Two Counties, Two Road Types, One Solution

Take an 11.1-mile stretch of country road, constructed of concrete and asphalt, which straddles two county jurisdictions, with one favoring concrete and the other asphalt, and you have project that calls for an innovative solution that satisfies both. That pretty much sums up the challenge Norris Asphalt Paving of Ottumwa, IA faced when submitting a bid to rebuild Route N58 in Western Iowa.

As a past Sheldon G. Hayes Award recipient, Norris proved to be up to the challenge and was awarded the $2+ million contract in 2003, completing the final top mat earlier this spring. Putting together a proposal that satisfied the engineering requirements of two different government bodies, Carroll and Greene counties, posed the initial challenge for Norris. The two end sections of the two-lane highway were constructed of Portland concrete, with the center section constructed of full-depth asphalt.

"We were working with one county engineer who was a staunch supporter of concrete and that required some extra work to convince him of the benefits of an asphalt constructed project," says Brady Meldrem, Norris president.

Crushin' concrete

The project called for rubblization of the six-inch Portland concrete cement of the three-mile north and four-mile south sections of the road, and cold in-place milling of the center 12-inch-thick asphalt section. The concrete was removed, crushed and metal rebar removed, and then placed back on the roadbed to create a base for the new road.

Manatt's Inc. of Brooklyn, IA was the subcontractor in charge of crushing the concrete. Jason Spooner, Manatt's project manager, says an Impact Tech Impactor 2000 was used to rubblize the concrete roadbed. Using a John Deere 4955 tractor, the concrete impactor was pulled over the road more than a dozen times to break the concrete into 12-inch or smaller chunks in preparation for the crushing operation. A Caterpillar 235 excavator was used to load the rubblized concrete into Manatt's mobile twin crushing plant, comprised of an Excel 2500 primary crusher and an Excel 1500 secondary crusher mounted on paving tracks. The primary crusher reduced the concrete rubble to three-inch chunks, with the secondary crusher reducing the concrete to 1 1/2-inch particles before placing a windrow of the crushed material back on the roadbed. Magnets inside the crushing units were used to extract rebar from the concrete.

After the crushed concrete was graded over the 12-foot-wide roadbed, a Caterpillar M565 reclaimer was used to incorporate the crushed material 12 inches into the soil sub-base. A portion of the south section of roadway required fly-ash stabilization to the crushed concrete and wet soil to help the incorporated material bind together during compaction.

It took Spooner and a crew of eight six to seven weeks to rubblize seven miles of concrete, crush the material, and to fine grade and compact the new roadbed.

Asphalt milling

Midstate Reclamation Inc. of Lakeville, MN was contracted to mill the three-mile center full-depth asphalt section of the project. Using a cold in-place recycling train comprised of a Caterpillar PR1000 milling machine that milled the top four inches of the 12-inch-thick asphalt road, and a CRMX2 recycling system to crush, screen and add an oil emulsion before placing a windrow back down on the roadbed, Midstate completed its portion of the project in three days. A Cedarapids 561 paver was used to apply the recycled asphalt back on the roadbed before Norris could begin laying fresh hot mix asphalt. A high-float oil emulsion was added to the milled asphalt to help stabilize the base.

Norris also had to remove and replace storm culverts located along the stretch of the road. Pre-cast concrete boxes were used to speed up that portion of the project.

New road takes shape

With all the prep work completed, Bob Mobley, Norris project superintendent, and his paving crews moved in to begin placing mats of fresh HMA. Twenty thousand tons of mix had to be placed over the crushed concrete sections to raise those portions of the road four inches to height of the center asphalt section.

Then, 11,200 tons of HMA was placed as an inch and a half intermediate course over the entire stretch of road late last fall. A Cedarapids 551 and a Vogele paver were used to lay the base and intermediate courses. An Ingersoll Rand 110 breakdown roller, a Bomag pneumatic roller, and a Sakai static finishing roller were used to achieve density specifications.

Earlier this year, Norris paving crews returned to place two 1 1/4-inch mats to finish the project. They used a new Low Tech 195 paver with a Roadtec Shuttle Buggy to lay 19,500 tons of asphalt in the final two lifts.

All the HMA used on the project was produced at Norris' portable Gencor 400-tph plant, and mix design had to meet Iowa DOT gyratory void standards and be comprised of at least 45 percent crushed aggregate measuring a 1/2 to 3/4 inches in size.

Dave Paulson, Carroll County engineer, says an additional inch of HMA was requested following completion of the intermediate course in order to achieve approximately eight inches of new road surfacing when the project was completed.

"That had always been a target we wanted to hit in the reconstruction of this road, due to the potential high truck traffic expected," Paulson says.

As primary contractor, Norris began work on the project in mid-August 2003, and completed initial paving by November, and then returned this spring to place the final two top lifts.

Norris had 130 construction days built into the original proposal, and completed the project in 70 days, receiving a $23,000 smoothness bonus, with a 97.26 percentage smoothness rating on the project.

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