The $245 million kcICON project in Kansas City included the rehabilitation of more than four miles of Interstates 29 and 35—upgrading them from four to six lanes, rebuilding numerous on and off ramps, and reconfiguring several interchanges. In addition, the construction of the new cable-stayed Christopher S. Bond Bridge replaced the Paseo Bridge that spanned the Missouri River since 1954. The Missouri Department of Transportation (MoDOT) estimated building the structures would require 50,000 cubic yards of concrete.
Once the project began, a unique challenge developed in completing a critical portion of the cable-stayed bridge. The deck construction included precast concrete panels, each weighing about 60,000 pounds. The panels, designed with post-tensioning bars, were formed in a precast yard and hauled to the site. Once placed and positioned, contractors noticed an 18-inch-wide, 12-inch-deep void that needed to be filled with poured concrete to connect and solidify the bridge deck. The contractors, Paseo Corridor Constructors, Kansas City—a joint venture of Clarkson Construction Co., Kansas City; Massman Construction Co., Kansas City; and Kiewit Construction, Omaha—knew the task could not be delayed and would have to accomplish the pour in the dead of winter.
“Taking into account the cold-weather concreting considerations for proper curing, we had to maintain our concrete pour at a minimum temperature of 46° F for seven consecutive days,” says Dale Helmig, project manager for Massman. “We were on a tight schedule and looking at outdoor temperatures near or below zero, so we had to find a way to keep the concrete warm.”
Various methods were contemplated, but it was decided the most effective and cost-efficient way was to use an electric-powered concrete curing blanket from Powerblanket LLC, Salt Lake City. Unlike radiant heat from furnace and blower alternatives, the blankets delivered direct heat, helping to cure the concrete without cracking or defects.
“We gave the engineers the boundary conditions we had to keep the concrete pour within at least 46° F at the bottom but no warmer than 82° F at the top,” says Helmig. “They performed the calculations and determined the appropriate blankets needed.”
The Extra Hot Series EH0612 blankets were chosen, and to ensure they did not overheat the concrete, Massman requested that each of the 34 blankets be equipped with an external digital thermostat. The 6x12-foot blankets, which exceeded the 18-inch width of the void, were used to preheat the precast concrete panels that formed the sides of the void prior to the pour. The process helped minimize each panel’s ability to absorb heat from the freshly poured concrete as well as preventing too rapid of a temperature change upon placement of the new concrete.
“It was awfully cold, but the blankets did their job keeping the concrete temperatures within spec,” says Helmig. “We achieved the psi levels we had targeted, and it turned out to be a successful operation. We didn’t have the time to wait out the winter for the temperatures to become more moderate. The curing blankets certainly played an important role in keeping us on schedule and not having to postpone the pour.”
The contractor kept the momentum of its significant winter construction going into the spring and summer and work progressed so well that by late October 2010, the Christopher S. Bond Bridge opened to traffic. Soon after, all Interstate 29 and 35 lanes and ramps opened in December 2010, marking the completion of the project six months ahead of schedule.
“Using the concrete curing blankets turned out to be the fastest, simplest means of getting the job done correctly,” says Helmig.