Steel fibers are thin filaments of steel often used for their high tensile and abrasive properties.
Unlike welded wire reinforcement or rebar, which is specifically located in a single plane, steel fibers are distributed uniformly throughout the concrete matrix. The primary function of steel fibers is to modify micro and macro cracking. While rebar are designed to bridge cracks once they appear. Steel fibers are used to control cracking so that the composite will behave in a manner that we want rather than what conventional reinforcement allows. Steel fibers go to where the cracks originate while conventional reinforcement lets the cracks grow until they reach the reinforcement
A few key attributes of concrete improved by steel fibers can be highlighted as:
• Increased flexural strength.
• Extreme fatigue resistance.
• Greater impact resistance.
• Less porous.
• More effective composition against and spalling.
• Elimination of shrinkage cracks.
• Excellent resistance to corrosion.
When added to the concrete mixture, steel fibers enhance many of concrete’s mechanical characteristics like toughness, durability and tensile strength. It also helps in eliminating shrinkage cracks.
Steel fibers can be introduced into the concrete at the batch plant or job-site. Consult ACI 544.3R or FIBMIX technical sheet for more details on the proper methods of adding fibers to concrete.
When fibers were first introduced to the market, balling was an issue due to the high aspect ratio and long length. Our standard fibers have aspect ratios of less than 50 and are either 1” or 1 1/2” in length. As the aspect ratio increase above 50 or the length exceeds 1 1/2”, the tendency of fibers to ball increases. This is the reason some of our competitors must collate their fibers to reduce the chances of fiber balls.
Pumping has been used to transport SFRC on many projects. In general a mixture that will pump satisfactorily without fibers will pump with fibers. In pumping SFRC, the chute from the ready mix truck should be 12” above the grate on the hopper. This will prevent the fiber from bridging the gaps in the grate and ensure a steady flow of concrete to the pump. The grate should never be removed from the hopper.
Both can be used on a SFRC floor. Shake-on toppings can act as a fiber suppressor and limit the number of fibers on the surface. If liquid hardeners are used the floor should be moist cured for 7 days and allowed to air dry per manufacturer’s recommendations before installing the liquid hardener.
Laser Screeds and steel fibers are an ideal combination for today’s floors. The Laser Screed improves the floor flatness and increases productivity while the steel fibers improve the performance of the slab. Another advantage is that the steel fiber reinforcing is included in the concrete mix and does not impede the movement of the Laser Screed. This is not true with conventional reinforcement as it must be “chaired” in position before the concrete is deposited on the subgrade. This decreases the mobility of the Laser Screed and makes it almost impossible to get the mesh in the proper position.
While there is always a chance of a fiber being on the surface of the slab, following the finishing techniques discussed in ACI 544.3R will keep them to a minimum. FIBMIX fibers are designed to be the best finishing fibers on the market. To quote TR-63, “While high-quality surfaces can be achieved with any fiber type, small slit sheet steel fibers tend to be easier to finish.” In fact many of our competitors recommend that a shake-on hardener should be used as a fiber suppressor to hide fibers which are on the surface of the slab.
No, there are no safety concerns to be imposed with good workplace safety practices in place of steel fibers. For more information, please refer to our safety data sheets.
The two of the primary purposes for reinforcing slabs-on-ground are for shrinkage and temperature control. SFRC is an economical way of controlling cracks due to changes in temperature or volume changes as the concrete ages. For rebar to control these cracks positioning is important. Positioning is important when using WWR or rebar. When on layer of reinforcement is used, it should not be allowed to be below mid depth. In general, positioning at ⅓ the depth below the surface is sufficient. This is extremely difficult with the common practice of using a Laser Screed to strike-off the concrete. This problem is eliminated with the use of SFRC since the fibers are randomly distributed throughout the concrete.
No. If you use steel fibers, and if the concrete mix is designed so that it would have good workability without fibers, you should expect no unusual difficulties in placing and finishing.
No fibers in concrete are purely mechanical in nature and, therefore, have absolutely no impact on the setting time of concrete. The setting time is a chemical function impacted by factors such as time and temperature. Water content and chemical admixtures also have an influence on set time.
No Steel fiber reinforced concrete has the advantage of reduced settlement and more uniform bleeding. To the uninformed eye, this may make the concrete look drier and unnecessary additional water. The typical saturated appearance of mixing water coursing to the surface in non-fiber concrete is absent when Steel fiber reinforcement is employed. Workability is not affected with standard application rates of fiber reinforcement and no additional water is needed.
Yes Steel fiber reinforced concrete develops an isotropic quality, having a uniform quality cross section, which allows the concrete to stiffen and set from the inside out.
Typical reinforced concrete with steel fiber contains less than 0.5% vol. Steel fibers and just over 0.75% vol. These fibers are discontinuous and are not interconnected. Due to the addition of steel fibers, tests show only a slight decrease in electrical resistivity. However, there is still substantial resistance to current flow. Much more dominant are the effects of moisture content and aggregate composition than the addition of steel fibers.
Steel fibers and vice versa are not a replacement for synthetic micro fibers. Both types of fibers provide very different concrete properties so that the fields of applications do not overlap. Both types of fibers can be used complementary rather than a substitute. While steel fibers provide post crack resistance and thus act as reinforcement, synthetic micro fibers reduce cracking due to plastic shrinkage and improve concrete fire resistance. They have no reinforcing effect.
For casting inside, the most commonly used choice for consolidating the concrete is innervibration. In prefabricated sector, form vibration is usually used. When removing the shapes.For instance, strengthened precast buildings are vibrated during casting of steel fiber to strengthen the concrete.This action results in an almost fiber free surface of the structures. So allowing a short period of form vibration in the all cast-in-place structures, in addition to internal vibration where possible, will provide the best finished surface.
Only from forms where there is a joint can fibers protrude. In the middle of a form, they can’t protrude. If the joints are caulked before concrete placement, this can be minimized. It is not always possible to calculate each joint, however. The number of fibers protruding is a function of joint accuracy and fiber dosage.
Wider joints are capturing more fibers than tighter joints. The fibers can be knocked down quickly with a hand sanding block or a small angle grinder after the formwork is removed.
Only from forms where there is a joint can fibers protrude. In the middle of a form, they can’t protrude. If the joints are caulked before concrete placement, this can be minimized. It is not always possible to calculate each joint, however. The number of fibers protruding is a function of joint accuracy and fiber dosage.
Wider joints are capturing more fibers than tighter joints. The fibers can be knocked down quickly with a hand sanding block or a small angle grinder after the formwork is removed.
Contraction joints can be installed using either a wet saw or an early entry saw. For wet saws the depth should be ¼ the depth for slabs less than 6” thick. For slabs over 6” thick or slabs with over 40 pounds of steel fiber per cubic yard of concrete, the saw cuts should be ⅓ the depth. For early entry saws, the manufacturer’s recommendation should be followed.
No plastic liner faults have ever been recognized owing to fiber punctures. During concrete positioning, the abrasion from sharp aggregates presents as great a risk to the liner as do the steel fibers. After positioning, the fibers tend to shift and reorient during vibration, which relieves the stress of an individual fiber on the liner produced during placement.Many SFRC projects are built with cast-in-place and sprayed in direct contact with waterproof membranes.
Steel fiber concrete compresses the schedule of construction, allows alternative methods of construction or design solutions and increases durability. The higher costs of steel fibers are overcompensated by the savings when a project is delivered faster with less effort and labor.
Highways and roadways. Shortcrete in mining/tunneling, explosive and impact resistance structures, industrial floorings etc.
No, power blade trowels and disc floaters are widely used to provide the blades with a smooth and even surface without excessive wear.
Yes, dowels are required at construction joints. Dowels at contraction joints are typically not necessary, due to aggregate interlock and steel fibers bridging the joint. Dowels may be needed at contraction joints if spacing exceeds industry standards.
Yeah, add steel fibers, after all other materials are in the truck already. Set the truck mixer to charge speed and add fibers at a pace of no more than 100 pounds / minute. Mix with the charging speed for a total of 40 revolutions.
Steel fibers come in several shapes and sizes, each with various levels of efficiency. It is recommended that each potential supplier be asked to provide approved test results for their goods by one of the globally recognized criteria in order to allow an objective comparison between different products and to ensure the appropriate selection is achieved.
SFRC can give considerable cost savings, depending on the quantity and nature of the reinforcement in conventional design. Steel fiber’s superior output also reduces maintenance over the life of the projects, thereby reducing project costs.
Forcetech team can help you to know the perfect dosage of our FIBMix Steel fiber according to the project design
Dosage levels for SFRCs depend on the application of the particular properties needed. Initially 40 lb about 100 pounds. Should meet most criteria. Lower dosages continue to be used when replacing traditional mesh wire. SFRC can satisfy the most exacting requirements at higher concentrations.
Adding steel fibers, particularly at higher levels, will give rise to an apparent loss as measured by the slump test. It is recommended that a superplasticizer be added to increase the slump 1-2″ higher than the final desired target slump.
Synthetic fibers help control plastic shrinkage cracking, which can occur in the very early stages of concrete drying. Steel fibers reinforce the concrete in its’ hardened state, thereby improving its’ strength and durability.
The significant difference between steel and synthetics is their respective Young’s modulus and tensile yield strength. Steel fibers have a sufficiently high modulus of elasticity and tensile strength to assume excess strain across a crack and hold it tightly.
Contraction joints are widely used to shape both wet-cut and early input saws. Cut the joints, if possible, to 1/3 slab depth according to ACI 302.1R guidelines. In general, restrict joint spacing for unreinforced concrete to the ACI and PCA guidelines.
We provide advice and technical support to all our clients. We share the practical experience of our partners, as well as confirm it with the test reports conducted in higher education institutions, scientific structures, accredited laboratories, etc.
Basalt fiber in concrete helps to prevent the appearance of micro cracks, increase the strength of concrete, and increase the durability of the structure and guarantees economic benefits.
The amount of fiber to be added to the concrete depends on the purpose you have. If the task is only to remove the microcracks, then 1 kg per m3 of concrete will suffice. If you want to increase the strength of concrete, then the amount of fiber depends on the concrete grade that you use: the higher concrete grade, the more fiber should be added to get the desired result. It is worth remembering that there is a point of saturation of concrete with fiber, that is, adding a large amount of fiber will not make any sense as growth will cease. In more detail, we consult each client individually, taking into account all the factors of the case.
Basalt fiber, unlike metal fiber, does not require extra labour for cutting from the surface, and polishing of basalt reinforced concrete.
Glued/ collated steel fibers are hard drawn, low carbon, high tensile steel fibers of specific length and diameter, glued together using water soluble glue. Steel fibers are added to concrete and can replace partially or completely the conventional reinforcement. Concrete made using steel fibers are called “steel fiber reinforced concrete “- SFRC. Typical dosage of steel fibers in concrete varies from 15 to 45 kgs/m3. In structural applications, higher dosages can be used to provide very high endurance properties. Glued steel fibers provide crack resistance, shear strength, fatigue resistance, impact resistance, flexural strength and post crack ductility.
The hooked ends of the glued steel fibers anchor itself firmly in the concrete matrix. These help in absorbing more deformations, providing strength and stability to concrete. The glued steel fibers are more or less evenly distributed in the concrete matrix. Typical spacing between two fibers is 10 to 25 mm. In the event of minor crack initiation, the steel fibers block them at the initiation stage itself and prevent it from developing into major cracks.
Loose steel fibers are supplied loose. They may not have uniform size and can be inconsistent in tensile strength. The major disadvantage of loose fibers is its tendency to clump together, forming fiber balls. Loose fibers also tend to occupy more volume when packed. Glued steel fibers are cold drawn and stuck together by water-soluble glue. Glued steel fibers are compact and tend to disperse readily and integrate into concrete, without forming balls. Since glued steel fibers are more compact, they occupy less space when packed.
Steel fibers can replace traditional reinforcement for non-structural applications viz. Floorings, highways, airstrips etc. For structural applications, complete ductility is required to avoid collapse after cracking, i.e. The structure should have a skeleton to support it; hence rebars are mandatory. In case of elements with low to medium bending movements, like slabs, it is possible to eliminate wire mesh substituting it with glued steel fibers. However, beams & beam-column joints can be additionally reinforced with fibers providing enhanced resistance against cyclic loads and higher shear strength.
When compared to a conventional concrete slab, slab thickness can be reduced up to 25% using steel fibers with dosages as low as 15 kg/m3. Detailed design manual has to be referred, and software needs to be adopted.
Glued steel fibers come with a small sectional area, and the concrete envelops it by forming an alkaline membrane, which prevents corroding. Since the fibers inhibit any major crack formation, the exposure of fibers is only limited to the concrete surface. Hence the chances of corrosion are very negligible.
Plate tests measure ductility. Concrete by nature is a brittle material. It exhibits elastic behaviour until cracking and then collapses completely. Rebars and fibers are added to support and overcome this complete collapse. These reinforcements ensure that load-bearing capacity is not totally lost after cracking. Full ductility means the cracked portion exhibits higher resistance than un-cracked section; while partial ductility means the cracked portion continues to offer resistance to load. Post cracking ductility can be full or partial depending on the fiber dosage.
The main parameter is mixing time. 1 minute per meter3 of concrete is sufficient to disperse the glued steel fibers. Give a minimum mixing time of 5 minutes at a full rotational speed. Never add glued steel fiber as the 1st ingredient. It may be added during or towards the end of the mixing cycle.
By the addition of glued steel fibers, the wet concrete stiffens a bit. In technical terms, there is a reduction in a slump. It is advisable to add admixtures or super plasticizes to overcome this slump. Correct dosage of super plasticizers can be ascertained by trials.
Recommended dosages are 15 to 60 kg/m3 of concrete. This depends on the criticality of the application and the ductility required. Structural engineer is the best judge to decide the optimum dosage. For structural applications, the dosage could be as high as 100 kg/ m3. Forcetech Team can help you to choose the right dosage of our FIBMIX steel fiber.
The dosage is best determined when the concrete if fresh and before it is laid. This allows corrections to be made in the concrete mix. As a practice, ten lots of the concrete mix need to be sampled out for analysis. The aggregates can be washed out, and the steel fibers can be extracted with a magnet, dried and weighed. After the concrete has hardened, the samples can be drawn only by drilling. This process is not only cumbersome, but the results are also not accurate as the fibers tend to get crushed. Other instrumental methods can be employed, but these are costly.
Steel fibers can be added during the process or after batching of concrete. However, steel fibers should never be dosed as the 1st ingredient. These can be added using conveyor, blasting machine or manually into the mixer. Adequate safety precautions need to be taken while handling the product.
Yes, it does. Steel fiber reinforced high-performance concrete can undergo large displacements without developing wider cracks. It imparts high ductility, which is one of the essential properties of beam-column joints. Addition of fibers decreases the rate of stiffness degradation appreciably when compared to structures without fibers. Load carrying capacity and resistance to cyclic loads are enhanced remarkably using steel fibers.
Typical fiber content is 0.5 to 2.5% by volume of concrete. For typical slab application, there could be around 42% cost savings. The cost impact will also depend upon the glued steel fiber dosage recommended by the structural engineer. Since FIBMIX glued steel fibers can wholly or partly replace rebars in non-structural applications, there are significant cost savings on material alone. Moreover, glued steel fibers can save time and labor. There are immense benefits by way of improved fatigue resistance, crack resistance, anti-seepage, ductility and impact resistance.
Steel fibers are in use for more than 30 years in structural & other applications worldwide. Unfortunately, there are no standards available for structural SFRC in India. The situation is no better in other countries. The only countries that have standards for structural SFRC are Austria & now Germany. ASTM A 820-04 [1] and En 14889-1:2006 [4] categorizes steel fibers based on the manufacturing process and their base materials.
Wire-guided vehicles follow a cable embedded into the floor. For embedded steel to affect the wire guidance, the mass of steel must be substantial, and it must lie very close (almost touching) the wire. Small, randomly distributed steel fibers do not meet the conditions that would cause trouble for the wire guidance. Steel fibers have been used successfully on many of the very narrow aisle applications.
Laser screeds and steel fibers are an ideal combination for today’s floors. The laser screed improves the floor flatness and increases productivity while the steel fibers improve the performance of the slab. Another advantage is that the steel fiber reinforcing is included in the concrete mix and does not impede the movement of the laser screed. This is not true with conventional reinforcement as it must be “chaired” in position before the concrete is deposited on the subgrade. This decreases the mobility of the laser screed and makes it almost impossible to get the mesh in the proper position.
No. FIBMIX steel fibers we produce and recommend are used regularly without any dry shake.
Not without risk. The design recommendations endorsed by Forcetech are based on the use of FIBMIX type of fibers, 1-inch long. Other steel fiber types and lengths could be less effective in controlling and preventing cracks. Other types could also make the concrete harder to place and finish, and might result in more visible fibers at the floor surface.
An accurate finishing according to national standards and regulations is a must despite the use of FIBMIX fibers. This process is crucial for a satisfying result and is not influenced by adding fibers.
The macro fiber content can practically only be determined in fresh concrete. At least 10 liters of concrete are necessary for washing out the macro fibers. The low specific weight of the synthetic fibers allows them to be skimmed off the surface of the water, then after drying, they are weighed and thus the added quantity approximately determined. In hardened concrete it is practically impossible to determine to the amount of fiber metered, since breaking and crushing the concrete sample also damage the fibers and thus, they can no longer be reliably measured. The absence of the reflecting property in the synthetic material means that x-ray techniques also cannot be used. Optical testing can only be carried out using an expensive instrument and subsequent data analysis.
In the case of jointless floors, attention must be paid to edge stresses occurring due to increased shrinkage stresses. Steel joint profiles along the outermost edges and partial edge reinforcement should be included. A further decisive factor is a concrete formulation, which must consist of a suitable type of cement, an appropriate cement dosage and a tailored water-binder ratio. The addition of micro monofilament fibers (type FIBMIX Steel Fiber) can be used to effectively assist optimal shrinkage behavior. The joint pattern should be reasonable and concreting sections should be taken into consideration. Finally, however, the standardized after-treatment of the surface also contributes to the success of the construction.
Due to the large surface area in 2-dimensional slabs such as industrial floors, there is an enormous potential for evaporation of water at the concrete surface. Thus it is absolutely necessary to limit the evaporation to a minimum. Spraying on of evaporation protection or covering with plastic sheeting or a moist textile, which has to be kept constantly damp, is required for this purpose. Loss of surface concrete mixing water leads to the formation of cracks and to curling of the slab edges. Another result of inadequate after-treatment is the so-called spider-web cracks, which give rise to cracks on the surface, as the name suggests, in the form of spider webs.
Yes, it does; the consistency of the concrete is reduced. This means the concrete becomes stiffer and, depending on its use, has to be optimised with a concrete plasticiser or liquefier (avoid the addition of more water).
Compared to plain or conventional reinforced concrete, the most noticeable differences are improved ductility & post crack performance. Shorter fibers with a high fiber count offer superior first crack strength & better fatigue endurance. For ground supported slabs we highly recommend the 1″ deformed fiber with a high fiber count.
Concrete has always been unpredictable material & no methodology can eliminate cracking. Using FIBMIX SFRC offers an extremely effective means of controlling cracks. This together with proper sub-base preparation, joints & curing all essential to overall job performance
