Heat of Hydration

   
     The term ‘heat of hydration’ is applied to the heat generated by the chemical reactions, which occur in setting concrete between the water and cement.
 
      The reaction of cement with water is exothermic.The reaction liberates a considerable quantity of heat.This can be easily observed if the cement is gauged with water and placed in a thermos flask.Much attention has been paid to the heat evolved during the hydration of cement in the interior of mass concrete dams.It is estimated that about 120 calories of heat is generated in the heat of hydration of of 1gm of cement.From that we can assessed the quantum of heat produced in a conservative system such as interior of a mass concrete dam.A temp. rise of 50oC has been observed.This unduly high temp. developer at the interior of concrete dam causes serious expansion of the body of the dam and with the subsequent cooling considerable shrinkage takes place resulting in serious cracking of concrete.
 
    The use of lean mix,use of pozzolanic cement,artificial cooling of constituent materials and incorporation of pipe system in the body of the dam as the concrete work progress for circulating cold brine solution through the pipe system to absorb the heat are some of the methods adopted to offset the heat generation in the body of dams due to heat of hydration.
Adiabatic Calorimeter
 
        Test for heat of hydration is essentially required  to be carried out for low heat cement only.This test is carried out over a few days by vaccum flak methods,or over a longer period in an adiabatic calorimeter.When tested in a standard manner the heat of hydration of low heat portland cement shall not be more than 65 cal/gm. at 7days and 75 cal/gm. at 28 days.

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