ASPIRE is a quarterly magazine published by PCI in cooperation with the associations of the National Concrete Bridge Council. The editorial content focuses on the latest technology and key issues in the Concrete Bridge Industry.
Issue link: http://www.aspiremagazinebyengineers.com/i/697527
32 | ASPIRE Summer 2016 cycles each year with deicing chemicals applied for at least 5 months out of the year. These environmental conditions, along with high traffic levels, require durable, crack- resistant concrete in order to maximize the service life of the epoxy-coated steel reinforced concrete bridge decks. Prior to 2013, the Illinois Tollway used a prescriptive concrete mixture proportioning approach and had standard superstructure mixtures for bridge decks with a cement content of 605 to 705 pounds of cement per cubic yard. The standard mixtures typically contained either no supplementary cementitious materials or only small amounts of fly ash, and would consist of only one coarse aggregate gradation. This required a concrete with excessive cement paste and, as a result, the mixture was susceptible to shrinkage cracking. Early age cracking was seen on many bridge decks built on the Illinois Tollway since the initial roadways were built and opened to traffic in 1958. In August 2011, the Illinois Tollway's Board of Directors adopted the 15-year, $12 billion capital program called Move Illinois: The Illinois Tollway Driving the Future . The Move Illinois program will improve mobility, relieve congestion, reduce pollution, and link economies across Northern Illinois. It includes rebuilding and widening the Jane Addams Memorial Tollway (Interstate 90); constructing the all-electronic Elgin O'Hare Western Access Project; constructing a new interchange to connect the Tri-State Tollway (Interstate 294) to Interstate 57; and many other system-wide projects to keep the existing tollway system in good repair. These projects will require the reconstruction or construction of more than 100 bridges. Tollway bridge decks built before 2013 have been shown to have a typical service life of only 20 to 35 years before the need for repeated deck or joint repairs begin. They also have a total life of only 35 to 50 years before a complete deck replacement is needed. Initial research was conducted by CTLGroup and the University of Illinois at Urbana- Champaign in 2012 and 2013 with the objective of extending the service life of Illinois Tollway bridge decks. That research developed mixture-proportioning specifications that would produce a deck concrete with minimal shrinkage cracking potential and with moderate resistance to chloride penetration. The Illinois Tollway elected to take a performance approach for high-performance concrete (HPC) bridge deck mixture proportions compared to the prescriptive approach that was used in the past, and is Early age bridge deck cracking is a major concern for transpor tation agencies, including the Illinois Tollway, which maintains 440 bridge decks ranging in thickness from 7.5 to 8 in. Early age cracking can lead to a reduction in the initiation time of steel reinforcement corrosion and a decrease in service life of the bridge deck. The negative effects of corrosion can be further compounded by freezing and thawing cycles and the use of chloride deicing chemicals. Given the location of the 286-mile Illinois Tollway system in Northern Illinois, bridge decks experience many freezing and thawing Improving Bridge Deck Service Life The Interstate 90 bridge over the Fox River is an eight-span structure with an overall length of just over 1300 ft. Photo: Joe Pitlik. C O N C R E T E B R I D G E T E C H N O L O G Y Use of crack-resistant, high-performance concrete bridge decks at the Illinois Tollway by Steven L. Gillen, Illinois Tollway and Daniel J. Gancarz, Applied Research Associates Inc. Crack-resistant, high-performance concrete and stainless steel reinforcement were used for the Interstate 90 bridge over the Fox River. Photo: Joe Pitlik.