Class 11 Chemistry The S Block Elements Cement

Cement

  • Combination of CaO with clay containing silica, SiO2 along with the oxides of aluminium, iron and magnesium leads to the formation of cement.

Composition of Portland cement

  • CaO = 50-60%;
  • SiO2 = 20-25%;
  • Al2O3 = 5-10%;
  • MgO = 2-3%;
  • Fe2O3 = 1-2%
  • SO3 = 1-2%.

Strong heating of clay andlime results in their fusion followed by the formation of cement clinker which is then mixed with 2-3% by weight of gypsum(CaSO42H2O). This leads to the formation of cement.

  • Important ingredients of Cement:

Dicalcium silicate (Ca2SiO4) = 26%,

Tricalcium silicate (Ca3SiO5) = 51%

Tricalcium aluminate (Ca3Al2O6) = 11%

  • Settling of cement:

Addition of water to cement hydrates the molecules of the constituents. Gypsum is added in order to slow down the process of setting of the cement to make it get hardened.

  • It is used to prepare concrete in plastering and constructingbridges, dams and buildings.

Fig. Cement used to build buildings, walls, bridges

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