Wacker Drive Video
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The recent re-opening of Wacker Drive in Chicago showcased the talents of Prairie Material's lab and production team. Working with Walsh Construction, Prairie completed the job on time and within budget.

Wacker Drive in Chicago is one of the most important thoroughfares in the city. This double-decked arterial street runs in all four directions into, out of, and around the center of the city and carries more than 60,000 vehicles and thousands of pedestrians each business day. Lower Wacker Drive provides service access for 57 high-rise buildings while the upper level serves as a roadway to distribute traffic for seven major north/south streets and nine east/west streets within the central business district.

The Chicago Department of Transportation reconstructed the crumbling two-mile section that runs from Michigan Avenue to Randolph Street. Because of its importance to Chicago's Loop, CDOT specified crack-resistant, durable concrete with an expected lifespan of 75 to 100 years. The project features the first major use of high-performance concrete (HPC) mix in Illinois.

Local Chicago firm Wiss Janney Elstner Associates Inc. researched more than 40 HPC mixes used in other states. Working with the University of Illinois at Chicago, WJE developed and tested performance criteria for the project which included reaching 6,000 psi in 28 days, while attaining a maximum compressive strength of 9,500 psi. Durability rather than ultra high strength was the goal to avoid cracking and placeability problems. Other requirements included air voids with maximum spacing, a fairly low water/cement ratio, and consistency of aggregates, materials and admixtures over time.

The city then conducted a pre-qualification process for concrete suppliers who could either use the recommended mix design or design their own. Fourteen mixes were tested. Prairie Material won the supply contract using the city's specs. "It's the most difficult job we've ever done," says Gary Hall, quality control technician for Prairie. The demands for consistency, the sheer size of the project and the deadlines created extreme challenges for Prairie's QC and operations teams. At least four QC technicians were constantly on site, testing air content, slump, temperature and weight, to make sure the concrete poured was within specifications. And in one memorable day, Prairie crews poured 2,100 cubic yards of concrete in 12 hours at Wabash and Wacker. One of the most impressive aspects of the project was its speed and efficiency-starting in February 2001 the job finished on schedule in November, 2002.