“This is kind of a nationwide issue people are dealing with in determining the bulk-specific gravity for RAP and shingles,” Jackson points out. “The problem is that the fine particles in the RAP and shingles float when you submerge them in water; this makes it very difficult to determine the bulk-specific gravity directly using the traditional AASHTO T-84 and T-85 test methods.” The National Center for Asphalt Technology (NCAT) has a method where 1 percent virgin binder is added to the RAP to keep the fine particles from floating. However, the methods all have different shortcomings, Jackson says. It makes it difficult when you are trying to come up with a hard and fast number and there are different approaches that people are using.

The RAS, “eliminates the potential for rutting in the roads because of the stiffer asphalt binder and the fibers they add to the road, but there is still concern about cold weather cracking and fatigue cracking,” says Jackson.

In 2012 the Missouri Department of Transportation (MoDOT) revised its specs and raised the minimum VMA requirement in lower-volume mix designs so cracking issues do not occur, says Jackson. “I think the ultimate solution is that we go to straight mixture performance testing instead of looking at each component,” Jackson says. “There are several performance tests out there. People have their own opinions on what is the best method; I think that a combination of fatigue cracking and rutting potential tests will provide the best performance predictors in the future.”

Go to www.facebook.com/BetterRoadsMagazine for a RAS photo album. For coverage of Illinois’ use of RAS and Illinois Tollway Authority, EPA and Illinois DOT testing, go to www.betterroads.com, then click on “Web Exclusives.”