Just yards inside the mouth of the Callahan Tunnel, workers are toiling around the clock, blasting away with high-pressured water guns at the five inches of concrete that separate the surface of the harbor tunnel from the steel beams that support the roadway.

It’s the eleventh day of construction on the 53-year-old tunnel, and already highway officials are optimistic that contractors will finish ahead of schedule, which calls for the tunnel connecting downtown Boston to Logan Airport to reopen mid-March.

MassDOT Highway Administrator Frank DePaola is so pleased with the progress that he’s already talking about doing it again in two years, only this time with the older, parallel Sumner Tunnel.

The Callahan Tunnel closed to traffic on Dec. 27, forcing motorists to devise alternate routes to Logan Airport or out of the city into East Boston. The state established three main detour routes through the Ted Williams Tunnel/Mass Turnpike Eastbound, over the Tobin Bridge, or for motorists coming from points north - along Rte. 16 East to 1A South.
“We think the contractor will be able to definitely finish on time and possibly ahead of schedule and get some of that bonus,” DePaola told reporters Tuesday as he prepared to lead a tour of the work.

DePaola said so far his department has not received much negative feedback about the traffic detours, and he believes the strategy to be working well save for some minor changes made to signage to ensure drivers understand the new routes.

Frigid temperatures that have blanketed the region for much of the past week have also presented few complications, according to project managers. A McCourt project official said workers feared the tunnel might turn into an “ice rink” after the brief warm-up and quick return to freezing temperatures this week, but have been able so far to avoid problematic icing.

The Callahan Tunnel opened in 1961, and last underwent a renovation in 1990s. Today it carries traffic from Interstate 93 southbound and downtown Boston under the harbor to Logan International Airport and Route 1A in East Boston, averaging 28,000 vehicles per day.

“It’s in pretty tough shape. The concrete’s coming up pretty good, so it’s time was up. We’re here just in time, as they say, to make sure this tunnel can last for another 50-plus years,” DePaola said.

Monday presented the first real test for traffic planners with most residents back to work after the holiday vacation season. DePaola said that by 7:30 p.m. traffic had cleared and was free flowing in the Ted Williams tunnel.

The $19.3 million project – awarded to McCourt Construction of South Boston – calls for replacement of the deck, curbing and wall panels. Including design, traffic management plans and other expenses, the total MassDOT budget for the project is $30 million.

For every day before March 12 that McCourt can finish the initial work to reopen the roadway, the company stands to receive a $71,000 bonus, up to $2 million.

The work began by scraping up the asphalt surface of the roadway. The next phase of demolition – currently underway – involves breaking up the concrete deck of the tunnel to expose the steel beams and rebar that support the roadway.

Construction workers are using a technique called hydraulic demolition that involves high-pressured water guns that blast the concrete into a mixture of mud and hand-sized rocks that can be carried away. While a traditional pressure washer might reach 1,500 pounds of water pressure, the guns being used by McCourt workers deliver a much bigger punch with 36,000 pounds of pressure being used to pulverize the concrete roadway.

The added benefit of using water, according to a construction official on the project, is that it suppresses dust in the tunnel and gives workers more control, compared to a jackhammer, over how deep they cut. Once the mile of concrete is removed and the rebar cut away, workers will lay a new concrete deck on the tunnel beams and replace the wall panels that have been gone since 2012 with new stainless steel anchors in hopes of avoiding the type of erosion they saw with the previous galvanized metal.

So far, about 20 percent of the concrete tunnel deck has been removed. Demolition is expected to continue for another couple of weeks.

It’s warmer in the tunnel than it is outside, the workers shielded from the biting winds howling on the city streets. As an added benefit, the water vapor from the pressure hoses creates a slight humidity in the tunnel that offers a reprieve from the dry winter air, while the ground that might otherwise be a mud pit is mostly solid from the cold.

In two 12-hour shifts, work continues around the clock starting near the mouth of the tunnel during the day and working deeper into the tunnel by night to mitigate noise in the surrounding neighborhoods. Still, DePaola said there have been some noise complaints since work started and those living above the tunnel can occasionally feel the rumble of construction equipment moving in the tunnel below.

The impetus for the reconstruction project to replace the deck and wall panels of the tunnel goes back more than a year to Christmas Eve 2012 when one of the tunnel’s 2,800 wall panels dislodged from its supports and crashed down into the roadway. No one was injured.
The day after the holiday, crews went into the tunnel to conduct pull tests on the remaining wall panels and found 127 additional tiles loose. As a safety precaution, all wall panels were removed.

While inspecting the condition of the tunnel, DePaola said, crews observed the deterioration of much of the concrete in the tunnel and over the next year hatched plans now in effect to replace the roadway and wall panels on a construction timeline expedited by closing the tunnel to all traffic for two-and-half months during the winter while no other work was being done on the roads carrying detoured traffic.

The Sumner Tunnel, which opened in 1934, runs parallel to the Callahan Tunnel and initially carried traffic under the Boston Harbor in both directions until the Callahan opened nearly 30 years later.

Though it was renovated in the 1990s, the condition of the concrete in the Sumner is similar to that in the Callahan, DePaola said.

“It can last a little bit longer but we think the concrete is probably in similar shape,” DePaola said.

Based on the experience so far in the Callahan, DePaola said he would lean toward a similar shutdown of the Sumner Tunnel for renovations the winter after next in 2016.