The term ‘Hardening’ refers to the gain of strength of a set cement paste, although during setting the cement paste acquires some strength.
The setting characteristics of Portland cement paste are defined by initial set and final set. Initial set indicates the approximate time at which the paste begins to stiffen considerably. Final set roughly indicates the time at which the cement paste has hardened and can support some load.
Initial setting time indicates the beginning of the setting process when the cement paste starts losing its plasticity. Final setting time is the time elapsed between the moment water is added to the cement and the time when the cement completely lost its plasticity and can resist certain definite pressure.
These times of set are tested according to standardized procedures and have no special relationship to concrete setting behavior. Setting types are affected by minor constituents in the cement such as alkalis and Sulfates, by fineness, water-cement ratio, ambient temperature and inclusion of mineral and chemical admixtures. Concrete generally sets more slowly than cement paste because of the higher water-cement ratios.
INITIAL SETTING TIME:
Initial setting time can be defined as the time when the cement paste starts losing its plasticity. As per IS specification, the minimum initial setting time is 30 minutes for ordinary portland cement and 60 minutes for low heat cement.
FINAL SETTING TIME:
The final setting is defined as the time taken to reach the cement paste to become into a hardened mass. As per IS specification, The maximum final setting time for all type of cement is 10 hours.