[Crowbob]

Zilwaukee:

It is the cables that hold all the segments in compression. At Zilwaukee, each cable is about the size of a man's wrist. Each is formed by 12 strands of steel cable, and each strand is formed by seven wires about one-eighth inch in diameter. There will be about 27,000 miles of eighth-inch wire in the completed 1.5-mile-long bridge.

Each cable is stretched with hydraulic jacks, stressed to nearly 200 tons, and then locked in place with tapered steel wedges, a process called post-tensioning...

Cables in the bridge run through galvanized steel ducts that have been cast into each segment. After a bridge span is complete and construction has progressed down the bridge, all the ducts in the completed span are filled with cement grout under high pressure. The grout cures to become concrete, forming another layer of protection for the steel cables.

Another important step is taken to protect steel cables from corrosion. MDOT's policy requires concrete cracks be repaired if they are larger than .004 inches (about the thickness of a human hair). High pressure injection of an epoxy resin makes the repaired area stronger than the concrete was originally and prevents water seepage. Cracks smaller than .004 inches cannot effectively be injected or sealed.