When ordinary portland cement and water are mixed together,the heat which is liberated during this process (which is actually a chemical reaction) is known as heat of hydration and the process is known as cement hydration.This process resulting in setting, hardening and liberating of heat.
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Heat Of Hydration is the Heat Generated and Liberated due to the Exothermic Chemical Reaction which takes place when water and cement comes in contact with together source Techno Genome