Superpave: quality control is essential

Asking what’s new in asphalt technology has generated basically the same response from many in the industry: keep your eyes on Superpave. The performance-based asphalt mix design and analysis system holds enormous ramifications for both asphalt technology and asphalt businesses.

Unfortunately for system proponents, last summer’s premature rutting and permanent deformation of Superpave test sections at the Federal Highway Administration WesTrack test facility in Nevada, along with some state failures, may have sent out the wrong signals to those highway departments and contractors considering laying down the asphalt design mix. But an independent team of investigators, along with Superpave supporters, are working to set the record straight.

"The consensus of the team is that the major cause of early rutting of the reconstructed test sections is a combination of a coarse-graded mixture with high optimum asphalt content (5.7%) and low binder stiffness (PG 64-22)," the team’s analysis report stated in August.

Elaborating further, and attempting to allay more worry, asphalt team leader John D’Angelo, of the FHWA’s Office of Technology Applications, said, "Some of the mixes used at WesTrack, including the one that recently failed, would probably not be selected by highway agencies for use on in-service pavements."

Trying to head off some of the negative publicity incurred by the Superpave failures has become part of the job of the recently formed Extended Superpave Technology Delivery Team, which was created to consolidate the efforts of highway departments and expand agency resources concerning all aspects of Superpave field implementation. The Extended STDT is made up of 20 FHWA and Federal Lands field engineers, all specially trained in both technology and communications at the Asphalt Institute last September.

"We’re in a critical phase now," an Extended STDT representative said. "Most highway departments have tried Superpave. It’s kind of taken off and it’s at the point now where it’s affecting the contractors."

While negative feedback on the system can eventually be overcome, proponents want field implementation to move along as rapidly as possible. But they don’t want to make big promises, either.

"As with any new technology, there are a few quirks that need to be ironed out," says Dale Decker, vice president of research and technology at the National Asphalt Pavement Association. "There are implementation problems, so we want to make sure we have the opportunity to make adjustments during the implementation process."

There are several factors working against the Superpave effort, some of which are pointed out in a survey conducted by the Lead State Program, established in September 1996 and designed to "reduce the new technology learning curve." Industry acceptance, state budget restrictions, facility limitations, and institutional issues, in that order, were identified as potential barriers to the implementation of Superpave.

Of course, that industry acceptance factor must include resistance to Superpave on a political level — some businesses are obviously going to be hurt by a national standard that does not allow their product in the range of specifications. And some agencies will only be able to justify the cost/budget factor if they can prove that the upfront increase in cost will offset future asphalt repair work.

Many projects

If figures from the past two years are any indication, it certainly appears that Superpave will overcome the various barriers. In 1996, there were 93 Superpave projects vs. 6,845 other hot-mix asphalt projects (in tonnage, 2.8 million vs. 118 million, respectively). Although final figures aren’t in yet for 1997, there were 326 planned Superpave projects in all but three states.

Reports gathered by the Extended STDT from several states also show a very strong support for Superpave, even though there have been some problems. In Florida, pavements placed in 1996 revealed that coarse-graded Superpave pavements were significantly more permeable than traditional fine-graded Marshall pavements.

"We found that the rules of thumb that applied to fine-graded mixes didn’t necessarily apply to coarse-graded, high-traffic Superpave mixes," said Gale Page, Florida DOT’s flexible pavement materials engineer. Solutions were using core samples for density measurement (rather than the nuclear device), increased lift thickness, and an increased level of density requirement.

But FDOT is still committed to Superpave and, in 1997, more than 850,000 tons of Superpave mixes were placed in about a dozen state projects, mostly on high-volume, high-traffic roads.

The state of Maryland is moving toward 100% Superpave implementation — that is, everything will be designed with performance-graded binders and the Superpave volumetric mix design system. After MDOT experienced some highly publicized and embarrassing failures of open-graded mixtures in the early 1990s, they moved to stone-matrix asphalt with performance-graded binders in 1994. In 1996, 12% of the total hot-mix asphalt placed in the state was Superpave, and that included portions of the Baltimore and Washington, D.C. beltways. All of those projects are performing well.

"Once you’re doing a million tons of SMA, Superpave is easy," said Larry Michael, the MDOT regional engineer in charge of Superpave implementation. "We are also blessed with high-quality binders and locally available aggregates that perform very well."

New York has a firm commitment to Superpave. The state constructed 44 Superpave projects in 1997 (representing about 20% of its total program), half of the projects in 1998 will be Superpave, and, by 1999, it will be used on all state projects.

The pluses

"We want to position ourselves to take early advantage of the benefits of Superpave," said New York DOT Deputy Chief Engineer Paul Mack. "We view the Superpave system as a way to extend the life of every hot-mix asphalt project. Even relatively small improvements in pavement life translate to huge returns in avoided maintenance and rehabilitation costs, and in reduction of time delays and disruptions on the highway."

The New York State Materials Bureau estimates that the state will save a minimum of $200 million over 30 years with the transition to Superpave.

"Fundamentally, Superpave is a much better system than Marshall," Mack said. "We think there are immediate benefits from using Superpave now, and the system will continue to improve as the results of continuing research and development are used to make refinements. Those of us who are familiar with what’s going on are confident that the research gaps will be filled in quickly. Our early involvement positions us to take full advantage of advances as soon as they occur."

New York is one of the six states in the Lead State Program for the SHRP technology area of Superpave, and it also serves as team leader. The other states involved are Florida, Indiana, Maryland, Texas, and Utah. According to the mission statement, the lead states will assist in the uniform implementation of the Superpave system by documenting and sharing experiences, furthering development, and providing guidance related to the practical implementation of the technology.

That information exchange and technical assistance is absolutely key in the facilitation of a smooth transition to Superpave. In fact, quality control may be the single most important aspect of field implementation because, if mix specifications aren’t properly met, agencies will report that Superpave doesn’t work.

And then there’s always the possibility of sabotage. One state DOT maintenance specialist recently said that 16% of work crews will intentionally try to sabotage anything new — one more reason to hold a tight rein on quality control.

The strongest recommendation of the Lead State Program survey was that a Lead State be contacted for assistance with the implementation of the Superpave system.

Reprinted from Better Roads Magazine
February 1998