Piers are threaded onto a matching pattern of rebar extending from the footings; ports in the piers will be grouted to lock the assembly together.
Credit: County Materials Corp. Piers are threaded onto a matching pattern of rebar extending from the footings; ports in the piers will be grouted to lock the assembly together.

A bridge built with prestressed concrete elements manufactured by County Materials Corporation, Marathon, Wis., earned special recognition from the Wisconsin Department of Transportation in January 2015. The bridge spans Siggelkow Road in Dane County, and is part of the I-39/90 Expansion Project currently underway to address safety and congestion concerns between Madison and the Wisconsin-Illinois border. Lunda Construction worked closely with County Materials to complete the project, which uses an accelerated bridge construction (ABC) process.

In contrast to typical bridge construction, where piers and pier caps would be cast in place, with ABC the piers and caps were precast offsite at County Materials’ fully enclosed plant in Janesville, Wis., and delivered to the jobsite by truck. County Materials supplied 20 prestressed girders (each 110 feet to 116 feet long); five 16.5-foot-tall pier columns (measuring 3.5x4 feet in cross section), and two 39-foot-long pier caps for the Siggelkow Road bridge project. The pier caps approached 100,000 pounds each, and were hauled to the site with a specialized transporter.

Before delivery of the precast elements, footings were cast in place by Lunda supported by piles. A precise pattern of reinforcing steel extended from each footing and was matched to splice sleeves cast into the piers. “There were tight tolerances of only about 0.25 inches,” says Chris Kirchner, corporate quality control manager for County Materials. “But everything matched perfectly.”

Once in place, grout was pumped in via ports in the piers and everything was plumbed and leveled. Similar rebar splices extending from the pier caps were also mated with splice sleeves in the piers and grouted. The girders were then positioned atop the pier caps. Using this technique, the onsite erection of the bridge structure took only days, followed by conventional concrete construction to place the deck.

The project required a great deal of cooperation between County Materials, Lunda Construction, and Wisconsin DOT. Lunda built the formwork and fabricated the templates to match the splices, and County Materials tied the rebar cages and executed the pour. “We used a high-performance concrete mix with entrained air, and a slump of about 7 inches achieved using a high-range water reducer. With this mix we were able to strip the forms the next day,” says Kirchner.

Wisconsin DOT expects ABC construction to benefit similar projects in the future. “This project allowed us to gain an understanding of the constructability for these types of prefabrication and assembly techniques and demonstrates the department’s use of innovative construction methods to accelerate bridge construction — that is, ABC concepts,” says Daniel Tyler with Wisconsin DOT’s Bureau of Project Development.

Anne Michelsen is a freelance writer with Green Ink Copywriting, Negaunee, Mich.