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Boulder City Magazine® October 2010 Issue
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Boulder City History
by Roseanne Shoaff, Manager
Boulder Dam Hotel
Hoover Dam Construction
When our museum visitors think about the construction of Hoover Dam, they think about the heavy equipment, the huge steel fabrications, the perilous jobs, the railroads and cableways, and the complex engineering and logistics required to complete the project. Not until they watch the Bureau of Reclamation’s film in our theater do most casual visitors become aware of the massive refrigeration plant required to assure proper cooling of the concrete.
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As mentioned in last month’s article, the dam required over three million cubic yards of concrete and if it was not for the cooling system and refrigeration plant, the heat generated by the chemical processes within the concrete would have caused cracking throughout the structure.
In smaller concrete structures with a large surface area relative to the total amount of concrete, the dissipation of heat is handled through a system of reinforcement rods and a process of grouting the cracks that do form once the concrete has fully set. Because of the size of the Hoover Dam and because if its relatively small ratio of surface area to volume, additional cooling was required. For a structure the size of Hoover Dam, 125 years would have had to elapse before grouting could be completed without risk of further cracking.
Bureau of Reclamation engineers specified the compressed ammonia cooling facility to deliver 3000 gallons of cooled water per minute to the concrete structure. The cooled water was delivered to the Dam in 14-inch pipes and diverted to 6-inch supply headers and ultimately into 1-inch cooling coils. 662 miles of cooling coils were imbedded in the Dam.
Specifications required the concrete to be cooled to 45 degrees at the upstream side of the Dam and 65 degrees at the downstream side. Engineers monitored the rate of cooling with a series of thermocouples and resistance thermometers, which measured the temperature of the concrete as well as the temperature of the water in the coils.
With the problem of heat dissipation solved, engineers did not have to account for the additional stresses resulting from the natural cooling process and could be confident in the load bearing capabilities of the structure.
On behalf of the Boulder City Museum and Historical Association. |
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