Building a 100-year bridge

Rebuilding Upper and Lower Wacker Drive in Chicago, workers place high-performance concrete on a 2,800-square-foot upper deck placement. The white plastic ducts house post-tensioning cables. Specifications call for a 100-year service life. Photos: Joe Nasvik

A worker sets up the form superstructure.

A worker puts the finishing touches on a beam form. Notice the close truss spacing for the deck spanning a traffic lane below.

Testing and quality control are seen as vital to the project's success. Flood Testing Laboratories represented McHugh Construction, making sure ready-mix trucks met specifications before unloading.

The top 2 inches of the deck is latex-modified concrete to provide an impermeable surface that resists chloride. This layer is intended to be sacrificial and will be replaced as needed.

The high-performance concrete used on this project included silica fume. Because slight amounts of water loss in silica-fume concrete results in cracking, curing blankets were placed and saturated shortly after the concrete was placed.

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