The Wonderful World of Completely Random Facts — Issue 66

How to Cool a Lot of Concrete

The Hoover Dam is as tall as a 60-story building and was the highest dam in the world when it was completed in 1935. It spans the Colorado River on the border between Arizona and Nevada, weighs more than 6.6 million tons, and withstands pressures of 45,000 pounds per square foot at its base. To achieve these feats, Hoover Dam was made with 3.25 million cubic yards of concrete.

But this much concrete couldn’t be laid in one solid block because of the massive release of heat generated from the chemical reaction that takes place as concrete cures. If the dam had been built in one continuous pour, it would have gotten so hot that it would have taken 125 years for the concrete to cool to ambient temperatures. The stress placed on this mass of concrete from this massive amount of dissipating heat would have caused cracks to form, leading to the dam’s failure.

One way engineers solved the heat problem was by constructing the dam in trapezoidal vertical columns measuring 60 feet square at the upstream face to around 25 feet at the downstream face. A total of 215 column blocks made up the dam, and each block was locked together with horizontal and radial joints. Workers poured only five feet of concrete in each block in a time frame of 72 hours. When the…