Every bridge is unique, whether it allows a person to walk across a sedate, rural creek, or it lets a train cross an industrial valley. Bridges allow people to go where nature did not intend.
Still, some spans are truly special. Take the San Francisco-Oakland Bay Bridge in California. Though not as famous as the Golden Gate Bridge, its neighbor five miles west, the Bay Bridge has been a godsend to area residents, saving them hours of commuting time. It has seen prisoners taken to the former Alcatraz prison. And it has seen the earth quake.
Now its eastern span is being replaced at a cost of more than $5 billion. And concrete is the star of the show.
When the contract to supply concrete for the Skyway portion of the eastern span was signed, everyone at Cemex knew we were beginning something special. We did not know it would tax the limits of our 80-plus years of industry experience. From the mixes, materials, delivery, and the plant itself, the project presented a unique challenge.
The multi-billion dollar expenditure is part of an initiative to make state-owned bridges more resistant to earthquakes. The bridge, combining a single-towered suspension skyway with a bike/pedestrian path, was designed to draw a modern and striking white line across the Bay. The project features the world's largest precast concrete segments that are three stories tall and require using the largest cranes available to set elements in place.
The owner is the State of California Department of Transportation (CalTrans). California ReadyMix, a Cemex subsidiary, contracted with Kiewit FCI Manson (KFM) to supply concrete for the skyway viaduct and the foundations for the self-anchored suspension construction.
In all, Cemex needed to supply more than 100,000 cubic yards of concrete, delivered by barge for this high-profile project.Batch plant
The batch plant was constructed on the outer harbor of the Port of Oakland, a site with historical significance as a loading pier during World War II. Because the site will be restored at the end of the project, no excavation or structural alterations were allowed. Construction was complicated because the pier had deteriorated over the years, so it could not support the weight of the batch plant and storage bunkers. To provide needed support, a massive concrete footing was built on imported fill 90 feet from the edge of the pier.
Although the plant site anticipated during bidding was 2¼ acres, it was actually built on 1½ acres, including aggregate and waste storage. Many contractors, the batch plant, and CalTrans share the site.
To determine traffic pattern and minimum turning radius, cement and aggregate trucks were brought to the site before plant layout. This was critical because there is less than 6 inches of clearance for the trucks delivering cement and aggregates. Once safe turnarounds were established, plant layout and conveyors were made possible.