Setting time of cement paste is that the interval during which the cement paste losses its plasticity after adding water in cement.

When cement is mixed with water, it starts hydrating with water and makes cement paste. This cement paste can be molded into any desired shape due to its plasticity. Within this time, cement continues reacting with water. Then slowly-slowly cement starts losing its elasticity and starts to harden. After some times the cement paste will completely hardened. This complete cycle is called the setting time of cement paste.

Setting time of cement is calculated in two parts:
(1) Initial setting time of cement and (2) Final setting time of cement.

Significance of Initial and Final Setting Time of Cement:-

Cement is a widely used material for making mortar and concrete for construction and building projects. After mixing cement with water, it takes time to place the cement paste in position. Initial setting time of cement possess a primary role in strength and it is mandated that cement paste is placed in position before it crosses initial setting time, that is approximately 30 minutes. It should not be disturbed until the final setting time is reached that is around 600 minutes to attain complete rigidity and tensile strength for Ordinary Portland Cement (OPC). This is the reason that determination of initial and final setting times is important.

Significance of Initial and Final Setting Time of Cement
Ordinary Portland Cement

  1. Cement should set neither too rapidly nor too slowly. In the first case if a cement paste sets very rapidly there might be there might be insufficient time to transport and place the concrete before it becomes too rigid. In the second case too long a setting period tends to slow up the work unduly, also it might postpone the actual use of the structure because of inadequate strength at the desired age.
  2. Setting of cement should not be confused with hardening, which refers to the gain in mechanical strength after the certain degree of resistance to the penetration of a special attachment pressed into it.
  3. Determination of setting time is the time required for concretizing of cement paste to a defined consistency.
  4. During setting of cement, the initial chemical reaction of cement with water indirectly related to form aluminum-silicate compound.
  5. Initial setting time of cement paste is regarded as the time within which the cement can be molded in any desired shape without losing its strength.
  6. Initial setting time of cement is the time when the hardening of the cement starts and the cement paste starts losing its plasticity. We have the only time available for mixing the paste and placing it in position.
  7. Initial setting time test of cement is important for transportation, placing and compaction of cement paste.
  8. Determination of initial setting time duration is required to delay the process of hydration or hardening.
  9. Final setting time of cement is regarded as the maximum time when the cement paste completely loses its plasticity and becomes hard.
  10. This is the time taken for the cement paste to reach its optimum strength to reach the highest tensile strength possible by the cement paste and attain the shape of the mould in which it is cast.
  11. Determination of final setting time facilitates safe removal of scaffolding or form.
  12. During the final setting time, primary chemical reaction of cement with water is almost completed.

Factors that Affect Initial and Final Setting Time of Cement Paste:-

  • The fineness of cement,
  • Amount of water,
  • The presence of salts in sand,
  • Atmospheric conditions.

For example, cement paste requires a temperature of 27°C to complete hydration, but during winters the climate is low which stops the hydration and takes a longer time to set harden. The time after manufacturing the cement also effect setting time. Moreover, the soundness of cement also rely on its initial and final setting time.

Determination of initial and final setting time of cement is important because different types of cement have different hydration and hardening time.

Read more:-
Determination of Initial Setting Time and Final Setting Time of Cement Paste by Vicat Apparatus
(including definitions, apparatus, IS code, test procedure, observations, formula, result and lab reports and much more).

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