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Structural Materials.pdf

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  • 8/13/2019 Structural Materials.pdf


    Structural Materials

  • 8/13/2019 Structural Materials.pdf



    Concrete is a mixture of paste and

    aggregates (sand and rock). The paste,composed of cement and water, costs the

    surface of the fine (sand) and coarse

    aggregates ( rock) and binds together into

    a rock-like mass known as concrete.

  • 8/13/2019 Structural Materials.pdf


    Unit weight :Normal concrete density = 23.6 kN/m3

  • 8/13/2019 Structural Materials.pdf



    The total aggregate (fine + coarse) are used inconcrete as filler and generally occupy 60% to75% of the concrete volume (70% to 85% byweight)

    Fine aggregate generally consist of natural sandor crushed stone with most particles smaller than4.6 mm size.

    Coarse aggregates consist of one or a

    combination of gravels or crushed aggregate withparticles larger than 4.6 mm.

    ( 10 mm < coarse aggregate < 20mm)

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    Type I : Normal

    It is general-purpose cement use in concrete for

    making pavements, floors, reinforced, concretebuildings, bridges, tanks, pipes, etc.

    It is for all uses where the special properties of

    other cement types are not required, such assulfate attack from soil and water, or to anobjectionable temperature rise.

  • 8/13/2019 Structural Materials.pdf


  • 8/13/2019 Structural Materials.pdf


    Type II: Moderate sulfate resistance

    It is used where precaution against moderatesulfate attack is important, as in drainage

    structures, which may be subjected to a moderatesulfate concentration from ground waters.

    It is generates less heat of hydration at a slowerthan type I cement therefore can be used in massstructures such as large piers, heavy abutments,

    and retaining walls. Due to less heat generation it can be preferred in

    hot weather.

  • 8/13/2019 Structural Materials.pdf


  • 8/13/2019 Structural Materials.pdf


    Type III: High early strength

    It is chemically and physically similar to type Icement, except that its particles have been groundfiner.

    It provide high early strengths at the early period,usually a week or less.

    It is used when forms need to be removed as soonas possible

    It used in precast factories It is preferred in cold weather for reduction in the

    curing period.

  • 8/13/2019 Structural Materials.pdf


  • 8/13/2019 Structural Materials.pdf


    Type IV: Low heat of hydration

    It is used where the rate and amount of heatgenerated from hydration must be minimized.

    It develops strength at a slower rate than othercement types.

    It is most suitably used in massive concretestructures, such as large gravity dams, where the

    temperature rise resulting from heat generatedduring hardening and must be minimized tocontrol the concrete cracking.

  • 8/13/2019 Structural Materials.pdf


  • 8/13/2019 Structural Materials.pdf


    Type V: High sulfate resistance

    It is used only in concrete exposed to severesulfate action principally where soils or ground

    waters have high sulfate content, levels reachfoundations.

    Its high sulfate resistance is due to its low C3Acontent of about 4%

    It is not resistant to acids and other highly

    corrosive substances It used in off-shore structures

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    Mixing water for concrete

    Water helps in hydration of cement. It

    should be clean and free from dirt and dustor salts. Drinkable water is good for making


  • 8/13/2019 Structural Materials.pdf


    Concrete Design Mix (BS 5328 : 1981)

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    To control certain properties of concrete, we addspecial materials, called admixtures, to givedesired properties:

    Air-Entraining admixtures: to create voids inconcrete, are used primarily to increaseconcretes resistance to freeing. Improvesdurability under temperature changes, but reducestrength (15%)

    Accelerating admixtures: such as calcium chlorideto concrete will accelerate its early strengthdevelopment.

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    Retarding admixtures: are used to show the sittingof the concrete and to retard temperate increases.Used in large mass structures, such as dams.

    Workability admixtures: used to make concreteeasier to handle and place into molds, without increating water/cement ratio.

    Superplasticizers admixtures: made from organic

    sulfonates, their use enables engineers to reducethe water content in concrete substantially whileat the same time increasing their slump.

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    The properties of concrete are its characteristics

    or basic qualities. The main properties of concrete


    Strength: the concrete resists compressive

    stresses and not tensile stresses; therefore,

    compressive strength is criterion of quality


    Workability: is used to describe the ease or

    difficulty with which the concrete is hadle.

  • 8/13/2019 Structural Materials.pdf


    As water to cement ratio increase, its strengthdecreases its workability increase.

    Workability is usually indirectly measured in thefield by the slump test. Workability of concrete (how easily the concrete flows) is an indication ofhow easy it is placed in its molds.

    For low w/c, strength is high, but concrete is difficult toplace in molds.

    For high w/c, strength is not high.

    We can obtain high strength concrete ( using loww/c ration) and high workability by usingadmixtures.

  • 8/13/2019 Structural Materials.pdf


  • 8/13/2019 Structural Materials.pdf



    1. Water-cement ratio: one of the most important factorsaffecting the strength of concrete. A w/c of 0.5 and 0.7 mayproduce a concrete strength of about 35 MPa and 21 MParespectively.

    2. Method of Mixing: the use of mechanical concrete mixersand the proper time of mixing both have favorable effectson strength of concrete. Also, the use of vibrators producesdense concrete with a minimum percentage of voids. A void

    ratio of 5% may reduce the concrete strength by about30%.

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    3. Method of curing: the curing conditions exercise

    an important influence on the strength of

    concrete. Both moisture and temperature have a

    direct effect on the hydration of cement.

    4. Age of the concrete: the strength of the concrete

    increases appreciably with age, and hydration ofcement continues for months.

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    5. Loading conditions: the compressive

    strength of concrete is estimated by

    testing a cylinder or cube to failure in afew minutes. Under sustained loads for

    years, the ultimate strength of uncrate is

    reduced by about 30%.

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    Typical concrete compressive strength,

    R/C structures: f c= 20 to 45 MPa

    Prestressed concrete: fc = 35 to 55 MPa

    High strength concrete: f c = 50 to 150 MPa

    (in high rise buildings)

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    Tensile strength of concrete

    The tensile strength of concrete is relativelylow, the direct tensile strength, for example,

    range from about 3 to 5 fc for normal

    density concrete.

  • 8/13/2019 Structural Materials.pdf


  • 8/13/2019 Structural Materials.pdf


    Thank You