Steel Fiber Reinforced Concrete

Introduction

Steel Fiber Reinforced Concrete (SFRC) is a type of concrete that contains small, discontinuous steel fibers distributed uniformly throughout the concrete matrix. These steel fibers enhance the properties and performance of the concrete, providing improved tensile strength, ductility, and crack resistance.

Uses/benefits:

Tunnel linings: SFRC is commonly used in tunnel construction for the lining of tunnels. The addition of steel fibers enhances the durability and structural integrity of the tunnel lining, providing resistance against cracking, spalling, and other forms of deterioration.
Shotcrete applications: SFRC is frequently used in shotcrete applications for tunnel construction. The steel fibers improve the cohesion and bond between the shotcrete and the substrate, resulting in enhanced structural strength and improved resistance to deformation and cracking.
Tunnel segments: SFRC is employed in the manufacturing of tunnel segments, which are precast concrete elements used in tunnel construction. The steel fibers in SFRC provide additional reinforcement, ensuring the integrity and strength of the tunnel segments.
Ground support systems: SFRC is utilized in ground support systems, such as sprayed or cast-in-place concrete linings, rock bolting, and shotcrete applications. It improves the stability and resistance of the surrounding ground, enhancing the safety of underground structures.
Impact resistance: SFRC exhibits excellent impact resistance, making it suitable for tunneling and underground structures where there is a risk of mechanical impacts or seismic activity.
Crack control: The inclusion of steel fibers in the concrete matrix helps to control and limit crack propagation, reducing the potential for water ingress, corrosion of reinforcing steel, and structural damage.
Fire resistance: SFRC has improved fire resistance compared to conventional concrete due to the presence of steel fibers. It helps to prevent rapid fire spread and maintains structural stability under high temperatures.

Specifications:

Fiber content: The steel fiber content in SFRC is specified based on the desired performance requirements, typically expressed as a percentage by volume or weight of concrete.
Fiber geometry: The geometry of the steel fibers, such as length, diameter, and aspect ratio, can affect the properties of the SFRC. The specific fiber geometry is selected based on the intended application and desired performance characteristics.
Concrete mix design: The concrete mix design for SFRC takes into account factors such as aggregate type, water-cement ratio, cement content, and admixtures to achieve the desired workability, strength, and durability properties.
Fiber distribution: The steel fibers should be uniformly distributed throughout the concrete matrix to ensure consistent reinforcement and avoid clumping or agglomeration.

Types:

Hooked-end steel fibers: These fibers have small hooks at the ends, providing improved anchorage and bond with the concrete matrix.
Straight steel fibers: These fibers are straight with no hooks or bends. They offer good tensile strength and are commonly used in tunneling applications.
Crimped steel fibers: These fibers have crimped or wavy shapes, enhancing their bond with the concrete and improving their ability to resist pull-out forces.
Slit sheet steel fibers: These fibers are in the form of thin sheets that are slit to create multiple individual fibers. They offer high aspect ratios and excellent crack resistance.

It's important to note that specific specifications and types of steel fibers may vary depending on project requirementsand regional standards. ISO 13270: 2013, EN 14889-1: 2016, ASTM A820: 2011 are some of the current standards that areused for the steel fibres for concrete.