Boulder City Magazine® September 2010 Issue
|Boulder City History
by Shirl Naegle, Manager
Boulder City/Hoover Dam Museum
Hoover Dam Construction
There is enough concrete in Hoover Dam to build a sidewalk four feet wide and two and three-quarters of an inch thick all the way around the earth at the equator. Or, if you were to build a pyramid on the same base as the Empire State Building, it would reach two-and-one-half times as high. It would take a freight train 160 miles long to haul the huge amounts of cement used in mixing the concrete for Hoover Dam.
Boulder City Magazine®
|Comparisons about the amount of cement or concrete used in the construction of Hoover Dam abound. Cement is the fine powder made from the process of heating and then grinding a limestone and clay mixture. Once aggregate is added to the cement, along with water, it becomes concrete.
I first became aware that there was more to mixing concrete than simply adding aggregate watching my father build our home on 7th street. While the mixer was running, my dad would plunge his hand into the tub and then rub the mixture between his thumb and fingers. He would then either approve of the consistency or suggest that there needed to be another shovel of sand or a little more water added. I witnessed other practitioners such as Jerry Morley and Frosty Traasdahl perform a similar ritual, so I am certain that there is validity to achieving the correct proportions to the mixture.
The concrete used in the construction of Hoover Dam had to meet stringent criteria set by the US Bureau of Reclamation. Two modern mixing plants were built to provide the 3,220,000 cubic yards of concrete needed for the job. The plants were built as close to the dam site as possible to reduce the delivery time of the relatively dry concrete mix required.
The logistics of obtaining enough high quality aggregate in all the sizes needed and enough “clean water cement” in one place are examples of the detailed technical expertise worked-out on the project.
The technical problem of the time required to cure the concrete and to dissipate the heat produced in the chemical process of hardening will have to be the topic for another article.
On behalf of the Boulder City Museum and Historical Association.
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