Types of Cement

• Cement is a binder that sets, hardens, and binds materials.
• Cement is a crystalline compound of calcium silicates, possessing hydraulic properties.
• Cements are hydraulic due to their capacity to set and harden with or without excess water through the hydration of chemical compounds or minerals.

Types of Cements

• Pozzolan cement is a hydraulic cement developed by the Romans, who mixed volcanic ash with lime.
• Pozzolan cement is made by mixing volcanic ash with lime.
• Portland cement is an artificial cement made by mixing clinker with gypsum, invented in 1824 by Joseph Aspdin from England.
• Masonry cements are portland cement mixed with other materials to increase plasticity, commonly calcium stearate, petroleum, and high-colloidal clays.
• High Alumina cement (Calcium Aluminate Cement) is made by melting bauxite and lime then grinding the mixture with clinker.
• High Alumina cement (Calcium Aluminate Cement) is used for refractory applications, like cementing furnace bricks, and applications needing rapid hardening; it is more expensive than portland cement.
• Special or corrosion resistance cement is used for corrosion proof linings in chemical equipment like reactors, storage tanks, and absorption towers.
• Controlled cement prevents shrinking and cracking upon setting, formed by combining 10 to 20% calcium sulfoaluminate (from bauxite, gypsum, and limestone) with portland cement.

Clinker

• Clinker is composed of hydraulic calcium silicates, containing calcium sulfate additives.
• Clinker compounds include:
  • Dicalcium Silicate (2 CaO.SiO₂) abbreviated as C₂S
  • Tricalcium Silicate (3CaO.SiO₂) abbreviated as C3S
  • Tricalcium Aluminate (3CaO.Al₂O₃) abbreviated as C3A
  • Tetracalcium Aluminoferrite (4CaO.Al₂O₃, Fe₂O₃) abbreviated as C4AF

Portland Cement

• Portland cement is a finely ground product made by calcinising argillaceous (clay) and calcareous (lime) raw materials at over 1500°C, without subsequent addition, except for gypsum which acts as a retarder.

• Chemical composition of Portland Cement:

  • Tricalcium silicate (CaO)₃ · SiO₂ (C3S) makes up 45-75%
  • Dicalcium silicate (CaO)₂ SiO₂ (C2S) makes up 7-32%
  • Tricalcium aluminate (CaO)₃. Al₂O₃ (C3A) makes up 0-13%
  • Tetracalcium aluminoferrite (CaO)₄·Al₂O₃ Fe₂O₃ (C4AF) makes up 0-18%
  • Gypsum CaSO₄· 2 H₂O makes up 2-10%
  • Calcium Oxide - CaO makes up 2%
  • Magnesium Oxide - MgO makes up 4%

Types of Portland Cement

• Ordinary Portland Cement (OPC) is widely used for general concrete construction.
• White cement is a variation of OPC containing less ferric oxide or manganese so it is white instead of grey.
• Moderate -heat- of hydrating and sulfate resisting Portland cement is used where moderate heat of hydration is needed, or for concrete exposed to moderate sulfate action.
• High-early-Strength (HES) cement attains early high strength for quicker removal of formworks.
• HES cement contains higher lime to silica ratio, finer particles, and a greater proportion of tricalcium silicate (C3S) leading to faster hardening and heat evolution.
• Low Heat Cement contains less than 6% tricalcium aluminate by increasing the proportion of C2S.
• Low Heat Cement is used in mass concrete construction like gravity dams to prevent cracking from the low heat of hydration.
• Sulphate Resisting Cement reduces the risk of sulfate attack on concrete in soils with high sulfate content.
• Sulphate Resisting Cement has lower content of C3A and higher content of C4AF.
• Sulphate Resisting Cement is suitable for constructions exposed to high sulfate action, like canals linings, culverts, retaining walls, and siphons.
• Air Entraining Cement is produced by adding air entraining agents like resins, glues, and sodium salts of sulphates during the grinding of clinker.
• Air Entraining Cement improves workability with smaller water-cement ratio and frost resistance of concrete.

Raw Materials of Portland Cement

• Calcareous materials, such as Limestone (CaO):
  • The principal ingredient requiring proportion regulation.
  • Excess lime weakens cement, causing expansion and disintegration.
  • Insufficient lime reduces strength leading to quick setting.
• Argillaceous materials, such as Clay (Al₂O₃ and SiO₂):
  • Impart strength.
  • Makes setting quicker.
  • Excess alumina weakens the cement.
• Powdered Coal or fuel oil is used for burning.

Abbreviations Used in Cement Industry

• CaO = C
• MgO = M
• CO₂ = C
• SiO₂ = S
• SO₃ = S
• H₂O = H
• Al₂O₃ = A
• Na₂O = N
• Fe₂O₃ = F
• K₂O = K
• Ca3SiO5 = 3CaO.SiO2 = C3S