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CE 5604 Advanced Concrete Technology

FRC – Part 1

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Fiber Reinforced Concrete (FRC)

• Geometry of fiber-reinforced materials

• Historical perspective

•BC horse hair

•1900 Asbestos fibers

•1960 FRC

•1970 search for asbestos replacement

•1970 Steel FRC, glass FRC, etc

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Fiber-Reinforced Concrete (FRC)

(Mindess et al 2003

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Fiber-Reinforced Concrete

• Fiber reinforcement is not a substitute for conventional steel reinforcement–Reinforcing bars are used to increase the load-bearing capacity of structural concrete members

–Fibers

• effective for crack control

• improve behavior of concrete under blast and impact loading, in seismic applications

• ACI 544-3R-84 states–In structural members where flexural and tensile loads will occur, such as in beams, columns, suspended floors, the conventional reinforcing steel must be capable of supporting the total tensile load.

–In applications where the presence of continuous reinforcement is not essential to the safety and integrity of the structure, e.g. pavements, the improvements in flexural strength can be used to reduce the section thickness

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Definitions of Some Terms

• Aspect ratio= fiber length/equivalent fiber diameter

(equivalent D is the D of a circle having the same cross-sectional area as the fiber)

–Typical aspect ratio: 50 – 150

• Orientation factor (or fiber efficiency factor)–Efficiency with which randomly oriented fibers can carry a tensile force in any one direction, ~0.2 to 1.0

• First crack strength–Stress corresponding to the load at which the load-deflection curve of the FRC first exhibits a significant non-linearity

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Mechanics of Fiber Reinforcement

• Stress field around an advancing crack in FRC

–Traction-free zone: crack is wide enough for all the fibers to be pulled out

–Fiber bridging zone: stresses are transferred by frictional slip of the fibers

–Microcracked matrix process zone: aggregate interlocking to transfer some stress within the matrix itself

(Mindess et al 2003)

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Controlled Crack Growth Test

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