Q.Describe steel fiber reinforced concrete.
For some applications, steel fibre reinforced concrete is a viable alternative to regular reinforced concrete. When steel fibres are incorporated into concrete, they become a discontinous, 3-dimensionally oriented, isotropic reinforcement. Steel fibres bridge cracks at very small fracture openings, transmit stresses, and help the concrete build post-crack strength.
There are many different sorts of fibres (material, form, size, etc.) and their impact on concrete varies. As a result, steel fibre reinforced concrete must never be referred to simply as “concrete containing steel fibres.” Steel fibres are classified into five categories:
Type I – cold-drawn wire
Type II – cut sheet
Type III – melt-extracted
Type IV – shaved cold drawn wire
Type V – milled from blocks
The “hooked end” is the most common and effective anchorage type, with the vast majority belonging to group i. The most significant influences on fibre performance are length/diameter and tensile strength for the same type of fibre. The higher the l/d ratio, the better the steel fibre reinforced concrete’s performance.
Q.Is it possible to incorporate steel fibers at the ready mix plant?
A.Yes. Steel fibres should be added after all other items have been loaded into the vehicle. Set the truck mixer to charging mode and slowly pour the fibres into the mixer. At charging speed, mix for roughly 5 minutes. If there is safe access, steel fibres can also be put to the aggregate batch belt.
Q.How long does it take to mix steel fibers into a ready mix truck?
A.After all steel fibres have been loaded into the truck, Fibpro recommends mixing at the highest drum speed for 4 to 5 minutes.
Q.Is it possible to add steel fibers on site?
A.Yes, fibres can be added to the truck mixer on the spot. Gradually add fibres to the mix, usually with the help of a conveyor belt.
Q.Is it possible to add steel fibers to any mix?
Concrete, cement, and grout can all benefit from steel fibres. Mixing and dispersion issues can be caused by severe mixes with a small number of particles and/or an uneven sieve curve at a greater fibre volume. Steel fibres will almost certainly not be used to their full potential in any concrete if they are just mixed in. Adjustments to the concrete mix may be required based on the type and number of fibres.
Increasing the fines’ content
altering the grading curve and
adjusting the amount of plasiticizer.
Typical fibres with regular strength wire are sufficient for concrete strength up to an actual strength of roughly 8000 psi (majority of applications). To avoid brittle behaviour, higher concrete strengths than middle strength or high strength fibres may be necessary. A preliminary mix/pump test is recommended if particular cements, aggregates, or admixtures are employed (which is rarely the case).
Q.Will the steel fibers clump together in the mix?
A.Fiber balling can be avoided with the use of a correctly prepared concrete mix. Glued fibre technology was created to avoid the possibility of fibre balling in fibres with a high l/d (aspect) ratio (indicating high performing fibres). Glued fibre bundles will distribute equally on a “macro level,” and the bundles will separate into individual fibres during mixing. In essence, the glued bundle lowers the aspect (l/d) ratio of the fibres temporarily to facilitate mixing. This is how balling can be efficiently avoided and a homogeneous mix of high-performance steel fibre reinforced concrete achieved.
Q.What are the effects of steel fibers on concrete mix design?
A.Steel fibre mix designs are comparable to those utilised in regular concrete mix designs. Local guidelines include acceptable aggregate gradations and mix amounts. Shrinkage can be reduced by using the largest practical top size aggregate and a well-graded combined aggregate blend rather than a gap-graded blend. Steel fibres may cause a reduction in slump due to their rigidity. This may not always imply a decrease in workability. Mid-range water reducers are typically utilised to improve workability for mixtures containing more than 30 to 40 pounds per cubic yard of steel fibres, depending on ambient temperatures and placement method.
Q.What effect do steel fibers have on concrete slump?
A.Steel fibres will lessen the apparent slump by 1” to 3” at common dose rates of 25 to 65 lb/yd3. However, this does not always imply a decrease in workability. The SFrc’s workability is restored with the use of vibratory consolidation.
Q.Is it possible to pump steel fiber reinforced concrete?
A.Yes, but depending on the steel fibre dosing rate, ambient temperatures, and hose length, expect a 0.4” to 1.2” droop loss via the hose. To improve workability and ease of flow via pump lines, a midrange water lowering agent (MrWr) is widely utilised. In some circumstances, high-range water reducers (HrWr) may be necessary. A hose with a diameter of 4” is usually required.
Q.Is steel fiber prone to rusting?
No, not for indoor applications like tunnels and warehouses. Minor rusting may occur in outdoor applications such as pavements. While individual fibres corrode at the surface, discoloration of the concrete surface does not develop, according to experience in highways and industrial pavements. Even when individual fibre corrosion is present, overall aesthetics and serviceability are maintained. applications for indoors Under normal climatic conditions, surface fibres in typical indoor tunnels or industrial floor applications remain bright and lustrous.
Applications in the Outdoors Without cracks—experience has shown that concrete with a 28-day compressive strength of above 3000 psi, mixed with conventional water/cement ratios, and installed with methods that ensure appropriate compaction, limits fibre corrosion to the concrete’s surface skin. There is no corrosion propagation more than 0.008” beneath the surface when surface fibres corrode. There is no continuous path for stray or induced currents between different sections of the concrete since the fibres are short, discontinuous, and rarely touch. applications for the outdoors Cracks in concrete can cause corrosion of the fibres flowing through the crack, according to laboratory and field testing of cracked SFrc in chloride-containing settings. Small cracks (crack widths less than 0.008”), on the other hand, do not allow corrosion of steel fibres to pass through. The consequences of localised corrosion are not structurally significant if the cracks are broader than 0.008” and restricted in depth.
Q.Do fibers cling to cast-in-place forms after they are removed?
Only fibres can emerge from shapes that have a junction. They are not permitted to protrude from the centre of a shape. If the joints are caulked before the concrete is placed, this can be reduced. However, calking every joint is not always practicable. The amount of projecting fibres is determined by the joint accuracy and fibre dosage.
More fibres will be caught in wider joints than in tighter ones. The fibres can be readily hammered down with a hand sanding block or a small angle grinder when the formwork is removed.
Q.When does cast-in-place SFRC use internal vibration and when does form vibration?
Internal vibration is the most common method of concrete consolidation for cast-in-place concrete. In the precast business, form vibration is commonly used.
After steel fibre concrete is cast into form work, a small amount of vibration helps keep the fibres from touching the forms and therefore being visible when the forms are removed. The forms are vibrated to consolidate the concrete during the casting of steel fibre reinforced precast constructions, for example. As a result of this activity, the structures’ surfaces are essentially fiber-free. As a result, allowing a brief time of form vibration in all cast-in-place constructions, as well as internal vibration where possible, will result in the best finish.
Q.Can SFRC be cast against water proof membranes without any problems?
There have never been any reported failures of the plastic liner due to fibre punctures. The abrasion caused by sharp particles during concrete laying is just as dangerous to the liner as the steel fibres. Following implantation, the fibres tend to move around and re-orient themselves during vibration, relieving any pressure imposed on the liner by a specific fibre. Cast-in-place and sprayed shotcrete in direct contact with water proof membranes are used in several SFrc projects.
Q.Can electrical shock occur because concrete is electrically conductive?
Q.Do finishers face any safety hazards?
Q.What are the differences between various steel fibers?
Q.What does residual strength mean?
Q.Do steel fiber reinforced concrete forms and tools wear out more quickly than plain concrete?
Q.What are the advantages of steel fibres against synthetic microfibers?
Q.What advantages do steel fibres have over synthetic macro fibres?
Steel fibres that are mechanically anchored have been demonstrated to be effective as reinforcement, even in structural applications. Steel fibres are formed of a material with well-known engineering qualities such as e modulus, Poisson’s ratio, tensile strength, and creep resistance. Steel’s e-modulus is higher than that of concrete. As a result, the steel fibres soak up the pressures fast and have an immediate impact on the cracking process. Steel fibre reinforced concrete has a strong long-term load carrying capacity. AStM A820 is the material specification for steel fibres. Macro synthetic fibres come in a wide range of colours and have a wide range of material qualities. AStM does not have a material definition for macro synthetic fibres. The e-modulus of all macro synthetic fibres is lower than that of concrete, and their tensile strengths are also lower. As a result, macro synthetic fibres require a specific crack width to engage in the concrete, and only moderate post-crack strength values can be produced. Macro synthetic fibres are also susceptible to creep, which reduces or eliminates the fiber’s long-term loading capability. With higher ambient temperatures, the rate of creep can be accelerated.
When considering reinforcement, there are at least four elements to consider: modulus of elasticity, Poisson’s ratio, tensile strength, and creep.
Q.Steel fibres are more expensive per pound than rebar or mesh, therefore why should I pay more for steel fibres?