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    CHAPTER 2

    REVIEW OF LITERATURE

    2.1 GENERAL

    The idea of adding a fibre or fibres into concrete in order to increase

    strength and fracture energy goes back to a patent dated 1918 by H. Alfsen and this fact

    is reported by Katzer [18]. Alfsen described a process to improve the tensile strength by

    adding longitudinal bodies (fibres) of different materials into the concrete. Afterwards

    several patents of different fibres and fibre geometries were proclaimed. In this chapter

    studies on the High Performance Concrete, Fibre reinforced Concrete, Hybrid Fibre

    Reinforced concrete and Ultra High Peformance Fibre Reinforced Concrete is reviewed.

    2.2 STUDIES ON HIGH PERFORMANCE CONCRETE

    High performance concrete (HPC) is a specialized series of concrete

    designed to provide several benefits in the construction of concrete structures that

    cannot always be achieved routinely using conventional ingredients, normal mixing and

    curing practices. In other words a high performance concrete is a concrete in which

    certain characteristics are developed for a particular application and environment, so

    that it will give excellent performance in the structure in which it will be placed, in the

    environment to which it will be exposed, and with the loads to which it will be

    subjected during its design life.

    It includes concrete that provides either substantially improved resistance to

    environmental influences (durability in service) or substantially increased structural

    capacity while maintaining adequate durability. It may also include concrete, which

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    significantly reduces construction time without compromising long-term serviceability.

    While high strength concrete, aims at enhancing strength and consequent advantages

    owing to improved strength, the term high-performance concrete (HPC) is used to refer

    to concrete of required performance for the majority of construction applications.

    The American Concrete Institute Committee 1993 [19] on HPC includes the

    following six criteria for material selections, mixing, placing, and curing procedures for

    concrete. They are (1) Ease of placement, (2) Long term mechanical properties,

    (3) Early-age strength, (4) Toughness, (5) Life in severe environments and

    (6) Volumetric stability

    The above-mentioned performance requirements can be grouped under the

    following three general categories.

    (a) Attributes that benefit the construction process

    (b) Attributes that lead to enhanced mechanical properties

    (c) Attributes that enhance durability and long-term performance.

    The performance requirements of concrete cannot be the same for different

    applications. Hence the specific definition of HPC required for each industrial

    application is likely to vary. The Strategic Highway Research Programme (SHRP) [20]

    has defined HPC for highway application on the following strength, durability, and

    water-cement ratio criteria.

    1. a maximum water-cementitious ratio (W/C) of 0.35;

    2. a minimum durability factor of 80% after 300 cycles of freezing and

    thawing, and

    3. a minimum strength criteria of either

    (a) 21 MPa within 4 hours after placement (Very Early Strength, VES),

    (b) 34 MPa within 24 hours (High Early Strength, HES), or

    (c) 69 MPa within 28 days (Very High Strength, VHS).

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    In general, a ―High performance Concrete‖ can be defined as that concrete

    which has the highest durability for any given strength class, and comparison between

    the concretes of different strength classes is not appropriate. This means that, with the

    available knowledge, one can always strive to achieve a better (most durable) concrete

    required for a particular application

    The use of high performance concrete results in many advantages, such as

    reduction in beam and column sizes and increase in the building height with many

    stories. In pre-stressed concrete construction, a greater span-depth ratio for beams may

    be achieved with the use of high performance concrete. In marine structures, the low

    permeability characteristics of high performance concrete reduce the risk of corrosion of

    steel reinforcement and improve the durability of concrete structures. In addition, high

    performance concrete can perform much better in extreme and adverse climatic

    conditions, and can reduce maintenance and repair costs [21, 22, 23]. Hence, HPC

    concretes are used for numerous applications and the studies related to HPC are

    discussed.

    Yogendran et al. (1987), have studied extensively High Strength Concrete

    using Silica Fume with no air entrainment to achieve compressive strength in the range

    of 50 to 70MPa in which cement was replaced by silica fume (0 to 30 percent by

    weight) [24]. The efficiency of silica fume in improving the properties of concrete was

    compared at medium and very low water cementitious ratios. Concretes with water

    cementitious ratios of 0.34 and 0.28 with and without a superplasticizer, at a constant

    slump (50 mm) and with varying slump were also investigated. It has been concluded

    that for concretes with 5 to 30 percent replacement of cement by silica fume and a

    constant slump of 50 mm there was no increase in water demand up to 5 percent

    replacement. The water required to maintain a constant slump, however, increased

    linearly as the percentage of silica fume replacement increased from 10 to 30 percent.

    A 5 percent replacement produced the highest compressive strength at 7 and 28 days.

    Replacement of 10 percent and 15 percent produced strength equal to the control mix at

    7 and 28 days. Replacement levels of 25 percent and 30 percent produced lower

    strengths at all test ages.

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    Ganesh Babu et al. (1993), has evaluated the efficiency of flyash in concrete

    over a wide range of percentage replacements (15-75%) [25]. It was concluded that at

    the replacement percentage of flyash and the water cement ratios increase the strength

    of concrete decreases. It has been reported that while concretes above 70 MPa can be

    produced with replacements up to 25% fly ash, replacements of about 75% can still lead

    to concretes of 40 MPa through suitable adjustments in water/cement ratio and other

    concrete constituents. It has been predicted that the strength of concretes varying from

    20 to 100 MPa with Ground Granulated Blast Furnace Slag (GGBS) levels varying from

    10% to 80% was found to result in a regression coefficient of 0.94, which was also the

    same for normal concretes.

    Khatri et al. (1995), has investigated the effect of different supplementary

    cementitious materials on mechanical properties of high performance concrete [26]. The

    investigation focussed on to compare the mechanical properties as well as fresh concrete

    properties of concretes containing silica fume, ground granulated blast furnace slag,

    fly ash and General Purpose (GP) Portland cement. Concrete mixes were prepared with

    GP Portland cement, high slag cement and slag cement, and also mixes were prepared

    with the addition of silica fume and fly ash The work focussed on concrete mixes

    having a fixed water/binder ratio of 0.35 and a constant total binder content of

    430 kg/m 3 . Apart from measuring fresh concrete properties, the mechanical properties

    evaluated were development of compressive strength, flexural strength, elastic modulus,

    and strain due to creep and drying shrinkage. The compressive strength of concrete

    containing GP cement, fly ash and silica fume is higher (46%) compared to the

    compressive strength of concrete containing only GP cement at the age of 28 days. It

    was also observed that the addition of silica fume significantly increases the flexural

    strength (45%) of GP concrete. The addition of silica fume also improved the elastic

    modulus of GP concrete.

    Duval et al. (1998), has studied the influence of silica fume on the

    workability and the compressive strength of high-performance concretes [27]. The

    workability and the compressive strength of silica fume concretes were investigated at

    low water-cementitious materials ratios with a naphthalene sulphonate superplasticizer.

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    The results show that partial cement replacement up to 10% silica fume does not reduce

    the concrete workability. Moreover, the superplasticizer dosage depends on the cement

    characteristics (C3A and alkali sulfates content). At low water-cementitious materials

    ratios, slump loss with time was observed and increases with high replacement levels.

    Silica fume at replacement contents up to 20% produce higher compressive strengths

    than control concretes.

    Shannag (2000), has studied the mechanical properties of High strength

    concrete containing natural pozzolan and silica fume [28]. Various combinations of a

    local natural pozzolan and silica fume were used to produce workable high to very high

    strength mortars and concretes with a compressive strength in the range of

    69 – 110 MPa. The mixtures were tested for workabilit

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