‘Green’ Paving Technique Reclaims Asphalt Surfaces

When Andrew Braham came to the University of Arkansas, he looked at the faculty members in his department and saw an impressive, if not intimidating, breadth of expertise. The new civil engineering professor asked himself what he could do to carve out his own niche among such a rich and talented group of researchers.

“Even within my area, there were people up and down the hall with years of experience in transportation materials – concrete and asphalt mixtures, not to mention the construction and evaluation techniques related to these materials. I didn’t want to compete with these folks. So I thought about what I could offer. Part of this was finding something that was my own, but I also wanted to contribute. How could I add to the breadth of expertise?”

The answer was maintenance and rehabilitation — or, perhaps more accurately, reclamation. Braham had previous industry experience with an innovative and “green” process by which asphalt surfaces – usually severely damaged roads, highways and parking lots – are removed, processed and treated and then re-applied. Known as full-depth reclamation, the entire process can be done at the construction site, which minimizes the need to transport construction waste or new materials.

“Full-depth reclamation is a pavement rehabilitation technique in which the full, flexible pavement section and a portion of the underlying materials of a damaged surface are pulverized and blended together to produce a homogenous, stabilized base,” says Braham. “In other words, we use all of the existing roadway materials, regardless of their condition, to create a new road that is smooth and structurally sound. All of this is done in situ.”

Because it reduces energy consumption and recycles materials in place, which reduces costs and environmental impact, full-depth reclamation may be the greenest construction process available, Braham says. One study demonstrated that recycling materials can cut overall construction costs in half compared to processes that require the removal and replacement of pavement at the end of its service life. Another study revealed that full-depth reclamation reduced energy consumption up to 70 percent compared to the complete removal and reconstruction of a deteriorated pavement structure.

The essential tool for this technique is a massive construction vehicle that eats pavement. Innocuously dubbed the “reclaimer/stabilizer,” this vehicle looks more like a Mad Max prop, like something Furiosa would drive. It contains a milling drum up to four feet in diameter that grinds and pulverizes distressed pavement and other granular material, mixes the material with dry or liquid stabilizing agents, and then, on the back end, lays down a deep, recycled layer that Braham describes as light and fluffy, like cotton candy.

“It’s sort of like plowing a field,” he says. “Or hoeing a garden.”

Following the reclaimer/stabilizer, other road equipment, including a grader, water truck and various types of compactors, treat the recycled layer to complete the process. The result is a new, smooth surface with greater structural capacity.

Depending on topography and the chemical composition of surface and sub-base materials, full-depth reclamation can be modified to include various stabilization measures. Mechanical, chemical and bituminous stabilization introduce additional granular materials – crushed virgin aggregate or concrete, emulsified asphalt, Portland cement, lime other materials, for example – during the milling process.

Full-depth reclamation can be used on any flexible pavement structure (not concrete), including parking lots, city streets, airport runways and highways, in addition to high-volume suburban roads and lower-volume rural roads. Though not a panacea for all bad roads and damaged pavement – the method is ideal for asphalt road beds 2- to 4-inches deep but typically does not work on road beds deeper than 6 inches – Braham conservatively estimates that full-depth reclamation is a competitive alternative for about 30 percent of all structurally deficient roadways in the United States.

“But there are certain areas, I think, where full-depth reclamation brings the greatest value,” he says. “These are areas experiencing a sudden increase in volume due to rapid growth or a change in the economy.”

Suburbs, Braham says, have grown around old farm roads that weren’t designed for a high volume of traffic, and similarly, in Arkansas and several other states, many rural highways have taken a beating from large trucks due to natural gas production and logging.

“Because full-depth reclamation delivers greater structural capacity quicker and at potentially less expense than other methods, these areas specifically are perfect candidates,” Braham says.

Braham has tested and refined the full-depth reclamation method at sites in Arkansas, Minnesota, Georgia and Iowa.