UPDATED 04/15/11 11:22 a.m.

CHICAGO (CBS) — Work on Wacker Drive has been in progress for a while, and now with new support columns in place, crews have started pouring new concrete for the upper debt.

As CBS 2’s Susan Carlson reports, despite a biting wind and less-than-ideal conditions for construction, work has been in progress since 5 a.m. nonstop.

The City of Chicago says 60,000 cars travel on Wacker Drive every day, and the new pavement is expected to last 100 years to come.

Officials have been preparing for this monumental step in the Wacker Drive project for two years.

“What you see behind us are the two concrete pumps. Each pump is running independently, and we have crews of workers that are setting and placing and finishing the concrete,” said Chicago Department of Transportation coordinating engineer John Sadler.

Right now, crews are rebuilding the intersection of Wacker Drive from Randolph Street. It is the first of seven intersections on the north-south leg of Wacker Drive to be rebuilt.

The current work, which extends from Randolph Street to about 200 feet south of Washington Street, will be completed midsummer. After that, crews will work on Wacker Drive from Washington Street to Monroe Street, and next year, from Monroe Street to Van Buren Street.

The amount of concrete being poured from the hoses Friday at Wacker and Randolph alone was 1,100 cubic yards. That is the equivalent of 18 city blocks, or 2 1/4 miles.

Sadler explained how the concrete will stay in place once it’s dry.

“Inside the majority of those white ducts are the post-tension strands, and that will be pulled taut once the concrete gains specific strength,” Sadler said, “so we’re taking cylinders out here, and we’ll be breaking those cylinders periodically to know how the concrete is hardening.”

It’s a process that can’t be interrupted.

“Once we start, we really can’t stop, and the concrete has a specific time, from the time that the water hits it at the plant to the time that we have it here on the deck,” Sadler said.

There is no viewing area for spectators to watch, but that didn’t stop curious onlookers.

“It’s kind of amazing how much they’re putting out in such a short time,” said John Neiman. “I had no idea they’d use cranes just to dump this stuff on. This is pretty crazy.”

For those in the thick of the project, Sadler said it was “very fun.”

Crews are supposed to be finished pouring the concrete at 1 p.m., but finishing touches will be undertaken until about 5 p.m. It takes 90 minutes for the concrete to start to harden, but engineers say it will take at least two weeks before the concrete reaches full strength.

The Wacker reconstruction began Jan. 3 and is proceeding south. The current phase is scheduled to last through mid-summer. Crews will then rebuild the roadway from just south of Washington to Monroe Street. In 2012, crews will rebuild between Monroe and Van Buren streets.

City officials said last week that the project is on schedule and within budget so far.

A double-decker road along the Chicago River was part of Daniel Burnham’s 1909 Plan for Chicago. The east-west Wacker Drive was completed in 1926, replacing River Street and most of South Water Street, while the north-south leg was finished in 1954, replacing Market Street.