The I-74 Mississippi River Bridge is the key link connecting the Quad Cities of Davenport and Bettendorf, Iowa to Rock Island and Moline, Ill. Consisting of two separate bridges (the westbound completed in 1935 and the eastbound in 1960), this iconic structure is a major connection for travel and commerce in the area. Built for an average daily traffic count of about 48,000, in 2016, traffic counts exceeded 74,000, causing delays, frequent repairs, and potential structural failure.
The states of Iowa and Illinois engaged partners to rebuild the bridge, and the project became a top transportation priority for the area. Terracon was chosen to play an instrumental role in the $1.2 billion project, which began construction in 2017.
Proficiency in all parts of the multi-faceted design – geotechnical work, state-of-the-art materials testing and project specifications – is how Terracon is contributing to a finished bridge that will provide safe, smooth travel for millions of residents and businesses in the coming years.
Additional details being handled by Terracon include vibration monitoring to prevent damage to existing sewer lines, concrete quality control, and pull testing for guard rail anchor bolts to provide structural safety – all while the current bridge is operable. This project also includes the construction and testing of viaducts connecting the bridge to downtown areas in both states.
With structures so large in nature, one of the most important aspects of the project is the concrete thermal control monitoring, which is Terracon’s main role in the project. Thermal control of the concrete in these large structures is key to prevent thermal cracking during construction. Temperature sensors with leads as short as 4 feet and as long as 100 feet are installed in all footings, columns, arches, and crossbeams (above and below the water) to record the temperature of the concrete 24 hours a day, 365 days per year. The readings are then monitored by the Terracon team, which check the temperatures remotely every four hours to verify they are within the project specifications. Concrete temperatures cannot exceed 160 degrees F, and the differential temperatures between the core and outside faces of the structure cannot differ by more than 20 to 50 degrees F depending upon the time after the pour is complete. Once the core temperatures are within 50 degrees of the average air temperature for the previous 7 days, monitoring is complete, and the forms can be removed.
Safety is always Terracon’s top priority. With the I-74 bridge project, the job site presents unique challenges. The condition of the Mississippi River – the second largest river connected to the second largest drainage system in North America – makes it an ever-changing job site. Distinctive considerations like materials transport via both the water and land, high river levels, extreme heights of the 150-foot columns and acute weather situations require specific experience and diligence. With an office in Bettendorf (one of the Quad Cities), Terracon’s local material technicians, project managers, and field engineers understand these distinct conditions, and are equipped to call on additional resources from our national network if needed.
Tony Jaeger, P.E., received his Bachelor of Science in Civil Engineering from Iowa State University and is the materials department manager in our Bettendorf, Iowa office. He has over 14 years of experience in overseeing and managing construction projects in Iowa, Illinois and Wisconsin and is a past president of the local ASCE chapter. His project experience includes wind farms, hospitals, schools, commercial development, industrial sites, and working with both the Iowa and Illinois Departments of Transportation.