Question

What is a clinker, which process should be applied to the clinker after production in order to obtain cement? Explain the reasons of that process

Answer 1

The cement manufacturing process is composed of the mixing and the heating of calcareous rocks, and argillaceous rocks.

• Calcareous rocks include chalk or limestone
• Argillaceous rocks include clay or shale

Formation of clinkers

• Heating of Calcareous rock such as ground limestone and Argillaceous rock such as clay at a temperature of about 1400 °C - 1500 °C for the cement manufacturing process leads to the formation of clinkers.
• The chemical reaction between the calcium, silicon, alumina and iron oxides present in the raw materials of cement manufacturing process is the reason for the formation of clinkers.

More details on clinkers

• It is a dark grey nodular material.
• It can be said as spherical (approximately).
• The diameter of the clinkers ranges from 5 to 50 mm.
• The components of a clinker are as follows:
  • Tricalcium Silicate (C3S)
  • Dicalcium Silicate (C2S)
  • Tricalcium Aluminate (C3A)
  • Tetracalcium Aluminoferrite (C4AF)

Clinkers definition

Clinkers are defined as dark grey nodular material which is formed due to the heating of Calcareous rock such as ground limestone and argillaceous rock such as clay at a temperature of about 1400 °C - 1500 °C for the cement manufacturing process.

After production in order to obtain cement, the clinkers are subjected to the following process

• Grinding process
• Gypsum addition

The purpose of grinding and gypsum addition process are as follows:

• Grinding process is done to obtain fine cement powder.
  • The minerals present in Clinkers on reaction with water produce hydrates. These hydrates are responsible for cement setting and cement strength.
  • If the clinker is not grounded, then the reaction with water occurs only at the surface of the clinker due to which incomplete and gradual hydration happens.
  • If the clinker is finely grounded, then the surface area of clinker available for reaction is large leading to rapid and complete hydration.
• Gypsum addition is done to enhance the setting behavior of cement
  • Gypsum addition will help to slow the hydration process while mixing with water.
    • The time taken for hydration is so low that the following process cannot be completed: transporting, mixing and placing.
    • Slowing down the hydration will allow the above mentioned processes to be completed as well as positively affects the strength and hardness of cement.
  • Gypsum is a coolant which helps to reduce the heat of hydration.
  • Gypsum helps to prevent the flash setting of cement.
  • Gypsum makes the cement to need less amount of water for hydration.