Fiber Reinforced Concrete

     Fiber reinforced concrete (FRC) is concrete containing fibrous material which increases its structural integrity.
Factors controlling performance of composites
•  Physical properties of reinforcement and matrix
•  Strength of bond between reinforcement and matrix
    Characteristics of fiber reinforced systems
    •  Fibers distributed through given cross section, reinforcement bars only placed where required
    •  Fibers are short and closely spaced, reinforcing bars are continuous
    •  Small reinforcement ratio when compared to reinforcement bars
      Reinforcement Ratio =Area of Reinforcement/Area of Concrete
      Advantages
      •  Easily placed
               –Cast
               –Sprayed
               –Less labor intensive than placing rebar
      •  Can be made into thin sheets or irregular shapes
      •  Used when placing rebar is difficult
      Disadvantages
      • Efficiency factors as low as .4 2-D(spray placement method), or .25 3-D placement (casting method)
      • Not highly effective in improving compressive strength comparison of fibre type properties
      Types of Natural Fibers
      • Sisal (Castro, 1981)
      – From AgaveSisalana in Mexico
      – Durability problems caused by chemical decomposition
      in alkaline environment
      • Coir (Balaguru, 1985)
      – Coconut husks
      – Very durable to natural weathering
      – Increases modulus of rupture of concrete (MOR)
      • Bamboo (Ghavami 2005; Rodrigues, 2006) longwood gardens
      – E is very similar to that of concrete
      – Susceptible to volume changes in water
      – Increases ultimate tensile strength and MOR
      • Jute (Balaguru, 1985)
      – Grow in India, Bangladesh, China, and Thailand
      – Increases tensile, flexural and compressive strengths,
      as well as flexural toughness
      • Akwara (Balaguru, 1985)
      – Abundant in Nigeria
      – No dimensional changes due to variations in water
      – Alkali resistant
      – No changes in flexural or compressive strengths
      – Impact strength 5 to 16 times greater than unreinforced
      cement matrix
      • Elephant Grass (Balaguru, 1985)
      – Very durable – good rot and alkali resistance as well as
      small dimensional changes
      – Increases flexural and impact strength
      History of Natural Fiber Reinforcement
      • Egyptians used straw in making mud bricks 1200-1400BC (Exodus 5:6)
      • 2500 BC asbestos fibers used in Finland to make clay pots (Active Asbestos )
      • Hornero bird native to South America builds nests out of straw and clay (Mehta, 2006)
      • Replacement for asbestosnatural fibreuses of carbon fibre Current Uses
      • Fiber Cement Board
           – Siding
           – Backer board
           – Roofing materials
           – Non pressure pipe
      • Buckeye Technologies
           – UltraFiber 500
           – Slab on grade concrete
           – Precast concrete
           – Decorative concrete
           – 85% crack reduction
           – Improved hydration
           – Improved freeze/thaw resistance
      wood pulp fibre composition
      Wood Pulp Fiber Composition untitled
      • Cellulose –(C6H12O5)n
      – n degree of polymerization
      – 600-1500 for commercial wood pulps
      – Determines the character of the fiber
      – As cellulose increases fiber tensile strength and E increase linearly
      • Hemicelluloses – polysaccharides of five different sugars
      – Easier to degrade than cellulose
      – Highly variable with fiber type
      • Lignin – complex polymer
      composition
      – Binds wood together
      – Found in the middle lamella
      – Used in concrete as a set retarder
      • Extractives
      – No physical structure
      – Give properties such as color, odor, taste
      – Some can be incompatible with concrete
       wood pulping prossess

      Fresh Properties
      • Workability
      • Setting time
      • Cement hydration
      • Fiber clumping/consolidation
      • Shrinkage
      – Plastic
      – Free
      – Drying
      • Internal curing and autogenous shrinkage
      Durability Improvement
      • Pressure treatment on fiber cement board
      • Reduction in w/c ratio to decrease porosity
      • Addition of SCMs eliminated degradation
      due to wet/dry cycles (Mohr, 2005)
      – 30%, 50% Silica Fume
      – 90% Slag
      – 30% Metakaolin 235
      – 10% SF / 70% SL
      – 10% MK235 / 70% SL
      – 10% MK235 / 10% SF / 70% SL
      • Chemically coated fibers
      Conclusions
      • Natural fibers offer many benefits for
      reinforcement
      – Low cost and abundant
      – Renewable
      – Non hazardous – replacement of asbestos
      • Can improve characteristics of concrete
      – Increase flexural strength and toughness
      – Increase impact resistance
      – Reduce shrinkage and cracking
      – Improve durability by stabilization of
      microcracks and decrease in permeability
      Future Research
      • Sources of pulp fibers
      – Thermomechanical fibers
      – Paper mill residual solids
      • Optimal fiber ratios for specific uses
      • Durability
      – Additional research on freeze thaw
      – Wet/dry cycle effects
      • SCM addition

      Follow by Email