Steel fibre in concrete

Types of Steel Fibre in Concrete

Steel fibers in concrete can significantly enhance the performance of concrete in a variety of applications. These fibers, when mixed into the concrete, help form a matrix that provides additional strength and durability to concrete.

Steel fibers are short strands of steel with a length between 20mm and 30mm and a width of about 0.5-1mm. They are usually added to the concrete mix in volumes between 0.5% and 2% by volume, depending on the intended use and application. When added to the concrete mix, they improve the tensile strength, ductility, and impact resistance of the concrete. This is because they help to reduce the formation and propagation of cracks, thus improving the overall lifespan of the concrete.

Moreover, using steel fibers reduces the need for traditional steel reinforcement, such as rebar and wire mesh. This not only reduces the overall costs of the project but also makes the process of pouring and setting the concrete much easier and faster. This is because it eliminates the time needed to place the rebar and mesh during the concrete pouring process.

There are different types of steel fibers in concrete, which include:

• Hooked-end fibers: These are the most commonly used fibers in concrete. They have hooks at the ends that help anchor the fibers within the concrete matrix. They come in various lengths and diameters and are usually added to the concrete mix to enhance its tensile strength and toughness.
• Straight steel fibers: These fibers are characterized by their straight and cylindrical shape. They are used to improve the flexural strength and impact resistance of the concrete. However, they are used less frequently compared to hooked-end fibers because they have less interlocking ability.
• Crimped steel fibers: These fibers have a wavy or crimped appearance. They improve the workability and ductility of the concrete. Their crimped shape helps to create a better bond between the fibers and the concrete matrix.
• Flat steel fibers: As the name suggests, these fibers are flat and thin. They are usually used when a high degree of surface finish is required. Their flat shape helps to improve the flexural strength and durability of the concrete slab.
• End-hooked steel fibers: These fibers have a hooked end that looks like a crimped or straight fiber. They provide better anchorage within the concrete matrix, which enhances the load-bearing capacity of the concrete.

Function and Feature of Steel Fibre in Concrete

Steel fibre concrete has gained popularity in the construction industry due to its improved structural capacity and durability. The features of steel fibre concrete and its functions include:

• Increased post-cracking resistance

  The main advantage of using steel fibre is that it improves the post-cracking resistance of concrete. When concrete cracks under load, the steel fibres act as a bridge across the crack, helping to transfer loads and reduce further crack propagation. This is particularly beneficial in applications where control of crack growth is important, such as in slabs on grade and shotcrete applications.

• Improved impact resistance

  Applications that involve frequent impact loading benefit from the use of steel-fibre-reinforced concrete. The distribution of steel fibres throughout the concrete matrix absorbs and dissipates impact energy, reducing the formation of cracks and spalling. This results in more durable concrete structures, such as industrial pavements and blast-resistant structures.

• Enhanced fatigue resistance

  Concrete structures subjected to repeated loading cycles, such as in bridges and heavy traffic areas, benefit from using steel fibres. Steel fibres help to reduce the accumulation of damage from cyclic loading, thereby improving the fatigue life of the structure. This leads to lower maintenance costs and extended service life for these types of structures.

• Reduced permeability

  The inclusion of steel fibres in the concrete mix can lead to a denser microstructure. A denser concrete matrix has lower permeability, which is crucial for protecting steel reinforcement from corrosion, especially in marine or de-icing salt exposure environments. This characteristic is important for structures like parking decks and bridge decks.

• Reduced shrinkage cracking

  Steel fibres can help mitigate shrinkage cracking, especially in the early stages of curing. The fibres provide reinforcement during the plastic shrinkage phase, which can be critical in preventing cracks from forming early in the life of the concrete. This is particularly useful in large slab-on-ground projects.

• Improved load-bearing capacity

  Steel fibre concrete can reduce the need for traditional reinforcement, such as welded wire mesh or rebar, especially in applications like industrial floors and shotcrete for tunnel linings. This can lead to cost savings and faster construction times. Moreover, structures built with steel fibre-reinforced concrete can support higher loads due to the tensile strength imparted by the fibres. This allows for thinner slabs or reduced beam sizes.

Scenarios of Steel Fibre in Concrete

Steel fiber reinforced concrete has diverse applications across various industries. Its ability to enhance the structural integrity and durability of concrete makes it a preferred choice for different construction projects. Here are some common application scenarios:

• Industrial Floors

  SFRC is widely used in industrial floors, such as warehouses, factories and power plants. The inclusions of steel fibers reduce the formation of cracks and control shrinkage, leading to a more durable and maintenance-friendly floor. These fibres also enhance the load-bearing capacity of the concrete, making it suitable for areas with heavy machinery and high traffic.

• Pavements

  Steel fiber in concrete is also used in both rigid and flexible pavements. In rigid pavements, it reduces the risk of cracking and improves the resistance to dynamic loads from traffic. For flexible pavements, steel fiber-reinforced concrete can be used in the base and sub-base layers to enhance durability and reduce deformation under traffic loads.

• Shotcrete Applications

  SFRC is extensively used in shotcrete applications, such as tunnels, slopes and underground constructions. The addition of steel fibers enhances the bond strength and reduces the rebound loss during application. This leads to a more efficient and stable shotcrete structure.

• Structural Elements

  Steel fibre reinforced concrete is used in constructing slabs, beams and columns. The uniform distribution of steel fibers within the concrete matrix improves the tensile strength and ductility of the structural elements. This results in a more resilient and crack-resistant structure.

• Parking Lots and Garages

  Steel fibre in concrete is a popular choice for constructing parking lots and garages. The enhanced load-carrying capacity and crack resistance of the SFRC ensure a long-lasting and low-maintenance parking surface. Additionally, the reduction of joints in fibre-reinforced slabs minimizes water infiltration and the formation of weeds.

• Precast Concrete

  The addition of steel fibers to precast concrete elements, such as walls, slabs and beams, improves their impact resistance and durability. This is particularly beneficial in applications where the precast elements are subjected to harsh environmental conditions or heavy loads.

How to Choose Steel fibre in concrete

• Project Requirements

  The first step in selecting the appropriate concrete fibre steel is to analyze the project specifications. What kind of structure are we going to build? Is it a slab, pavement, shotcrete walls or something else? Each application has its ideal metal fibre dosage. For instance, a higher dosage is suitable for industrial and commercial slabs, while a lower dosage is adequate for residential applications.

• Concrete Design

  The concrete mixture should be compatible with the chosen steel fibre. Consider the type of fibre - crimped, flat or hooked. Crimped fibres bond well with cement, while flat and hooked fibres provide superior strength. The selection depends on the strength and workability requirements.

• Construction Methods

  The construction techniques used can affect the choice of metal fibres. Hooked fibres are ideal for reinforced concrete using a mixer truck and a concrete pump. However, crimped and flat fibres are better when mixing and pouring manually.

• Cost-Benefit Analysis

  While steel fibre concrete may appear more expensive than traditional rebar, a thorough cost-benefit analysis can reveal long-term advantages. Consider the labour and time savings during installation. Fibres eliminate the need for rebar tying and positioning, which can significantly reduce labour costs and construction time. This is particularly beneficial for large-scale projects.

• Sustainability Goals

  If environmental impact is a concern, look for sustainable aspects of different fibres. Some manufacturers offer recycled content in their products. Additionally, the durability of steel fibre-reinforced concrete can contribute to a longer lifespan of the structure, which is environmentally friendly. Reducing the need for repairs or replacements is a way of saving resources.

• Consultation with Experts

  When in doubt, consult with professionals who have experience with metal fibre-reinforced concrete. This includes structural engineers, concrete suppliers, and contractors. Their expertise can guide the selection process and ensure the concrete meets the project's needs.

Steel Fibre in Concrete Q&A

Q1: What are the advantages of using steel fibre in concrete?

A1: Steel fibres enhance the post-cracking behavior of concrete, leading to improved toughness and durability. Steel fibre-reinforced concrete (SFRC) structures have higher resistance to cracking, deformation, and dynamic loads. This reduces the need for conventional reinforcement bars, saving time and costs in construction.

Q2: Are there any disadvantages of using steel fibres in concrete?

A2: While steel fibres offer significant advantages, there are some considerations. Proper dosage and distribution of fibres are crucial to achieving the desired performance. Excessive fibres can lead to workability issues. Additionally, the bond between fibres and concrete matrix must be optimized for maximum strength. This is done through appropriate surface treatments or fibre coatings.

Q3: How do steel fibres affect the workability of concrete?

A3: The addition of steel fibres can slightly reduce the workability of fresh concrete, depending on the fibre dosage and aspect ratio. However, this can be mitigated by using high-aspect-ratio fibres or adding superplasticizers to the mix.

Q4: Can steel fibre-reinforced concrete be used for aesthetic applications?

A4: Yes, SFRC can be used for aesthetic applications such as decorative pavements and architectural panels. The surface finish and appearance depend on the concrete mix design and surface treatment.

Q5: What are the common methods for adding steel fibres to the concrete mix?

A5: Steel fibres are commonly added to the concrete mix using a forced concrete mixer or a special steel fibre dispenser. A continuous steel fibre dispenser can be integrated into the batching system for precast applications. For cast-in-place applications, a drum-type fibre dispenser is used.