Most frequent questions and answers
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 CFS’s brochure titled Mixing, Placing and Finishing SFRC 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. CFS’s 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.