Rehabilitating Dams with Roller Compacted Concrete

More than 77,000 dams are currently listed on the National Inventory of Dams with several hundred new ones added each year. By the year 2020 over 80% of these dams will be at least 50 years old. Many of these dams will require some degree of rehabilitation to stay current with state and federal dam design criteria, particularly in the areas of spillway capacity and seismic loading. Older dams, once located in rural settings, are now in areas where development is occurring in the drainage basins, which increases the runoff. Also development is occurring below the dams in the dam break flood zone resulting in low hazard dams now being reclassified as high hazard dams. These developments create situations where existing spillways are now inadequate to meets state and federal dam safety design standards. In the seismic active areas of the country dam projects are being reviewed in light of changes to the project's maximum credible earthquake prediction. New modeling tools and the discovery of new faults add to the changes being made to magnitude of earthquake loading on dams. Over the past 20 years a new product has been developed called roller compacted concrete (RCC). RCC has the strength and durability of conventional concrete but at a much less in-place unit cost because of its mix proportion and method of placement. RCC has been used in over 175 applications in providing overtopping protection, auxiliary spillways, buttresses, and lining for stilling basins and outlet channels for both rehabilitating older dams and in the construction of new dams and spillways.