In conventional concrete, micro-cracks develop before structure is loaded because of drying shrinkage and other causes of volume change. When the structure is loaded, the micro cracks open up and propagate because of development of such micro cracks, results in inelastic deformation in concrete. Fibre reinforced concrete (FRC) is cementing concrete reinforced mixture with more or less randomly distributed small fibres. In the FRC, a number of small fibres are dispersed and distributed randomly in the concrete at the time of mixing, and thus improve concrete properties in all directions. The fibers help to transfer load to the internal micro cracks. FRC is cement based composite material that has been developed in recent years. It has been successfully used in construction with its excellent flexural-tensile strength, resistance to spitting, impact resistance and excellent permeability and frost resistance. It is an effective way to increase toughness, shock resistance and resistance to plastic shrinkage cracking of the mortar. These fibers have many benefits. Steel fibers can improve the structural strength to reduce in the heavy steel reinforcement requirement. Freeze thaw resistance of the concrete is improved. Durability of the concrete is improved to reduce in the crack widths. Polypropylene and Nylon fibers are used to improve the impact resistance. Many developments have been made in the fiber reinforced concrete. Key words: Fiber Reinforced Concrete; Steel Fiber; Glass Fiber; Natural Fiber; Aspect Ratio; Mechanical and Structural Properties.

Introduction

Concrete made from Portland cement, is relatively strong in compression but weak in tension and tends to be brittle. The weakness in tension can be overcome by the use of conventional steel bars reinforcement and to some extent by the mixing of a sufficient volume of certain fibers. The use of fibers also recalibrates the behaviour of the fiber-matrix composite after it has cracked through improving its toughness (Nataraja M.C., Dhang N) .This thesis is aims to provide information on the properties and applications of the more commonly available fibers and their uses to produce concrete with certain characteristics.

A new kind of fibre reinforced concrete is developed which is made from cellulose fibers. A fibre is a small discrete reinforcing material produced from various materials like steel, plastic, glass, carbon and natural materials in various shapes and size.

A numerical parameter describing a fibre as its aspect ratio, which is defined as the fibre length, divided by an equivalent fibre diameter. Typical aspect ratio[l/d] range from 30 to 150 forlength dimensions of 0.1 to 7.62 cm typical fibre diameters are 0.25 to 0.76 mm for steel and 0.02 to 0.5 mm for plastic.

The plain concrete fails suddenly when the deflection corresponding to the ultimate flexural strength is exceeded, on the other hand fiber reinforced concrete continue to sustain considerable loads even at deflections considerably in excess of the fracture deflection of the plain concrete.

What is Fiber Reinforced Concrete ?

Fiber-reinforced concrete (FRC) is concrete containing fibrous material which increases its structural integrity. It contains short discrete fibers that are uniformly distributed and randomly oriented. Fibers include steel fibers, glass fibers, synthetic fibers and natural fibers – each of which lend varying properties to the concrete. In addition, the character of fiber-reinforced concrete changes with varying concretes, fiber materials, geometries, distribution, orientation, and densities.

Fiber reinforced concrete (FRC) is a new structural material which is gaining increasing importance. Addition of fiber reinforcement in discrete form improves many engineering properties of concrete.

Continuous meshes, woven fabrics and long wire or rods are not considered to be discrete fibre.

Why we need Fiber Reinforced Concrete (FRC) ?

Plain unreinforced concrete is a brittle material with a low tensile strength and low strain capacity .so when they are exposed to heavy load cracks appear and they collapse.

But it has been recognised that the addition of small, closely spaced and uniformly dispersed fibres to concrete would act as crack arrester and would substantially improves its static and dynamic properties. The uniformly/randomly distributed discontinuous fibres bridges across the cracks that develop provides some post cracking ductility and protect it from sudden collapse.

According to Griffith theory the concrete has low tensile strength due to existence of cracks. So, the reinforced fibre helps in increasing the tensile strength of concrete by bridging the cracks with the fibre.