Every day about 140,000 motorists travel the bone-shaking, 1.6-mile Interstate 70 viaduct in Denver between Brighton and Colorado boulevards.
Bouncing over the 44-year-old bridge’s worn joints isn’t fun, but travelers might be even more alarmed to see what is happening below.
In many locations, water and de-icing fluids have leaked through the expansion joints and infiltrated concrete piers, girders and columns.
The seepage has caused reinforcing steel embedded in the structure to corrode and swell, and that expansion, in turn, has caused surface sections of the concrete to crack off.
“We have reports that magnesium chloride can decrease the compressive strength of concrete up to 70 percent,” said Colorado Department of Transportation engineer Jeff Anderson, referring to the corrosive effect of the de-icing material.
The I-70 viaduct is one of 125 state-owned and maintained bridges rated in “poor” condition and needing replacement.
Yet because CDOT has no prospect for covering the $800 million cost of rebuilding the structure, workers in the next week or so will start applying what agency officials describe as a $21.6 million “Band-Aid.”
Contractors will spend at least two years replacing 60 expansion joints on the bridge. Thirty-two of the joints will be “locked” — reconstructed as solid bridge deck — while 28 will be rebuilt as new expansion joints.
Engineers determined that the 28 are enough “to allow the bridge to breathe,” Anderson said.
The viaduct was built in the early 1960s for $12.5 million, and a complete reconstruction would easily make it CDOT’s most expensive bridge project.
To replace or do major rehabilitation on the other 124 bridges in the state system that are rated in poor condition will cost a total of $600 million, according to CDOT.
Setting priorities
At an estimated cost of $800 million, replacing the I-70 viaduct alone “represents all of our annual budget,” said CDOT chief engineer Pamela Hutton. “The dilemma for us is how in the world do we fund just that piece?”
Last week, Anderson and another CDOT engineer, Steve Pineiro, pointed out the viaduct’s defects as they toured the mile-plus stretch of East 46th Avenue running beneath the elevated highway.
Leaking liquids and Denver’s freeze- and-thaw cycles have led to the heaving of the asphalt roadbed at expansion joints, Pineiro said. Motorists on the bridge experience the failed joints as a series of bumps every 200 feet or so.
Fluids also have leaked below along the length of the viaduct where the east- and westbound lanes meet in the middle. Here too, it has resulted in cracked or missing concrete and exposed rebar underneath.
As part of the expansion-joint repair, the bridge median will be reconstructed as new roadbed with upgraded safety barriers.
Collapse of the I-35W bridge in Minneapolis in August 2007 caused states to step up bridge inspection and highlighted the shortfall in the billions of dollars needed to rebuild the nation’s “structurally deficient” bridges.
The I-70 viaduct carries that rating, though it does not necessarily mean it is unsafe or in danger of collapse, Anderson said.
If a girder connection failed because of eroded concrete and steel, it might cause a “deflection,” or sinking of the bridge deck, but likely not a collapse since the load carried by that girder would be redistributed to adjacent girders, he said.
Looking to the long term
CDOT hopes the expansion-joint project on the viaduct will give it at least another 10 to 15 years of useful life, time enough for the state to figure out how to pay for reconstruction or relocation of I-70 in that area.
The portion of the I-70 viaduct between Washington Street and Brighton Boulevard was rebuilt between 1998 and 2003 for about $89 million.
A current environmental study considering possible widening of I-70 from the Mousetrap east to Tower Road includes the option of reconstructing the rest of the viaduct.
An alternative to that plan would reroute I-70 out of its current alignment — eliminating the viaduct — and run the highway from a point near Brighton Boulevard to the northeast until it ties in with Interstate 270. At that point, it would share the right of way with 270 before rejoining the old I-70 alignment at Quebec Street.
In about a year, the study will settle on one of the alternatives as the preferred option.
On last week’s tour of the viaduct, Anderson agreed that officials eventually must consider a long-term solution.
At a spot under the elevated highway near the Purina pet food factory, Anderson looked up at a pier cap pocked with missing concrete and exposed rebar. It sits under one of the deteriorated expansion joints.
Similarly damaged girders tie in to the pier, which rests on columns that also display eroded concrete and steel.
“You can replace the joint,” he said, “but it’s a temporary fix.”
Jeffrey Leib: 303-954-1645 or jleib@denverpost.com
