After nearly nine years of work and the placement of 450,000 cubic yards of concrete, a dedicated construction team completed a much-needed facelift to Arizona's historic Theodore Roosevelt Dam. The $430 million dam modifications raised the original cyclopean-masonry arch structure 77 feet to a towering 357 feet, increasing the dam's water conservation storage capacity 20%. Two other deficiencies were also corrected by the renovation: Foundation drainage was improved to stabilize the dam against earthquakes, and low-level outlet capacity was increased, so the reservoir could be emptied quickly in an emergency.
To deliver concrete anywhere along the dam site, the construction team set up a 25-ton-capacity overhead cableway that stretched from a stationary tower on the left dam abutment to a mobile tower on the right abutment that could move 790 feet along radial tracks. Trucks carried the concrete from a nearby batch plant to the tower's elevated delivery dock, and then discharged the concrete into 8-cubic-yard buckets for cable transport. The final mix contained 4-inch maximum-size aggregate and 270 pounds per cubic yard of cementitious material, including a special low-heat Type II cement (80%) and fly ash (20%). With a water-cementitious materials ratio of 0.53 and a 2-inch slump, the mix displayed excellent workability. It also achieved sufficient early-age compressive strengths to allow crews to raise the forms to the next lift four to seven days after concrete placement.