Better Roads September 2014 15
National perspective
Studies show that many state transportation departments are
not even using the amounts of RAP permitted by their own
specifi cations. In 2007, a survey was conducted by the North
Carolina Department of Transportation (NCDOT) and sponsored
by the AASHTO Subcommittee on Materials. Survey responses
were collected from all 50 States as well as Ontario, Canada.
The survey showed that the majority of states allowed the use of
RAP in asphalt mixtures. The 2007 average national usage rate
was estimated to be 12 percent. RAP was typically permitted
in subsurface, base, and shoulder mixtures but may have been
restricted in surface/wearing courses. Very few states allowed
little or no RAP due to concerns regarding performance.
The survey data also indicated the potential for increasing the
amount of RAP used across the United States. For example, only
10 state transportation departments used up to 29 percent RAP
in the intermediate layer – compared with more than 35 State
transportation departments that were authorized to use up to
29 percent RAP. Similarly, fewer than fi ve State transportation
departments used up to 29 percent RAP in the surface layer,
while 20 state transportation departments were authorized by
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The Green Asphalt Plant is shown
here as a RAP dryer on batch plant.
Photo
courtesy
of
Bob
Frank,
RAP
Technologies
