Set Control & Hardening Accelerators - Concrete Reinforcing Fibers

SikaFiber & Fibermesh Product Technology

Fibers are an ideal ingredient for use in concrete and mortars as a method for improving these materials where they may otherwise have weaknesses. Concrete fibers reduce shrinkage crack formation and crack widths whilst also increasing performance in energy absorption and fire resistance. Additional benefits such as reduction or elimination of reinforcing steel and increased durability can also be seen. Applications with concrete fibers have expanded and new fiber materials are also increasingly capable of replacing traditional fibers such as steel and glass.

In 2018, Sika® has acquired the global Concrete Fibers business from Propex Holding, LLC, which includes a US plant manufacturing synthetic fibers for use in concrete reinforcement, sales operations across Sika’s geographical regions, and Fibermesh® a strong brand in FRC. The acquired business was the perfect addition to Sika’s concrete admixture product lines making Sika® a true single source supplier for all ready mix and precast concrete applications. With the addition of Fibermesh®,Novomesh®, Novocan®, and Enduro® to Sika’s product portfolio, Sika® can better supply the needs of concrete customers, engineers, general contractors, owners, and architects.

• Reduced incidence of early age plastic shrinkage cracking
• Improved load capacity and ductility
  
• Protection against freeze-thaw cycles
  
• Better cohesion in the fresh concrete
  
• Increased abrasion resistance
  
• Higher flexural and shear strengths
  
• Reinforcement replacement
  
• Joint Extension
  

Concrete fibers have an innumerable amount of applications in concrete construction. Not only will benefits in fresh and hardened properties be seen, secondary benefits will be made as well. By reducing or replacing traditional meshes and steel reinforcement, labor costs will be reduced and construction schedules can be accelerated. Safety is increased by reducing the chances of tripping or impalement by traditional steel reinforcement. With concrete fiber being integral (well mixed) throughout the concrete, there is no opportunity for reinforcement to end up in the bottom of your slab.

• Integral Reinforcement
• Increased safety
• Less opportunities for callbacks
• Long term durability increase
• Reduction in labor for placement of reinforcement

The first step to choosing the right fiber is to understand the type of fiber required for your application. The main standards for fiber reinforced concrete are ASTM C 116 and EN14889. ASTM C 116, Standard Specification for Fiber Reinforced Concrete, outlines four (4) classifications for fiber reinforced concrete:

• Type I - Steel fiber-reinforced concrete or shotcrete (ASTM A820)
• Type II - Glass fiber-reinforced concrete or shotcrete (ASTM C1666)
• Type III - Synthetic fiber-reinforced concrete or shotcrete (ASTM D7508)
• Type IV - Natural fiber-reinforced concrete or shotcrete (ASTM D7357)

Micro fibers have a diameter that is less than 0.3 mm. Micro fibers are either monofilament or fibrillated. Micro fibers should be used for plastic shrinkage control (cracking that can occur in the first 24 hours of concrete cure), impact protection, and reduction of explosive spalling during a fire. The fibrillated micro fibers are often used in replacement of the lightest welded wire fiber (6x6 W1.4/W1.4) for temperature and shrinkage characteristics.

Structural macro fibers have a diameter greater than 0.3 mm. Macro fiber are used as a replacement for temperature and shrinkage reinforcement (WWF) or as structural reinforcement in concrete or shotcrete. Macro fibers are used where an increase in residual (post-cracking) flexural strength is required (ASTM C1609 or EN14845).

Steel fibers may be collated (glued) together in a clip. The collation of the fibers does not improve performance of the fiber reinforced concrete. Collated fibers improve the ease of mixing of high aspect ratio fibers. Collated fibers are added to the concrete mix, the bundles are spread throughout the concrete. Continued mixing action breaks apart the clips to let the individual fibers separate quickly throughout the mix.

Fiber performance is influenced by three characteristics; tensile strength, aspect ratio (calculated as the length/diameter) and anchorage (hooked, crimp, emboss, fibrillation, etc.). One characteristic does not outweigh another; all three items have to work together for optimal performance.

Fiber reinforced concrete is a composite material and therefore, all fibers are tested in the concrete to prove their performance.

Fibers begin to function in a structural supportive manner when the concrete matrix starts to crack, just like traditional reinforcement. The crack has to occur for the load to switch from the concrete to the reinforcement. The fibers then provide ductility and support by bridging cracks and thus providing post crack strength to the concrete.

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