Control of concrete dams cracking
CONTROL OF CONCRETE DAM CRACKING

Control of concrete dams cracking

CONTROL OF CONCRETE DAM CRACKING

  • 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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