Project Portfolio - New North Avenue Bridge

Our second North Avenue Bridge venture provided even more of a challenge than the temporary bridge. We were pleased (and relieved) that the temporary bridge deck had performed beyond anyone’s expectations. But the project would not go away.

By early December 2007, the contractor for the new bridge had experienced delays that had pushed construction past normal paving season. The new bridge was essentially complete, except that specified 2-inch latex concrete wearing course had not been poured over the new HPC deck. The contract required the bridge to open before the holidays, and the City of Chicago wanted to keep that pledge to the neighborhood.

So, we were again looking for an answer to an unusual paving question. A concrete solution was considered and rejected; favorable weather conditions required for concrete placement and curing were unlikely. Asphalt paving is possible in cold weather; it is just not usually done in the Midwest, where HMA plants and paving equipment are not set up for regular cold-weather operations. Excuses aside, the paving project was planned and executed over a 10-day period. Highlights:

• Decisions, mix designs and approvals were competed in a few days.
• Bigane Paving had not expected to be working on the bridge again, either. They re-opened their nearby plant for the project. They procured aggregate and arranged for AC delivery. Their paving crews restarted equipment that had been shut down for winter maintenance.
• Seneca Petroleum also brought their terminal back from winter shut-down to provide the asphalt cement.
• Knowing the weather was likely to be below freezing (and it was), equipment to heat and dry the deck was ordered from Florida.
• Because of the uncertainty of using normal emulsion prime, the deck was primed with neat PG 64-22.
• An IL-4.75 mm mix was chosen for the binder lift. The asphalt cement was switched to GTR AC because of its proven toughness and flexibility. This is the first known use of GTR AC with an IL-4.75 mix.
• The SMA surface mix was also GTR-modified. Diabase traprock was selected as the coarse aggregate. Diabase, a dark and dense rock, provides a consistent, low absorptive and skid resistant mix. Also, Diabase seems to hold heat better than other aggregates - a definite advantage on this project. This combination of materials had been first tried on an IL Tollway project earlier in the year. But, the project conditions were not comparable.

This unique project was a challenge and adventure; and one that makes this a special business.

The weather for Bigane Paving was less than ideal on December 13, 2007

The McHugh webcam provided a warm view through the construction fence