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  • 7/8/13 Performance of Hybrid Fibre Reinforced Concrete

    www.nbmcw.com/articles/concrete/26928-investigation.html 1/12

    Performance of Hybrid Fibre Reinforced Concrete UnderCompression and Flexure

    This paper focuses on the experimental investigation carried out on hybrid fibre reinforced concrete

    (combination of hooked end dramix steel fibre and a non-metallic recron3s - polyester fibre) up to a

    total fibre volume fraction of 0.5%, 1%, 1.5% and 2% which was prepared using normal mixing,

    compaction and curing conditions. The workability studies and the mechanical properties namely,

    compressive strength on cubes and cylinders, modulus of rupture, modulus of elasticity, flexural

    strength, the loaddeflection curve and stress-strain relationships were studied for concrete prepared

    using different proportions of hybrid fibre combinations hooked end dramix steel fibre and recron 3s

    fibre. Pulse velocity test is conducted at different ages to assess the quality of concrete. It is found that

    all concrete specimens could be classified under good quality. As a result of hybridization it has the

    ability to arrest cracks, increased extensibility and tensile strength, both at first crack and at ultimate,

    particular under flexural loading; and the fibres are able to hold the matrix together even after

    extensive cracking. The net result of all these is to impart to the fibre composite pronounced post

    cracking ductility which is unheard of in ordinary concrete. The transformation from a brittle to a ductile

    type of material would increase substantially the energy absorption characteristics of the fibre

    composite and its ability to withstand repeatedly applied, shock or impact loading. The eect of steel

    bers and recron 3s on ordinary concrete is investigated. The flexural properties were studied using

    two point bending tests on prism specimens as per codes recommendation. Fibre addition was seen to

    enhance an increase in flexural strength and ductility, respectively. Addition of hybrid fibres generally

    Contributed towards the energy absorbing mechanism (bridging action) whereas, the non-metallic

    fibres resulted in delaying the formation of micro-cracks.

    Dr.A.S.S.Sekar, Asst. Prof. Dept. of Civil Department,

    D.Kesavan, M.E. (Structural Engg) A.C College of Engg & Tech, Karaikudi.

    Introduction

    Fibre reinforced cement and concrete materials (FRC) have been developed progressively since the

    early work by Romualdi and Batson in the 1960s. By the 1990s, a wide range of fibre composites and

    FRC products were commercially available and novel manufacturing techniques were developed for use

    with high fibre content. In parallel with the commercial development of FRC materials and products, an

    extensive research programme was undertaken to quantify the enhanced properties of FRC materials

    and more specifically to allow comparisons to be made between various types of fibres.

    Fibre reinforced concrete (FRC) is a composite material consisting of cement, sand, coarse aggregate,

    water and fibres. In this composite material, short discrete fibres are randomly distributed throughout

    the concrete mass. The behavioral efficiency of this composite material is far superior to that of plain

    concrete and many other construction materials of equal cost. Due to this benefit, the use of FRC has

    steadily increased during the last two decades and its current field of application includes: airport and

    highway pavements, earthquake-resistant and explosive-resistant structures, mine and tunnel linings,

    bridge deck overlays, hydraulic structures, rock-slope stabilization, etc.

    Extensive research work on FRC has established that addition of various types of fibres such as metallic

    and non-metallic fibers like (steel), glass, synthetic, and carbon, in plain concrete improves strength,

    toughness, ductility, post-cracking resistance, etc. These dramix hooked end steel fibres and recron3s

    fibres can effectively be used for making high-strength FRC after exploring their suitability. In this

    investigation, therefore, an attempt has been made to study the feasibility of using two kinds of fibres

    for making FRC. Cementitious materials are generally quite brittle, with relatively low strength and

    strain capacity under tension. Hence a hand-laid steel bar reinforcement is usually necessary to

    increase tensile strength. For low reinforcement levels, the partial or even complete replacement of this

    conventional reinforcement by fibers is an advantageous alternative. For special applications, highly

    ductile fiber reinforced cementitious materials like ultra-high performance concrete or engineered

    cementitious compo- sites have been developed. Fibers may also be applied to control the detrimental

    effects of shrinkage. A significant reduction in crack width and crack spacing is possible, especially at

    early ages. They possess a high tensile strength (>5001000 MPa) and a high elastic modulus (>200

    GPa) and are available at relatively low costs. The high modulus, which is much higher than the one of

    concrete (3040 GPa) or cement paste (1520 MPa), prevents the fiber from stretching or cross

  • 7/8/13 Performance of Hybrid Fibre Reinforced Concrete

    www.nbmcw.com/articles/concrete/26928-investigation.html 2/12

    contraction upon load, which hence leads to a good fibermatrix bond and smaller crack widths. A

    variety of tests have been performed to determine the actual characteristics and advantages of brous

    materials. The addition of steel fibers help in converting the brittle characteristics to ductile ones. To

    faster the compressive strength without sacrificing the ductility, a strategy adopted is to add discrete

    steel fibers as reinforcement in concrete. It is obvious that the behavior of HFRC depends on the

    orientations, distributions, aspect ratios, geometrical shapes and mechanical properties of fibers in

    concrete mixtures. The orientations and distributions of fibers affect the properties of FRC such as

    toughness, strength, ductility and crack width. A compromise to obtain good fresh concrete properties

    (including workability and reduced early-age cracking) and good toughness of hardened concrete can

    be obtained by adding two different fiber types, which can function individually at different scales to

    yield optimum performance. The addition of non-metallic fibres results in good fresh concrete properties

    and reduced early age cracking.

    The beneficial effects of non-metallic fibres could be attributed to their high aspect ratios and increased

    fibre availability (because of lower density as compared to steel) at a given volume fraction. Because of

    their lower stiffness, these fibres are particularly effective in controlling the propagation of micro cracks

    in the plastic stage of concrete. The hybrid combination of metallic and non-metallic fibres can offer

    potential advantages in improving concrete properties as well as reducing the overall cost of concrete

    production. It is important to have a combination of low and high modulus fibres to arrest the micro and

    macro cracks, respectively. Another beneficial combination of fibres is that of long and short fibres. Once

    again, different lengths of fibres would control different scales of cracking. The objective of this study

    was to evaluate the mechanical properties of various fibre reinforced concrete systems, containing

    individual steel fibres and hybrid combinations of steel and non-metallic fibres. The total dosage of

    fibres was maintained at 0.5%, 1%, 1.5% & 2% primarily from the point of view of providing good

    workability. A comparative evaluation of various hybrid fibre concretes was made based on hardened

    concrete properties compressive, split and flexural strengths, and flexural toughness. Concrete is a

    quasi-brittle material with a low strain capacity. Fibers provide mechanisms that abate their unstable

    propagation, provide effective bridging, and impart sources of strength gain, toughness and ductility.

    Materials & Mix Proportion

    Materials

    The materials used in this experimental investigation are:

    1.Cement: Ultra Tech 43 grade Fly Ash based Portland pozzolana Cement (PPC) (IS 1489 PART I 1991).

    2. Fine aggregate: Locally available river sand Zone II having a specific gravity of 2.43, fineness

    modulus of 3.425,

    3. Coarse aggregate: crushed granite coarse aggregate of maximum size 20 mm and having a specific

    gravity of 2.99, fineness modulus of 7.54,

    4. Water: water available in the college campus conforming to the Requirements of water for concreting

    and curing as per IS: 456 2000.

    5. Fibres:

    (i) Commercially available Dramix Hooked End Steel Fibre having properties of

    Length : 30mm

    Diameter : 0.5mm

    Aspect ratio : 60

    (ii) Commercially available Recron3s Fibre

    Recron 3s fibres is Polyester staple fibres having properties of

    Length : 12mm

    Diameter : 0.036mm

    Aspect ratio : 334

    Mix Proportion

    Mix design as per IS Code method Concrete proportion used for the study

  • 7/8/13 Performance of Hybrid Fibre Reinforced Concrete

    www.nbmcw.com/articles/concrete/26928-investigation.html 3/12

    MATERIALS Cement Fine aggregate Coarse aggregate Water

    Kg/m3 348.33 551.27 1316.22 191.6

    Ratio 1 1.584 3.782 0.55(w/c)

    Grade of concrete = 20N/mm2

    Water cement ratio = 0.55

    Experimental Program

    Specimens

    In this experimental work, conc