Friday, April 5, 2013

Heat of Hydration in Concrete Mixture

for aqueous ionic solutions,
• Solvent attractive forces and Mixing forces are
combined into a term called the heat of hydration
∆Hsolvent + ∆Hmix = ∆hhydration
 attractive forces in water = H-bonds
 attractive forces between ion and water = ion-dipole
 ∆Hhydration = heat released when 1 mole of gaseous ions
dissolves in water
 ∆Hsolute = - ∆Hlatic

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 heat causes the concrete first to expand and then to shrink as it cools. If there is a temperature gradient across the concrete or the concrete is otherwise restrained, cracking may occur. The two factors, which are most likely to cause excessive generation of heat, are very large pours and high cement contents. Some specifications set a maximum cement content in order to limit the generation of heat.

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