SALT LAKE CITY (AP) — Just two to four years after the rebuilding of nearly 130 bridges in the fast-track Interstate 15 reconstruction, some of the new decks are showing cracking.
Water containing salt used to melt snow and ice has seeped through the decks of several of the bridges, leaving behind salt-encrusted cracks that can be seen from below.
Some innovative construction methods were used in the hurried project, and the problems raise the question of whether costly maintenance will be needed over the freeway’s promised 75-year life.
David Nazare, bridge engineer for the Utah Department of Transportation, does not believe so, “but we do want to know what effects these innovative things will have on deck cracking. It becomes a durability issue, and (tells UDOT) what we have to do for maintenance,” he told The Salt Lake Tribune.
Another problem associated with bridge construction was disclosed last summer. Crews discovered that a new type of joint used in some places was causing concrete to break up. Work began last fall and will continue this spring to repair the joints. UDOT’s insurance carrier is to pay the bill.
UDOT has commissioned a yearlong study by a University of Utah civil-engineering professor and his students to evaluate up to 72 I-15 bridges where nontraditional methods were used in their construction.
Professor Lawrence Reaveley, chairman of the university’s Civil and Environmental Engineering Department, said he is just getting started.
“We have no conclusions, no results at this point,” he said. “We know there is some cracking, but the extent of it, I couldn’t tell you. We will be looking to see if there is a trend.”
Nazare said such cracking is common in bridge structures, no matter whether they are built with traditional or innovative methods. “Most of the cracks occur within the first one or two years,” he said.
Eventually, the decks deteriorate to the point where they must be replaced. While the freeway and its bridges are designed to last 75 years —more than twice as long as the original I-15, built in the 1960s and 1970s — engineers expect the bridge decks will have to be replaced within the next 30 to 40 years.
That is how long it should take for the chlorides in the salt to eventually start deteriorating the reinforcing steel buried deep within the decks.
Traditionally, bridge decks are poured between girders, with plywood sheets holding the deck concrete in place while it dries.
On some of the bridges for this project, builders used 4-in. (10 cm) thick concrete panels instead of wood and the panels were kept in place after the concrete dried.
In addition, a silica fume was tried with the intent of making the concrete denser and stalling saturation by the salt solutions.
“We want to ask:, did it (silica fume) add to the cracking we now see? If (Reaveley’s research) shows it did, we do not want to use it any more,” Nazare said.
Reconstruction of the freeway through Salt Lake Valley was on an accelerated timetable to have it done before the Olympics.
Critics said that for political reasons, Gov. Mike Leavitt waited until his second term to propose the reconstruction. Leavitt said the project was not feasible until then.
