When cement starts setting, heat of hydration is developed.
Concrete dams are large masses of concrete.
The heat of hydration is dissipated easily from the surface of the dam as the surface remains exposed to the atmosphere.
It is very difficult to dissipate the heat of hydration from the interior of the dam.
If some arrangement for this is not made, very high temperatures may develop inside the dam.
The surface of the dam being cool and temperature in the interior being very high, cracks are likely to develop and cause difficulties.
The dam may also develop surface cracks due to daily variation of the temperature at the surface.
Surface cracks are not harmful for short durations but cause very bad effects in the long run.
Water enters the surface cracks and solidifies to ice if the temperature falls down to zero.
The ice thus formed expands and causes the surface cracks to deepen.
Following measures may be adopted to prevent cracking of the concrete dams:
Low heat cement should be used in the concrete, being used for the dam construction.
Low cement content should be used in the interior parts of the dam.
Ice cold or refrigerated water should be used for the preparation of cement concrete.
The thickness of the lift of the concrete, should not be allowed to exceed 1.5 m.
Considerable (at least 5 days) time should be allowed for a lift to set before the next lift is laid over it.
Contraction joints should be laid at suitable intervals, both longitudinally and transversely.
The heat of hydration from the interior of the dam should be dissipated by embedding pipes in the newly laid concrete and circulating cold water through them.
The spacing of the pipes may be from 0.5 m to 2 m.
Thin-walled 2.5 cm external diameter tubes are used for this purpose.
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