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Concrete damage-cavitation damage


Cavitation damage occurs when high-velocity water flows into discontinuity on the flow surface. The discontinuities will cause water to lift off the surface, which creates negative pressure zone, and this will result in bubbles of water vapor. If the bubbles collapse against the concrete surface. The impact will cause high pressure that can remove particles of the concrete surface and extend the discontinuities of concrete surface. The continuation of this process will extend the cavitation damage.
Figure 1

Cavitation damage is common in zones of high flow velocity, such as control gates in dams. The speed of flow is high at the time of opening the gate and when the gate opened slightly. Such flow will extend the discontinuities in concrete surfaces and cause severe cavitation damage. The repairing of cavitation damage should include eliminating the cause of cavitation damage. In general, the cavitation damage will not occur when the flow speed is less than 12 m/s (40ft/s) at ambient temperature. When it is expected that the flow is 12 m/s or more. The flow surface should be checked to ensure that there are no discontinuities on the flow surface. The finishing of the concrete surface that expected to be imposed on high-speed flow should be finished appropriately to eliminate all discontinuities. Newly concrete surfaces that don’t meet the specification should be repaired by grinding or removed and replaced with concrete or epoxy-bonded replacement concrete.

Cavitation damage near the control gate can be repaired by replacing the damaged concrete with epoxy-bonded concrete, epoxy-bonded mortar, and polymer concrete. It is recommended to coat the concrete with 100-percent solids epoxy coating. This coating will help in preventing the occurrence of cavitation damage. However, using the solid epoxy coating cannot fully protect the surface flow from cavitation damage.

Successful repairing of damage flow surface in the spillway, outlet, or silting basins should involve hydraulic studies and the modification of design to reduce the velocity of flow and prevent the reoccurrence of cavitation damage again. The speed of flow can be modified by the installation of air slots in spillways and tunnels, and it is very successful in eliminating or significantly reducing cavitation damage.

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