Fibrous Concrete Repair of Cavitation Damage

Libby Dam is a high head concrete structure on the Columbia River System. After moderate usage, one of the sluices (low level outlets) developed severe cavitation damage. The concrete was investigated thoroughly and found to exceed design criteria with strength ranging between 6,530 psi (45,057 kN/m²) and 9,650 psi (66,585 kN/m²). Since the cause of cavitation was not known, the damaging forces could not be eliminated. The repair had to be strong, practical, and more cavitation resistant than the original material. Several procedures were considered before a fibrous concrete pour back was decided upon. A mix design procedure for the fibrous concrete was developed that would insure the workability necessary to place the pour back around severe congestion of reinforcing and anchor bars. The placement was successful and service to date shows no damage of the repaired area.