Henningsen Construction and Dallas County Partner for Repaving Project
When torrential rain delayed a routine Iowa road rehabilitation project, the county and contractors came together to develop a workable solution.
"I like to look at the project as a perfect storm of a lot of little problems," says Andy Case, Assistant Engineer, Dallas County Road Department in Adel, Iowa. "In the end, we got a good final project."
Henningsen Construction of Atlantic, Iowa, began work in May 2014 on a $3.3 million, 7-mile repaving project on P48 and F59 between the towns of Dexter and Redfield for the Dallas County Road Department in Iowa. The old road was more than 40 years old. The company started the road project in dry weather, then the rains came.
"It was a project like we've done before, but like with any project, some unexpected things happened," said Brad Henningsen, Vice President of Henningsen Construction. "This one was a struggle, but we found the right answer. And it turned out to be a good road."
The county closed the road, for safety reasons, while Hennngsen maintained access for residents and farm operations. The road reopened in May 2015.
"Between the rain and the soft subgrade, we needed to stabilize the base," Henningsen says. "If we hadn't done that, we'd probably still be out there."
The Rehabilitation Project
A limited right-of-way situation on P48/F59 precluded stacking pavements, so the contractor had to remove the existing pavement and build fresh. Purchasing additional right-of-way proved too costly and making the road higher would have left the road with a shoulder that would not have met standards.
Crews began by removing and crushing the existing concrete pavement and 4-inches of natural subgrade material beneath that to flatten the foreslopes. As with many Iowa counties, Dallas County in the past paved many roads with 6 inches of non-reinforced, slip-form concrete on top of the natural ground, explains Larry Mattusch, PE, Field Engineer for the Asphalt Paving Association of Iowa.
"They are getting to the point of asking what do we do with them now," Mattusch says. "The roads have done a good job, but they are at the point of needing rehab."
Dallas County opted to replace the road with asphalt perpetual pavement. Crews can mill off a couple inches in future years to replace it, rather than the road needing another complete rehabilitation.
"One of the reasons we chose it was on a low-volume county road, the damage the traffic does to it is equivalent to the drastic changes in Iowa temperatures," says Bryan DeJong, Assistant County Engineer/Construction at the Dallas County Road Department. "Perpetual pavement gave us a nice blend, starting at the bottom with a low-void, high-binder content material with less rock that creates a flexible base. As we came up with the intermediate and surface lift, we added more crushed rock and stiffer binder materials."
The 21,600 tons of base material includes a 4-inch thick low-void base, covered with 13,200 tons of a 2.5-inches of intermediate base and 7,800 tons of surface lift materials of 1.5 inches, for smoother riding. The harder top surface can handle farm loads.
"The base will never crack," Mattusch says. He estimates the road will last 25 years, before the surface needs remilling and a century overall.
The costs for concrete and asphalt were about the same, but DeJong reports that the longevity of the perpetual pavement convinced Dallas County to choose asphalt for this job.
"A total replacement of the road is not an easy process," DeJong says. In the future, "we look forward to doing a mill and replace with a much more limited scope of project, with a more limited interruption."
Mattusch says he considers the use of perpetual pavement on this project significant for the asphalt industry in Iowa, as it is the first project of this scale.
The county selected an echelon paving technique for the project, in which multiple lanes are paved side by side, with the rollers passing over the longitudinal joint while it is hot, closing the seam so tightly that it becomes nonexistent. Two pavers were staggered by a few feet.
"We have been doing this for the last 15 years and found it to be a positive thing for eliminating centerline joint problems," DeJong says. "We feel it's a long-term, better-quality product in the end."
Rain and Other Delays
Initially, subcontractor Peterson Contractors of Reinbeck, Iowa, employed a heavy crushing machine, which slowed production as it began sinking into the moist, fragile ground, DeJong explains. The county met with the general and subcontractor to devise an alternative plan, where the crusher could continue to move without interfering with the natural sub base.
"The existing pavement had performed well over the years, so we didn't expect to see soft spots, but when we opened it up and let the crusher run on top of it, it exposed weak spots," Case says.
The county had planned to reuse the crushed pavement as a base material for the new road and shoulder. After removing the pavement and the Iowa soil subgrade, heavy rains created a curb and gutter effect, and the water became trapped under the road, Case reports.
"The crushed concrete disappeared into the soil," Case says. "We actually used all of the material trying to keep some rock in the base."
With all of the rain, the base had to be reworked so many times and dried, and more material brought in, that much of the original shape, profiles and slopes determined by the GPS machine control system used by the contractor also vanished. Traditionally, the county would have placed stakes, Case explains, but the contract had called for the contractor to handle construction surveying.
The county met with representatives of the Asphalt Paving Association of Iowa (APAI) and geotechnical engineers Construction Materials Testing of Des Moines, Iowa, to come up with solution.
"We decided to use fly ash and mix it in with the subbase to firm it up and dry it up, so it would be strong enough to pave on," DeJong recalls. "It was expensive and hard to get enough of that much fly ash on short notice, but it worked very well. It made a nice firm base to pave in that I think will hold up for a long time."
Henningsen completed grading and base work and placed an intermediate layer in 2014. Then this spring, Henningsen milled off a portion of the intermediate layer and paved the surface layer. Shouldering, painting of the centerline and edge lines and seeding of grass followed paving.
DeJong credits Mattusch and Bill Rosener, Executive Vice President of APAI with helping to keep the job rolling and serving as a liaison with the contractors.
"I don't know if we would have the product we do without their help," DeJong says.