Concrete naturally has the ability of developing high compressive strength but has a weak tension force. As it is fragile in type, cracks are formed easily, which leads to shrinkage or deformation of the concrete structure. Fibres are added to concrete to increase its strength and endurance and prevent structural failure. This method improves the sturdiness of the structures that have steel fibres integrated with reinforced concrete.
What is Steel Fibre Reinforced Concrete?
Steel fibres are isotropic and have the same size or physical properties when measured in different directions. They are short and discontinuous metal reinforcements that frequently resemble metal threads or filaments. They also have the same strength and stiffness when measured along different axes. Typically, they have flat or shaped ends and are smooth, folded, or irregular.
They are usually recycled from industrial wastes, such as used tyres from cars and trucks. Depending on the amount of reinforcement needed, the short steel fibre strands, which are typically 4 to 5 cm long, are added to the concrete mix in amounts ranging from 25 to 100 kilograms per cubic metre. After that, the liquid is dumped straight onto the building site.
Concrete is improved in all directions by the consistent dispersion of steel fibres. When the steel fibres are integrated with reinforced concrete, they show exceptional bending, tension, and compression resistance.
Composition of Steel Fibre Reinforced Concrete
Steel fibre reinforced concrete usually comprises cement, water, coarse aggregate, fine aggregate, and steel fibres. The traditional mesh-reinforced concrete can be replaced by this SFRC. They are used to create a concrete floor without expansion joints instead of steel bars. The steel fibres are mixed along with the concrete mix and directly poured into the steel reinforcement.
The mix design ratio for 1 m³ of M25 grade concrete is as follows:
Cement: 400 Kg
Water: 200 Kg
Coarse aggregate: 1185.83 kg
Fine aggregate: 671.90 kg
This mixture can produce a durable concrete floor that resists cracking and lasts for a long time.
Properties of Steel Fibre Reinforced Concrete
Depending on the project requirements, different types of fibres are used in the construction project. The properties of the steel fibres can be modified according to the purpose of the project. The steel fibres are added to resist the tensile stresses. The properties of steel fibres that can be reinforced into the concrete are as follows:
| S.No | Properties | Description |
| 1. | Measurement of steel fibres | They are distinct, short, and available in rectangles, rounds, and deformed bundles. |
| 2. | Aspect Ratio | Ranges from 20 to 100 |
| 3. | Diametre | 0.25 mm to 0.75 mm |
| 4. | Tensile Strength | 280 to 420 MPa |
| 5. | Poisson’s Ratio | 0.30 |
| 6. | Young’s Modulus | 200 GPa |
| 7. | Ultimate Elongation | 3.6% |
| 8. | Specific Gravity | 7.86 |
Manufacturing Process of Steel Fibre Reinforced Concrete
Steel fibre is one type of reinforced concrete. Usually, it is made up of sand, cement, water, gravel, and steel fibres. Additives may be added in some cases based on the project requirements. They are similar to metal filaments or threads. They are recycled from many other industrial activities. They are popularly available in automobile and truck scrap tyres.
Depending on the required level of reinforcement, short fibres, usually 4 to 5 cm long, are mixed into steel fibre-reinforced concrete (SFRC) at a ratio of 25 to 100 kg per cubic meter.
The mixture is then poured directly into the site. Steel fibres have less tendency to crack. Using the dry shake method, a granular mixture is spread across the new concrete pouring. Finally, the concrete is levelled to attain a smooth surface.
Applications of Steel Fibre Reinforced Concrete
In modern construction techniques, SFRC is widely used in a variety of applications, which are as follows:
- Pavements
- Airfields
- Overlays or roads
- Bridge decks
- Flooring
- Roads
- Pipes
- Sleepers
- Septic tanks
SFRC can reduce the thickness of the pavement. SFRC is highly used in repairing works of roads and laying highway roads. Its high bending strength and ability to resist deformation when a heavy load is applied make this material more suitable for building roads and highways. Hydraulic structures like dams, weirs, breakwaters, barrages, and pontoon bridges can be built using this SFRC material due to its corrosion-resistant capacity. This material can also be used to make precast concrete. Fibre shotcrete is manufactured from this material to support tunnel lining, bridges, pipes, stabilisation of rocks, dams, and steel structure protection, etc. It improves the mechanical strength of the reinforced rebar concrete.
Advantages of Steel Fibre Reinforced Concrete
- Consistent performance in all directions is ensured by the equally dispersed fibres.
- Boosts resistance against erosion and abrasion.
- Increases the lifespan of concrete flooring by reducing cracks and fissures.
- A higher load-bearing capacity is made possible by increased resistance to compression, tension, torsion, and shear pressures.
- Increases conventional concrete’s ductility and durability.
- Provides improved protection against dynamic loads like cyclic loads, collisions, and explosions.
- For an even more resilient system, wire mesh can be added.
- Makes it possible to build lighter, thinner structures while conserving materials.
- Concrete floors are easier to clean and maintain because they may be installed without joints over 2500 m².
- By measuring up to 50% thinner than conventional floor slabs, floor slabs can save money on materials.
Disadvantages of Steel Fibre Reinforced Concrete
- Structures run the risk of developing steel fibres on their surface, which could detract from the final product’s visual appeal.
- Fibre clumping may result from improper mixing of the steel fibres with the concrete, threatening the material’s consistent performance.
- Concrete’s elasticity may be diminished by the addition of steel fibres.
- To ensure optimum performance, it is crucial to carefully choose the right kind, amount, and length of fibres.
Conclusion
Because of its dependable and appealing mechanical qualities, steel-reinforced concrete, is frequently utilised in concrete applications. This substance efficiently increases the strength and durability of concrete, enabling the construction of sturdy, lightweight, and thin structures. It is widely used in a variety of applications that can be built in modern construction.
FAQ’s
Concrete is improved in distinct ways by steel fibres and synthetic microfibres, which are not interchangeable. Steel fibres strengthen the concrete after it has cracked, and synthetic microfibres increase fire resistance and lessen plastic shrinkage cracking. When it comes to fortifying concrete, both kinds of fibres play different roles.
Steel fibres are no more likely to rust than steel bars, as they are small and discontinuous.
Concrete’s ductility and effective concrete strength are considered as the residual concrete strength, which are enhanced by the addition of steel fibres and also serve to reduce cracks.