Better Roads Magazine, 13 November 2011
by Tom Kuennen, Contributing Editor
What percentage of RAP is best? It depends.
There are powerful inducements today to reuse reclaimed asphalt pavement (RAP) in a variety of applications. And the big question about RAP has shifted from whether it belongs in mixes at all, to how much can safely be accommodated in a mix.
It is this question that is driving an enormous amount of attention and research today. Many road agencies are closely observing the research as they permit higher percentages of RAP in a mix. Environmental legislation at the state level also is compelling higher percentages of RAP.
In the meantime, research continues on the questions of to what degree does the residual asphalt on RAP replace performance-graded (PG) binders; how will larger percentages of RAP impact the type of PG binder that should be specified for a Superpave mix in a particular location; and how important is the processing and analysis of RAP stockpiles in allowing higher percentages of RAP in asphalt mixes.
New guidance was released this year and last from the Federal Highway Administration (FHWA) and the National Cooperative Highway Research Program (NCHRP) on higher amounts of RAP in asphalt mixes.