In concrete dams, the cracks are mainly form due to the shrinkage of concrete due to temperature variations. These cracks develop externally on the surface of the dam or internally on the surface of the dam. Surface cracks are dangerous than the interior cracks.
The Methods of Control Cracking in the Concrete Dams are as follows:
By using the low heat cement:
In dams the mass concrete structures are used, it involves the heat during the hydration process is disappears slowly. The low cement should be use in the place of the ordinary Portland cement. The rate of production of heat, as well as the rate of the hardening, is slow in that case.
Pre-cooling the concrete
Pre-cooling works to prevent the cracking of the concrete and the concrete ingredients like aggregate and coarse aggregate. Blowing them by the aggregates or by washing them with chilled water it can be done. The heat generated by the hydration and it prevents the thermal cracking it all can be balanced by this.
By post-cooling the concrete:
Bypassing through the cold water throughout the pipes embedded in the concrete the post-cooling method is done. 250m long and the thin pipes of 25mm external diameter are place in the concrete, each lift is poured. The pipes is space in between 0.5m to 2.0 m horizontally.
By reducing the percentage of concrete:
If there is higher cement content than there is a higher generation during the hydration. The cement content is used for the construction of the interior portion of the dam. The separation of heat is very slow in the interior part of the dam in comparison to the exterior part.
By providing the contraction joints:
In concrete dams, contractions joints are provided to prevent the cracks due to t the shrinkage of the concrete temperature variation. Longitudinal joints are the parallel joints to the axis of the dam. They are spaced off the distance of the height of 15m or the dam whichever is less.
There should be a time interval in the concrete intervals:
The concrete mass structure like dams, in that the concrete is pour lifts wise and there should be a good time interval between the ensuing lifts which prevents cracking due to the shrinkage