“Before the bid we conducted a fairly extensive trial program because the arch is 10,000 psi concrete,” Goodyear says. “CTLGroup was very much involved and demonstrated to everyone's satisfaction that concrete production could go off without a hitch. We did not have one cylinder break (for the arch), which is pretty impressive.”
Jeff St. John arrived at the project just four months after excavation started. The engineering and deputy project manager for project contractor Obayashi/PSM learned a lot about concrete production after five years on the job, especially since Obayashi supplied its own concrete for the arch starting in 2007. He has a newly found respect for concrete production.
St. John was pleasantly surprised by the quality of the centrally batched concrete. “By using a central batch system and pan mixer, the level of quality and uniformity from load to load improved so much,” he says. “We never had to worry about getting a stiff load of concrete that would plug a pumping system or getting concrete that did not come up to strength. On these technical bridges that are becoming more commonplace, the strength requirements have shot through the roof.”
For ready-mixed concrete, the trucks sometimes cause inconsistency, St. John explains. Trucks have different fin configurations, sometimes the washwater from a previous batch is not completely removed, and the speed of the drum revolutions varies. Sometimes the material sticks to the fins and is not agitated.
“Consistency is huge with these high-performance concretes,” St. John explains. “You're not allowed to add water at the jobsite, so you either deliver it right or throw it away. There is no water redosing. It has to show up right and be consistent for every load.”
His advice for producers: “For high-performance concrete, it's all about quality control. You have to test every load. Central batching assures your results are a lot better. It takes out a lot of variables.” St. John also credits the batch plant operator. “We had a gentleman who ran our batch plant and it was his baby,” he says. “He knew every part. He could almost tell by feel if the concrete was coming out right or not.”
Every day brought its own challenges, but there was one major setback during construction. Wind is suspected of causing a temporary 330-foot-tall twin cableway crane to collapse in 2006, resulting in an 18-month delay. Despite this, the project came in on its $120 million budget for the bridge owners. Upon completion, the Federal Highway Administration turned the span over to its new owners, the states of Nevada and Arizona. Nevada is responsible for maintenance.
St. John moved to San Francisco to work on a repair project at the Golden Gate Bridge a few months before the bridge over the Colorado River was completed. But he came back for the ceremonial opening in October.
“I hadn't seen the absolute finished project,” he says. “It was nice to see a lot of the guys who worked on it and their families. I have a feeling it may be the most important project I will ever get a chance to work on.”Up Close and Personal
The Concrete Producer and Concrete Construction magazines will again host Hoover Dam Bypass Tours just before and after World of Concrete. Learn about the challenges that had to be overcome to build two iconic concrete structures: the Mike O'Callaghan-Pat Tillman Memorial Bridge and Hoover Dam. For tour details, see our World of Concrete preview.
You also can purchase a CD at the World of Concrete Bookstore in Las Vegas, which includes TCP magazine articles about the bridge project and presentations by concrete historian Luke Snell about the concrete history of Hoover Dam.
[WEB EXTRA SLIDESHOW] Hoover Dam & Bypass: From Start to Finish
Follow the project through the years, including photos of the bridge construction underway.
Also, see www.hooverdambypass.org, the Federal Highway Administration's official project website.
Sources: U.S. Bureau of Reclamation, Obayashi/PSM, Luke Snell