As a rule of thumb, small fibres tend to be used where control of crack propagation is the most important design consideration. High fibre count (number of fibres per kg) permits finer distribution of steel fibre reinforcement throughout the matrix &#; and consequently, greater crack control during drying process. On the other hand, because they exhibit better matrix anchorage at high deformations and large crack widths, longer, heavily deformed fibres afford better post-crack "strength". However, unlike shorter fibres, the dramatically reduced fibre count of longer product yields correspondingly less control of initial crack propagation.
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Properties of reinforcement
When steel fibres are added to mortar, Portland cement concrete or refractory concrete, the flexural strength of the composite is increased from 25% to 100% - depending on the proportion of fibres added and the mix design. Steel fibre technology actually transforms a brittle material into a more ductile one. Catastrophic failure of concrete is virtually eliminated because the fibres continue supporting the load after cracking occurs. And while measured rates of improvement vary, Steel fibre reinforced concrete exhibits higher post-crack flexural strength, better crack resistance, improved fatigue strength, higher resistance to spalling, and higher first crack strength, Figure 2 shows concrete flexural strengths when reinforced at various fibre proportions. Additionally, deformed fibres provide a positive mechanical bond within the concrete matrix to resist pull-out. Steel fibres are available in lengths from 38 mm to 50 mm and aspect ratios between 40 and 60. The fibres are manufactured either deformed or hook end, and conform to ASTM A-820.
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Steel fibre reinforced concrete (SFRC) Floor slabs.
Conventional practice usually concentrates welded wire fabric reinforcement within a single plane of a floor slab. Fabric does very little to reinforced the outer zones, which is why spalling is common at the joints and edges. The primary function of welded wire fabric is to hold the floor slab together after the first small hairline cracks have propagate to larger fractures. This serves to maintain some degree of "structural integrity". Conventional wisdom&#;s approach to floor slabs is to maintain "material integrity" through SFRC mix designs. This integrity is accomplished by:
- Increasing the initial first crack strength.
- Large numbers of fibres intercepting the micro-cracks and preventing propagation by controlling tensile strength.
- Unlike rebar and welded wire fabric, fibres are dispersed throughout the slab to reinforce isotropically, so there is no weak plane for a crack to follow.
- Increases in flexural strength can make it possible to use a thinner slab and eliminate the cumbersome welded wire fabric.
- Whether it is for lighter duty commercial service or for heavy manufacturing, SFRC slabs are capable of withstanding any load. The only variable is the addition rate of fibre, which could be as low as 12.5kg/m3 to as high as 100 kg/m3.
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How they save time and money
COMPLETELY ELIMINATE STEEL FABRIC REINFORCEMENT, SAVING ON BOTH MATERIALS AND LABOUR
- Reduce slab thickness giving savings in concrete and placement costs.
- Possibilities of wider joint spacing. Save on joint forming costs and joint maintenance
- Simplicity of construction. Simpler joints and no more errors in steel fabric positioning
- Increase speed of construction. Save time and reduce costs.
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Technical and user benefits
- Significantly reduced risk of cracking.
- Reduced spalling joint edges.
- Stronger joints.
- High impact resistance.
- Greater fatigue endurance.
- Reduced maintenance costs.
- Longer useful working life
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Typical areas of applications include
Industrial Ground Floor Slabs &#; Warehouses, Factories, Aircraft Hangers, Roads, Bridge Decks, Parking Areas, Runways, Aprons and Taxiways, Commercial and Residential Slabs, Piling, Shotcrete, Tunnels, Dams and stabilisation.
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Improved strength and durability
Steel fibre reinforced concrete is a castable or sprayable composite material of hydraulic cements, fine, or fine and coarse aggregates with discrete steel fibres of rectangular cross-section randomly dispersed throughout the matrix. Steel fibres strengthen concrete by resisting tensile cracking. Fibre reinforced concrete has a higher flexural strength than that of unreinforced concrete and concrete reinforced with welded wire fabric. But unlike conventional reinforcement &#; which strengthens in one or possibly two directions &#; Steel fibres reinforce iso tropically, greatly improving the concrete&#;s resistance to cracking, fragmentation, spalling and fatigue. When an unreinforced concrete beam is stressed by bending, its deflection increases in proportion with the load to a point at which failure occurs and the beam breaks apart. This is shown in Figure 1. Note that the unreinforced beam fails at point A and a deflection of B. A Steel fibre reinforced beam will sustain a greater load before the fist crack occurs (point C). It will also undergo considerably more deflection before the beam breaks apart (point D). The increased deflection from point B to point D represents the toughness imparted by fibre reinforcement. The load at which the first crack occurs is called the "first crack strength". The first crack strength is generally proportional to the amount of fibre in the mix and the concrete mix design.
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Two theories have been proposed to explain the strengthening mechanism. The first proposes that as the spacing between individual fibres become closer, the fibres are better able to arrest the propagation of micro cracks in the matrix. The second theory holds that the strengthening mechanism of fibre reinforcement relates to the bond between the fibres and the cement. It has been shown that micro cracking of the cement matrix occurs at very small loads. Steel fibres, then service as small reinforcing bars extending across the cracks. So as long as the bond between the fibres and cement matrix remains intact the Steel fibres can carry the tensile load. The surface area of the fibre is also a factor in bond strength. Bond strength can also be enhanced with the use of deformed fibres, which are available in a variety of sizes.
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Product mix designs
The proportions of Steel fibres in mix designs usually range from 0.2% to 2.0% (15 to 150 kg/m3 ) of the composite&#;s volume. Key factors to consider largely depend on the application under consideration and/or the physical properties desired in the finished project. Mix designs with fibre proportions above 60kg/m3 are usually adjusted to accommodate the presence of millions of steel fibre reinforcing elements. The adjustments are an increase in the cement factor, a reduction in the top size of the coarse aggregate and the addition of a super plasticiser. Prototype testing is recommended to determine the optimum design for each application.
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Advantages
- Reinforcing concrete with Steel fibres results in durable concrete with a high flexural and fatigue flexural strength, improved abrasion, spalling and impact resistance.
- The elimination of conventional reinforcement, and in some cases the reduction in section thickness can contribute to some significant productivity improvements. Steel fibres can deliver significant cost savings, together with reduced material volume, more rapid construction and reduced labour costs.
- The random distribution of Steel fibres in concrete ensures that crack free stress accommodation occurs throughout the concrete. Thus micro cracks are intercepted before they develop and impair the performance of the concrete.
- Steel fibres are a far more economical design alternative.
Disadvantages
- Steel fibres will not float on the surface of a properly finished slab, however, rain damaged slabs allow both aggregate and fibres to be exposed and will present as aesthetically poor whilst maintaining structural soundness.
- Fibres are capable of substituting reinforcement in all structural elements (including primary reinforcement), however, within each element there will be a point where the fibre alternative&#;s cost saving and design economies are diminished.
- Strict control of concrete wastage must be monitored in order to keep it at a minimum. Wasted concrete means wasted fibres.
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Steel fibers are commonly used as a reinforcement material in concrete to enhance its mechanical properties and performance. When added to concrete, steel fibers act as a secondary reinforcement to improve tensile, flexural, and shear strength. There are other options in the market such as synthetic macro fibers, which are a type of reinforcement used in concrete to enhance its mechanical properties and performance. To better understand how adding steel fibers can be the best choice for your construction project, keep reading.
Benefits of steel fiber reinforced concrete
Here are some key roles and benefits of steel fibers in concrete:
- Crack control: Steel fibers help control the formation and propagation of cracks in concrete. By distributing throughout the concrete matrix, the fibers resist the development of small cracks and limit their growth.
- Tensile strength: Concrete is strong in compression but relatively weak in tension. Steel fibers enhance the tensile strength of concrete, making it more resistant to cracking and improving its overall durability.
- Flexural strength: The addition of steel fibers increases the flexural strength of concrete, making it better able to withstand bending and other types of deformation.
- Impact resistance: Steel fibers enhance the resistance of concrete. This is crucial in applications such as industrial floors, pavements, and precast concrete elements that may be subjected to impact loads.
- Ductility: Steel fibers contribute to the ductility of concrete, allowing it to deform without complete failure under certain loads.
- Fatigue resistance: The use of steel fibers improves the fatigue resistance of concrete, making it more capable of withstanding repeated loading cycles without developing significant damage or deterioration.
- Temperature resistance: Steel fibers can improve the resistance of concrete to elevated temperatures and fire. The presence of steel fibers can help prevent spalling and maintain the structural integrity of the concrete during exposure to high temperatures.
- Abrasion resistance: In applications where concrete is subjected to abrasion, such as industrial floors, steel fibers can enhance the resistance of the concrete surface to wear.
Uses of steel fiber reinforced concrete
Steel fibers are commonly added to concrete to enhance its mechanical properties and overall performance in various applications. Here are some specific uses of steel fibers in concrete:
- Industrial floors: Steel fibers are used to improve the durability and resistance of industrial floors, which often experience heavy traffic, loads, and potential impacts from equipment.
- Pavements and road construction: Steel fibers help control cracking and increase the tensile strength of concrete in pavements and road construction, improving the overall performance and longevity of the structures.
- Tunnel linings: Steel fibers are added to concrete used in tunnel linings to enhance crack control, flexural strength, and overall structural integrity, especially in environments with high ground movement.
- Precast concrete elements: Steel fibers improve the flexural and tensile strength of precast concrete elements, such as panels, beams, and pipes, contributing to their structural performance.
- Shotcrete applications: Steel fibers are commonly used in shotcrete applications, such as slope stabilization, tunnel construction, and repair work, to provide rapid and durable structural solutions.
- Bridge decks: Steel fibers enhance the durability and resistance to cracking in concrete bridge decks, where the structure is exposed to dynamic loads, environmental factors, and potential aggressive agents.
- Airport runways: Steel fibers contribute to the impact resistance and overall durability of concrete in airport runways, which need to withstand heavy aircraft loads and potential impacts.
- Seismic-resistant structures: Steel fibers are used in seismic-resistant structures to provide additional ductility and energy absorption, helping the concrete withstand the dynamic forces associated with earthquakes.
- High-performance concrete: In applications where high-performance concrete is required, such as in advanced engineering projects, steel fibers enhance the material&#;s strength, durability, and resistance to various stresses.
- Industrial and warehouse floors: Steel fibers are added to concrete in industrial and warehouse floors to improve abrasion resistance, reduce cracking, and enhance the overall durability of the flooring.
- Underground structures: Steel fibers are used in the construction of underground structures, such as subway tunnels and utility tunnels, to provide additional strength and crack resistance.
- Waterfront structures: In marine environments, where structures are exposed to corrosive elements, steel fibers with corrosion-resistant coatings are used to improve the durability of the concrete.
How can Mid-Continent Steel and Wire provide steel fiber solutions?
Steel fiber concrete mix can benefit your construction projects in many ways. Our high-strength steel fibers are filaments with hook ends used as reinforcing steel in concrete structures such as industrial floor and pavements, shotcrete, and precast elements. Made of low carbon wire, our steel fibers has a polished and bright finish. Its length and diameter will depend on the required application.
- Designs: P50-100 , P50-75 , L33-55 , L33-75
- Units: 20 kg Box and 1,200 kg Polypropylene Bag
- Uses and Applications: Precast, shotcrete, industrial floors, concrete slabs, seamless floors
- Made With: Polished Cold Drawn LC Wire
- ASTM: A-820, ISO-, EN -1
Its material properties and strain capacity can support structures and provide load stability for any project.
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