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.