What is the composition of Portland cement and describe about its manufacturing.
1 Answer
  • Cement May be defined as material possessing adhesive and cohesive properties and capable of joining rigid masses like bricks, stones tiles etc. into coherent structures.

  • Raw materials for Portland cement are the calcareous material:

    CaO (such as lime stone, marble, chalk etc.)

    Argillaceous materials: Al2O3 and SiO2

    Gypsum: CaSO4.2H2O

    Powdered coal or fuel oil.

  • Compound composition of Portland cement-

    tricalcium silicate, dicalcium silicate, tricalcium aluminate

  • Steps including in manufacture are:

    1) Mixing of materials

    1.1) Dry process

    Raw materials are individually crushed, grounded to fine powder, and stored in separate hopper. These powdered materials are then mixed in required proportion to get dry raw mix.

    1.2) Wet process

    Ca raw materials are crushed, powdered and stored in big tanks. Argillaceous materials are mixed with water to remove any organic matter. Raw materials are then mixed in right proportions to form paste/slurry. This slurry contains 38 to 40% of the water.

    2) Burning method

    Raw mix is injected into Kiln at its upper part where the temperature is 4000C, water in slurry evaporates. At central part of Kiln, temperature is 10000C, dry mix forms small lumps called nodules. In lower part of Kiln, temperature is 1500 to 17000C, lime and clay undergo fusion to yield small hard stones called clinkers.

    3) Grinding

    The cooled clinkers are ground to fine powder in ball mills or tube mills.

    During grinding, small quantity (2-3%) of powdered gypsum is added.

    4) Packing

    The grounded cement is stored in silos which is later packed.

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