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The Bay Bridge: Special Job, Special Equipment

The Bay Bridge: Special Job, Special Equipment

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    At a cost of more than $5 billion, the bridge's new eastern span is scheduled to be complete in 2013. The span saves commuters time driving from San Francisco east to Oakland and beyond.

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    The plant supplying concrete for the San Francisco - Oakland Bay Bridge project sits on 1½acres at the Port of Oakland. Cemex is supplying 100,000 cubic yards of concrete for the new eastern span.

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    One of the three delivery barges delivers concrete to the project. They are named Micki, Margo, and Kathy, after the names of the wives of the Cemex management team.

We selected a 150-cubic-yard per hour Erie Strayer batch plant. But because a central mixer was required, a conventional tilt drum mixer was not possible since there were foundation and clearance issues. A 12-cubic-yard Inventure mixer was selected. This near-horizontal-lined steel drum floats on rollers with specialized fins that mix when the drum rotates clockwise, and discharges when rotation is counter clockwise, similar to a ready-mix truck.

Conveyor system

The plant conveyor system was designed for three options. We can load from the mixer to the barges. Or we can load concrete onto barges from the ready-mix trucks. We can also load concrete from the Inventure mixer into ready-mix trucks.

The discharge from the Inventure mixer feeds onto a 30-foot-long conveyor. This conveyor pivots at the discharge hopper and can be moved laterally to discharge into a ready-mix truck or onto an extendable radial conveyor for loading barges. The radial conveyor can be raised or lowered, extended from 80 feet to 120 feet, and moved laterally from controls in the batch room.

The same discharge hopper is also low enough to receive concrete from a ready-mix truck. The discharge end of the radial conveyor is fitted with a vertical spout to direct concrete into the barge mixer drum gob hopper.

Although highly fluid self-consolidating concrete (SCC) mixes were easily delivered to the barges, the conveyors could not handle the annular grout. The solution: Make the conveyors and initial gathering hopper from the Inventure mixer swing away so that grout could be discharged directly into the hopper of a concrete pump.

This and a custom discharge pipe assembly, allowed the fluid-like consistency grout to be pumped to the barge. Installing this swing chute allows discharge of clean up waste into a front loader for transport to the disposal area.

Delivery barges

When searching for the right type of barge, we found no traditional concrete delivery equipment was available to satisfy the unique project challenges.

Barge Design Criteria
  1. Environmental (no spills)
  2. Provision for handling comeback waste concrete
  3. 80 cubic yards/hour delivery capability
  4. Low maintenance
  5. Easy and safe clean-up

Clearly, we needed a non-conventional approach to this project.

Al Kaufman started the design process with a sketch on the back of an envelope. The final barge design evolved after several months of brainstorming by Kaufman, James Van Nest, and Bob Macquoid, former equipment manager. Coordinating the equipment and determining the number of barges needed came out of many hours with Grant Scott, KFM concrete superintendent. We determined that three customized delivery barges the same length of the freeboard would meet the required production rate of 80 cubic yards/hr.

But finding suitable barges took time. The initial plan to buy military barges from the U.S. Navy fell through. Just before the purchase agreement could be finalized, the Sept. 11, 2001, attacks prompted the military to cancel all sales of surplus equipment. We were back to square one.