Applications & Innovations
Better Roads Staff
Recycled asphalt shingles are an acquired taste
When going from the roof to the road in recycled asphalt pavement (RAP) mixes, “it’s all in the details,” says John Christensen, technical marketing manager for MeadWestvaco (MWV).
It’s not impossible to get density in RAP mixes incorporating recycled asphalt shingles (RAS), “but it helps to pay a little more attention to details. It’s definitely a more difficult mix to work with once you put shingles in there.”
But agencies and contractors are able to save money on virgin asphalt by using RAS. “This is what pushes a lot of contractors to use [RAS] now that it’s about $600 per liquid ton for asphalt,” Christensen says.
“When I first started working with contractors, RAP was a ‘four letter word,’” Christensen says. “It was a waste material that was usually given away or used by state or local DOTs who retained ownership. If it was used, it wasn’t more than 10 percent. It was easier to just use virgin asphalt and not deal with the headaches of the inconsistencies caused by putting RAP in a mix, because virgin asphalt was cheap and readily available. Those days are gone. Liquid asphalt is not cheap anymore, and sometimes it’s not as readily available and many specifications would not allow more than 10 percent – if any at all .”
RAS has provided an environmentally responsible option, and its economy is added-value for agencies, says Steve Jackson, P.E., quality control manager of Missouri-based NB West. But like Christensen says, Jackson notes that RAS must be dealt with carefully to ensure it will meet specs and perform well.
Jackson says he is seeing RAP mixes in early spring and in late fall, when temperatures aren’t as hot. In the summer, more shingle mixes are being used. “When temperatures get below 40 degrees F, people look at not using shingle mixes or [contractors] using ones with 6 to 7 percent going down to 2 to 3 percent because [the mixes] are getting stiffer,” Jackson says. “In spring and late fall, it’s wetter so it’s harder to dry them.” Jackson suggests keeping the shingles under a tarp or in a storage building to help deter moisture.
But there’s more to using recycled asphalt shingles than just keeping them dry. “You have to determine the specific gravity for your mix design,” Jackson says. This can get tricky because different states use different methods. Missouri uses the effective specific gravity as the value for the bulk-specific gravity to determine the voids in the mineral aggregate (VMA). This is just one method that may be used for VMA calculation.