A trip to Hoover Dam is a must for people in the concrete industry. You will be awestruck by its size, the rugged landscape, amd the challenges crews faced when they built it in the 1930s. It truly is a 20th century wonder.
Attendees at World of Concrete in January again had a chance to not only tour Hoover Dam, but to get a personal, up-close look at the Colorado River Bridge project just downstream. Sika Corp. was the event's sponsor.
More than 300 people on two days toured the construction site of the 2000-foot, four lane bridge, about 25 miles south of Las Vegas. Even though much of the work was halted becuase of a crane accident last fall, there was still a lot to see. Jeff St. John, deputy project manager for Obayashir/JSM,answered attendees' questions.
After the construction site, it was on to the visitor Center for a close look at the dam and for a fascinating talk by Luke Snell, director for the Concrete Industry Management program at the Del E. Webb School of Construction at Arizona State University. Snell recalled many amazing facts surrounding Hoover Dam's construction:
- The Hard Hat: Workers on the face of the rock (high scalers) were consistently in danger of falling rock. As a result, some manufactured their own hard hats by dipping their cloth ball caps into tar and letting it harden. These hardned hats were so effective that the contractor, using the worker's invention as a model, purchased thousands of them.
- Drinking Water: At the start of the job many workers would colapse, vomit, and convulse. Several others would die. Many blamed being in poor physical shape, overeating, and drinking too much water. A group from Harvard University Fatigue Laboratory concluded in 1932 that the workers were not drinking enough water. From that point, the contractor made sure enough water was available.
- Blending of Aggregates: When you make 3.4 million cubic yards of concrete, you need an economical way to place the material, so carefully blending the aggregate became necessary. After research, four aggregates were blended together to achieve a more dense, economical mix.
- Internal Vibration: The concrete had a slump of 3 inches and had no admixtures. To achieve the needed consolidation, the contractor used a relatively new piece of equipment: the internal vibrator. If you look at the core sample at the Visitor Center, you will see a well-consolidated concrete.
We should be thankful the workers, contractors, and researchers of Hoover Dam developed safer practices, efficient concrete mixtures, and better equipment that we still use today.
More of the bridge will be complete by January, when we offer the tour again. Look for details in THE CONCRETE PRODUCER and at www.theconcreteproducer.com.