Cement Production

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Cement Production

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  • CLE 513 Advanced Concrete

    Technology

    Cement Production

  • 1824 Joseph Aspdin, while obtaining a patent for his

    hydraulic cement, termed it as Portland cement, upon

    Portland stone (limestone from Dorset, UK), which had

    a high quality and durability and a similar appearance

    ProtoPortland cement

    Later, William Aspdin (son) MesoPort land cement

  • Hewlett, 2001

    Kiln for burning

    A Alite, or C3S

    B Belite, or C2S

    Aspdins creation

  • Portland Cement

    An unusual industrial product produced in huge quantities in

    special plants that can produce nothing else

    The product is produced by a combination of unusual unit

    operations involving mining, very fine scale blending of raw

    materials, very high temperature clinkering reactions,

    controlled cooling, grinding, blending, and finally shipping

    under controlled conditions

    Chemical composition is maintained within narrow limits

    despite huge tonnages

  • Raw Materials for Cement

    Calcareous material Containing CaCO3(primary

    source limestone); impurities such as iron and

    alumina are sometimes present

    Argillaceous material Containing clayey matter,

    source of SiO2, Al2O3

    Gypsum Added in the final stages of manufacture as

    a set regulator

    Sometime, ground limestone is also added to cement

  • Mamloukand Zaniewski, 2000

  • Schematic depiction of process

    www.ieagreen.org.uk/jan46.htm

  • Pulverization

    Raw material feedstock should be

    pulverized to the right size

    Reduces overall power consumption

    Better blending and burning possible

    with reduced size of material

  • Blending of raw materials

    Choice of blending process-Wet or dry

    Wet process more uniform mixing

    Dry process higher output, lower power

    consumption

    Dry process with pre calciners are the order of

    the day

  • Blending Wet Vs. Dry

    Blending Wet Vs. Dry

    When moisture content of raw materials is > 15%, wet

    blending (in slurry form) is preferred

    When MC < 8%, dry blending is done

    For 8% < MC < 15%, dry blending with precalciners

    used

    Wet blending better blend

  • Reactions in the kiln

    The clinkering reactions involve conversion of

    mixtures of calcium carbonate and silica and

    alumina-bearing components to a mixture of special

    crystalline components capable of reacting with

    water to produce controlled setting and strength gain

    The major components in clinker are impure but well

    crystallized fine crystals of tri calcium silicate and di

    calcium silicate

  • Kiln reactions (continued)

    Minor but important crystalline components are

    extremely fine crystals of tricalcium aluminate and

    calcium aluminate ferrite solid solution (ferrite)

    Of great importance despite minor amount

    present are deposits of soluble crystalline

    components (alkali sulfates and calcium alkali

    sulfates) on the surfaces of clinkers

  • Kiln reactions -schematic

    Mindess and Young, 1981

  • Hewlett, 2001

    Up to 700 deg.C: activation of

    silicates through removal of water

    and changes in crystal structure

    700 900 deg.C: decarbonation of

    CaCO3, initial combination of A, F,

    and activated silica with lime

    900 1200 deg.C: Belite(C2S)

    formation

    > 1250 deg.C (more particularly, >

    1300 deg.C): liquid phase appears

    and promotes the reaction between

    beliteand free lime to form alite

    (C3S)

    Cooling stage: molten phase

    (containing C3A and C4AF) gets

    transformed to a glass; if cooling is

    slow, C3A crystallizes out (causes

    setting problems), or alite converts

    to beliteand free lime

  • Inter grinding with gypsum

    Final step in cement manufacture

    Gypsum added as a set regulator (absence flash

    set)

    Strict control on temperature required

    Done in ball mills

    Cement of required fineness produced

  • Quality control

    Sampling and evaluation should be performed

    after excavation from the quarry, before and

    after blending the feedstock, after formation of

    clinker, after inter grinding clinker with

    gypsum, and finally before packaging in the

    bags and drums

  • Quality control parameters

    Parameters:

    Lime saturation factor (LSF) = C/(2.8S + 1.2A +

    0.65F), where C, S, A, and F are the % amounts

    of CaO, SiO2, Al2O3, and Fe2O3, respectively.

    Silica ratio (or modulus) = S/(A + F)Alumina ratio

    (or modulus) = A/F

    Potential C3S from Bogue formulation

    The LSF is particularly important because it

    dictates the amount of free lime that will be

    present in the product. Too much free lime can

    cause unsoundness of the cement.