The use of foamed asphalt full-depth recycling to reclaim a scenic road in Utah’s Zion National Park shows how roads in environmentally sensitive areas can be reconstructed economically, and with minimal impact on the ecology.

It also reminds us that the repair and reclamation of roads in our most pristine and vulnerable environments is becoming an increasingly important issue because the popularity of our national parks has grown tremendously over the years. And with the rising popularity has come increased traffic loads that far exceed the structural design of the original pavements.

According to the National Parks Conservation Association, 65% of the 5,000 miles of paved roads in U.S. National Parks are in poor to fair condition. Now stakeholders must ask, "How should these failed roads be rehabilitated in a cost-effective but environmentally sustainable way?"

In the case of Zion Canyon Scenic Drive — and many other National Park roads as well — adding several layers of hot-mix asphalt would not economically or aesthetically solve the inadequate structural strength of the pavement. Instead, the Federal Lands Highway Division of the Federal Highway Administration has turned to full depth reclamation with foamed asphalt as the pavement rehabilitation method of choice.

In FDR, the entire thickness of an asphalt pavement is pulverized in-place and blended with a specified amount of the underlying granular road base materials. To this reclaimed material is added a combination of foamed asphalt and cement stabilizing agents. Just enough asphalt and cement are added to produce a strong yet flexible road base. This process has been used successfully throughout the world and in the U.S., including all Federal Lands Highway Divisions, on roads in Canyon de Chelly National Monument, Arizona; Helena National Forest, Montana; Delaware Water Gap National Recreation Area, New Jersey; and Rocky Mountain National Park, Colorado.

Use of foamed asphalt in Zion National Park minimized the disruption of tourist traffic, eliminated the noise, dust and commotion of pavement demolition and the "ant train" of haul trucks removing demolition materials and replacement with virgin base, and saved countless gallons of expensive fuel used by those trucks and by autos caught in construction-related congestion.

Fatigued and cracked pavement

The highlight of Zion National Park is Zion Canyon, a half-mile deep gorge formed by the Virgin River cutting through the red sandstone of the Colorado Plateau. The Zion Canyon Scenic Drive — a 5-mile-long paved road within the canyon — is one of the most splendid drives in the United States. However, the pavement had moderate to high severity fatigue and block cracking, with rut depths in excess of 0.5 inches. The roadway was in need of a structural rehabilitation.

At the same time, the number of yearly visitors to Zion has more than doubled in the last 20 years, to over 2.5 million. Traffic jams had become so bad that in 1991 cars were banned and a tandem shuttle bus service was begun. These buses are used to continually transport visitors into the main part of the Park and make several stops along the road. Other parks have instituted similar restrictions on the use of cars in their most popular areas.

In 2005, the FHWA Central Federal Lands in Denver funded a pavement rehabilitation project in the park. The 5 miles of the Scenic Drive, and about 1 mile of roadway from the south park entrance to the Scenic Drive, were to be rehabilitated.

The general contractor was Interstate Rock Products of Hurricane, Utah, and the reclamation/ stabilization portion of the work was subcontracted to Son-Haul of Fort Morgan, Colorado. The contract called for full-depth

reclamation of the asphalt pavement and base soils to a depth of 8 inches. The reclaimed material was stabilized with foamed asphalt and Portland cement. After the stabilized base had cured, a 2.5-inch hot-mix asphalt overlay was placed. A single chip seal was to be applied in early 2006 so the roads will have the red color desired by the NPS.

Scott Wolfert, P.E., project manager of the FHWA’s Central Federal Lands, and Robert Quadland of Parsons Brinckerhoff were the inspectors for the FHWA. All quality control testing was done by Travis Howlett of Earth Engineering Consultants of Fort Collins, Colorado. The initial mix design for the foamed asphalt stabilization process was also done be EEC. Sonny Weimer, president of Son-Haul, was the contractor’s QC supervisor.