Hydration of Cement:
The chemical reaction of cement with water is popularly known as hydration of cement. Hydration of cement in turn produces the hydrated compounds, which are rich of setting and hardening properties, and provides the strength to concrete. Basically, cement itself does not possess any cementing property unless it is mixed with water. So, it is essential to ensure full hydration of cement particles in order to develop full strength of concrete. The hydration of cement is not an instantaneous process but it may last for indefinite time with varying rate of hydration. At the early stage the rate of hydration is large which reduces with the time. For example, during hydration of Ordinary Portland Cement, about 50% of total hydration of cement is achieved within first 1-3 days as compared to about 75% hydration which completes within 7 days and up to 90% is in about 6 months or so.
The hydration process is exothermic reaction, which generates considerable amount of heat of hydration. For example, during mass concreting the inside temperature of concrete may rise even up to 50oC.