What is fiber reinforced concrete?
Fiber-reinforced concrete is concrete mixed with suitable fiber which increases its toughness. Fiber acts as micro reinforcement which increases the structural reliability of concrete.
Concrete is weak in tension. The tensile strength of concrete is only one-tenth of the compressive strength of concrete. Cracks develop in the structure during load. Because of the addition of the fiber in concrete cracks forms at the same load but the structure won’t fall apart, it will be held together by these fibers.
Let’s see a short Experiment on Normal Concrete and fiber reinforced concrete
Fibers do not stop the cracks from forming in concrete but hold the structure together for a longer period of time. Fibers keep the crack small which leads to longer life of the structure. Fibers give post cracking strength. It increases the properties like toughness, tensile strength, ductility.
Some of the material of fiber used in concrete are steel, glass, synthetic material like nylon, polyester and natural fibers. Fibers can be circular or flat.
Fiber is described according to aspect ratio. The aspect ratio is the ratio of the length of fiber to its diameter. Increase of aspect ratio up to 75 increases the relative strength and toughness. If the length of the fiber is longer then it can cause strangulation of fibers during mixing.
Types of fiber reinforced concrete
- Steel fibers
- Glass fibers
- Synthetic fibers (Polypropylene Fibers and Nylon Fibers)
1) Steel Fibers
The aspect ratio for steel fibers is 20 to 100. Different types of steel reinforcement are available as reinforcement. Round steel fiber is commonly used. The diameters of the steel reinforcement vary from 0.25mm to 0.75m.
Steel fibers improve structural strength and reduce the steel reinforcement required. Steel fibers are used in precast and structural applications, canal linings, flooring, bridges, etc.
2) Glass Fibers
Glass fibers provide high tensile strength. Glass fibers of length 10mm to 50mm are used. It increases ductility, resistance to thermal shock, and flexural strength which enhances the resistance of structure against bending. Glass fiber has a limitation.
When mixing of aggregate, cement, and glass fiber due to the abrasion and impact forces there is a chance it can damage glass fiber. So the addition of glass fiber should be done in controlled conditions. Glass fibers are used in sewer linings, ducts, roofs, building renovation works, etc.
Glass fiber improves concrete strength at low cost.
3) Synthetic Fibers
Synthetic fibers are manmade fibers from petrochemical which is prepared from raw material petroleum. Synthetic fibers improve ductility and structural strength. It has high chemical resistance.
Synthetic fibers increase the resistance to plastic shrinkage during curing. Synthetic fibers are cheap as compared to natural fibers.
How Fiber-reinforced concrete is Prepared?
Fiber-reinforced concrete is obtained by adding a single type or blend of fibers to the concrete mix.
Application of Fiber reinforced concrete
- Agriculture: Farm and animal storage structures
- Airports and highway paving for thin members or members that are too complicated for rebar, curb, and gutter work
- Used as shotcrete material, tunnel linings, and rock slope stabilization
- Hydraulic structures: construction of Dams, spillways, and other hydraulic structure to provide resistance against cavitation
- A combination of fiber reinforced concrete with reinforcing bars can be used as an explosion resistant structure
- Adds tensile reinforcement in all directions
- Reduces damage in a fire
- The addition of fiber increases strength after cracking bridging the cracks that develop in concrete
- Life safety of people increases.
- The method of construction of fiber concrete reinforcement is faster, cheaper, and safer.
- Instead of providing strength in distinct locations fibers forms network throughout the entire concrete structure increasing its overall ductility.
- It reduces the bleeding of water avoiding plastic shrinkage crack by reducing the permeability of concrete.
- Fibers may sometimes stick up out of the surface, rain allows fibers to be exposed
- Fibers randomly orient in concrete and maybe concentrated at few places which cause poor quality of concrete.
- Fibers increase the cost of concrete by 10 to 15%.
- The addition of fibers increases the specific gravity of concrete which may result in heavier concrete in some fibers.
- Fibers in concrete reduce the workability.
I hope this article remains helpful for you.
Happy Learning – Civil Concept
Civil Engineer – Sristi Koju