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Water, cement, soil studies, surveying, engineering, GPS, milling, recycling, paving and striping. Individually, these words might not seem like they’re related. However, each plays a role in full depth reclamation (FDR), a unique process used by the Weld County Department of Public Works to create more resilient paved roads and save taxpayers money in the process.
“We want to eliminate moisture from getting under the asphalt and causing cracks and potholes in the road surface,” Weld County Public Works Director Jay McDonald said, explaining the goal of FDR. “Water that runs alongside a road will migrate and get under the asphalt if we don’t do something.”
Public Works has chosen FDR as a repair method on many county roads because the process focuses on what’s beneath the road to ensure the quality and extend the life of what’s on top.
“Asphalt is only as good as what’s underneath it,” said Weld County Public Works Road and Bridge Construction Supervisor Duane Naibauer, explaining how a stronger road base below the asphalt repels water before it settles underneath and damages the road’s surface.
By using a mixture of the road’s existing asphalt and subgrade combined with water and cement, Public Works can sculpt road surfaces — many of which have helped roads exceed their expected design life. FDR can be applied on two- to three-mile projects or on bigger ones such as Weld County Road 49.
“The initial design life for asphalt roads is 20 years, but right now, data shows we’re getting 23 to 25 years,” Weld County Pavement Management Supervisor Josh Holbrook said. “We expect those numbers to keep growing.”
The benefits of FDR extend beyond building better roads. Improvements are also done more quickly compared to other methods. On a two-mile repair project underway on Weld County Road 79 outside of Hereford, the ability to reuse the existing asphalt eliminates the need for trucks to export and import material, which makes project completion take just a few weeks as opposed to nearly the entire summer.
“With FDR, a project like 79 will take us about three weeks. The conventional construction method would turn it into a 12-week project,” Naibauer said.
Perhaps more noteworthy are the taxpayer dollars saved as all of the work in the FDR process is done by Public Works staff. This keeps the department from having to hire a private contractor — a move that could make a project like county road 79 double in price.
Every FDR project begins with surveying the road surface elevations and recommending how much existing asphalt should be reclaimed — typically between one to six inches depending on the existing road conditions — to construct the new road base. The Public Works soils lab studies the soils deep in the road’s subsurface, which helps staff know how much cement to add to the recycled road base. Once the soil results have been analyzed, engineers are responsible for the new design of the road. The information is then loaded into operations equipment, where GPS technology assists the drivers of motor graders in the repair process.
“The surveyor loads the desired design into a computer in our motor graders,” Naibauer said. “When our crew brings that up, it shows the desired horizonal and vertical alignment of the road and how much asphalt should be removed.”
From there, the appropriate amount of cement is milled in and water is added to hydrate the cement treated base that will serve as the new base. After that, the reclaimed asphalt and existing road base are mixed in with the cement. Then, the cement treated base is processed and a new driving surface is paved and striped before a final inspection is done.
Given the expense of new asphalt – $250,000 per mile – the many steps taken to recycle and reuse old asphalt are well worth it, both to the traveling public and taxpayers.
“Public Works is always trying to find innovative ways to improve our product by not overpaying for projects or reducing costs when possible. With this process, we are recycling materials we’ve already paid for,” Weld County Public Works Deputy Director Elizabeth Relford said. “We’re reusing material, and that’s better on the environment. Nothing goes to waste.”
By Baker Geist, Weld County Communications Specialist
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