Classifications

• • E—FIXED CONSTRUCTIONS
  • E04—BUILDING
  • E04C—STRUCTURAL ELEMENTS; BUILDING MATERIALS
  • E04C5/00—Reinforcing elements, e.g. for concrete; Auxiliary elements therefor
  • E04C5/01—Reinforcing elements of metal, e.g. with non-structural coatings
  • E04C5/012—Discrete reinforcing elements, e.g. fibres
• • E—FIXED CONSTRUCTIONS
  • E04—BUILDING
  • E04C—STRUCTURAL ELEMENTS; BUILDING MATERIALS
  • E04C5/00—Reinforcing elements, e.g. for concrete; Auxiliary elements therefor
  • E04C5/01—Reinforcing elements of metal, e.g. with non-structural coatings

Definitions

• the present invention pertains to improvements in the field of fiber reinforced cement-based materials.
• the invention relates to a metal fiber having an optimized geometry for reinforcing cement-based materials.
• All cement-based materials are weak in tension. In addition, these materials have a very low strain capacity which places them in a brittle category with other brittle materials such as glass and ceramics. It is well known that concrete and other portland cement- based materials may be reinforced with short, randomly distributed fibers of steel to improve upon their mechanical properties. It is also known that for any improvement in the tensile strength, fiber volume fraction has to exceed a certain critical value. Beyond matrix cracking, fibers form stress transfer bridges and hold matrix cracks together such that a further crack opening or propagation causes the fibers to undergo pull-out from the matrix.
• the property of interest is the overall composite toughness.
• the composite toughness although dependent on the pull-out resistance of fibers, cannot quantitatively be derived from the results of an ideal fiber pull-out test where the fiber is aligned with respect to the load direction, since in a real composite, once the brittle cementitious matrix cracks, the fibers are not only embedded to various depths on both sides of the matrix but also inclined at various angles with respect to the loading direction. Further, fibers pulling out as a bundle have a very different performance as compared to a single fiber owing primarily to fiber-fiber interaction.
• a metal fiber for reinforcing cement- based materials which comprises an elongated. substantially straight central portion and sinusoid shaped end portions.
• ⁇ c compressive strength of the cement-based material in MPa
• a f cross-sectional area of the fiber in mm 2 .
• P f perimeter of the fiber in mm.
• the sinusoid further has a wavelength L s defined by:
• L m length of the fiber central portion, and wherein 0.5 L f ⁇ L m ⁇ 0.75 L f .
• equation (1) both the ultimate tensile strength and the ductility of the fiber material as well as the compressive strength of the cement-based material are important factors in defining the optimum amplitude.
• the equation also takes into account the cross-sectional area and perimeter of the fiber. It is therefore possible to tailor the fiber geometry according to the properties of the fiber and matrix materials chosen, and ultimately to the composite toughness desired in an actual structure.
• the value of k 1 ( ⁇ c ) k 2 in equation ( 1 ) then ranges from about 6 x 10 -2 to about 7.5 x 10 -2 .
• a preferred value of k 1 ( ⁇ c ) k 2 which provides an optimum amplitude A o/opt in the concrete compressive strength range of 30-60 MPa is about 7 x 10 -2 .
• the fiber according to the invention preferably has an end angle ⁇ less than 20°, the angle ⁇ being defined by
• the angle ⁇ preferably ranges from about 12° to about 15°. Such a small end angle ⁇ prevents the fibers from undergoing balling so that there is no problem with mixing.
• the fibers of the invention which have sinusoids only at the end portions as opposed to those that have sinusoids along their entire length, such as in the case of US Patent N° 4,585,487, provide better reinforcing.
• those with deformations over the entire length transmit the entire pull-out force immediately back to the matrix through anchorage.
• the stresses are slowly transferred from the crack face to the interior of the matrix with the major transfer of forces taking place only at the extremities.
• Such a gradual transfer of stresses averts a possible crushing and splitting of the matrix at the crack face which is commonly observed in fibers deformed all along the length.
• a particularly preferred metal fiber according to the invention has a uniform rectangular cross-section with a thickness of about 0.4 mm and a width of about 0.8 mm, a length L f of about 50 mm and a length L m of about 25 mm.
• the wavelenth L s of the sinusoid at each end portion of the fiber is about 12.5 mm.
• Fiber reinforced concrete incorporating the fibers of the invention can be used in slabs on grade, shotcrete, architectural concrete, precast products, offshore structures, structures in seismic regions, thin and thick repairs, crash barriers, footings, hydraulic structures and many other applications.
• Figure 1 is a side elevational view of a steel fiber according to the intention
• Figure 2 is a load deflection plot in which the toughness of concrete reinforced with the fiber illustrated in Fig. 1 is compared with that of concrete reinforced with conventional fibers;
• Figure 3 is a graph showing the relationship between post-crack strength and beam mid-span deflection expressed as a fraction of the span for the same fibers.
• the steel fiber illustrated which is generally designated by reference numeral 10 comprises an elongated, substantially straight central portion 12 with sinusoid shaped end portions 14 and
• the coordinate system is as illustrated in Fig. 1 and A O is the amplitude of the sinusoid.
• Fig. 1 Also illustrated in Fig. 1 are the length L f of the fiber 10, the length L m of the central portion 12 and the length L S of the end portions 14,14', as well as the end angle ⁇ .
• the length L f of the fiber 10 may vary from about 25 to about 60 mm.
• the fiber geometry is optimized by giving to the sinusoid an optimum amplitude A o,opt as defined in equation (1).
• the fiber 10 has a uniform rectangular cross-section. Such a fiber may also have a circular cross-section.
• Fibers with optimized geometry at a dosage rate of 40 kg/m 3 were used in reinforcing concrete matrices having an unreinforced compressive strength of 40 MPa. Beams made from the fiber-reinforced concrete were tested in third point flexure, along with their unreinforced companions. The beam displacements were measured using a yoke around the specimen such that the spurious component of the load point displacement due to the settlement of supports was automatically eliminated.
• the resulting load deflections plots are set forth in Fig. 2, where the toughness of concrete reinforced with the fibers of the invention (F1) is compared with that of concrete reinforced with conventional fibers (F2 to F5).
• the conventional fibers investigated for comparative purpose were the following:
• E c is the elastic modulus of concrete as per ASTM C-469.
• the JSCE SF-4 technique takes the total area (elastic and plastic) under the curve up to a deflection of span/150 and converts into an equivalent post-crack strength.
• the fibers of the inventions even at a low dosage of 40 kg/m 3 lead to strengthening in the system as evident from the increase in the load carrying capacity over the plain, unreinforced matrix. Also, after the matrix cracking, the composite is capable of carrying approximately the same level of stresses as when at matrix cracking and as such very high toughness is derived. The composite behaves almost in an elastoplastic manner.
• the fiber with optimized geometry according to the invention behaves superior to existing commercial fibers and provides higher flexural toughness. It is believed that the fiber geometry fully utilizes the potential of steel and that of the cement matrix to produce an optimized composite.

Landscapes

• Engineering & Computer Science (AREA)
• Architecture (AREA)
• Civil Engineering (AREA)
• Structural Engineering (AREA)
• Curing Cements, Concrete, And Artificial Stone (AREA)
• Inorganic Fibers (AREA)
• Artificial Filaments (AREA)
• Manufacture Of Alloys Or Alloy Compounds (AREA)

Applications Claiming Priority (3)

Publications (2)

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Family Applications (1)

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• 1994
  • 1994-08-31 CA CA002131212A patent/CA2131212C/en not_active Expired - Lifetime
• 1995
  • 1995-04-21 AU AU22517/95A patent/AU688031B2/en not_active Ceased
  • 1995-04-21 EP EP95915725A patent/EP0725871B1/de not_active Expired - Lifetime
  • 1995-04-21 DK DK95915725T patent/DK0725871T3/da active
  • 1995-04-21 KR KR1019960702073A patent/KR100353732B1/ko not_active Expired - Lifetime
  • 1995-04-21 KR KR1019960702073A patent/KR960706001A/ko active Granted
  • 1995-04-21 WO PCT/CA1995/000225 patent/WO1996006995A1/en not_active Ceased
  • 1995-04-21 AT AT95915725T patent/ATE194198T1/de not_active IP Right Cessation
  • 1995-04-21 DE DE69517668T patent/DE69517668T2/de not_active Expired - Lifetime
  • 1995-04-21 ES ES95915725T patent/ES2151059T3/es not_active Expired - Lifetime
• 1996
  • 1996-04-22 MX MX9601504A patent/MX192955B/es unknown

Non-Patent Citations (1)

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