Addressing Mass Concrete Issues in Dam Repair
Ketch Lake, near Fort Sills, Okla., began as a stock pond for cattle. It was created in 1929, when the landowner, Frank Ketch, built a 3-foot-thick dam out of stone masonry. Today, Ketch Lake is a recreational lake that holds 180 million to 200 million gallons of water. When the original masonry dam began giving way in 2010, the Army Corps of Engineers developed a reconstruction plan that would keep the lake secure while preserving the appearance of the old stonework. Federal money was obtained to fund the repair project, and White Hawk/Todd, a Lawton, Okla.-based joint venture, was awarded the general contract.
In late summer 2010, the lake was drained temporarily and a new concrete dam was constructed behind the existing masonry. The new dam is 36 feet high, 20 feet thick, and 82 feet wide at its widest point. In such a massive concrete structure, the heat generated by cement hydration as the concrete cures can cause volume changes that lead to serious cracking problems. In this project, these potential problems were addressed through both concrete mix design and construction technique.
To help reduce the heat of hydration, the concrete mix contained significant amounts of supplementary cementitious materials. Of the 400 total pounds of cementitious material per cubic yard of concrete, 30 percent was Lafarge Type I/II Portland Cement, 50 percent was NewCem® Slag Cement, and 20 percent was Lafarge Class C Fly Ash. In addition to the cementitious materials, the mix included a set retarder and air-entraining, water-reducing, and waterproofing admixtures.
Concrete was placed in six-foot lifts. The concrete contractor, M.L. Young Construction of Oklahoma City, Okla., waited about seven days between lifts to allow the heat of hydration to dissipate after each placement.
Lawton Transit Mix, Inc., of Lawton, Okla., served as the ready-mix supplier. Lawton Vice President Steve Rohde says the temperature control requirement was the project's major challenge. "The specification required us to supply concrete that was no more than 85 degrees Fahrenheit when it reached the jobsite," says Rohde. "Our plant is only 20 miles from the site, but it took the trucks about an hour to make the trip. Lafarge helped us come up with a mix design that could meet all the requirements."