Still, says Raney, Louisville is using its asset management system to establish priorities for bridge and pavement rehabilitation, and the city’s maintenance department is focused on critical preservation activities, including replacement of deteriorated cross drains and shoulder repairs.

Ironically, our conversation with Raney was delayed and truncated by severe weather and flooding in the Louisville area last spring, a reminder to us all in this period of taut budgets and growing needs that all strategies and tactics are subject to the whims of natural events.

Working a Watershed in Winter

Recession or not, the environment needs help

Even in the dark shadows of the Great Recession, the need to develop road designs with sounder environmental attributes is a driving force in many areas.

In the Twin Cities suburb of Robbinsdale, a partnership of road and watershed management agencies is working with the Minnesota Asphalt Pavement Association and the consulting firm of Wenck Associates on a three-year study to see if the use of porous asphalt can reduce the need for road salt in an environmentally sensitive watershed area.

The Shingle Creek Paired Intersection Project was launched in 2009 with a $282,000 research grant and the construction of 150-foot test sections of porous asphalt and conventional asphalt on a Robbinsdale residential street with a sandy subgrade. A second test site was built in 2010 on a clay/loam subgrade.

“We will monitor these sections for three years,” says Ed Matthiesen, a consultant with Wenck Associates. “We want to estimate the effectiveness of porous asphalt in reducing the need for salt as a de-icer and determine whether porous asphalt can stand up to the rigors of residential street use.” In addition, the study will determine short-term maintenance requirements and project long-term requirements, and the team will measure the water quality and quantity performance of porous asphalt.

Though the study won’t be completed until 2013, the intermediate results have been promising. “The control sections with salt tend to melt faster than the unsalted porous asphalt sections, but there is less refreezing of melted snow and ice on the porous pavement,” says Matthiesen. “And it appears to work just as well as salted pavement at clearing ice buildup.”

After two winters for one section, and one winter for the other, Matthiesen says the porous pavements are holding up well with no visible signs of distress from traffic, plows or weather.

The porous test sections include 1.5 to 2.5 inches of asphalt with 40-percent void, a choker layer of 0.5 to 1.0 inches, and a 0.25- to 0.75-inch layer of porous aggregate. Cellulose fiber and mineral filler were added to the binder to achieve a draindown of less than 0.3 percent.

Temperature sensors have shown the porous asphalt has insulating properties; the test sections are warmer than the control sections an inch below the surface. In addition, the porous sections have been more responsive to solar radiation, producing a faster melt and more bare pavement on sunny days compared to the control sections.